DETAILS OF CONSTRUCTIONMain Planes and Struts. It is preferable to begin with the construction of the main planes and their struts and truss wires, the ribs already described being the first step.The main beams offer no special difficulties. They are ovals 1 1/4 by 1 5/8 inches, all 6 feet long except the eight end ones, which are 6 feet 2 inches. The beams of the central section should be of ash, or should be thicker than the others. In the latter case, they must be tapered at the ends so that the clamping sleeves will fit and the additional wood must be all on the lower side, so that the rib will not be thrown out of alignment. The spruce used for the other beams should be reasonably clear and straight grained, but a small knot or two does not matter, provided it does not come near the ends of the beam. The beams may be cut to the oval shape by the sawmill or planed down by hand."Fish-shaped" or "stream-line" section, as it is more commonly termed, is used for the struts, Fig. 15. It is questionable whether this makes any material difference in the wind resistance, but it is common practice to follow it in order to minimize this factor. It is more important that the struts be larger at their centers than at the ends, as this strengthens them considerably. At their ends the struts have ferrules of the 1-inch brass or steel tubing, and fit into the sockets which clamp the ribs and beams together. The material is spruce but the four central struts which carry the engine bed should either be ash or of larger size, say 1 1/4 by 3 inches.Care Necessary to Get Planes Parallel. The front struts must be longer than the rear ones by the thickness of a main rib at the point where the rear strut bolt passes through it, less the thickness of the rib ferrule through which the bolt of the front strut must pass. However, the first distance is not really the actual thickness of the rib, but the distance between the top of the rear beam and the bottom of the strut socket. In the drawings the difference in length between the front and rear struts is given as 2 inches, but it is preferable for the builder to leave the rear struts rather long and then measure the actual distance when assembling, cutting the struts to fit. The ends of the struts should also be countersunk enough to clear the head of the socket bolt.One of the items which the builder can not well escape buying in finished form is the strut sockets. These are cup-shaped affairs of pressed steel which sell at 20 cents each. Sixteen of them will be required for the main frame, and a dozen more can advantageously be used in the front and rear controls, though for this purpose they are not absolutely necessary. They can also be obtained in a larger oval size suitable for the four central struts that carry the engine bed, as well as in the standard 1-inch size. The bolts which project through the bottom of the sockets are ordinary 1/4-inch stove bolts, with their heads brazed to the sockets.For the rear struts, where the bolt must pass through the slanting main rib, it is advisable to make angle washers to put under the socket and also between the beam and rib. These washers are made by sawing up a piece of heavy brass tubing, or a bar with a 1/4-inch hole drilled in its center, the saw cuts being taken alternately at right angles and at 60 degrees to the axis of the tube.The sleeves which clamp together the ends of the beams are made of sheet steel of about 20 gauge. The steel is cut out on the pattern given in the drawing, Fig. 16, and the 3/16-inch bolt holes drilled in the flanges. The flanges are bent over by clamping the sheet in a vise along the bending line and then beating down with a hammer. Then the sleeves can be bent into shape around a stray end of the beam wood. The holes for the strut socket bolts should not be drilled until ready to assemble. Ordinarily, 3/16-inch stove bolts will do to clamp the flanges together.Having reached this stage, the amateur builder must now supply himself with turnbuckles. As already mentioned, these may either be purchased or made by hand. It is permissible to use either one or two turnbuckles on each wire. One is really sufficient, but two—one at each end—add but little weight and give greater leeway in making adjustments. As there are about 115 wires in the machine which need turnbuckles, the number required will be either 115 or 230, depending upon the plan which is followed. Those of the turnbuckles to be used on the front and rear controls and the ailerons, about one-fifth of the total number, may be of lighter stock than those employed on wires which carry part of the weight of the machine.Making Turnbuckles for the Truss Wires. On the supposition that the builder will make his own turnbuckles, a simple form is described here. As will be seen from Fig. 16, the turnbuckles are simply bicycle spokes, with the nipple caught in a loop of sheet steel and the end of the spoke itself twisted into an eye to which the truss wire can be attached. The sheet steel used should be 18 or 16 gauge, and may be cut to pattern with a heavy pair of tin snips. The spokes should be 3/32 inch over the threaded portion. The eye should be twisted up tight and brazed so that it can not come apart. The hole in the middle of each strip is, of course, drilled the same size as the spoke nipple. The holes in the ends are 3/16 inch.In the original Curtiss machines, the turnbuckles were strung on the socket bolts one after another, sometimes making a pack of them half an inch thick. A much neater construction is shown in the drawings, in which the bolt pierces a single plate with lugs to which to make the turnbuckles fast by riveting. The plates are of different shapes, with two, three, or four lugs, according to the places where they are to be used. They are cut from steel stock 3/32 inch thick, with 1/4-inch holes for the socket bolts and 3/16 inch, or other convenient size, for the rivets that fasten on the turnbuckles.The relative merits of cable and piano wire for trussing have not been thoroughly threshed out. Each has its advantages and disadvantages. Most of the well-known builders use cable; yet if the difference between 1,000 feet of cable at 2 1/4 cents per foot (the price for 500-foot spools), and 8 pounds of piano wire at 70 cents a pound, looks considerable to the amateur builder, let him by all means use the wire. The cable, if used, should be the 3/32-inch size, which will stand a load of 800 pounds; piano wire should be 24 gauge, tested to 745 pounds. It should be noted that there is a special series of gauges for piano wire, known as the music wire gauge, in which the size of the wire increases with the gauge numbers, instead of the contrary, as is usual with machinery wire gauges.One by no means unimportant advantage of the piano wire is that it is much easier to fasten into the turnbuckles. A small sleeve or ferrule, a 1/4-inch length of 1/8-inch tubing, is first strung on the wire. The end of the wire is then passed through the turnbuckle eye, bent up, thrust through the sleeve, and again bent down. When the machine is taken apart, the wire is not disconnected from the eye, but instead the turnbuckle spoke is unscrewed from the nipple. The shape of the sheet-steel loop should be such as to hold the latter in place. Cable, on the other hand, must be cut with about 2 inches to spare. After being threaded through the turnbuckle eye, the end is wound back tightly on itself and then soldered, to make certain that it can not loosen.With a supply of turnbuckles and cable or piano wire at hand, the builder may go ahead with the main box-like structure or cell, which should be completed except for the cloth covering, and in proper alignment, before taking up the construction of the running gear and controls.Running Gear. The running gear of the machine is built of seamless steel tubing, those parts which carry the weight of the machine direct being of 3/4-inch outside diameter, 16-gauge tubing, while the others are 5/8-inch outside diameter, either 18 or 20 gauge. About 25 feet of the heavy and 45 feet of the light tubing will be required, in lengths as follows: Heavy, four 3-foot, three 4-foot; light, one 6-foot, two 4-foot 6-inch, and seven 4-foot pieces. Referring to Fig. 17, two diagonal braces from the rear beam to the engine bed, the V-shaped piece under the front engine bed struts and all of the rear frame except the horizontal piece from wheel to wheel, are of heavy tubing. The horizontal in the rear frame, diagonals from the rear wheels and the rear end of the skid to the front beam, the two horizontals between the front and rear beam, and the forward V are of light tubing.Fig. 17. Details of Curtiss Running GearFig. 17. Details of Curtiss Running GearThree ash beams are used in the running gear. Two of these run diagonally from the rear end of the engine bed to the front wheel. These are about 10 feet long and 1 by 1 3/4 inches section. The third, which on rough ground acts as a skid, is 8 1/2 feet long and about 2 inches square. Between the joints where the tubing frames are attached to it, the upper corners may be beveled off with a spoke shave an inch or more down each side. The beams are attached to the front wheel with strips of steel stock 1 1/2 inches wide and 1/8 inch thick. The engine bed beams are also ash about 1 by 1 3/4 inches section. Their rear ends are bolted to the middle of the rear engine bed struts and the front ends may be 1/2 inch higher.SCENE AT AVIATION MEET AT ROUEN, FRANCE, SHOWING AN ANTOINETTE MONOPLANE MAKING A TURNSCENE AT AVIATION MEET AT ROUEN, FRANCE, SHOWING AN ANTOINETTE MONOPLANE MAKING A TURNThis Photograph Protected By International CopyrightA FRENCH MONOPLANE TRAVELLING SIXTY-FIVE MILES AN HOURA FRENCH MONOPLANE TRAVELLING SIXTY-FIVE MILES AN HOURThis Photograph Protected By International CopyrightThe wheels are usually 20 by 2 inches, and of the bicycle type, but heavier and wider in the hub; the tires are single tube. These wheels, complete with tires, cost about $10 each. This size is used on the standard Curtiss machines, but novice operators, whose landings are not quite as gentle as they might be, find them easily broken. Therefore, it may be more economical in the end to pay a little more and get heavier tires—at least to start with.For working the tubing into shape, a plumber's blow torch is almost indispensable—most automobilists will already possess one of these. The oval, flat variety, holding about one pint, is very handy and packs away easily, but on steady work requires filling somewhat too frequently. With a dozen bricks a shield can be built in front of the torch to protect the flame and concentrate the heat. Whenever it is to be flattened and bent, the tubing should be brought to a bright red or yellow heat. Screwing the vise down on it will then flatten it quickly without hammer marks. Where the bend is to be made in the middle of the piece, however, it may be necessary to resort to the hammer and anvil.It is convenient to start with the framework under the rear beam. This may be drawn accurately to full size on the workshop floor, and the tubes bent to fit the drawing. With this framework once in place, a definite starting point for the remainder of the running gear is established. Here and in all other places, when boring through wood, the holes should be drilled out full, and larger washers should be placed under the bolt head and nut. All nuts should be provided with some sort of locking device The perspective drawing. Fig. 17, should show the general arrangement clearly enough to enable the builder to finish the running gear.Outriggers. Both the front and rear control members, or "outriggers" as they are termed, Fig. 12, may be conveniently built up on the central section of the main frame, which, it is assumed, has now been fitted with the running gear.The horizontal rudder, or "elevator," is a biplane structure like the main cell of the machine, but with fewer struts; it is carried in front of the main planes on twoA-shaped frames. The vertical rudder, at the rear, is split along the middle and straddles a fixed horizontal plane, ortail. This also is carried on twoA-shaped frames. Lateral stability is controlled by two auxiliary planes or ailerons, one at each side of the machine and carried on the two outer front struts. These three control units—elevator,tailandrudder, andailerons—will now be taken up separately and their construction, location on the machine, and operation will be described.Fig. 18. Details of Rudders and Ailerons, Curtiss BiplaneFig. 18. Details of Rudders and Ailerons, Curtiss BiplaneHorizonal Rudder or Elevator. The two planes of the elevator are 2 feet wide by 5 feet 8 inches long and are spaced 2 feet apart, being held in this position by ten struts. The frames of the planes are built of spruce sticks 1/2 by 1 inch, each plane having two sticks the full length and five evenly spaced crosspieces or ribs. These are joined together with squares of X-sheet tin, as shown in the detailed drawing, Fig. 18. With a little experimenting, paper patterns can be made from which the tin pieces can be cut out. The sticks are then nailed through the tin with 3/4-inch brads.It is convenient to draw the frames out accurately on a smooth wood floor and then work over this drawing. The first few brads will hold the sticks in place. When all the brads have been driven, a little drop of solder should be run in around the head of each one. This is a tedious job. One must be careful to use no more solder than necessary as it increases the weight very rapidly. Two pounds of wire solder should be sufficient for all the control members which are built in this way. When the top side is soldered, pry the frame loose from the floor with a screwdriver and turn it over. Then the projecting points of the brads must be clinched and the soldering repeated.At this stage, the two frames should be covered on both sides with the prepared cloth used for covering the main planes. The method of preparing this cloth is detailed a little farther along.The struts, so-called, to continue the analogy with the main planes, are turned sticks of spruce 3/8 inch in diameter. They are fitted at each end with ferrules of thin 3/8-inch brass, or steel tubing, driven on tight. Instead of using sockets, the struts are held at each end, simply by a long wood screw driven through the tin and wood of the plane frame and into the strut. These screws also hold the turnbuckles for the truss wires. For trussing purposes, the elevator is regarded as consisting of two sections only, the intermediate struts being disregarded.The turnbuckles and wire used here and in the other control members may well be of lighter stock than those used in the main planes. Piano wire, No. 18, or 1/16-inch cable is amply strong. The sheet steel may be about 22 gauge, instead of 16, and the bicycle spokes smaller in proportion. No turnbuckle plates are necessary. The screws running into the struts may be passed directly through the eyes of the turnbuckles, where they would have been attached to the turnbuckle plate. In order to secure a square and neat structure, those struts which have turnbuckles at their ends should be made a trifle shorter than the others.At each end, the elevator has anX-shaped frame of 1/4-inch steel tubing; at the intersection of theX's are pivots on which the elevator is supported. EachXis made of two tubes, bent into a y and flattened and brazed together at the points. The ends of theX's are flattened and bent over so that the screws which hold the struts in place may pass through them.Fig. 19. Curtiss Biplane Ready for FlightFig. 19. Curtiss Biplane Ready for FlightTo the front middle strut is attached an extension which acts as a lever for operating the elevator. This is a stick of spruce 3/4 inch in diameter and 3 feet 3 inches long. At its upper end it has a ferrule of steel tubing, flattened at the end. The lower part of the stick may be fastened to the strut by wrapping the tube with friction tape, or by improvising a couple of sheet steel clamps. The upper end of the stick is braced by a 1/4-inch steel tube, extending to the top of the rear middle strut, and held by the same screw as the strut. This extension lever is connected to the steering column by a bamboo rod, 1 inch in diameter and about 10 feet long, provided with flattened ferrules of steel tubing at each end. Each ferrule should be held on by a 1/8-inch stove bolt passing through it.Front and Rear Outrigger Frames. Both the front elevator and the tail and rudder at the rear, are carried, as mentioned above, each on a pair ofA-shaped frames, similar to one another, except that those in the rear are longer than those in the front. Both are made of spruce of about the same section as used for the struts of the main frame. These pieces may either be full length, or they may be jointed at the intersection of the crosspieces, the ends being clamped in a sheet-steel sleeve, just like that used on the beams of the main frame. In this case, it is advisable to run a 1/8-inch stove bolt through each of the ends.Fig. 20. Details of Outriggers and Front Elevating Planes as Seen from Driver's SeatFig. 20. Details of Outriggers and Front Elevating Planes as Seen from Driver's SeatThe crosspieces of theA-frames are spruce of the same section, or a little smaller. At their ends may be used strut sockets like those of the main frame; or, if it is desired to save this expense, they may be fastened by strips of 1/16-inch steel stock with through bolts.The front outrigger has, besides the two A-frames, a rather complicated arrangement of struts designed to brace the front wheel against the shocks of landing. This arrangement does not appear very plain in a plan or elevation, and may best be understood by reference to the photograph, Fig. 19, and the perspective drawing, Fig. 20. Fig. 20 is a view from the driver's seat. The elevator is seen in front, theA-frames at each side, and at the bottom the two diagonal beams to the engine bed and the skid.Reference to this drawing will show the two diagonals run from the front wheel up and back to the top of the main frame, and two more from the wheel forward to the short crosspieces near the apexes of theA-frame: there is also a vertical strut which intersects two horizontal pieces running between the ends of the longer crosspieces of theA-frames. Altogether, there are five attachments on each side of the front wheel, through which the axle bolt must pass, viz, the connections to the skid, to one of the diagonals to the engine bed, to one of the rear diagonals, to one of the front diagonals, and to one side of the fork carrying the vertical strut. Of these the skid attachments should be on the inside closest to the wheel, and the engine bed diagonals next.The four additional diagonals running to the front wheel may be spruce of the same section used in theA-frames, or turned one inch round. At each end they have flattened ferrules of steel tubing. The beams of theA-frames have similar ferrules at the ends where they attach to the main frames. These attachments should be made on the socket bolts of the struts on either side of the middle 6-foot section and on the outer side of the main beams—not between the beam and the socket itself.It is possible, of course, to make all theA-frames and diagonal braces of bamboo, if desired, the qualities of this material already having been referred to. Bamboo rods for this purpose should be between 1 and 1 1/4 inches in diameter. Where ferrules are fitted on the ends, the hole of the bamboo should be plugged with wood glued in place.Generally, in the construction of the outrigger frames, the builder can use his own discretion to a considerable extent. There tire innumerable details which can be varied—far too many to consider even a part of the possibilities in this connection. If the builder runs across any detail which he does not see mentioned here, he may safely assume that any workmanlike job will suffice. Often, the method may be adapted to the materials on hand. The diagonal wires from the crosspieces of the A-frames to the struts should be crossed.Rudder and Tail Construction. The frame for the rudder and tail are constructed in much the same way as those for the elevator, Fig. 18. Spruce sticks 1 by 1/2 inch are used throughout, except for the piece at the back edge of the rudder and the long middle piece across the tail; these should be 1 1/2 by 1/2 inch. This long middle piece of the tail is laid across on top of the rest of the framework. When the cloth is put on, this makes the upper surface slightly convex while the lower surface remains flat. The ends of this piece should be reinforced with sheet steel, fairly heavy and drilled for 1/4-inch bolts, attaching the tail to theA-frames.The rudder is hung from two posts extending above and below the tail. These posts may be set in cast aluminum sockets, such as may be obtained from any supply house for 20 cents apiece. The posts need not be more than 3/4 inch in diameter. At their outer ends, they should have ferrules of steel tubing, and the turnbuckles or other attachments for the truss wires should be attached by a wood screw running into the end of each. From these posts the rudder may be hung on any light hinges the builder may find convenient, or on hinges improvised from screw eyes or eye bolts, with a bolt passing through the eyes of each.In steering, the rudder is controlled by a steering wheel carried on a hinged post in front of the pilot. This post should be ash about 1 by 1 1/4 inches. It hinges at the bottom on a steel tube of 1/2-inch diameter which passes through it and is supported at the ends on diagonal beams to the engine bed. Two diagonals of lighter tubing may be put in to hold the posts centered between the two beams.The post is, of course, upright, and the hub of the wheel is horizontal. The wheel may be conveniently mounted on a piece of tubing of the same size as the hub hole, run through the post and held by a comparatively small bolt, which passes through it and has a big washer on either end. The wheel is preferably of the motor-boat variety with a groove around the rim for the steering cable.The rear edge of the tail should be about 1 inch lower than the front. To make the rudder post stand approximately vertical, wedge-shaped pieces of wood may be set under the sockets.The steering connections should be of flexible cables of steel such as are made for this purpose. There should be a double pulley on the post just under the wheel, and the cables should be led off the post just at the hinge at the bottom, so that swinging the post will not affect them. The cable is then carried under the lower main plane and out the lower beams of theA-frames. It is attached to the rudder at the back edge; snap hooks should be used for easy disconnection in packing. Perhaps the best way of guiding the cable, instead of using pulleys, is to run it through short pieces of tubing lashed to the beams with friction tape. The tubing can be bent without flattening by first filling it with melted lead, which, after the bending, can be melted out again.Ailerons for Lateral Stability. The framework of the ailerons is made in the same way as that for the elevator, tail, and rudder, Fig. 18. The pieces around the edges should be 1 1/2 by 1/2 inch, as also the long strip laid over the top of the ribs. The ribs should be 1/2 by 3/4 inch. Each aileron has two holes, one for the strut to pass through, and the other for the diagonal truss wires at their intersection. The back edge also has a notch in it to clear the fore and aft wires. Each aileron is hung on four strips of soft steel about 1/2 by 3/16 inch, twisted so that one end is at right angles to the other. These are arranged one on each side of the strut which passes through the aileron, and one at each end. Bolts through the struts carry three of them and the outer one is trussed by wires to each end of the outer strut.A frame of 1/4-inch steel tubing fits around the aviator's shoulders and is hinged to the seat, so that he can move it by leaning from one side to the other. This is connected by flexible cable to the rear edges of the ailerons, so that when the aviator leans to the left, he will raise the left and lower the right aileron. The upper edges of the ailerons are directly connected to each other by a cable running along the upper front beam, so that they must always move together.Covering of the Planes. Mention has already been made of the fact, in the general description of the machine, that light sail cloth, as employed on the Wright machines, may be used for the planes or wings. As a matter of fact, many different materials may be successfully employed, the selection depending upon the builder himself and his financial resources. About 55 square yards of material will be required, and in comparing prices always compare the width as this may vary from 28 to 55 inches. Rubberized silk which is used on the standard Curtiss machines is the most expensive covering, its cost running up to something like two hundred dollars. There are also several good aero fabrics on the market which sell at 60 cents a square yard, as well as a number of brands of varnish for the cloth—most of them, however, quite expensive. The most economical method is to employ a strong linen cloth coated with shellac, which will be found very satisfactory.The covering of the frames with the cloth may well be postponed until after the engine has been installed and tested, thus avoiding the splashing of oil and dirt which the fabric is apt to receive during this operation. The wire to which the cloth is laced, must be strung along the rear ends of the ribs of each plane. The wires pass through holes in the ends of the small ribs and are attached to the main ribs with turnbuckles. At the ends of the planes the main ribs must be braced against the pull of the wire by a piece of 1/4-inch tubing running from the end of the rib diagonally up to the rear beam. Both turnbuckles and tube are fastened with one wood screw running into the end of the rib.The cloth should be cut to fit the panels between the main ribs and hemmed up, allowing at least an inch in each direction for stretch. Small eyelets should be put along the sides and rear edges an inch apart for the lacing. At the front edge, the cloth is tacked directly to the beam, the edge being taken well under and around to the back. Strong fish line is good material for the lacing.After the cloth is laced on, it must be tacked down to the small ribs. For this purpose, use upholstery tacks as they have big cup-shaped heads which grip the cloth and do not tear out. As an extra precaution a strip of heavy tape must be run over each rib under the tack heads. All the control members are covered on both sides, the edges being folded under and held by tacks.Making the Propeller. If the completed biplane is to fly properly and also have sufficient speed to make it safe, considerable care must be devoted to the design and making of the propeller. Every aeroplane has a safe speed, usually referred to in technical parlance as itscritical speed. In the case of the Curtiss biplane under consideration, this speed is about 40 miles an hour. By speeding up the motor considerably, it may be able to make 42 to 43 miles an hour in a calm, such a condition representing the only true measure of an aeroplane's ability in this direction, while on the other hand, it would not be safe to let its speed with relation to the wind (not to the ground) fall much below 35 miles an hour. At any slower rate of travel, its dynamic stability would be precarious and the machine would be likely to dive to the ground unexpectedly. The reasons for this have been explained more in detail under the heading of "The Internal Work of the Wind."The necessity of making the propeller need not discourage the ambitious builder—if he can spare the time to do it right, it will be excellent experience. If not, propellers designed for driving a machine of this size can be purchased ready to mount from any one of quite a number of manufacturers. But as the outlay required will be at least $50, doubtless most experimenters will prefer to undertake this part of the work as well as that of building the framework and main cell, particularly as more than 90 per cent of the sum mentioned is represented by labor. The cost of the material required is insignificant by comparison.True-Screw Design. First it will be necessary to design the propeller to meet the requirements of the biplane itself. As this is a matter that has already been gone into in considerable detail under the appropriate heading, no further explanation of propeller characteristics or of the technical terms employed, should be needed here. We will assume that the biplane is to have a speed of 40 miles per hour in still air with the motor running at 1,200 r.p.m. With this data, it will not be difficult to calculate the correct pitch of the propeller to give that result. Thus40 X 5,280 X 100 / 60 X 1,200 X 85 = 3.45or in round numbers a pitch of 3 1/2 feet. 40 (the speed in miles per hour) times 5,280 (feet per mile) divided by 00 (minutes in an hour) gives the speed of the aeroplane in feet per minute. Dividing this by 1,200 (revolutions per minute) gives the number of feet the aeroplane is to advance per revolution of the propeller. The "100/85" part of the equation represents the efficiency of the propeller which can safely be figured on,i.e., 85 per cent, or an allowance for slip of 15 per cent. Forty miles an hour is the maximum speed to be expected, while the r.p.m. rate of the engine should be that at which it operates to the best advantage.The merits of thetrue-screwandvariable-pitchpropellers have already been dwelt upon. The former is not only more simple to build, but experience has shown that, as generally employed, it gives better efficiency. Hence, the propeller under consideration will, be of the true-screw type. Its pitch has already been calculated as 3 1/2 feet. For a machine of this size and power, it should be 6 feet in diameter. Having worked out the pitch and decided upon the diameter, the next and most important thing is to calculate the pitch angle. It will be evident that no two points on the blade will travel through the air at the same speed. Obviously, a point near the tip of the propeller moves faster than one near the hub, just as in rounding a curve, the outer wheel of an automobile has to travel faster than the inner, because it has to travel farther to cover the same ground. For instance, taking the dimensions of the propeller in question it will be seen that its tips will be traveling through the air at close to 4.3 miles per minute, that is,6 X π X 1200 / 5,280 = 4.28in which 6, the diameter of the propeller in feet, times π gives the circumference of the circle which is traveled by the blade tips 1,200 times per minute; this divided by the number of feet per mile gives the miles per minute covered. On the other hand, a point on the blade but 6 inches from the hub will turn at only approximately 3,500 feet per minute. Therefore, if every part of the blade is to advance through the air equally, the inner part must be set at a greater angle than the outer part. Each part of the blade must be set at such an angle that at each revolution it will move forward through the air a distance equal to the pitch. This is known as the pitch angle. The pitch divided by the circumference of the circle described by any part of the blade, will give a quantity known as the tangent of an angle for that particular part. The angle corresponding to that tangent may most easily be found by referring to a book of trigonometric tables.Table II. Propeller Blade DataFor example, take that part of the blade of a 3 1/2-foot pitch propeller which is 6 inches from the center of the hub. Then3.5 X 12 / 6 X 2 π = 1.1141 tangent of 48 degrees 5 minutesin which 3.5 X 12 reduces the pitch to inches, while 6 X 2π is the circumference of the circle described by the point 6 inches from the hub. However, in order to give the propeller blade a proper hold on the air, it must be set at a greater angle than these figures would indicate. That is, it must be given an angle of incidence similar to that given to every one of the supporting planes of the machine. This additional angle ranges from 2 degrees 30 minutes, to 4 degrees, depending upon the speed at which the particular part of the blade travels; the greater the speed, the less the angle. This does not apply to that part of the blade near the hub as the latter is depended upon solely for strength and is not expected to add to the effective thrust of the propeller.Table II shows the complete set of figures for a blade of 3 1/2-foot pitch, the angles being worked out for sections of the blade 3 inches apart.These angles are employed in Fig. 21, which shows one blade of the propeller and its cross sections.It should be understood that these calculations apply only to the type of propeller known as thetrue screw, as distinguished from thevariable pitch. The design of the latter is a matter of personal skill and experience in its making which is hardly capable of expression in any mathematical formula. There are said to be only about three men in this country who know how to make a proper variable-pitch propeller, and it naturally is without advantage when made otherwise.Fig. 21. Details of Propeller Construction, Curtiss BiplaneFig. 21. Details of Propeller Construction, Curtiss BiplaneShaping the Blades. Like the ribs, the propeller is made up of a number of laminations of boards finished true and securely glued, afterward being cut to the proper shape, though this process, of course, involves far more skill than in the former case. Spruce is the strongest wood for its weight, but it is soft and cracks easily. Maple, on the other hand, is tough and hard, so that it will be an advantage to alternate the layers of these woods with an extra maple board, in order to make both outside strips of the harder wood, so as to form a good backing for the steel flanges at the hub, the rear layer extending the full length of the thin rear edges of the blades. Other woods may be employed and frequently are used by propeller manufacturers, such as mahogany (not the grained wood used for furniture, but a cheaper grade which is much stronger), walnut, alternate spruce and whitewood, and others.The boards should be selected with the greatest care so as to insure their being perfectly clear,i.e., absolutely free of knots, cross-grained streaks, or similar flaws, which would impair their strength and render them difficult to work smoothly. They should measure 6 inches wide by 6 feet 1 inch in length. Their surfaces must be finished perfectly true, so that they will come together uniformly all over the area on which they bear on one another, and the various pieces must be glued together with the most painstaking care. Have the glue hot, so that it will spread evenly, and see that it is of a uniform consistency, in order that it may be smoothly applied to every bit of the surface. They must then be clamped together under as much pressure as it is possible to apply to them with the means at hand, the rib press already described in detail forming an excellent tool for this purpose. Tighten up the nuts evenly a little at a time, avoiding the application of excessive or uneven pressure at one point, continuing the gradual tightening up process until it can not be carried any farther. This is to prevent the boards from assuming a curve in drying fast. Allow at least twenty-four hours for drying, during which period the laminated block should be kept in a cool, dry place at as even a temperature as possible.Before undertaking the remainder of the work, all of which must be carried out by hand, with the exception of cutting the block to the outline of the propeller, which may be done with a band saw, a set of templates or gauges should be made from the drawings. These will be necessary as guides for finishing the propeller accurately. Draw the sections out full size on sheets of cardboard or tin and cut out along the curves, finally dividing each sheet into two parts, one for the upper side and one for the lower. Care must be taken to get the sides of the template square, and when they are used, the propeller should be laid on a perfectly true and flat block. Each template should be marked as it is finished, to indicate what part of the blade it is a gauge for. The work of cutting the laminated block down to the lines represented by the templates is carried out with the aid of the plane, spoke shave, and gouge. After the firstroughing outto approximate the curvature of the finished propeller is completed, the cuts taken should be very fine, as it will be an easy matter to go too deep, thus spoiling the block and necessitating a new start with fresh material. For finishing, pieces of broken glass are employed to scrape the wood to a smooth surface, followed by coarse and finally by fine sandpaper.Mounting. The hub should be of the same diameter as the flange on the engine crank shaft to which the flywheel was bolted, and should have its bolt holes drilled to correspond. To strengthen the hub, light steel plates of the same diameter are screwed to it, front and back, and the bolt holes drilled right through the metal and wood. This method of fastening is recommended where it is possible to substitute the propeller for the flywheel formerly on the engine, it being common practice to omit the use of the flywheel altogether. The writer does not recommend this, however, as the advantages of smoother running and more reliable operation gained by the use of a flywheel in addition to the propeller far more than offset any disadvantage represented by its weight. It will be noted that the Wright motors have always been equipped with a flywheel of ample size and weight and this is undoubtedly responsible, in some measure at least, for the fact that the Wright biplanes fly with considerably less power than is ordinarily employed for machines of the same size. If the motor selected be equipped with an unusually heavy flywheel, and particularly where the wheel is of comparatively small diameter, making it less effective as a balancer, it may be replaced with one of lighter weight and larger diameter. It may be possible to attach it by keying to the forward end of the crank shaft, thus leaving the flange from which the flywheel was taken free for mounting the propeller. An ordinary belt pulley will serve excellently as the new flywheel, as most of its weight is centered in its rim, but as the common cast-iron belt pulley of commerce is seldom intended to run at any such speed as that of an automobile motor, it should be examined carefully for flaws. Otherwise, there will be danger of its blunting with disastrous results under the influence of centrifugal force. Its diameter should not exceed 16 inches in order to keep its peripheral speed within reasonable limits. Where the mounting of the motor permits of its use, a wood pulley 18 to 20 inches in diameter with a steel band about 1/8 to 1/4-inch thick, shrunk on its periphery, may be employed. Most builders will ridicule the idea of a flywheel other than the propeller itself. "You do not need it; so why carry the extra weight?" will be their query. It is not absolutely necessary, but it is an advantage.In case the flywheel of the engine selected is keyed to the crank shaft, or in case it is not possible to mount both the flywheel and the propeller on different ends of the crank shaft, some other expedient rather than that of bolting to the flange must be adopted. In such a case, the original flywheel, where practical to retain it, may be drilled and tapped and the propeller attached directly to it. Where the flywheel can not be kept, it will usually be found practical to cut off its rim and bolt the propeller either to the web or spokes, or to the flywheel hub, if it be cut down to the latter.The drawing. Fig. 21, shows the rear or concave side of the propeller. From the viewpoint of a man standing in its wind and facing forward, it turns to the left, or anti-clockwise. On many of the propellers now on the market, the curved edge is designed to go first. This type may have greater advantages over that described, but the straight front edge propeller is easier for the amateur to make.Mounting the Engine. Having completed the propeller, the next step is the mounting of the engine. Reference to the types available to the amateur aeroplane builder has already been made. There are a number of motors now on the market that have been designed specially for this purpose and not a few of them are of considerable merit. Their cost ranges from about $250 up to $2,500, but it may be possible to pick up a comparatively light-weight automobile motor second hand which will serve all purposes and which will cost far less than the cheapest aeronautic motor on the market. It must be capable of developing 30 actual horse-power at 1,000 to 1,200 r.p.m. and must not exceed 400 pounds complete with all accessories, such as the radiator and piping, magneto, water, oil, etc. Considerable weight may be saved on an automobile motor by removing the exhaust manifold and substituting a lighter flywheel for the one originally on the engine—or omitting it altogether, as just mentioned. A light-weight aeronautic radiator should be used in preference to the usual automobile radiator.When placing the engine in position on the ash beams forming its bed or support, it must be borne in mind that the complete machine, with the operator in the aviator's seat, is designed to balance on a point about 1 1/2 feet back of the front edge of the main planes. As the operator and the motor represent much the larger part of the total weight, the balance may easily be regulated by moving them slightly forward or backward, as may be required. It will be necessary, of course, to place the engine far enough back in any case to permit the propeller blades to clear the planes. The actual installation of the engine itself will be an easy matter for anyone who has had any experience in either automobile or marine gasoline motor work. It is designed to be bolted to the two engine beams in the same manner as on the side members of the frame of an automobile, or the engine bed in a boat. Just in front of the engine is the best place for the gasoline tank, which should be cylindrical with tapering ends, to cut down its wind resistance. If the designer is not anxious to carry out points as fine as this, a light copper cylindrical tank may be purchased from stock. It should hold at least ten gallons of gasoline. In front of the tank is the radiator.Controls. The controls may be located to conform to the builder's own ideas of accessibility and convenience. Usually the switch is placed on the steering column, and it may be of the ordinaryknifevariety, or one of the special switches made for this purpose, as taste may dictate. The throttle control and spark advance may either be in the form of pedals, working against springs, or of small levers working on a notched sector, at the side of the seat. The complete control, levers, and sector may be purchased ready to mount whenever desired, as they are made in this form for both automobile and marine work. This likewise applies to the wheel, which it would not pay the amateur to attempt to make.Another pedal should work a brake on the front wheel, the brake shoe consisting of a strip of sheet steel, fastened at one end to the fore part of the skid and pressed against the wheel by a bamboo rod directly connected with the brake pedal. An emergency brake can also be made by loosely bolting a stout bar of steel on the skid near its rear end; one end of this bar is connected to a lever near the seat, so that when this lever is pulled back the other end of the bar tends to dig into the ground. As making a landing is one of the most difficult feats for the amateur aviator to master and sufficient space for a long run after alighting is not always available, these brakes will be found a very important feature of the machine.Fig. 22. Method of Starting the Engine of an AeroplaneFig. 22. Method of Starting the Engine of an AeroplaneThe engine is started by swinging the propeller, and this is an operation requiring far more caution than cranking an automobile motor. Both hands should be placed on the same blade. Fig. 22, and the latter should always be pulled downward—never upward. With the switch off, first turn the propeller over several times to fill the cylinders with gas, leaving it just ahead of dead center of one of the cylinders, and with one blade extending upward and to the left at a 45-degree angle. After closing the switch, take the left blade with both hands and swing it downward sharply, getting out of the way of the following blade as quickly as possible.Tests. The first thing to be done after the propeller is finished and mounted on the engine is to test the combination, or power plant of the biplane, for speed and thrust, or pulling power. From these two quantities it will be easy to figure the power that the engine is delivering. The only instruments necessary are a spring balance reading to 300 pounds or over; a revolution counter, such as may be procured at any machinist's supply house for a dollar or two; and a watch. One end of the spring balance is fastened to the front end of the skid and the other to a heavy stake firmly driven in the ground a few feet back. The wheels of the biplane should be set on smooth boards so that they will not offer any resistance to the forward thrust. When the engine is started the spring balance will give a direct reading of the pull of the propeller.With one observer noting the thrust, another should check the number of revolutions the engine is turning per minute. To do this, a small hole should previously have been countersunk in the hub of the propeller to receive the conical rubber tip of the revolution counter. The observer stands behind the propeller, watch in one hand and revolution counter in the other. At the beginning of the minute period, the counter is pressed firmly against the hub, and quickly withdrawn at the end of the minute. A stop watch is naturally an advantage for the purpose. The horse-power is figured as follows, assuming, for example, a thrust of 250 pounds at 1,200 r.p.m.250 X 1200 X 3.5 X 100 / 33.000 X 85 = 37 h. p.As before, the "100/85" allows for the slip and represents the efficiency of the propeller; 33,000 is the number of foot pounds per minute or the equivalent of one horse-power, and 3.5 is the pitch of the propeller.Assembling the Biplane. Assembling the machine complete requires more space than is available in the average workshop. However, it is possible to assemble the sections of the planes in a comparatively small room, carrying the work far enough to make sure that everything will go together properly when the time comes for complete assembly at the testing ground. In this case, it is preferable to assemble the end sections first, standing them away when complete to make room for the central section, on which the running gear and outriggers are to be built up.The builder will have decided by this time whether he will make his machine on the regular plan, with one main rib between each section, or on the quick-detachable plan, which has two main ribs on either side of the central section, as previously explained.It is desirable to be able to assemble two sections at once and this should be possible anywhere as it requires a space only about 6 by 13 feet. Two wood 2X4's, about 12 feet long, should be nailed down on the blocks on the floor; make these level and parallel to each other at a distance of 3 feet 6 inches on centers, one being 3 inches higher than the other. Strips of wood should be nailed on them, so as to hold the main beams of the frame in place while assembling.The two front and two rear beam sections are laid in place and joined with the sheet-steel sleeves, the flanges of the sleeves on the inner side of the beams. Then through the sleeves in the front beams, which are, of course, those on the higher bed, drill the holes for the strut socket bolts (1/4 inch). The holes for the outer ones go through the projecting ends of the beams; those for the inner ones are half in each of the two abutting beams. At the end where the central section joins on, a short length of wood of the same section may be inserted in the sleeve while drilling the hole. An assistant should hold the beams firmly together while the holes are being drilled.Now lay in place the three main ribs belonging to the two sections under construction and fasten them at the front ends by putting in place the strut sockets for which the holes have been drilled, with a turnbuckle plate under each socket, Fig. 16. The strut socket bolt passes through the main rib and the beam. The bed on which the assembling is being done, should be cut when sufficiently under the joints to leave room for the projecting bolt ends. Set the ribs square with the front beams, then arrange the rear beams so that their joints come exactly under the ribs; clamp the ribs down and drill a true, vertical hole through the rib beam, holding the two sections of the beam together as before. Then put the rear strut sockets in place, using the angle washers previously described, above and below the rib.When the quick-detachable plan is followed, the ribs at the inner ends of the double section, where they join the central section, should be bolted on an inch from the ends of the beam, using 1/4-inch stove bolts instead of the socket bolts. The sleeves should be slotted, so that they can slide off without removing these bolts, as the sleeves and ribs which occupy the position over the joints of the beams, belong to the central section.The sections should now be strung up with the diagonal truss wires which will make them rigid enough to stand handling. The wires are attached at each end to the flange bolts of the sleeves. Either one or two turnbuckles may be used on each wire, as already explained; if but one turnbuckle be used, the other end of the wire may be conveniently attached to a strip of sheet steel bent double and drilled for the bolt, like the sheet-steel slip of a turnbuckle. The attachment, of whatever nature, should be put between the end and the flange of the sleeve, not between the two flanges.Three or four ribs can be used on each section; four are preferable on sections of full 6-foot length. They are, of course, evenly spaced on centers. At the front ends, they are attached to the beam by wood screws through their flattened ferrules. The attachment to the rear beam is made with a slip of sheet steel measuring 1/2 by 3 inches, bent over the rib and fastened to the beam at each side with a wood screw. A long wire nail is driven through the rib itself on the beam.Four double sections should be built up in this manner, the right and left upper and the right and left lower sections. Uppers and lowers are alike except for the inversion of the sockets in the upper sections. Rights and lefts differ in that the outer beams are long enough to fill up the sleeves, not leaving room for another beam to join on.Inserting the struts in their sockets between the upper and lower sections of the same side will now form either of the two sides of the machine complete. Care should be taken to get the rear struts the proper length with respect to the front ones to bring the upper and lower planes parallel. The distance from the top of the lower front beam to the top of the upper front beam should be the same as the distance between the rows of bracing holes in the upper and lower main ribs just above and below the rear struts—about 4 feet 6 inches. It should hardly be necessary to mention that the thick edges of the struts come to the front—they are fish-shaped and a fish is thicker at the head than at the tail.The truss wires may now be strung on in each square of the struts, beams, and main ribs, using turnbuckles as previously described. The wires should be taut enough to sing a low note when plucked between the thumb and forefinger. If the construction is carried out properly, the framework will stand square and true with an even tension on all the wires. It is permissible for the struts to slant backward a little as seen from the side, but all should be perfectly in line.For adjusting the turnbuckles, the builder should make for himself a handy little tool usually termed a nipple wrench. It is simply a strip of steel 1 1/2 by 1/2 by 3/32 inches, with a notch cut in the middle of the long sides to fit the flattened ends of the turnbuckle nipples. This is much handier than the pliers and does not burr up the nipples.It has been assumed in this description of the assembling that the builder is working in a limited space; if, on the contrary, he has room enough to set up the whole frame at once, the work will be much simpler. In this case, the construction bed should be 30 feet long. First build up the upper plane complete, standing it against the wall when finished; then build the lower plane, put the struts in their sockets, and lay on the upper plane complete.Returning to the plan of assembly by sections, after the side sections or wings of the machine have been completed, the struts may be taken out and the sections laid aside. The middle section, to which the running gear and outriggers will be attached, is now to be built up in the same way. If the builder is following the plan in which there is one main rib between each section, it will be necessary to take off the four inner main ribs from the sections already completed, to be used at the ends of the central section. The plan drawing of the complete machine shows that the ribs of the central section are cut off just back of the rear beam to make room for the propeller. This is necessary in order to set the motor far enough forward to balance the machine properly. The small ribs in this section have the same curve but are cut off 10 inches shorter at their rear ends, and the stumps are smoothed down for ferrules like those for the other small ribs. In the plan which has one main rib between each section, the main rib on each side of the central section must be left full length. In the quick-detachable plan with two main ribs on each side of the central section, the inner ones, which really belong to this section, are cut off short like the small ribs.In the drawing of the complete machine, the distance between the struts which carry the engine bed is shown as 2 feet. This is only approximate, as the distance must be varied to suit the motor employed. By this time, the builder will have decided what engine he is going to use—or can get—and should drill the holes for the sockets of these struts with due respect to the width of the engine's supporting feet or lugs, remembering that the engine bed beams go on the inside of the struts. In the drawing of the running gear. Fig. 17, the distance between the engine-bed struts has been designatedA. The distances,B, on each side are, of course, approximately (6'— 2*A*), whateverAmay be.VIEW OF THE FRENCH AVIATION GROUNDS SHOWING THE HANGARS RANGED ALONG THE EDGES OF THE FIELDVIEW OF THE FRENCH AVIATION GROUNDS SHOWING THE HANGARS RANGED ALONG THE EDGES OF THE FIELDThis Photograph Protected By International CopyrightEXAMINATION PAPERBUILDING AND FLYING ANAEROPLANEPART IRead Carefully: Place your name and full address at the head of the paper. Any cheap, light paper like the sample previously sent you may be used. Do not crowd your work, but arrange it neatly and legibly.Do not copy the answers from the Instruction Paper; use your own words so that we may be sure that you understand the subject.What type of machine, biplane or monoplane, makes the best glider and why?Give the dimensions of a glider which will support a man's weight.In a glider which has no rudder, how is the machine controlled?Give carefully the details of the start in making a glide.In what direction relative to the wind should a glide be made? Justify your answer.How must the stability and balance of a glider in flight be controlled?State the proper conditions for a successful glide.Give the essential characteristics of a Curtiss aeroplane, defining the various parts.Describe briefly the details of construction of the main supporting surfaces of a Curtiss.Draw a diagram of the assembled planes showing how the struts and cross wires are placed to give the required rigidity.Give the details of the running gear of the Curtiss.What is the office of the Curtiss ailerons and how are they controlled from the operator's seat? Draw sketch.Describe the details of the front and rear outriggers.What type of propeller is advised for the Curtiss? Give the details of its construction.Describe carefully the manner in which a propeller should move through the air in order to give the maximum propulsion.What determines the exact location of the motor in the aeroplane?Give correct method of starting the motor when ready for a flight.What tests should be conducted before a flight is undertaken?After completing the work, add and sign the following statement:I hereby certify that the above work is entirely my own.(Signed)
DETAILS OF CONSTRUCTIONMain Planes and Struts. It is preferable to begin with the construction of the main planes and their struts and truss wires, the ribs already described being the first step.The main beams offer no special difficulties. They are ovals 1 1/4 by 1 5/8 inches, all 6 feet long except the eight end ones, which are 6 feet 2 inches. The beams of the central section should be of ash, or should be thicker than the others. In the latter case, they must be tapered at the ends so that the clamping sleeves will fit and the additional wood must be all on the lower side, so that the rib will not be thrown out of alignment. The spruce used for the other beams should be reasonably clear and straight grained, but a small knot or two does not matter, provided it does not come near the ends of the beam. The beams may be cut to the oval shape by the sawmill or planed down by hand."Fish-shaped" or "stream-line" section, as it is more commonly termed, is used for the struts, Fig. 15. It is questionable whether this makes any material difference in the wind resistance, but it is common practice to follow it in order to minimize this factor. It is more important that the struts be larger at their centers than at the ends, as this strengthens them considerably. At their ends the struts have ferrules of the 1-inch brass or steel tubing, and fit into the sockets which clamp the ribs and beams together. The material is spruce but the four central struts which carry the engine bed should either be ash or of larger size, say 1 1/4 by 3 inches.Care Necessary to Get Planes Parallel. The front struts must be longer than the rear ones by the thickness of a main rib at the point where the rear strut bolt passes through it, less the thickness of the rib ferrule through which the bolt of the front strut must pass. However, the first distance is not really the actual thickness of the rib, but the distance between the top of the rear beam and the bottom of the strut socket. In the drawings the difference in length between the front and rear struts is given as 2 inches, but it is preferable for the builder to leave the rear struts rather long and then measure the actual distance when assembling, cutting the struts to fit. The ends of the struts should also be countersunk enough to clear the head of the socket bolt.One of the items which the builder can not well escape buying in finished form is the strut sockets. These are cup-shaped affairs of pressed steel which sell at 20 cents each. Sixteen of them will be required for the main frame, and a dozen more can advantageously be used in the front and rear controls, though for this purpose they are not absolutely necessary. They can also be obtained in a larger oval size suitable for the four central struts that carry the engine bed, as well as in the standard 1-inch size. The bolts which project through the bottom of the sockets are ordinary 1/4-inch stove bolts, with their heads brazed to the sockets.For the rear struts, where the bolt must pass through the slanting main rib, it is advisable to make angle washers to put under the socket and also between the beam and rib. These washers are made by sawing up a piece of heavy brass tubing, or a bar with a 1/4-inch hole drilled in its center, the saw cuts being taken alternately at right angles and at 60 degrees to the axis of the tube.The sleeves which clamp together the ends of the beams are made of sheet steel of about 20 gauge. The steel is cut out on the pattern given in the drawing, Fig. 16, and the 3/16-inch bolt holes drilled in the flanges. The flanges are bent over by clamping the sheet in a vise along the bending line and then beating down with a hammer. Then the sleeves can be bent into shape around a stray end of the beam wood. The holes for the strut socket bolts should not be drilled until ready to assemble. Ordinarily, 3/16-inch stove bolts will do to clamp the flanges together.Having reached this stage, the amateur builder must now supply himself with turnbuckles. As already mentioned, these may either be purchased or made by hand. It is permissible to use either one or two turnbuckles on each wire. One is really sufficient, but two—one at each end—add but little weight and give greater leeway in making adjustments. As there are about 115 wires in the machine which need turnbuckles, the number required will be either 115 or 230, depending upon the plan which is followed. Those of the turnbuckles to be used on the front and rear controls and the ailerons, about one-fifth of the total number, may be of lighter stock than those employed on wires which carry part of the weight of the machine.Making Turnbuckles for the Truss Wires. On the supposition that the builder will make his own turnbuckles, a simple form is described here. As will be seen from Fig. 16, the turnbuckles are simply bicycle spokes, with the nipple caught in a loop of sheet steel and the end of the spoke itself twisted into an eye to which the truss wire can be attached. The sheet steel used should be 18 or 16 gauge, and may be cut to pattern with a heavy pair of tin snips. The spokes should be 3/32 inch over the threaded portion. The eye should be twisted up tight and brazed so that it can not come apart. The hole in the middle of each strip is, of course, drilled the same size as the spoke nipple. The holes in the ends are 3/16 inch.In the original Curtiss machines, the turnbuckles were strung on the socket bolts one after another, sometimes making a pack of them half an inch thick. A much neater construction is shown in the drawings, in which the bolt pierces a single plate with lugs to which to make the turnbuckles fast by riveting. The plates are of different shapes, with two, three, or four lugs, according to the places where they are to be used. They are cut from steel stock 3/32 inch thick, with 1/4-inch holes for the socket bolts and 3/16 inch, or other convenient size, for the rivets that fasten on the turnbuckles.The relative merits of cable and piano wire for trussing have not been thoroughly threshed out. Each has its advantages and disadvantages. Most of the well-known builders use cable; yet if the difference between 1,000 feet of cable at 2 1/4 cents per foot (the price for 500-foot spools), and 8 pounds of piano wire at 70 cents a pound, looks considerable to the amateur builder, let him by all means use the wire. The cable, if used, should be the 3/32-inch size, which will stand a load of 800 pounds; piano wire should be 24 gauge, tested to 745 pounds. It should be noted that there is a special series of gauges for piano wire, known as the music wire gauge, in which the size of the wire increases with the gauge numbers, instead of the contrary, as is usual with machinery wire gauges.One by no means unimportant advantage of the piano wire is that it is much easier to fasten into the turnbuckles. A small sleeve or ferrule, a 1/4-inch length of 1/8-inch tubing, is first strung on the wire. The end of the wire is then passed through the turnbuckle eye, bent up, thrust through the sleeve, and again bent down. When the machine is taken apart, the wire is not disconnected from the eye, but instead the turnbuckle spoke is unscrewed from the nipple. The shape of the sheet-steel loop should be such as to hold the latter in place. Cable, on the other hand, must be cut with about 2 inches to spare. After being threaded through the turnbuckle eye, the end is wound back tightly on itself and then soldered, to make certain that it can not loosen.With a supply of turnbuckles and cable or piano wire at hand, the builder may go ahead with the main box-like structure or cell, which should be completed except for the cloth covering, and in proper alignment, before taking up the construction of the running gear and controls.Running Gear. The running gear of the machine is built of seamless steel tubing, those parts which carry the weight of the machine direct being of 3/4-inch outside diameter, 16-gauge tubing, while the others are 5/8-inch outside diameter, either 18 or 20 gauge. About 25 feet of the heavy and 45 feet of the light tubing will be required, in lengths as follows: Heavy, four 3-foot, three 4-foot; light, one 6-foot, two 4-foot 6-inch, and seven 4-foot pieces. Referring to Fig. 17, two diagonal braces from the rear beam to the engine bed, the V-shaped piece under the front engine bed struts and all of the rear frame except the horizontal piece from wheel to wheel, are of heavy tubing. The horizontal in the rear frame, diagonals from the rear wheels and the rear end of the skid to the front beam, the two horizontals between the front and rear beam, and the forward V are of light tubing.Fig. 17. Details of Curtiss Running GearFig. 17. Details of Curtiss Running GearThree ash beams are used in the running gear. Two of these run diagonally from the rear end of the engine bed to the front wheel. These are about 10 feet long and 1 by 1 3/4 inches section. The third, which on rough ground acts as a skid, is 8 1/2 feet long and about 2 inches square. Between the joints where the tubing frames are attached to it, the upper corners may be beveled off with a spoke shave an inch or more down each side. The beams are attached to the front wheel with strips of steel stock 1 1/2 inches wide and 1/8 inch thick. The engine bed beams are also ash about 1 by 1 3/4 inches section. Their rear ends are bolted to the middle of the rear engine bed struts and the front ends may be 1/2 inch higher.SCENE AT AVIATION MEET AT ROUEN, FRANCE, SHOWING AN ANTOINETTE MONOPLANE MAKING A TURNSCENE AT AVIATION MEET AT ROUEN, FRANCE, SHOWING AN ANTOINETTE MONOPLANE MAKING A TURNThis Photograph Protected By International CopyrightA FRENCH MONOPLANE TRAVELLING SIXTY-FIVE MILES AN HOURA FRENCH MONOPLANE TRAVELLING SIXTY-FIVE MILES AN HOURThis Photograph Protected By International CopyrightThe wheels are usually 20 by 2 inches, and of the bicycle type, but heavier and wider in the hub; the tires are single tube. These wheels, complete with tires, cost about $10 each. This size is used on the standard Curtiss machines, but novice operators, whose landings are not quite as gentle as they might be, find them easily broken. Therefore, it may be more economical in the end to pay a little more and get heavier tires—at least to start with.For working the tubing into shape, a plumber's blow torch is almost indispensable—most automobilists will already possess one of these. The oval, flat variety, holding about one pint, is very handy and packs away easily, but on steady work requires filling somewhat too frequently. With a dozen bricks a shield can be built in front of the torch to protect the flame and concentrate the heat. Whenever it is to be flattened and bent, the tubing should be brought to a bright red or yellow heat. Screwing the vise down on it will then flatten it quickly without hammer marks. Where the bend is to be made in the middle of the piece, however, it may be necessary to resort to the hammer and anvil.It is convenient to start with the framework under the rear beam. This may be drawn accurately to full size on the workshop floor, and the tubes bent to fit the drawing. With this framework once in place, a definite starting point for the remainder of the running gear is established. Here and in all other places, when boring through wood, the holes should be drilled out full, and larger washers should be placed under the bolt head and nut. All nuts should be provided with some sort of locking device The perspective drawing. Fig. 17, should show the general arrangement clearly enough to enable the builder to finish the running gear.Outriggers. Both the front and rear control members, or "outriggers" as they are termed, Fig. 12, may be conveniently built up on the central section of the main frame, which, it is assumed, has now been fitted with the running gear.The horizontal rudder, or "elevator," is a biplane structure like the main cell of the machine, but with fewer struts; it is carried in front of the main planes on twoA-shaped frames. The vertical rudder, at the rear, is split along the middle and straddles a fixed horizontal plane, ortail. This also is carried on twoA-shaped frames. Lateral stability is controlled by two auxiliary planes or ailerons, one at each side of the machine and carried on the two outer front struts. These three control units—elevator,tailandrudder, andailerons—will now be taken up separately and their construction, location on the machine, and operation will be described.Fig. 18. Details of Rudders and Ailerons, Curtiss BiplaneFig. 18. Details of Rudders and Ailerons, Curtiss BiplaneHorizonal Rudder or Elevator. The two planes of the elevator are 2 feet wide by 5 feet 8 inches long and are spaced 2 feet apart, being held in this position by ten struts. The frames of the planes are built of spruce sticks 1/2 by 1 inch, each plane having two sticks the full length and five evenly spaced crosspieces or ribs. These are joined together with squares of X-sheet tin, as shown in the detailed drawing, Fig. 18. With a little experimenting, paper patterns can be made from which the tin pieces can be cut out. The sticks are then nailed through the tin with 3/4-inch brads.It is convenient to draw the frames out accurately on a smooth wood floor and then work over this drawing. The first few brads will hold the sticks in place. When all the brads have been driven, a little drop of solder should be run in around the head of each one. This is a tedious job. One must be careful to use no more solder than necessary as it increases the weight very rapidly. Two pounds of wire solder should be sufficient for all the control members which are built in this way. When the top side is soldered, pry the frame loose from the floor with a screwdriver and turn it over. Then the projecting points of the brads must be clinched and the soldering repeated.At this stage, the two frames should be covered on both sides with the prepared cloth used for covering the main planes. The method of preparing this cloth is detailed a little farther along.The struts, so-called, to continue the analogy with the main planes, are turned sticks of spruce 3/8 inch in diameter. They are fitted at each end with ferrules of thin 3/8-inch brass, or steel tubing, driven on tight. Instead of using sockets, the struts are held at each end, simply by a long wood screw driven through the tin and wood of the plane frame and into the strut. These screws also hold the turnbuckles for the truss wires. For trussing purposes, the elevator is regarded as consisting of two sections only, the intermediate struts being disregarded.The turnbuckles and wire used here and in the other control members may well be of lighter stock than those used in the main planes. Piano wire, No. 18, or 1/16-inch cable is amply strong. The sheet steel may be about 22 gauge, instead of 16, and the bicycle spokes smaller in proportion. No turnbuckle plates are necessary. The screws running into the struts may be passed directly through the eyes of the turnbuckles, where they would have been attached to the turnbuckle plate. In order to secure a square and neat structure, those struts which have turnbuckles at their ends should be made a trifle shorter than the others.At each end, the elevator has anX-shaped frame of 1/4-inch steel tubing; at the intersection of theX's are pivots on which the elevator is supported. EachXis made of two tubes, bent into a y and flattened and brazed together at the points. The ends of theX's are flattened and bent over so that the screws which hold the struts in place may pass through them.Fig. 19. Curtiss Biplane Ready for FlightFig. 19. Curtiss Biplane Ready for FlightTo the front middle strut is attached an extension which acts as a lever for operating the elevator. This is a stick of spruce 3/4 inch in diameter and 3 feet 3 inches long. At its upper end it has a ferrule of steel tubing, flattened at the end. The lower part of the stick may be fastened to the strut by wrapping the tube with friction tape, or by improvising a couple of sheet steel clamps. The upper end of the stick is braced by a 1/4-inch steel tube, extending to the top of the rear middle strut, and held by the same screw as the strut. This extension lever is connected to the steering column by a bamboo rod, 1 inch in diameter and about 10 feet long, provided with flattened ferrules of steel tubing at each end. Each ferrule should be held on by a 1/8-inch stove bolt passing through it.Front and Rear Outrigger Frames. Both the front elevator and the tail and rudder at the rear, are carried, as mentioned above, each on a pair ofA-shaped frames, similar to one another, except that those in the rear are longer than those in the front. Both are made of spruce of about the same section as used for the struts of the main frame. These pieces may either be full length, or they may be jointed at the intersection of the crosspieces, the ends being clamped in a sheet-steel sleeve, just like that used on the beams of the main frame. In this case, it is advisable to run a 1/8-inch stove bolt through each of the ends.Fig. 20. Details of Outriggers and Front Elevating Planes as Seen from Driver's SeatFig. 20. Details of Outriggers and Front Elevating Planes as Seen from Driver's SeatThe crosspieces of theA-frames are spruce of the same section, or a little smaller. At their ends may be used strut sockets like those of the main frame; or, if it is desired to save this expense, they may be fastened by strips of 1/16-inch steel stock with through bolts.The front outrigger has, besides the two A-frames, a rather complicated arrangement of struts designed to brace the front wheel against the shocks of landing. This arrangement does not appear very plain in a plan or elevation, and may best be understood by reference to the photograph, Fig. 19, and the perspective drawing, Fig. 20. Fig. 20 is a view from the driver's seat. The elevator is seen in front, theA-frames at each side, and at the bottom the two diagonal beams to the engine bed and the skid.Reference to this drawing will show the two diagonals run from the front wheel up and back to the top of the main frame, and two more from the wheel forward to the short crosspieces near the apexes of theA-frame: there is also a vertical strut which intersects two horizontal pieces running between the ends of the longer crosspieces of theA-frames. Altogether, there are five attachments on each side of the front wheel, through which the axle bolt must pass, viz, the connections to the skid, to one of the diagonals to the engine bed, to one of the rear diagonals, to one of the front diagonals, and to one side of the fork carrying the vertical strut. Of these the skid attachments should be on the inside closest to the wheel, and the engine bed diagonals next.The four additional diagonals running to the front wheel may be spruce of the same section used in theA-frames, or turned one inch round. At each end they have flattened ferrules of steel tubing. The beams of theA-frames have similar ferrules at the ends where they attach to the main frames. These attachments should be made on the socket bolts of the struts on either side of the middle 6-foot section and on the outer side of the main beams—not between the beam and the socket itself.It is possible, of course, to make all theA-frames and diagonal braces of bamboo, if desired, the qualities of this material already having been referred to. Bamboo rods for this purpose should be between 1 and 1 1/4 inches in diameter. Where ferrules are fitted on the ends, the hole of the bamboo should be plugged with wood glued in place.Generally, in the construction of the outrigger frames, the builder can use his own discretion to a considerable extent. There tire innumerable details which can be varied—far too many to consider even a part of the possibilities in this connection. If the builder runs across any detail which he does not see mentioned here, he may safely assume that any workmanlike job will suffice. Often, the method may be adapted to the materials on hand. The diagonal wires from the crosspieces of the A-frames to the struts should be crossed.Rudder and Tail Construction. The frame for the rudder and tail are constructed in much the same way as those for the elevator, Fig. 18. Spruce sticks 1 by 1/2 inch are used throughout, except for the piece at the back edge of the rudder and the long middle piece across the tail; these should be 1 1/2 by 1/2 inch. This long middle piece of the tail is laid across on top of the rest of the framework. When the cloth is put on, this makes the upper surface slightly convex while the lower surface remains flat. The ends of this piece should be reinforced with sheet steel, fairly heavy and drilled for 1/4-inch bolts, attaching the tail to theA-frames.The rudder is hung from two posts extending above and below the tail. These posts may be set in cast aluminum sockets, such as may be obtained from any supply house for 20 cents apiece. The posts need not be more than 3/4 inch in diameter. At their outer ends, they should have ferrules of steel tubing, and the turnbuckles or other attachments for the truss wires should be attached by a wood screw running into the end of each. From these posts the rudder may be hung on any light hinges the builder may find convenient, or on hinges improvised from screw eyes or eye bolts, with a bolt passing through the eyes of each.In steering, the rudder is controlled by a steering wheel carried on a hinged post in front of the pilot. This post should be ash about 1 by 1 1/4 inches. It hinges at the bottom on a steel tube of 1/2-inch diameter which passes through it and is supported at the ends on diagonal beams to the engine bed. Two diagonals of lighter tubing may be put in to hold the posts centered between the two beams.The post is, of course, upright, and the hub of the wheel is horizontal. The wheel may be conveniently mounted on a piece of tubing of the same size as the hub hole, run through the post and held by a comparatively small bolt, which passes through it and has a big washer on either end. The wheel is preferably of the motor-boat variety with a groove around the rim for the steering cable.The rear edge of the tail should be about 1 inch lower than the front. To make the rudder post stand approximately vertical, wedge-shaped pieces of wood may be set under the sockets.The steering connections should be of flexible cables of steel such as are made for this purpose. There should be a double pulley on the post just under the wheel, and the cables should be led off the post just at the hinge at the bottom, so that swinging the post will not affect them. The cable is then carried under the lower main plane and out the lower beams of theA-frames. It is attached to the rudder at the back edge; snap hooks should be used for easy disconnection in packing. Perhaps the best way of guiding the cable, instead of using pulleys, is to run it through short pieces of tubing lashed to the beams with friction tape. The tubing can be bent without flattening by first filling it with melted lead, which, after the bending, can be melted out again.Ailerons for Lateral Stability. The framework of the ailerons is made in the same way as that for the elevator, tail, and rudder, Fig. 18. The pieces around the edges should be 1 1/2 by 1/2 inch, as also the long strip laid over the top of the ribs. The ribs should be 1/2 by 3/4 inch. Each aileron has two holes, one for the strut to pass through, and the other for the diagonal truss wires at their intersection. The back edge also has a notch in it to clear the fore and aft wires. Each aileron is hung on four strips of soft steel about 1/2 by 3/16 inch, twisted so that one end is at right angles to the other. These are arranged one on each side of the strut which passes through the aileron, and one at each end. Bolts through the struts carry three of them and the outer one is trussed by wires to each end of the outer strut.A frame of 1/4-inch steel tubing fits around the aviator's shoulders and is hinged to the seat, so that he can move it by leaning from one side to the other. This is connected by flexible cable to the rear edges of the ailerons, so that when the aviator leans to the left, he will raise the left and lower the right aileron. The upper edges of the ailerons are directly connected to each other by a cable running along the upper front beam, so that they must always move together.Covering of the Planes. Mention has already been made of the fact, in the general description of the machine, that light sail cloth, as employed on the Wright machines, may be used for the planes or wings. As a matter of fact, many different materials may be successfully employed, the selection depending upon the builder himself and his financial resources. About 55 square yards of material will be required, and in comparing prices always compare the width as this may vary from 28 to 55 inches. Rubberized silk which is used on the standard Curtiss machines is the most expensive covering, its cost running up to something like two hundred dollars. There are also several good aero fabrics on the market which sell at 60 cents a square yard, as well as a number of brands of varnish for the cloth—most of them, however, quite expensive. The most economical method is to employ a strong linen cloth coated with shellac, which will be found very satisfactory.The covering of the frames with the cloth may well be postponed until after the engine has been installed and tested, thus avoiding the splashing of oil and dirt which the fabric is apt to receive during this operation. The wire to which the cloth is laced, must be strung along the rear ends of the ribs of each plane. The wires pass through holes in the ends of the small ribs and are attached to the main ribs with turnbuckles. At the ends of the planes the main ribs must be braced against the pull of the wire by a piece of 1/4-inch tubing running from the end of the rib diagonally up to the rear beam. Both turnbuckles and tube are fastened with one wood screw running into the end of the rib.The cloth should be cut to fit the panels between the main ribs and hemmed up, allowing at least an inch in each direction for stretch. Small eyelets should be put along the sides and rear edges an inch apart for the lacing. At the front edge, the cloth is tacked directly to the beam, the edge being taken well under and around to the back. Strong fish line is good material for the lacing.After the cloth is laced on, it must be tacked down to the small ribs. For this purpose, use upholstery tacks as they have big cup-shaped heads which grip the cloth and do not tear out. As an extra precaution a strip of heavy tape must be run over each rib under the tack heads. All the control members are covered on both sides, the edges being folded under and held by tacks.Making the Propeller. If the completed biplane is to fly properly and also have sufficient speed to make it safe, considerable care must be devoted to the design and making of the propeller. Every aeroplane has a safe speed, usually referred to in technical parlance as itscritical speed. In the case of the Curtiss biplane under consideration, this speed is about 40 miles an hour. By speeding up the motor considerably, it may be able to make 42 to 43 miles an hour in a calm, such a condition representing the only true measure of an aeroplane's ability in this direction, while on the other hand, it would not be safe to let its speed with relation to the wind (not to the ground) fall much below 35 miles an hour. At any slower rate of travel, its dynamic stability would be precarious and the machine would be likely to dive to the ground unexpectedly. The reasons for this have been explained more in detail under the heading of "The Internal Work of the Wind."The necessity of making the propeller need not discourage the ambitious builder—if he can spare the time to do it right, it will be excellent experience. If not, propellers designed for driving a machine of this size can be purchased ready to mount from any one of quite a number of manufacturers. But as the outlay required will be at least $50, doubtless most experimenters will prefer to undertake this part of the work as well as that of building the framework and main cell, particularly as more than 90 per cent of the sum mentioned is represented by labor. The cost of the material required is insignificant by comparison.True-Screw Design. First it will be necessary to design the propeller to meet the requirements of the biplane itself. As this is a matter that has already been gone into in considerable detail under the appropriate heading, no further explanation of propeller characteristics or of the technical terms employed, should be needed here. We will assume that the biplane is to have a speed of 40 miles per hour in still air with the motor running at 1,200 r.p.m. With this data, it will not be difficult to calculate the correct pitch of the propeller to give that result. Thus40 X 5,280 X 100 / 60 X 1,200 X 85 = 3.45or in round numbers a pitch of 3 1/2 feet. 40 (the speed in miles per hour) times 5,280 (feet per mile) divided by 00 (minutes in an hour) gives the speed of the aeroplane in feet per minute. Dividing this by 1,200 (revolutions per minute) gives the number of feet the aeroplane is to advance per revolution of the propeller. The "100/85" part of the equation represents the efficiency of the propeller which can safely be figured on,i.e., 85 per cent, or an allowance for slip of 15 per cent. Forty miles an hour is the maximum speed to be expected, while the r.p.m. rate of the engine should be that at which it operates to the best advantage.The merits of thetrue-screwandvariable-pitchpropellers have already been dwelt upon. The former is not only more simple to build, but experience has shown that, as generally employed, it gives better efficiency. Hence, the propeller under consideration will, be of the true-screw type. Its pitch has already been calculated as 3 1/2 feet. For a machine of this size and power, it should be 6 feet in diameter. Having worked out the pitch and decided upon the diameter, the next and most important thing is to calculate the pitch angle. It will be evident that no two points on the blade will travel through the air at the same speed. Obviously, a point near the tip of the propeller moves faster than one near the hub, just as in rounding a curve, the outer wheel of an automobile has to travel faster than the inner, because it has to travel farther to cover the same ground. For instance, taking the dimensions of the propeller in question it will be seen that its tips will be traveling through the air at close to 4.3 miles per minute, that is,6 X π X 1200 / 5,280 = 4.28in which 6, the diameter of the propeller in feet, times π gives the circumference of the circle which is traveled by the blade tips 1,200 times per minute; this divided by the number of feet per mile gives the miles per minute covered. On the other hand, a point on the blade but 6 inches from the hub will turn at only approximately 3,500 feet per minute. Therefore, if every part of the blade is to advance through the air equally, the inner part must be set at a greater angle than the outer part. Each part of the blade must be set at such an angle that at each revolution it will move forward through the air a distance equal to the pitch. This is known as the pitch angle. The pitch divided by the circumference of the circle described by any part of the blade, will give a quantity known as the tangent of an angle for that particular part. The angle corresponding to that tangent may most easily be found by referring to a book of trigonometric tables.Table II. Propeller Blade DataFor example, take that part of the blade of a 3 1/2-foot pitch propeller which is 6 inches from the center of the hub. Then3.5 X 12 / 6 X 2 π = 1.1141 tangent of 48 degrees 5 minutesin which 3.5 X 12 reduces the pitch to inches, while 6 X 2π is the circumference of the circle described by the point 6 inches from the hub. However, in order to give the propeller blade a proper hold on the air, it must be set at a greater angle than these figures would indicate. That is, it must be given an angle of incidence similar to that given to every one of the supporting planes of the machine. This additional angle ranges from 2 degrees 30 minutes, to 4 degrees, depending upon the speed at which the particular part of the blade travels; the greater the speed, the less the angle. This does not apply to that part of the blade near the hub as the latter is depended upon solely for strength and is not expected to add to the effective thrust of the propeller.Table II shows the complete set of figures for a blade of 3 1/2-foot pitch, the angles being worked out for sections of the blade 3 inches apart.These angles are employed in Fig. 21, which shows one blade of the propeller and its cross sections.It should be understood that these calculations apply only to the type of propeller known as thetrue screw, as distinguished from thevariable pitch. The design of the latter is a matter of personal skill and experience in its making which is hardly capable of expression in any mathematical formula. There are said to be only about three men in this country who know how to make a proper variable-pitch propeller, and it naturally is without advantage when made otherwise.Fig. 21. Details of Propeller Construction, Curtiss BiplaneFig. 21. Details of Propeller Construction, Curtiss BiplaneShaping the Blades. Like the ribs, the propeller is made up of a number of laminations of boards finished true and securely glued, afterward being cut to the proper shape, though this process, of course, involves far more skill than in the former case. Spruce is the strongest wood for its weight, but it is soft and cracks easily. Maple, on the other hand, is tough and hard, so that it will be an advantage to alternate the layers of these woods with an extra maple board, in order to make both outside strips of the harder wood, so as to form a good backing for the steel flanges at the hub, the rear layer extending the full length of the thin rear edges of the blades. Other woods may be employed and frequently are used by propeller manufacturers, such as mahogany (not the grained wood used for furniture, but a cheaper grade which is much stronger), walnut, alternate spruce and whitewood, and others.The boards should be selected with the greatest care so as to insure their being perfectly clear,i.e., absolutely free of knots, cross-grained streaks, or similar flaws, which would impair their strength and render them difficult to work smoothly. They should measure 6 inches wide by 6 feet 1 inch in length. Their surfaces must be finished perfectly true, so that they will come together uniformly all over the area on which they bear on one another, and the various pieces must be glued together with the most painstaking care. Have the glue hot, so that it will spread evenly, and see that it is of a uniform consistency, in order that it may be smoothly applied to every bit of the surface. They must then be clamped together under as much pressure as it is possible to apply to them with the means at hand, the rib press already described in detail forming an excellent tool for this purpose. Tighten up the nuts evenly a little at a time, avoiding the application of excessive or uneven pressure at one point, continuing the gradual tightening up process until it can not be carried any farther. This is to prevent the boards from assuming a curve in drying fast. Allow at least twenty-four hours for drying, during which period the laminated block should be kept in a cool, dry place at as even a temperature as possible.Before undertaking the remainder of the work, all of which must be carried out by hand, with the exception of cutting the block to the outline of the propeller, which may be done with a band saw, a set of templates or gauges should be made from the drawings. These will be necessary as guides for finishing the propeller accurately. Draw the sections out full size on sheets of cardboard or tin and cut out along the curves, finally dividing each sheet into two parts, one for the upper side and one for the lower. Care must be taken to get the sides of the template square, and when they are used, the propeller should be laid on a perfectly true and flat block. Each template should be marked as it is finished, to indicate what part of the blade it is a gauge for. The work of cutting the laminated block down to the lines represented by the templates is carried out with the aid of the plane, spoke shave, and gouge. After the firstroughing outto approximate the curvature of the finished propeller is completed, the cuts taken should be very fine, as it will be an easy matter to go too deep, thus spoiling the block and necessitating a new start with fresh material. For finishing, pieces of broken glass are employed to scrape the wood to a smooth surface, followed by coarse and finally by fine sandpaper.Mounting. The hub should be of the same diameter as the flange on the engine crank shaft to which the flywheel was bolted, and should have its bolt holes drilled to correspond. To strengthen the hub, light steel plates of the same diameter are screwed to it, front and back, and the bolt holes drilled right through the metal and wood. This method of fastening is recommended where it is possible to substitute the propeller for the flywheel formerly on the engine, it being common practice to omit the use of the flywheel altogether. The writer does not recommend this, however, as the advantages of smoother running and more reliable operation gained by the use of a flywheel in addition to the propeller far more than offset any disadvantage represented by its weight. It will be noted that the Wright motors have always been equipped with a flywheel of ample size and weight and this is undoubtedly responsible, in some measure at least, for the fact that the Wright biplanes fly with considerably less power than is ordinarily employed for machines of the same size. If the motor selected be equipped with an unusually heavy flywheel, and particularly where the wheel is of comparatively small diameter, making it less effective as a balancer, it may be replaced with one of lighter weight and larger diameter. It may be possible to attach it by keying to the forward end of the crank shaft, thus leaving the flange from which the flywheel was taken free for mounting the propeller. An ordinary belt pulley will serve excellently as the new flywheel, as most of its weight is centered in its rim, but as the common cast-iron belt pulley of commerce is seldom intended to run at any such speed as that of an automobile motor, it should be examined carefully for flaws. Otherwise, there will be danger of its blunting with disastrous results under the influence of centrifugal force. Its diameter should not exceed 16 inches in order to keep its peripheral speed within reasonable limits. Where the mounting of the motor permits of its use, a wood pulley 18 to 20 inches in diameter with a steel band about 1/8 to 1/4-inch thick, shrunk on its periphery, may be employed. Most builders will ridicule the idea of a flywheel other than the propeller itself. "You do not need it; so why carry the extra weight?" will be their query. It is not absolutely necessary, but it is an advantage.In case the flywheel of the engine selected is keyed to the crank shaft, or in case it is not possible to mount both the flywheel and the propeller on different ends of the crank shaft, some other expedient rather than that of bolting to the flange must be adopted. In such a case, the original flywheel, where practical to retain it, may be drilled and tapped and the propeller attached directly to it. Where the flywheel can not be kept, it will usually be found practical to cut off its rim and bolt the propeller either to the web or spokes, or to the flywheel hub, if it be cut down to the latter.The drawing. Fig. 21, shows the rear or concave side of the propeller. From the viewpoint of a man standing in its wind and facing forward, it turns to the left, or anti-clockwise. On many of the propellers now on the market, the curved edge is designed to go first. This type may have greater advantages over that described, but the straight front edge propeller is easier for the amateur to make.Mounting the Engine. Having completed the propeller, the next step is the mounting of the engine. Reference to the types available to the amateur aeroplane builder has already been made. There are a number of motors now on the market that have been designed specially for this purpose and not a few of them are of considerable merit. Their cost ranges from about $250 up to $2,500, but it may be possible to pick up a comparatively light-weight automobile motor second hand which will serve all purposes and which will cost far less than the cheapest aeronautic motor on the market. It must be capable of developing 30 actual horse-power at 1,000 to 1,200 r.p.m. and must not exceed 400 pounds complete with all accessories, such as the radiator and piping, magneto, water, oil, etc. Considerable weight may be saved on an automobile motor by removing the exhaust manifold and substituting a lighter flywheel for the one originally on the engine—or omitting it altogether, as just mentioned. A light-weight aeronautic radiator should be used in preference to the usual automobile radiator.When placing the engine in position on the ash beams forming its bed or support, it must be borne in mind that the complete machine, with the operator in the aviator's seat, is designed to balance on a point about 1 1/2 feet back of the front edge of the main planes. As the operator and the motor represent much the larger part of the total weight, the balance may easily be regulated by moving them slightly forward or backward, as may be required. It will be necessary, of course, to place the engine far enough back in any case to permit the propeller blades to clear the planes. The actual installation of the engine itself will be an easy matter for anyone who has had any experience in either automobile or marine gasoline motor work. It is designed to be bolted to the two engine beams in the same manner as on the side members of the frame of an automobile, or the engine bed in a boat. Just in front of the engine is the best place for the gasoline tank, which should be cylindrical with tapering ends, to cut down its wind resistance. If the designer is not anxious to carry out points as fine as this, a light copper cylindrical tank may be purchased from stock. It should hold at least ten gallons of gasoline. In front of the tank is the radiator.Controls. The controls may be located to conform to the builder's own ideas of accessibility and convenience. Usually the switch is placed on the steering column, and it may be of the ordinaryknifevariety, or one of the special switches made for this purpose, as taste may dictate. The throttle control and spark advance may either be in the form of pedals, working against springs, or of small levers working on a notched sector, at the side of the seat. The complete control, levers, and sector may be purchased ready to mount whenever desired, as they are made in this form for both automobile and marine work. This likewise applies to the wheel, which it would not pay the amateur to attempt to make.Another pedal should work a brake on the front wheel, the brake shoe consisting of a strip of sheet steel, fastened at one end to the fore part of the skid and pressed against the wheel by a bamboo rod directly connected with the brake pedal. An emergency brake can also be made by loosely bolting a stout bar of steel on the skid near its rear end; one end of this bar is connected to a lever near the seat, so that when this lever is pulled back the other end of the bar tends to dig into the ground. As making a landing is one of the most difficult feats for the amateur aviator to master and sufficient space for a long run after alighting is not always available, these brakes will be found a very important feature of the machine.Fig. 22. Method of Starting the Engine of an AeroplaneFig. 22. Method of Starting the Engine of an AeroplaneThe engine is started by swinging the propeller, and this is an operation requiring far more caution than cranking an automobile motor. Both hands should be placed on the same blade. Fig. 22, and the latter should always be pulled downward—never upward. With the switch off, first turn the propeller over several times to fill the cylinders with gas, leaving it just ahead of dead center of one of the cylinders, and with one blade extending upward and to the left at a 45-degree angle. After closing the switch, take the left blade with both hands and swing it downward sharply, getting out of the way of the following blade as quickly as possible.Tests. The first thing to be done after the propeller is finished and mounted on the engine is to test the combination, or power plant of the biplane, for speed and thrust, or pulling power. From these two quantities it will be easy to figure the power that the engine is delivering. The only instruments necessary are a spring balance reading to 300 pounds or over; a revolution counter, such as may be procured at any machinist's supply house for a dollar or two; and a watch. One end of the spring balance is fastened to the front end of the skid and the other to a heavy stake firmly driven in the ground a few feet back. The wheels of the biplane should be set on smooth boards so that they will not offer any resistance to the forward thrust. When the engine is started the spring balance will give a direct reading of the pull of the propeller.With one observer noting the thrust, another should check the number of revolutions the engine is turning per minute. To do this, a small hole should previously have been countersunk in the hub of the propeller to receive the conical rubber tip of the revolution counter. The observer stands behind the propeller, watch in one hand and revolution counter in the other. At the beginning of the minute period, the counter is pressed firmly against the hub, and quickly withdrawn at the end of the minute. A stop watch is naturally an advantage for the purpose. The horse-power is figured as follows, assuming, for example, a thrust of 250 pounds at 1,200 r.p.m.250 X 1200 X 3.5 X 100 / 33.000 X 85 = 37 h. p.As before, the "100/85" allows for the slip and represents the efficiency of the propeller; 33,000 is the number of foot pounds per minute or the equivalent of one horse-power, and 3.5 is the pitch of the propeller.Assembling the Biplane. Assembling the machine complete requires more space than is available in the average workshop. However, it is possible to assemble the sections of the planes in a comparatively small room, carrying the work far enough to make sure that everything will go together properly when the time comes for complete assembly at the testing ground. In this case, it is preferable to assemble the end sections first, standing them away when complete to make room for the central section, on which the running gear and outriggers are to be built up.The builder will have decided by this time whether he will make his machine on the regular plan, with one main rib between each section, or on the quick-detachable plan, which has two main ribs on either side of the central section, as previously explained.It is desirable to be able to assemble two sections at once and this should be possible anywhere as it requires a space only about 6 by 13 feet. Two wood 2X4's, about 12 feet long, should be nailed down on the blocks on the floor; make these level and parallel to each other at a distance of 3 feet 6 inches on centers, one being 3 inches higher than the other. Strips of wood should be nailed on them, so as to hold the main beams of the frame in place while assembling.The two front and two rear beam sections are laid in place and joined with the sheet-steel sleeves, the flanges of the sleeves on the inner side of the beams. Then through the sleeves in the front beams, which are, of course, those on the higher bed, drill the holes for the strut socket bolts (1/4 inch). The holes for the outer ones go through the projecting ends of the beams; those for the inner ones are half in each of the two abutting beams. At the end where the central section joins on, a short length of wood of the same section may be inserted in the sleeve while drilling the hole. An assistant should hold the beams firmly together while the holes are being drilled.Now lay in place the three main ribs belonging to the two sections under construction and fasten them at the front ends by putting in place the strut sockets for which the holes have been drilled, with a turnbuckle plate under each socket, Fig. 16. The strut socket bolt passes through the main rib and the beam. The bed on which the assembling is being done, should be cut when sufficiently under the joints to leave room for the projecting bolt ends. Set the ribs square with the front beams, then arrange the rear beams so that their joints come exactly under the ribs; clamp the ribs down and drill a true, vertical hole through the rib beam, holding the two sections of the beam together as before. Then put the rear strut sockets in place, using the angle washers previously described, above and below the rib.When the quick-detachable plan is followed, the ribs at the inner ends of the double section, where they join the central section, should be bolted on an inch from the ends of the beam, using 1/4-inch stove bolts instead of the socket bolts. The sleeves should be slotted, so that they can slide off without removing these bolts, as the sleeves and ribs which occupy the position over the joints of the beams, belong to the central section.The sections should now be strung up with the diagonal truss wires which will make them rigid enough to stand handling. The wires are attached at each end to the flange bolts of the sleeves. Either one or two turnbuckles may be used on each wire, as already explained; if but one turnbuckle be used, the other end of the wire may be conveniently attached to a strip of sheet steel bent double and drilled for the bolt, like the sheet-steel slip of a turnbuckle. The attachment, of whatever nature, should be put between the end and the flange of the sleeve, not between the two flanges.Three or four ribs can be used on each section; four are preferable on sections of full 6-foot length. They are, of course, evenly spaced on centers. At the front ends, they are attached to the beam by wood screws through their flattened ferrules. The attachment to the rear beam is made with a slip of sheet steel measuring 1/2 by 3 inches, bent over the rib and fastened to the beam at each side with a wood screw. A long wire nail is driven through the rib itself on the beam.Four double sections should be built up in this manner, the right and left upper and the right and left lower sections. Uppers and lowers are alike except for the inversion of the sockets in the upper sections. Rights and lefts differ in that the outer beams are long enough to fill up the sleeves, not leaving room for another beam to join on.Inserting the struts in their sockets between the upper and lower sections of the same side will now form either of the two sides of the machine complete. Care should be taken to get the rear struts the proper length with respect to the front ones to bring the upper and lower planes parallel. The distance from the top of the lower front beam to the top of the upper front beam should be the same as the distance between the rows of bracing holes in the upper and lower main ribs just above and below the rear struts—about 4 feet 6 inches. It should hardly be necessary to mention that the thick edges of the struts come to the front—they are fish-shaped and a fish is thicker at the head than at the tail.The truss wires may now be strung on in each square of the struts, beams, and main ribs, using turnbuckles as previously described. The wires should be taut enough to sing a low note when plucked between the thumb and forefinger. If the construction is carried out properly, the framework will stand square and true with an even tension on all the wires. It is permissible for the struts to slant backward a little as seen from the side, but all should be perfectly in line.For adjusting the turnbuckles, the builder should make for himself a handy little tool usually termed a nipple wrench. It is simply a strip of steel 1 1/2 by 1/2 by 3/32 inches, with a notch cut in the middle of the long sides to fit the flattened ends of the turnbuckle nipples. This is much handier than the pliers and does not burr up the nipples.It has been assumed in this description of the assembling that the builder is working in a limited space; if, on the contrary, he has room enough to set up the whole frame at once, the work will be much simpler. In this case, the construction bed should be 30 feet long. First build up the upper plane complete, standing it against the wall when finished; then build the lower plane, put the struts in their sockets, and lay on the upper plane complete.Returning to the plan of assembly by sections, after the side sections or wings of the machine have been completed, the struts may be taken out and the sections laid aside. The middle section, to which the running gear and outriggers will be attached, is now to be built up in the same way. If the builder is following the plan in which there is one main rib between each section, it will be necessary to take off the four inner main ribs from the sections already completed, to be used at the ends of the central section. The plan drawing of the complete machine shows that the ribs of the central section are cut off just back of the rear beam to make room for the propeller. This is necessary in order to set the motor far enough forward to balance the machine properly. The small ribs in this section have the same curve but are cut off 10 inches shorter at their rear ends, and the stumps are smoothed down for ferrules like those for the other small ribs. In the plan which has one main rib between each section, the main rib on each side of the central section must be left full length. In the quick-detachable plan with two main ribs on each side of the central section, the inner ones, which really belong to this section, are cut off short like the small ribs.In the drawing of the complete machine, the distance between the struts which carry the engine bed is shown as 2 feet. This is only approximate, as the distance must be varied to suit the motor employed. By this time, the builder will have decided what engine he is going to use—or can get—and should drill the holes for the sockets of these struts with due respect to the width of the engine's supporting feet or lugs, remembering that the engine bed beams go on the inside of the struts. In the drawing of the running gear. Fig. 17, the distance between the engine-bed struts has been designatedA. The distances,B, on each side are, of course, approximately (6'— 2*A*), whateverAmay be.VIEW OF THE FRENCH AVIATION GROUNDS SHOWING THE HANGARS RANGED ALONG THE EDGES OF THE FIELDVIEW OF THE FRENCH AVIATION GROUNDS SHOWING THE HANGARS RANGED ALONG THE EDGES OF THE FIELDThis Photograph Protected By International CopyrightEXAMINATION PAPERBUILDING AND FLYING ANAEROPLANEPART IRead Carefully: Place your name and full address at the head of the paper. Any cheap, light paper like the sample previously sent you may be used. Do not crowd your work, but arrange it neatly and legibly.Do not copy the answers from the Instruction Paper; use your own words so that we may be sure that you understand the subject.What type of machine, biplane or monoplane, makes the best glider and why?Give the dimensions of a glider which will support a man's weight.In a glider which has no rudder, how is the machine controlled?Give carefully the details of the start in making a glide.In what direction relative to the wind should a glide be made? Justify your answer.How must the stability and balance of a glider in flight be controlled?State the proper conditions for a successful glide.Give the essential characteristics of a Curtiss aeroplane, defining the various parts.Describe briefly the details of construction of the main supporting surfaces of a Curtiss.Draw a diagram of the assembled planes showing how the struts and cross wires are placed to give the required rigidity.Give the details of the running gear of the Curtiss.What is the office of the Curtiss ailerons and how are they controlled from the operator's seat? Draw sketch.Describe the details of the front and rear outriggers.What type of propeller is advised for the Curtiss? Give the details of its construction.Describe carefully the manner in which a propeller should move through the air in order to give the maximum propulsion.What determines the exact location of the motor in the aeroplane?Give correct method of starting the motor when ready for a flight.What tests should be conducted before a flight is undertaken?After completing the work, add and sign the following statement:I hereby certify that the above work is entirely my own.(Signed)
DETAILS OF CONSTRUCTIONMain Planes and Struts. It is preferable to begin with the construction of the main planes and their struts and truss wires, the ribs already described being the first step.The main beams offer no special difficulties. They are ovals 1 1/4 by 1 5/8 inches, all 6 feet long except the eight end ones, which are 6 feet 2 inches. The beams of the central section should be of ash, or should be thicker than the others. In the latter case, they must be tapered at the ends so that the clamping sleeves will fit and the additional wood must be all on the lower side, so that the rib will not be thrown out of alignment. The spruce used for the other beams should be reasonably clear and straight grained, but a small knot or two does not matter, provided it does not come near the ends of the beam. The beams may be cut to the oval shape by the sawmill or planed down by hand."Fish-shaped" or "stream-line" section, as it is more commonly termed, is used for the struts, Fig. 15. It is questionable whether this makes any material difference in the wind resistance, but it is common practice to follow it in order to minimize this factor. It is more important that the struts be larger at their centers than at the ends, as this strengthens them considerably. At their ends the struts have ferrules of the 1-inch brass or steel tubing, and fit into the sockets which clamp the ribs and beams together. The material is spruce but the four central struts which carry the engine bed should either be ash or of larger size, say 1 1/4 by 3 inches.Care Necessary to Get Planes Parallel. The front struts must be longer than the rear ones by the thickness of a main rib at the point where the rear strut bolt passes through it, less the thickness of the rib ferrule through which the bolt of the front strut must pass. However, the first distance is not really the actual thickness of the rib, but the distance between the top of the rear beam and the bottom of the strut socket. In the drawings the difference in length between the front and rear struts is given as 2 inches, but it is preferable for the builder to leave the rear struts rather long and then measure the actual distance when assembling, cutting the struts to fit. The ends of the struts should also be countersunk enough to clear the head of the socket bolt.One of the items which the builder can not well escape buying in finished form is the strut sockets. These are cup-shaped affairs of pressed steel which sell at 20 cents each. Sixteen of them will be required for the main frame, and a dozen more can advantageously be used in the front and rear controls, though for this purpose they are not absolutely necessary. They can also be obtained in a larger oval size suitable for the four central struts that carry the engine bed, as well as in the standard 1-inch size. The bolts which project through the bottom of the sockets are ordinary 1/4-inch stove bolts, with their heads brazed to the sockets.For the rear struts, where the bolt must pass through the slanting main rib, it is advisable to make angle washers to put under the socket and also between the beam and rib. These washers are made by sawing up a piece of heavy brass tubing, or a bar with a 1/4-inch hole drilled in its center, the saw cuts being taken alternately at right angles and at 60 degrees to the axis of the tube.The sleeves which clamp together the ends of the beams are made of sheet steel of about 20 gauge. The steel is cut out on the pattern given in the drawing, Fig. 16, and the 3/16-inch bolt holes drilled in the flanges. The flanges are bent over by clamping the sheet in a vise along the bending line and then beating down with a hammer. Then the sleeves can be bent into shape around a stray end of the beam wood. The holes for the strut socket bolts should not be drilled until ready to assemble. Ordinarily, 3/16-inch stove bolts will do to clamp the flanges together.Having reached this stage, the amateur builder must now supply himself with turnbuckles. As already mentioned, these may either be purchased or made by hand. It is permissible to use either one or two turnbuckles on each wire. One is really sufficient, but two—one at each end—add but little weight and give greater leeway in making adjustments. As there are about 115 wires in the machine which need turnbuckles, the number required will be either 115 or 230, depending upon the plan which is followed. Those of the turnbuckles to be used on the front and rear controls and the ailerons, about one-fifth of the total number, may be of lighter stock than those employed on wires which carry part of the weight of the machine.Making Turnbuckles for the Truss Wires. On the supposition that the builder will make his own turnbuckles, a simple form is described here. As will be seen from Fig. 16, the turnbuckles are simply bicycle spokes, with the nipple caught in a loop of sheet steel and the end of the spoke itself twisted into an eye to which the truss wire can be attached. The sheet steel used should be 18 or 16 gauge, and may be cut to pattern with a heavy pair of tin snips. The spokes should be 3/32 inch over the threaded portion. The eye should be twisted up tight and brazed so that it can not come apart. The hole in the middle of each strip is, of course, drilled the same size as the spoke nipple. The holes in the ends are 3/16 inch.In the original Curtiss machines, the turnbuckles were strung on the socket bolts one after another, sometimes making a pack of them half an inch thick. A much neater construction is shown in the drawings, in which the bolt pierces a single plate with lugs to which to make the turnbuckles fast by riveting. The plates are of different shapes, with two, three, or four lugs, according to the places where they are to be used. They are cut from steel stock 3/32 inch thick, with 1/4-inch holes for the socket bolts and 3/16 inch, or other convenient size, for the rivets that fasten on the turnbuckles.The relative merits of cable and piano wire for trussing have not been thoroughly threshed out. Each has its advantages and disadvantages. Most of the well-known builders use cable; yet if the difference between 1,000 feet of cable at 2 1/4 cents per foot (the price for 500-foot spools), and 8 pounds of piano wire at 70 cents a pound, looks considerable to the amateur builder, let him by all means use the wire. The cable, if used, should be the 3/32-inch size, which will stand a load of 800 pounds; piano wire should be 24 gauge, tested to 745 pounds. It should be noted that there is a special series of gauges for piano wire, known as the music wire gauge, in which the size of the wire increases with the gauge numbers, instead of the contrary, as is usual with machinery wire gauges.One by no means unimportant advantage of the piano wire is that it is much easier to fasten into the turnbuckles. A small sleeve or ferrule, a 1/4-inch length of 1/8-inch tubing, is first strung on the wire. The end of the wire is then passed through the turnbuckle eye, bent up, thrust through the sleeve, and again bent down. When the machine is taken apart, the wire is not disconnected from the eye, but instead the turnbuckle spoke is unscrewed from the nipple. The shape of the sheet-steel loop should be such as to hold the latter in place. Cable, on the other hand, must be cut with about 2 inches to spare. After being threaded through the turnbuckle eye, the end is wound back tightly on itself and then soldered, to make certain that it can not loosen.With a supply of turnbuckles and cable or piano wire at hand, the builder may go ahead with the main box-like structure or cell, which should be completed except for the cloth covering, and in proper alignment, before taking up the construction of the running gear and controls.Running Gear. The running gear of the machine is built of seamless steel tubing, those parts which carry the weight of the machine direct being of 3/4-inch outside diameter, 16-gauge tubing, while the others are 5/8-inch outside diameter, either 18 or 20 gauge. About 25 feet of the heavy and 45 feet of the light tubing will be required, in lengths as follows: Heavy, four 3-foot, three 4-foot; light, one 6-foot, two 4-foot 6-inch, and seven 4-foot pieces. Referring to Fig. 17, two diagonal braces from the rear beam to the engine bed, the V-shaped piece under the front engine bed struts and all of the rear frame except the horizontal piece from wheel to wheel, are of heavy tubing. The horizontal in the rear frame, diagonals from the rear wheels and the rear end of the skid to the front beam, the two horizontals between the front and rear beam, and the forward V are of light tubing.Fig. 17. Details of Curtiss Running GearFig. 17. Details of Curtiss Running GearThree ash beams are used in the running gear. Two of these run diagonally from the rear end of the engine bed to the front wheel. These are about 10 feet long and 1 by 1 3/4 inches section. The third, which on rough ground acts as a skid, is 8 1/2 feet long and about 2 inches square. Between the joints where the tubing frames are attached to it, the upper corners may be beveled off with a spoke shave an inch or more down each side. The beams are attached to the front wheel with strips of steel stock 1 1/2 inches wide and 1/8 inch thick. The engine bed beams are also ash about 1 by 1 3/4 inches section. Their rear ends are bolted to the middle of the rear engine bed struts and the front ends may be 1/2 inch higher.SCENE AT AVIATION MEET AT ROUEN, FRANCE, SHOWING AN ANTOINETTE MONOPLANE MAKING A TURNSCENE AT AVIATION MEET AT ROUEN, FRANCE, SHOWING AN ANTOINETTE MONOPLANE MAKING A TURNThis Photograph Protected By International CopyrightA FRENCH MONOPLANE TRAVELLING SIXTY-FIVE MILES AN HOURA FRENCH MONOPLANE TRAVELLING SIXTY-FIVE MILES AN HOURThis Photograph Protected By International CopyrightThe wheels are usually 20 by 2 inches, and of the bicycle type, but heavier and wider in the hub; the tires are single tube. These wheels, complete with tires, cost about $10 each. This size is used on the standard Curtiss machines, but novice operators, whose landings are not quite as gentle as they might be, find them easily broken. Therefore, it may be more economical in the end to pay a little more and get heavier tires—at least to start with.For working the tubing into shape, a plumber's blow torch is almost indispensable—most automobilists will already possess one of these. The oval, flat variety, holding about one pint, is very handy and packs away easily, but on steady work requires filling somewhat too frequently. With a dozen bricks a shield can be built in front of the torch to protect the flame and concentrate the heat. Whenever it is to be flattened and bent, the tubing should be brought to a bright red or yellow heat. Screwing the vise down on it will then flatten it quickly without hammer marks. Where the bend is to be made in the middle of the piece, however, it may be necessary to resort to the hammer and anvil.It is convenient to start with the framework under the rear beam. This may be drawn accurately to full size on the workshop floor, and the tubes bent to fit the drawing. With this framework once in place, a definite starting point for the remainder of the running gear is established. Here and in all other places, when boring through wood, the holes should be drilled out full, and larger washers should be placed under the bolt head and nut. All nuts should be provided with some sort of locking device The perspective drawing. Fig. 17, should show the general arrangement clearly enough to enable the builder to finish the running gear.Outriggers. Both the front and rear control members, or "outriggers" as they are termed, Fig. 12, may be conveniently built up on the central section of the main frame, which, it is assumed, has now been fitted with the running gear.The horizontal rudder, or "elevator," is a biplane structure like the main cell of the machine, but with fewer struts; it is carried in front of the main planes on twoA-shaped frames. The vertical rudder, at the rear, is split along the middle and straddles a fixed horizontal plane, ortail. This also is carried on twoA-shaped frames. Lateral stability is controlled by two auxiliary planes or ailerons, one at each side of the machine and carried on the two outer front struts. These three control units—elevator,tailandrudder, andailerons—will now be taken up separately and their construction, location on the machine, and operation will be described.Fig. 18. Details of Rudders and Ailerons, Curtiss BiplaneFig. 18. Details of Rudders and Ailerons, Curtiss BiplaneHorizonal Rudder or Elevator. The two planes of the elevator are 2 feet wide by 5 feet 8 inches long and are spaced 2 feet apart, being held in this position by ten struts. The frames of the planes are built of spruce sticks 1/2 by 1 inch, each plane having two sticks the full length and five evenly spaced crosspieces or ribs. These are joined together with squares of X-sheet tin, as shown in the detailed drawing, Fig. 18. With a little experimenting, paper patterns can be made from which the tin pieces can be cut out. The sticks are then nailed through the tin with 3/4-inch brads.It is convenient to draw the frames out accurately on a smooth wood floor and then work over this drawing. The first few brads will hold the sticks in place. When all the brads have been driven, a little drop of solder should be run in around the head of each one. This is a tedious job. One must be careful to use no more solder than necessary as it increases the weight very rapidly. Two pounds of wire solder should be sufficient for all the control members which are built in this way. When the top side is soldered, pry the frame loose from the floor with a screwdriver and turn it over. Then the projecting points of the brads must be clinched and the soldering repeated.At this stage, the two frames should be covered on both sides with the prepared cloth used for covering the main planes. The method of preparing this cloth is detailed a little farther along.The struts, so-called, to continue the analogy with the main planes, are turned sticks of spruce 3/8 inch in diameter. They are fitted at each end with ferrules of thin 3/8-inch brass, or steel tubing, driven on tight. Instead of using sockets, the struts are held at each end, simply by a long wood screw driven through the tin and wood of the plane frame and into the strut. These screws also hold the turnbuckles for the truss wires. For trussing purposes, the elevator is regarded as consisting of two sections only, the intermediate struts being disregarded.The turnbuckles and wire used here and in the other control members may well be of lighter stock than those used in the main planes. Piano wire, No. 18, or 1/16-inch cable is amply strong. The sheet steel may be about 22 gauge, instead of 16, and the bicycle spokes smaller in proportion. No turnbuckle plates are necessary. The screws running into the struts may be passed directly through the eyes of the turnbuckles, where they would have been attached to the turnbuckle plate. In order to secure a square and neat structure, those struts which have turnbuckles at their ends should be made a trifle shorter than the others.At each end, the elevator has anX-shaped frame of 1/4-inch steel tubing; at the intersection of theX's are pivots on which the elevator is supported. EachXis made of two tubes, bent into a y and flattened and brazed together at the points. The ends of theX's are flattened and bent over so that the screws which hold the struts in place may pass through them.Fig. 19. Curtiss Biplane Ready for FlightFig. 19. Curtiss Biplane Ready for FlightTo the front middle strut is attached an extension which acts as a lever for operating the elevator. This is a stick of spruce 3/4 inch in diameter and 3 feet 3 inches long. At its upper end it has a ferrule of steel tubing, flattened at the end. The lower part of the stick may be fastened to the strut by wrapping the tube with friction tape, or by improvising a couple of sheet steel clamps. The upper end of the stick is braced by a 1/4-inch steel tube, extending to the top of the rear middle strut, and held by the same screw as the strut. This extension lever is connected to the steering column by a bamboo rod, 1 inch in diameter and about 10 feet long, provided with flattened ferrules of steel tubing at each end. Each ferrule should be held on by a 1/8-inch stove bolt passing through it.Front and Rear Outrigger Frames. Both the front elevator and the tail and rudder at the rear, are carried, as mentioned above, each on a pair ofA-shaped frames, similar to one another, except that those in the rear are longer than those in the front. Both are made of spruce of about the same section as used for the struts of the main frame. These pieces may either be full length, or they may be jointed at the intersection of the crosspieces, the ends being clamped in a sheet-steel sleeve, just like that used on the beams of the main frame. In this case, it is advisable to run a 1/8-inch stove bolt through each of the ends.Fig. 20. Details of Outriggers and Front Elevating Planes as Seen from Driver's SeatFig. 20. Details of Outriggers and Front Elevating Planes as Seen from Driver's SeatThe crosspieces of theA-frames are spruce of the same section, or a little smaller. At their ends may be used strut sockets like those of the main frame; or, if it is desired to save this expense, they may be fastened by strips of 1/16-inch steel stock with through bolts.The front outrigger has, besides the two A-frames, a rather complicated arrangement of struts designed to brace the front wheel against the shocks of landing. This arrangement does not appear very plain in a plan or elevation, and may best be understood by reference to the photograph, Fig. 19, and the perspective drawing, Fig. 20. Fig. 20 is a view from the driver's seat. The elevator is seen in front, theA-frames at each side, and at the bottom the two diagonal beams to the engine bed and the skid.Reference to this drawing will show the two diagonals run from the front wheel up and back to the top of the main frame, and two more from the wheel forward to the short crosspieces near the apexes of theA-frame: there is also a vertical strut which intersects two horizontal pieces running between the ends of the longer crosspieces of theA-frames. Altogether, there are five attachments on each side of the front wheel, through which the axle bolt must pass, viz, the connections to the skid, to one of the diagonals to the engine bed, to one of the rear diagonals, to one of the front diagonals, and to one side of the fork carrying the vertical strut. Of these the skid attachments should be on the inside closest to the wheel, and the engine bed diagonals next.The four additional diagonals running to the front wheel may be spruce of the same section used in theA-frames, or turned one inch round. At each end they have flattened ferrules of steel tubing. The beams of theA-frames have similar ferrules at the ends where they attach to the main frames. These attachments should be made on the socket bolts of the struts on either side of the middle 6-foot section and on the outer side of the main beams—not between the beam and the socket itself.It is possible, of course, to make all theA-frames and diagonal braces of bamboo, if desired, the qualities of this material already having been referred to. Bamboo rods for this purpose should be between 1 and 1 1/4 inches in diameter. Where ferrules are fitted on the ends, the hole of the bamboo should be plugged with wood glued in place.Generally, in the construction of the outrigger frames, the builder can use his own discretion to a considerable extent. There tire innumerable details which can be varied—far too many to consider even a part of the possibilities in this connection. If the builder runs across any detail which he does not see mentioned here, he may safely assume that any workmanlike job will suffice. Often, the method may be adapted to the materials on hand. The diagonal wires from the crosspieces of the A-frames to the struts should be crossed.Rudder and Tail Construction. The frame for the rudder and tail are constructed in much the same way as those for the elevator, Fig. 18. Spruce sticks 1 by 1/2 inch are used throughout, except for the piece at the back edge of the rudder and the long middle piece across the tail; these should be 1 1/2 by 1/2 inch. This long middle piece of the tail is laid across on top of the rest of the framework. When the cloth is put on, this makes the upper surface slightly convex while the lower surface remains flat. The ends of this piece should be reinforced with sheet steel, fairly heavy and drilled for 1/4-inch bolts, attaching the tail to theA-frames.The rudder is hung from two posts extending above and below the tail. These posts may be set in cast aluminum sockets, such as may be obtained from any supply house for 20 cents apiece. The posts need not be more than 3/4 inch in diameter. At their outer ends, they should have ferrules of steel tubing, and the turnbuckles or other attachments for the truss wires should be attached by a wood screw running into the end of each. From these posts the rudder may be hung on any light hinges the builder may find convenient, or on hinges improvised from screw eyes or eye bolts, with a bolt passing through the eyes of each.In steering, the rudder is controlled by a steering wheel carried on a hinged post in front of the pilot. This post should be ash about 1 by 1 1/4 inches. It hinges at the bottom on a steel tube of 1/2-inch diameter which passes through it and is supported at the ends on diagonal beams to the engine bed. Two diagonals of lighter tubing may be put in to hold the posts centered between the two beams.The post is, of course, upright, and the hub of the wheel is horizontal. The wheel may be conveniently mounted on a piece of tubing of the same size as the hub hole, run through the post and held by a comparatively small bolt, which passes through it and has a big washer on either end. The wheel is preferably of the motor-boat variety with a groove around the rim for the steering cable.The rear edge of the tail should be about 1 inch lower than the front. To make the rudder post stand approximately vertical, wedge-shaped pieces of wood may be set under the sockets.The steering connections should be of flexible cables of steel such as are made for this purpose. There should be a double pulley on the post just under the wheel, and the cables should be led off the post just at the hinge at the bottom, so that swinging the post will not affect them. The cable is then carried under the lower main plane and out the lower beams of theA-frames. It is attached to the rudder at the back edge; snap hooks should be used for easy disconnection in packing. Perhaps the best way of guiding the cable, instead of using pulleys, is to run it through short pieces of tubing lashed to the beams with friction tape. The tubing can be bent without flattening by first filling it with melted lead, which, after the bending, can be melted out again.Ailerons for Lateral Stability. The framework of the ailerons is made in the same way as that for the elevator, tail, and rudder, Fig. 18. The pieces around the edges should be 1 1/2 by 1/2 inch, as also the long strip laid over the top of the ribs. The ribs should be 1/2 by 3/4 inch. Each aileron has two holes, one for the strut to pass through, and the other for the diagonal truss wires at their intersection. The back edge also has a notch in it to clear the fore and aft wires. Each aileron is hung on four strips of soft steel about 1/2 by 3/16 inch, twisted so that one end is at right angles to the other. These are arranged one on each side of the strut which passes through the aileron, and one at each end. Bolts through the struts carry three of them and the outer one is trussed by wires to each end of the outer strut.A frame of 1/4-inch steel tubing fits around the aviator's shoulders and is hinged to the seat, so that he can move it by leaning from one side to the other. This is connected by flexible cable to the rear edges of the ailerons, so that when the aviator leans to the left, he will raise the left and lower the right aileron. The upper edges of the ailerons are directly connected to each other by a cable running along the upper front beam, so that they must always move together.Covering of the Planes. Mention has already been made of the fact, in the general description of the machine, that light sail cloth, as employed on the Wright machines, may be used for the planes or wings. As a matter of fact, many different materials may be successfully employed, the selection depending upon the builder himself and his financial resources. About 55 square yards of material will be required, and in comparing prices always compare the width as this may vary from 28 to 55 inches. Rubberized silk which is used on the standard Curtiss machines is the most expensive covering, its cost running up to something like two hundred dollars. There are also several good aero fabrics on the market which sell at 60 cents a square yard, as well as a number of brands of varnish for the cloth—most of them, however, quite expensive. The most economical method is to employ a strong linen cloth coated with shellac, which will be found very satisfactory.The covering of the frames with the cloth may well be postponed until after the engine has been installed and tested, thus avoiding the splashing of oil and dirt which the fabric is apt to receive during this operation. The wire to which the cloth is laced, must be strung along the rear ends of the ribs of each plane. The wires pass through holes in the ends of the small ribs and are attached to the main ribs with turnbuckles. At the ends of the planes the main ribs must be braced against the pull of the wire by a piece of 1/4-inch tubing running from the end of the rib diagonally up to the rear beam. Both turnbuckles and tube are fastened with one wood screw running into the end of the rib.The cloth should be cut to fit the panels between the main ribs and hemmed up, allowing at least an inch in each direction for stretch. Small eyelets should be put along the sides and rear edges an inch apart for the lacing. At the front edge, the cloth is tacked directly to the beam, the edge being taken well under and around to the back. Strong fish line is good material for the lacing.After the cloth is laced on, it must be tacked down to the small ribs. For this purpose, use upholstery tacks as they have big cup-shaped heads which grip the cloth and do not tear out. As an extra precaution a strip of heavy tape must be run over each rib under the tack heads. All the control members are covered on both sides, the edges being folded under and held by tacks.Making the Propeller. If the completed biplane is to fly properly and also have sufficient speed to make it safe, considerable care must be devoted to the design and making of the propeller. Every aeroplane has a safe speed, usually referred to in technical parlance as itscritical speed. In the case of the Curtiss biplane under consideration, this speed is about 40 miles an hour. By speeding up the motor considerably, it may be able to make 42 to 43 miles an hour in a calm, such a condition representing the only true measure of an aeroplane's ability in this direction, while on the other hand, it would not be safe to let its speed with relation to the wind (not to the ground) fall much below 35 miles an hour. At any slower rate of travel, its dynamic stability would be precarious and the machine would be likely to dive to the ground unexpectedly. The reasons for this have been explained more in detail under the heading of "The Internal Work of the Wind."The necessity of making the propeller need not discourage the ambitious builder—if he can spare the time to do it right, it will be excellent experience. If not, propellers designed for driving a machine of this size can be purchased ready to mount from any one of quite a number of manufacturers. But as the outlay required will be at least $50, doubtless most experimenters will prefer to undertake this part of the work as well as that of building the framework and main cell, particularly as more than 90 per cent of the sum mentioned is represented by labor. The cost of the material required is insignificant by comparison.True-Screw Design. First it will be necessary to design the propeller to meet the requirements of the biplane itself. As this is a matter that has already been gone into in considerable detail under the appropriate heading, no further explanation of propeller characteristics or of the technical terms employed, should be needed here. We will assume that the biplane is to have a speed of 40 miles per hour in still air with the motor running at 1,200 r.p.m. With this data, it will not be difficult to calculate the correct pitch of the propeller to give that result. Thus40 X 5,280 X 100 / 60 X 1,200 X 85 = 3.45or in round numbers a pitch of 3 1/2 feet. 40 (the speed in miles per hour) times 5,280 (feet per mile) divided by 00 (minutes in an hour) gives the speed of the aeroplane in feet per minute. Dividing this by 1,200 (revolutions per minute) gives the number of feet the aeroplane is to advance per revolution of the propeller. The "100/85" part of the equation represents the efficiency of the propeller which can safely be figured on,i.e., 85 per cent, or an allowance for slip of 15 per cent. Forty miles an hour is the maximum speed to be expected, while the r.p.m. rate of the engine should be that at which it operates to the best advantage.The merits of thetrue-screwandvariable-pitchpropellers have already been dwelt upon. The former is not only more simple to build, but experience has shown that, as generally employed, it gives better efficiency. Hence, the propeller under consideration will, be of the true-screw type. Its pitch has already been calculated as 3 1/2 feet. For a machine of this size and power, it should be 6 feet in diameter. Having worked out the pitch and decided upon the diameter, the next and most important thing is to calculate the pitch angle. It will be evident that no two points on the blade will travel through the air at the same speed. Obviously, a point near the tip of the propeller moves faster than one near the hub, just as in rounding a curve, the outer wheel of an automobile has to travel faster than the inner, because it has to travel farther to cover the same ground. For instance, taking the dimensions of the propeller in question it will be seen that its tips will be traveling through the air at close to 4.3 miles per minute, that is,6 X π X 1200 / 5,280 = 4.28in which 6, the diameter of the propeller in feet, times π gives the circumference of the circle which is traveled by the blade tips 1,200 times per minute; this divided by the number of feet per mile gives the miles per minute covered. On the other hand, a point on the blade but 6 inches from the hub will turn at only approximately 3,500 feet per minute. Therefore, if every part of the blade is to advance through the air equally, the inner part must be set at a greater angle than the outer part. Each part of the blade must be set at such an angle that at each revolution it will move forward through the air a distance equal to the pitch. This is known as the pitch angle. The pitch divided by the circumference of the circle described by any part of the blade, will give a quantity known as the tangent of an angle for that particular part. The angle corresponding to that tangent may most easily be found by referring to a book of trigonometric tables.Table II. Propeller Blade DataFor example, take that part of the blade of a 3 1/2-foot pitch propeller which is 6 inches from the center of the hub. Then3.5 X 12 / 6 X 2 π = 1.1141 tangent of 48 degrees 5 minutesin which 3.5 X 12 reduces the pitch to inches, while 6 X 2π is the circumference of the circle described by the point 6 inches from the hub. However, in order to give the propeller blade a proper hold on the air, it must be set at a greater angle than these figures would indicate. That is, it must be given an angle of incidence similar to that given to every one of the supporting planes of the machine. This additional angle ranges from 2 degrees 30 minutes, to 4 degrees, depending upon the speed at which the particular part of the blade travels; the greater the speed, the less the angle. This does not apply to that part of the blade near the hub as the latter is depended upon solely for strength and is not expected to add to the effective thrust of the propeller.Table II shows the complete set of figures for a blade of 3 1/2-foot pitch, the angles being worked out for sections of the blade 3 inches apart.These angles are employed in Fig. 21, which shows one blade of the propeller and its cross sections.It should be understood that these calculations apply only to the type of propeller known as thetrue screw, as distinguished from thevariable pitch. The design of the latter is a matter of personal skill and experience in its making which is hardly capable of expression in any mathematical formula. There are said to be only about three men in this country who know how to make a proper variable-pitch propeller, and it naturally is without advantage when made otherwise.Fig. 21. Details of Propeller Construction, Curtiss BiplaneFig. 21. Details of Propeller Construction, Curtiss BiplaneShaping the Blades. Like the ribs, the propeller is made up of a number of laminations of boards finished true and securely glued, afterward being cut to the proper shape, though this process, of course, involves far more skill than in the former case. Spruce is the strongest wood for its weight, but it is soft and cracks easily. Maple, on the other hand, is tough and hard, so that it will be an advantage to alternate the layers of these woods with an extra maple board, in order to make both outside strips of the harder wood, so as to form a good backing for the steel flanges at the hub, the rear layer extending the full length of the thin rear edges of the blades. Other woods may be employed and frequently are used by propeller manufacturers, such as mahogany (not the grained wood used for furniture, but a cheaper grade which is much stronger), walnut, alternate spruce and whitewood, and others.The boards should be selected with the greatest care so as to insure their being perfectly clear,i.e., absolutely free of knots, cross-grained streaks, or similar flaws, which would impair their strength and render them difficult to work smoothly. They should measure 6 inches wide by 6 feet 1 inch in length. Their surfaces must be finished perfectly true, so that they will come together uniformly all over the area on which they bear on one another, and the various pieces must be glued together with the most painstaking care. Have the glue hot, so that it will spread evenly, and see that it is of a uniform consistency, in order that it may be smoothly applied to every bit of the surface. They must then be clamped together under as much pressure as it is possible to apply to them with the means at hand, the rib press already described in detail forming an excellent tool for this purpose. Tighten up the nuts evenly a little at a time, avoiding the application of excessive or uneven pressure at one point, continuing the gradual tightening up process until it can not be carried any farther. This is to prevent the boards from assuming a curve in drying fast. Allow at least twenty-four hours for drying, during which period the laminated block should be kept in a cool, dry place at as even a temperature as possible.Before undertaking the remainder of the work, all of which must be carried out by hand, with the exception of cutting the block to the outline of the propeller, which may be done with a band saw, a set of templates or gauges should be made from the drawings. These will be necessary as guides for finishing the propeller accurately. Draw the sections out full size on sheets of cardboard or tin and cut out along the curves, finally dividing each sheet into two parts, one for the upper side and one for the lower. Care must be taken to get the sides of the template square, and when they are used, the propeller should be laid on a perfectly true and flat block. Each template should be marked as it is finished, to indicate what part of the blade it is a gauge for. The work of cutting the laminated block down to the lines represented by the templates is carried out with the aid of the plane, spoke shave, and gouge. After the firstroughing outto approximate the curvature of the finished propeller is completed, the cuts taken should be very fine, as it will be an easy matter to go too deep, thus spoiling the block and necessitating a new start with fresh material. For finishing, pieces of broken glass are employed to scrape the wood to a smooth surface, followed by coarse and finally by fine sandpaper.Mounting. The hub should be of the same diameter as the flange on the engine crank shaft to which the flywheel was bolted, and should have its bolt holes drilled to correspond. To strengthen the hub, light steel plates of the same diameter are screwed to it, front and back, and the bolt holes drilled right through the metal and wood. This method of fastening is recommended where it is possible to substitute the propeller for the flywheel formerly on the engine, it being common practice to omit the use of the flywheel altogether. The writer does not recommend this, however, as the advantages of smoother running and more reliable operation gained by the use of a flywheel in addition to the propeller far more than offset any disadvantage represented by its weight. It will be noted that the Wright motors have always been equipped with a flywheel of ample size and weight and this is undoubtedly responsible, in some measure at least, for the fact that the Wright biplanes fly with considerably less power than is ordinarily employed for machines of the same size. If the motor selected be equipped with an unusually heavy flywheel, and particularly where the wheel is of comparatively small diameter, making it less effective as a balancer, it may be replaced with one of lighter weight and larger diameter. It may be possible to attach it by keying to the forward end of the crank shaft, thus leaving the flange from which the flywheel was taken free for mounting the propeller. An ordinary belt pulley will serve excellently as the new flywheel, as most of its weight is centered in its rim, but as the common cast-iron belt pulley of commerce is seldom intended to run at any such speed as that of an automobile motor, it should be examined carefully for flaws. Otherwise, there will be danger of its blunting with disastrous results under the influence of centrifugal force. Its diameter should not exceed 16 inches in order to keep its peripheral speed within reasonable limits. Where the mounting of the motor permits of its use, a wood pulley 18 to 20 inches in diameter with a steel band about 1/8 to 1/4-inch thick, shrunk on its periphery, may be employed. Most builders will ridicule the idea of a flywheel other than the propeller itself. "You do not need it; so why carry the extra weight?" will be their query. It is not absolutely necessary, but it is an advantage.In case the flywheel of the engine selected is keyed to the crank shaft, or in case it is not possible to mount both the flywheel and the propeller on different ends of the crank shaft, some other expedient rather than that of bolting to the flange must be adopted. In such a case, the original flywheel, where practical to retain it, may be drilled and tapped and the propeller attached directly to it. Where the flywheel can not be kept, it will usually be found practical to cut off its rim and bolt the propeller either to the web or spokes, or to the flywheel hub, if it be cut down to the latter.The drawing. Fig. 21, shows the rear or concave side of the propeller. From the viewpoint of a man standing in its wind and facing forward, it turns to the left, or anti-clockwise. On many of the propellers now on the market, the curved edge is designed to go first. This type may have greater advantages over that described, but the straight front edge propeller is easier for the amateur to make.Mounting the Engine. Having completed the propeller, the next step is the mounting of the engine. Reference to the types available to the amateur aeroplane builder has already been made. There are a number of motors now on the market that have been designed specially for this purpose and not a few of them are of considerable merit. Their cost ranges from about $250 up to $2,500, but it may be possible to pick up a comparatively light-weight automobile motor second hand which will serve all purposes and which will cost far less than the cheapest aeronautic motor on the market. It must be capable of developing 30 actual horse-power at 1,000 to 1,200 r.p.m. and must not exceed 400 pounds complete with all accessories, such as the radiator and piping, magneto, water, oil, etc. Considerable weight may be saved on an automobile motor by removing the exhaust manifold and substituting a lighter flywheel for the one originally on the engine—or omitting it altogether, as just mentioned. A light-weight aeronautic radiator should be used in preference to the usual automobile radiator.When placing the engine in position on the ash beams forming its bed or support, it must be borne in mind that the complete machine, with the operator in the aviator's seat, is designed to balance on a point about 1 1/2 feet back of the front edge of the main planes. As the operator and the motor represent much the larger part of the total weight, the balance may easily be regulated by moving them slightly forward or backward, as may be required. It will be necessary, of course, to place the engine far enough back in any case to permit the propeller blades to clear the planes. The actual installation of the engine itself will be an easy matter for anyone who has had any experience in either automobile or marine gasoline motor work. It is designed to be bolted to the two engine beams in the same manner as on the side members of the frame of an automobile, or the engine bed in a boat. Just in front of the engine is the best place for the gasoline tank, which should be cylindrical with tapering ends, to cut down its wind resistance. If the designer is not anxious to carry out points as fine as this, a light copper cylindrical tank may be purchased from stock. It should hold at least ten gallons of gasoline. In front of the tank is the radiator.Controls. The controls may be located to conform to the builder's own ideas of accessibility and convenience. Usually the switch is placed on the steering column, and it may be of the ordinaryknifevariety, or one of the special switches made for this purpose, as taste may dictate. The throttle control and spark advance may either be in the form of pedals, working against springs, or of small levers working on a notched sector, at the side of the seat. The complete control, levers, and sector may be purchased ready to mount whenever desired, as they are made in this form for both automobile and marine work. This likewise applies to the wheel, which it would not pay the amateur to attempt to make.Another pedal should work a brake on the front wheel, the brake shoe consisting of a strip of sheet steel, fastened at one end to the fore part of the skid and pressed against the wheel by a bamboo rod directly connected with the brake pedal. An emergency brake can also be made by loosely bolting a stout bar of steel on the skid near its rear end; one end of this bar is connected to a lever near the seat, so that when this lever is pulled back the other end of the bar tends to dig into the ground. As making a landing is one of the most difficult feats for the amateur aviator to master and sufficient space for a long run after alighting is not always available, these brakes will be found a very important feature of the machine.Fig. 22. Method of Starting the Engine of an AeroplaneFig. 22. Method of Starting the Engine of an AeroplaneThe engine is started by swinging the propeller, and this is an operation requiring far more caution than cranking an automobile motor. Both hands should be placed on the same blade. Fig. 22, and the latter should always be pulled downward—never upward. With the switch off, first turn the propeller over several times to fill the cylinders with gas, leaving it just ahead of dead center of one of the cylinders, and with one blade extending upward and to the left at a 45-degree angle. After closing the switch, take the left blade with both hands and swing it downward sharply, getting out of the way of the following blade as quickly as possible.Tests. The first thing to be done after the propeller is finished and mounted on the engine is to test the combination, or power plant of the biplane, for speed and thrust, or pulling power. From these two quantities it will be easy to figure the power that the engine is delivering. The only instruments necessary are a spring balance reading to 300 pounds or over; a revolution counter, such as may be procured at any machinist's supply house for a dollar or two; and a watch. One end of the spring balance is fastened to the front end of the skid and the other to a heavy stake firmly driven in the ground a few feet back. The wheels of the biplane should be set on smooth boards so that they will not offer any resistance to the forward thrust. When the engine is started the spring balance will give a direct reading of the pull of the propeller.With one observer noting the thrust, another should check the number of revolutions the engine is turning per minute. To do this, a small hole should previously have been countersunk in the hub of the propeller to receive the conical rubber tip of the revolution counter. The observer stands behind the propeller, watch in one hand and revolution counter in the other. At the beginning of the minute period, the counter is pressed firmly against the hub, and quickly withdrawn at the end of the minute. A stop watch is naturally an advantage for the purpose. The horse-power is figured as follows, assuming, for example, a thrust of 250 pounds at 1,200 r.p.m.250 X 1200 X 3.5 X 100 / 33.000 X 85 = 37 h. p.As before, the "100/85" allows for the slip and represents the efficiency of the propeller; 33,000 is the number of foot pounds per minute or the equivalent of one horse-power, and 3.5 is the pitch of the propeller.Assembling the Biplane. Assembling the machine complete requires more space than is available in the average workshop. However, it is possible to assemble the sections of the planes in a comparatively small room, carrying the work far enough to make sure that everything will go together properly when the time comes for complete assembly at the testing ground. In this case, it is preferable to assemble the end sections first, standing them away when complete to make room for the central section, on which the running gear and outriggers are to be built up.The builder will have decided by this time whether he will make his machine on the regular plan, with one main rib between each section, or on the quick-detachable plan, which has two main ribs on either side of the central section, as previously explained.It is desirable to be able to assemble two sections at once and this should be possible anywhere as it requires a space only about 6 by 13 feet. Two wood 2X4's, about 12 feet long, should be nailed down on the blocks on the floor; make these level and parallel to each other at a distance of 3 feet 6 inches on centers, one being 3 inches higher than the other. Strips of wood should be nailed on them, so as to hold the main beams of the frame in place while assembling.The two front and two rear beam sections are laid in place and joined with the sheet-steel sleeves, the flanges of the sleeves on the inner side of the beams. Then through the sleeves in the front beams, which are, of course, those on the higher bed, drill the holes for the strut socket bolts (1/4 inch). The holes for the outer ones go through the projecting ends of the beams; those for the inner ones are half in each of the two abutting beams. At the end where the central section joins on, a short length of wood of the same section may be inserted in the sleeve while drilling the hole. An assistant should hold the beams firmly together while the holes are being drilled.Now lay in place the three main ribs belonging to the two sections under construction and fasten them at the front ends by putting in place the strut sockets for which the holes have been drilled, with a turnbuckle plate under each socket, Fig. 16. The strut socket bolt passes through the main rib and the beam. The bed on which the assembling is being done, should be cut when sufficiently under the joints to leave room for the projecting bolt ends. Set the ribs square with the front beams, then arrange the rear beams so that their joints come exactly under the ribs; clamp the ribs down and drill a true, vertical hole through the rib beam, holding the two sections of the beam together as before. Then put the rear strut sockets in place, using the angle washers previously described, above and below the rib.When the quick-detachable plan is followed, the ribs at the inner ends of the double section, where they join the central section, should be bolted on an inch from the ends of the beam, using 1/4-inch stove bolts instead of the socket bolts. The sleeves should be slotted, so that they can slide off without removing these bolts, as the sleeves and ribs which occupy the position over the joints of the beams, belong to the central section.The sections should now be strung up with the diagonal truss wires which will make them rigid enough to stand handling. The wires are attached at each end to the flange bolts of the sleeves. Either one or two turnbuckles may be used on each wire, as already explained; if but one turnbuckle be used, the other end of the wire may be conveniently attached to a strip of sheet steel bent double and drilled for the bolt, like the sheet-steel slip of a turnbuckle. The attachment, of whatever nature, should be put between the end and the flange of the sleeve, not between the two flanges.Three or four ribs can be used on each section; four are preferable on sections of full 6-foot length. They are, of course, evenly spaced on centers. At the front ends, they are attached to the beam by wood screws through their flattened ferrules. The attachment to the rear beam is made with a slip of sheet steel measuring 1/2 by 3 inches, bent over the rib and fastened to the beam at each side with a wood screw. A long wire nail is driven through the rib itself on the beam.Four double sections should be built up in this manner, the right and left upper and the right and left lower sections. Uppers and lowers are alike except for the inversion of the sockets in the upper sections. Rights and lefts differ in that the outer beams are long enough to fill up the sleeves, not leaving room for another beam to join on.Inserting the struts in their sockets between the upper and lower sections of the same side will now form either of the two sides of the machine complete. Care should be taken to get the rear struts the proper length with respect to the front ones to bring the upper and lower planes parallel. The distance from the top of the lower front beam to the top of the upper front beam should be the same as the distance between the rows of bracing holes in the upper and lower main ribs just above and below the rear struts—about 4 feet 6 inches. It should hardly be necessary to mention that the thick edges of the struts come to the front—they are fish-shaped and a fish is thicker at the head than at the tail.The truss wires may now be strung on in each square of the struts, beams, and main ribs, using turnbuckles as previously described. The wires should be taut enough to sing a low note when plucked between the thumb and forefinger. If the construction is carried out properly, the framework will stand square and true with an even tension on all the wires. It is permissible for the struts to slant backward a little as seen from the side, but all should be perfectly in line.For adjusting the turnbuckles, the builder should make for himself a handy little tool usually termed a nipple wrench. It is simply a strip of steel 1 1/2 by 1/2 by 3/32 inches, with a notch cut in the middle of the long sides to fit the flattened ends of the turnbuckle nipples. This is much handier than the pliers and does not burr up the nipples.It has been assumed in this description of the assembling that the builder is working in a limited space; if, on the contrary, he has room enough to set up the whole frame at once, the work will be much simpler. In this case, the construction bed should be 30 feet long. First build up the upper plane complete, standing it against the wall when finished; then build the lower plane, put the struts in their sockets, and lay on the upper plane complete.Returning to the plan of assembly by sections, after the side sections or wings of the machine have been completed, the struts may be taken out and the sections laid aside. The middle section, to which the running gear and outriggers will be attached, is now to be built up in the same way. If the builder is following the plan in which there is one main rib between each section, it will be necessary to take off the four inner main ribs from the sections already completed, to be used at the ends of the central section. The plan drawing of the complete machine shows that the ribs of the central section are cut off just back of the rear beam to make room for the propeller. This is necessary in order to set the motor far enough forward to balance the machine properly. The small ribs in this section have the same curve but are cut off 10 inches shorter at their rear ends, and the stumps are smoothed down for ferrules like those for the other small ribs. In the plan which has one main rib between each section, the main rib on each side of the central section must be left full length. In the quick-detachable plan with two main ribs on each side of the central section, the inner ones, which really belong to this section, are cut off short like the small ribs.In the drawing of the complete machine, the distance between the struts which carry the engine bed is shown as 2 feet. This is only approximate, as the distance must be varied to suit the motor employed. By this time, the builder will have decided what engine he is going to use—or can get—and should drill the holes for the sockets of these struts with due respect to the width of the engine's supporting feet or lugs, remembering that the engine bed beams go on the inside of the struts. In the drawing of the running gear. Fig. 17, the distance between the engine-bed struts has been designatedA. The distances,B, on each side are, of course, approximately (6'— 2*A*), whateverAmay be.VIEW OF THE FRENCH AVIATION GROUNDS SHOWING THE HANGARS RANGED ALONG THE EDGES OF THE FIELDVIEW OF THE FRENCH AVIATION GROUNDS SHOWING THE HANGARS RANGED ALONG THE EDGES OF THE FIELDThis Photograph Protected By International CopyrightEXAMINATION PAPERBUILDING AND FLYING ANAEROPLANEPART IRead Carefully: Place your name and full address at the head of the paper. Any cheap, light paper like the sample previously sent you may be used. Do not crowd your work, but arrange it neatly and legibly.Do not copy the answers from the Instruction Paper; use your own words so that we may be sure that you understand the subject.What type of machine, biplane or monoplane, makes the best glider and why?Give the dimensions of a glider which will support a man's weight.In a glider which has no rudder, how is the machine controlled?Give carefully the details of the start in making a glide.In what direction relative to the wind should a glide be made? Justify your answer.How must the stability and balance of a glider in flight be controlled?State the proper conditions for a successful glide.Give the essential characteristics of a Curtiss aeroplane, defining the various parts.Describe briefly the details of construction of the main supporting surfaces of a Curtiss.Draw a diagram of the assembled planes showing how the struts and cross wires are placed to give the required rigidity.Give the details of the running gear of the Curtiss.What is the office of the Curtiss ailerons and how are they controlled from the operator's seat? Draw sketch.Describe the details of the front and rear outriggers.What type of propeller is advised for the Curtiss? Give the details of its construction.Describe carefully the manner in which a propeller should move through the air in order to give the maximum propulsion.What determines the exact location of the motor in the aeroplane?Give correct method of starting the motor when ready for a flight.What tests should be conducted before a flight is undertaken?After completing the work, add and sign the following statement:I hereby certify that the above work is entirely my own.(Signed)
DETAILS OF CONSTRUCTIONMain Planes and Struts. It is preferable to begin with the construction of the main planes and their struts and truss wires, the ribs already described being the first step.The main beams offer no special difficulties. They are ovals 1 1/4 by 1 5/8 inches, all 6 feet long except the eight end ones, which are 6 feet 2 inches. The beams of the central section should be of ash, or should be thicker than the others. In the latter case, they must be tapered at the ends so that the clamping sleeves will fit and the additional wood must be all on the lower side, so that the rib will not be thrown out of alignment. The spruce used for the other beams should be reasonably clear and straight grained, but a small knot or two does not matter, provided it does not come near the ends of the beam. The beams may be cut to the oval shape by the sawmill or planed down by hand."Fish-shaped" or "stream-line" section, as it is more commonly termed, is used for the struts, Fig. 15. It is questionable whether this makes any material difference in the wind resistance, but it is common practice to follow it in order to minimize this factor. It is more important that the struts be larger at their centers than at the ends, as this strengthens them considerably. At their ends the struts have ferrules of the 1-inch brass or steel tubing, and fit into the sockets which clamp the ribs and beams together. The material is spruce but the four central struts which carry the engine bed should either be ash or of larger size, say 1 1/4 by 3 inches.Care Necessary to Get Planes Parallel. The front struts must be longer than the rear ones by the thickness of a main rib at the point where the rear strut bolt passes through it, less the thickness of the rib ferrule through which the bolt of the front strut must pass. However, the first distance is not really the actual thickness of the rib, but the distance between the top of the rear beam and the bottom of the strut socket. In the drawings the difference in length between the front and rear struts is given as 2 inches, but it is preferable for the builder to leave the rear struts rather long and then measure the actual distance when assembling, cutting the struts to fit. The ends of the struts should also be countersunk enough to clear the head of the socket bolt.One of the items which the builder can not well escape buying in finished form is the strut sockets. These are cup-shaped affairs of pressed steel which sell at 20 cents each. Sixteen of them will be required for the main frame, and a dozen more can advantageously be used in the front and rear controls, though for this purpose they are not absolutely necessary. They can also be obtained in a larger oval size suitable for the four central struts that carry the engine bed, as well as in the standard 1-inch size. The bolts which project through the bottom of the sockets are ordinary 1/4-inch stove bolts, with their heads brazed to the sockets.For the rear struts, where the bolt must pass through the slanting main rib, it is advisable to make angle washers to put under the socket and also between the beam and rib. These washers are made by sawing up a piece of heavy brass tubing, or a bar with a 1/4-inch hole drilled in its center, the saw cuts being taken alternately at right angles and at 60 degrees to the axis of the tube.The sleeves which clamp together the ends of the beams are made of sheet steel of about 20 gauge. The steel is cut out on the pattern given in the drawing, Fig. 16, and the 3/16-inch bolt holes drilled in the flanges. The flanges are bent over by clamping the sheet in a vise along the bending line and then beating down with a hammer. Then the sleeves can be bent into shape around a stray end of the beam wood. The holes for the strut socket bolts should not be drilled until ready to assemble. Ordinarily, 3/16-inch stove bolts will do to clamp the flanges together.Having reached this stage, the amateur builder must now supply himself with turnbuckles. As already mentioned, these may either be purchased or made by hand. It is permissible to use either one or two turnbuckles on each wire. One is really sufficient, but two—one at each end—add but little weight and give greater leeway in making adjustments. As there are about 115 wires in the machine which need turnbuckles, the number required will be either 115 or 230, depending upon the plan which is followed. Those of the turnbuckles to be used on the front and rear controls and the ailerons, about one-fifth of the total number, may be of lighter stock than those employed on wires which carry part of the weight of the machine.Making Turnbuckles for the Truss Wires. On the supposition that the builder will make his own turnbuckles, a simple form is described here. As will be seen from Fig. 16, the turnbuckles are simply bicycle spokes, with the nipple caught in a loop of sheet steel and the end of the spoke itself twisted into an eye to which the truss wire can be attached. The sheet steel used should be 18 or 16 gauge, and may be cut to pattern with a heavy pair of tin snips. The spokes should be 3/32 inch over the threaded portion. The eye should be twisted up tight and brazed so that it can not come apart. The hole in the middle of each strip is, of course, drilled the same size as the spoke nipple. The holes in the ends are 3/16 inch.In the original Curtiss machines, the turnbuckles were strung on the socket bolts one after another, sometimes making a pack of them half an inch thick. A much neater construction is shown in the drawings, in which the bolt pierces a single plate with lugs to which to make the turnbuckles fast by riveting. The plates are of different shapes, with two, three, or four lugs, according to the places where they are to be used. They are cut from steel stock 3/32 inch thick, with 1/4-inch holes for the socket bolts and 3/16 inch, or other convenient size, for the rivets that fasten on the turnbuckles.The relative merits of cable and piano wire for trussing have not been thoroughly threshed out. Each has its advantages and disadvantages. Most of the well-known builders use cable; yet if the difference between 1,000 feet of cable at 2 1/4 cents per foot (the price for 500-foot spools), and 8 pounds of piano wire at 70 cents a pound, looks considerable to the amateur builder, let him by all means use the wire. The cable, if used, should be the 3/32-inch size, which will stand a load of 800 pounds; piano wire should be 24 gauge, tested to 745 pounds. It should be noted that there is a special series of gauges for piano wire, known as the music wire gauge, in which the size of the wire increases with the gauge numbers, instead of the contrary, as is usual with machinery wire gauges.One by no means unimportant advantage of the piano wire is that it is much easier to fasten into the turnbuckles. A small sleeve or ferrule, a 1/4-inch length of 1/8-inch tubing, is first strung on the wire. The end of the wire is then passed through the turnbuckle eye, bent up, thrust through the sleeve, and again bent down. When the machine is taken apart, the wire is not disconnected from the eye, but instead the turnbuckle spoke is unscrewed from the nipple. The shape of the sheet-steel loop should be such as to hold the latter in place. Cable, on the other hand, must be cut with about 2 inches to spare. After being threaded through the turnbuckle eye, the end is wound back tightly on itself and then soldered, to make certain that it can not loosen.With a supply of turnbuckles and cable or piano wire at hand, the builder may go ahead with the main box-like structure or cell, which should be completed except for the cloth covering, and in proper alignment, before taking up the construction of the running gear and controls.Running Gear. The running gear of the machine is built of seamless steel tubing, those parts which carry the weight of the machine direct being of 3/4-inch outside diameter, 16-gauge tubing, while the others are 5/8-inch outside diameter, either 18 or 20 gauge. About 25 feet of the heavy and 45 feet of the light tubing will be required, in lengths as follows: Heavy, four 3-foot, three 4-foot; light, one 6-foot, two 4-foot 6-inch, and seven 4-foot pieces. Referring to Fig. 17, two diagonal braces from the rear beam to the engine bed, the V-shaped piece under the front engine bed struts and all of the rear frame except the horizontal piece from wheel to wheel, are of heavy tubing. The horizontal in the rear frame, diagonals from the rear wheels and the rear end of the skid to the front beam, the two horizontals between the front and rear beam, and the forward V are of light tubing.Fig. 17. Details of Curtiss Running GearFig. 17. Details of Curtiss Running GearThree ash beams are used in the running gear. Two of these run diagonally from the rear end of the engine bed to the front wheel. These are about 10 feet long and 1 by 1 3/4 inches section. The third, which on rough ground acts as a skid, is 8 1/2 feet long and about 2 inches square. Between the joints where the tubing frames are attached to it, the upper corners may be beveled off with a spoke shave an inch or more down each side. The beams are attached to the front wheel with strips of steel stock 1 1/2 inches wide and 1/8 inch thick. The engine bed beams are also ash about 1 by 1 3/4 inches section. Their rear ends are bolted to the middle of the rear engine bed struts and the front ends may be 1/2 inch higher.SCENE AT AVIATION MEET AT ROUEN, FRANCE, SHOWING AN ANTOINETTE MONOPLANE MAKING A TURNSCENE AT AVIATION MEET AT ROUEN, FRANCE, SHOWING AN ANTOINETTE MONOPLANE MAKING A TURNThis Photograph Protected By International CopyrightA FRENCH MONOPLANE TRAVELLING SIXTY-FIVE MILES AN HOURA FRENCH MONOPLANE TRAVELLING SIXTY-FIVE MILES AN HOURThis Photograph Protected By International CopyrightThe wheels are usually 20 by 2 inches, and of the bicycle type, but heavier and wider in the hub; the tires are single tube. These wheels, complete with tires, cost about $10 each. This size is used on the standard Curtiss machines, but novice operators, whose landings are not quite as gentle as they might be, find them easily broken. Therefore, it may be more economical in the end to pay a little more and get heavier tires—at least to start with.For working the tubing into shape, a plumber's blow torch is almost indispensable—most automobilists will already possess one of these. The oval, flat variety, holding about one pint, is very handy and packs away easily, but on steady work requires filling somewhat too frequently. With a dozen bricks a shield can be built in front of the torch to protect the flame and concentrate the heat. Whenever it is to be flattened and bent, the tubing should be brought to a bright red or yellow heat. Screwing the vise down on it will then flatten it quickly without hammer marks. Where the bend is to be made in the middle of the piece, however, it may be necessary to resort to the hammer and anvil.It is convenient to start with the framework under the rear beam. This may be drawn accurately to full size on the workshop floor, and the tubes bent to fit the drawing. With this framework once in place, a definite starting point for the remainder of the running gear is established. Here and in all other places, when boring through wood, the holes should be drilled out full, and larger washers should be placed under the bolt head and nut. All nuts should be provided with some sort of locking device The perspective drawing. Fig. 17, should show the general arrangement clearly enough to enable the builder to finish the running gear.Outriggers. Both the front and rear control members, or "outriggers" as they are termed, Fig. 12, may be conveniently built up on the central section of the main frame, which, it is assumed, has now been fitted with the running gear.The horizontal rudder, or "elevator," is a biplane structure like the main cell of the machine, but with fewer struts; it is carried in front of the main planes on twoA-shaped frames. The vertical rudder, at the rear, is split along the middle and straddles a fixed horizontal plane, ortail. This also is carried on twoA-shaped frames. Lateral stability is controlled by two auxiliary planes or ailerons, one at each side of the machine and carried on the two outer front struts. These three control units—elevator,tailandrudder, andailerons—will now be taken up separately and their construction, location on the machine, and operation will be described.Fig. 18. Details of Rudders and Ailerons, Curtiss BiplaneFig. 18. Details of Rudders and Ailerons, Curtiss BiplaneHorizonal Rudder or Elevator. The two planes of the elevator are 2 feet wide by 5 feet 8 inches long and are spaced 2 feet apart, being held in this position by ten struts. The frames of the planes are built of spruce sticks 1/2 by 1 inch, each plane having two sticks the full length and five evenly spaced crosspieces or ribs. These are joined together with squares of X-sheet tin, as shown in the detailed drawing, Fig. 18. With a little experimenting, paper patterns can be made from which the tin pieces can be cut out. The sticks are then nailed through the tin with 3/4-inch brads.It is convenient to draw the frames out accurately on a smooth wood floor and then work over this drawing. The first few brads will hold the sticks in place. When all the brads have been driven, a little drop of solder should be run in around the head of each one. This is a tedious job. One must be careful to use no more solder than necessary as it increases the weight very rapidly. Two pounds of wire solder should be sufficient for all the control members which are built in this way. When the top side is soldered, pry the frame loose from the floor with a screwdriver and turn it over. Then the projecting points of the brads must be clinched and the soldering repeated.At this stage, the two frames should be covered on both sides with the prepared cloth used for covering the main planes. The method of preparing this cloth is detailed a little farther along.The struts, so-called, to continue the analogy with the main planes, are turned sticks of spruce 3/8 inch in diameter. They are fitted at each end with ferrules of thin 3/8-inch brass, or steel tubing, driven on tight. Instead of using sockets, the struts are held at each end, simply by a long wood screw driven through the tin and wood of the plane frame and into the strut. These screws also hold the turnbuckles for the truss wires. For trussing purposes, the elevator is regarded as consisting of two sections only, the intermediate struts being disregarded.The turnbuckles and wire used here and in the other control members may well be of lighter stock than those used in the main planes. Piano wire, No. 18, or 1/16-inch cable is amply strong. The sheet steel may be about 22 gauge, instead of 16, and the bicycle spokes smaller in proportion. No turnbuckle plates are necessary. The screws running into the struts may be passed directly through the eyes of the turnbuckles, where they would have been attached to the turnbuckle plate. In order to secure a square and neat structure, those struts which have turnbuckles at their ends should be made a trifle shorter than the others.At each end, the elevator has anX-shaped frame of 1/4-inch steel tubing; at the intersection of theX's are pivots on which the elevator is supported. EachXis made of two tubes, bent into a y and flattened and brazed together at the points. The ends of theX's are flattened and bent over so that the screws which hold the struts in place may pass through them.Fig. 19. Curtiss Biplane Ready for FlightFig. 19. Curtiss Biplane Ready for FlightTo the front middle strut is attached an extension which acts as a lever for operating the elevator. This is a stick of spruce 3/4 inch in diameter and 3 feet 3 inches long. At its upper end it has a ferrule of steel tubing, flattened at the end. The lower part of the stick may be fastened to the strut by wrapping the tube with friction tape, or by improvising a couple of sheet steel clamps. The upper end of the stick is braced by a 1/4-inch steel tube, extending to the top of the rear middle strut, and held by the same screw as the strut. This extension lever is connected to the steering column by a bamboo rod, 1 inch in diameter and about 10 feet long, provided with flattened ferrules of steel tubing at each end. Each ferrule should be held on by a 1/8-inch stove bolt passing through it.Front and Rear Outrigger Frames. Both the front elevator and the tail and rudder at the rear, are carried, as mentioned above, each on a pair ofA-shaped frames, similar to one another, except that those in the rear are longer than those in the front. Both are made of spruce of about the same section as used for the struts of the main frame. These pieces may either be full length, or they may be jointed at the intersection of the crosspieces, the ends being clamped in a sheet-steel sleeve, just like that used on the beams of the main frame. In this case, it is advisable to run a 1/8-inch stove bolt through each of the ends.Fig. 20. Details of Outriggers and Front Elevating Planes as Seen from Driver's SeatFig. 20. Details of Outriggers and Front Elevating Planes as Seen from Driver's SeatThe crosspieces of theA-frames are spruce of the same section, or a little smaller. At their ends may be used strut sockets like those of the main frame; or, if it is desired to save this expense, they may be fastened by strips of 1/16-inch steel stock with through bolts.The front outrigger has, besides the two A-frames, a rather complicated arrangement of struts designed to brace the front wheel against the shocks of landing. This arrangement does not appear very plain in a plan or elevation, and may best be understood by reference to the photograph, Fig. 19, and the perspective drawing, Fig. 20. Fig. 20 is a view from the driver's seat. The elevator is seen in front, theA-frames at each side, and at the bottom the two diagonal beams to the engine bed and the skid.Reference to this drawing will show the two diagonals run from the front wheel up and back to the top of the main frame, and two more from the wheel forward to the short crosspieces near the apexes of theA-frame: there is also a vertical strut which intersects two horizontal pieces running between the ends of the longer crosspieces of theA-frames. Altogether, there are five attachments on each side of the front wheel, through which the axle bolt must pass, viz, the connections to the skid, to one of the diagonals to the engine bed, to one of the rear diagonals, to one of the front diagonals, and to one side of the fork carrying the vertical strut. Of these the skid attachments should be on the inside closest to the wheel, and the engine bed diagonals next.The four additional diagonals running to the front wheel may be spruce of the same section used in theA-frames, or turned one inch round. At each end they have flattened ferrules of steel tubing. The beams of theA-frames have similar ferrules at the ends where they attach to the main frames. These attachments should be made on the socket bolts of the struts on either side of the middle 6-foot section and on the outer side of the main beams—not between the beam and the socket itself.It is possible, of course, to make all theA-frames and diagonal braces of bamboo, if desired, the qualities of this material already having been referred to. Bamboo rods for this purpose should be between 1 and 1 1/4 inches in diameter. Where ferrules are fitted on the ends, the hole of the bamboo should be plugged with wood glued in place.Generally, in the construction of the outrigger frames, the builder can use his own discretion to a considerable extent. There tire innumerable details which can be varied—far too many to consider even a part of the possibilities in this connection. If the builder runs across any detail which he does not see mentioned here, he may safely assume that any workmanlike job will suffice. Often, the method may be adapted to the materials on hand. The diagonal wires from the crosspieces of the A-frames to the struts should be crossed.Rudder and Tail Construction. The frame for the rudder and tail are constructed in much the same way as those for the elevator, Fig. 18. Spruce sticks 1 by 1/2 inch are used throughout, except for the piece at the back edge of the rudder and the long middle piece across the tail; these should be 1 1/2 by 1/2 inch. This long middle piece of the tail is laid across on top of the rest of the framework. When the cloth is put on, this makes the upper surface slightly convex while the lower surface remains flat. The ends of this piece should be reinforced with sheet steel, fairly heavy and drilled for 1/4-inch bolts, attaching the tail to theA-frames.The rudder is hung from two posts extending above and below the tail. These posts may be set in cast aluminum sockets, such as may be obtained from any supply house for 20 cents apiece. The posts need not be more than 3/4 inch in diameter. At their outer ends, they should have ferrules of steel tubing, and the turnbuckles or other attachments for the truss wires should be attached by a wood screw running into the end of each. From these posts the rudder may be hung on any light hinges the builder may find convenient, or on hinges improvised from screw eyes or eye bolts, with a bolt passing through the eyes of each.In steering, the rudder is controlled by a steering wheel carried on a hinged post in front of the pilot. This post should be ash about 1 by 1 1/4 inches. It hinges at the bottom on a steel tube of 1/2-inch diameter which passes through it and is supported at the ends on diagonal beams to the engine bed. Two diagonals of lighter tubing may be put in to hold the posts centered between the two beams.The post is, of course, upright, and the hub of the wheel is horizontal. The wheel may be conveniently mounted on a piece of tubing of the same size as the hub hole, run through the post and held by a comparatively small bolt, which passes through it and has a big washer on either end. The wheel is preferably of the motor-boat variety with a groove around the rim for the steering cable.The rear edge of the tail should be about 1 inch lower than the front. To make the rudder post stand approximately vertical, wedge-shaped pieces of wood may be set under the sockets.The steering connections should be of flexible cables of steel such as are made for this purpose. There should be a double pulley on the post just under the wheel, and the cables should be led off the post just at the hinge at the bottom, so that swinging the post will not affect them. The cable is then carried under the lower main plane and out the lower beams of theA-frames. It is attached to the rudder at the back edge; snap hooks should be used for easy disconnection in packing. Perhaps the best way of guiding the cable, instead of using pulleys, is to run it through short pieces of tubing lashed to the beams with friction tape. The tubing can be bent without flattening by first filling it with melted lead, which, after the bending, can be melted out again.Ailerons for Lateral Stability. The framework of the ailerons is made in the same way as that for the elevator, tail, and rudder, Fig. 18. The pieces around the edges should be 1 1/2 by 1/2 inch, as also the long strip laid over the top of the ribs. The ribs should be 1/2 by 3/4 inch. Each aileron has two holes, one for the strut to pass through, and the other for the diagonal truss wires at their intersection. The back edge also has a notch in it to clear the fore and aft wires. Each aileron is hung on four strips of soft steel about 1/2 by 3/16 inch, twisted so that one end is at right angles to the other. These are arranged one on each side of the strut which passes through the aileron, and one at each end. Bolts through the struts carry three of them and the outer one is trussed by wires to each end of the outer strut.A frame of 1/4-inch steel tubing fits around the aviator's shoulders and is hinged to the seat, so that he can move it by leaning from one side to the other. This is connected by flexible cable to the rear edges of the ailerons, so that when the aviator leans to the left, he will raise the left and lower the right aileron. The upper edges of the ailerons are directly connected to each other by a cable running along the upper front beam, so that they must always move together.Covering of the Planes. Mention has already been made of the fact, in the general description of the machine, that light sail cloth, as employed on the Wright machines, may be used for the planes or wings. As a matter of fact, many different materials may be successfully employed, the selection depending upon the builder himself and his financial resources. About 55 square yards of material will be required, and in comparing prices always compare the width as this may vary from 28 to 55 inches. Rubberized silk which is used on the standard Curtiss machines is the most expensive covering, its cost running up to something like two hundred dollars. There are also several good aero fabrics on the market which sell at 60 cents a square yard, as well as a number of brands of varnish for the cloth—most of them, however, quite expensive. The most economical method is to employ a strong linen cloth coated with shellac, which will be found very satisfactory.The covering of the frames with the cloth may well be postponed until after the engine has been installed and tested, thus avoiding the splashing of oil and dirt which the fabric is apt to receive during this operation. The wire to which the cloth is laced, must be strung along the rear ends of the ribs of each plane. The wires pass through holes in the ends of the small ribs and are attached to the main ribs with turnbuckles. At the ends of the planes the main ribs must be braced against the pull of the wire by a piece of 1/4-inch tubing running from the end of the rib diagonally up to the rear beam. Both turnbuckles and tube are fastened with one wood screw running into the end of the rib.The cloth should be cut to fit the panels between the main ribs and hemmed up, allowing at least an inch in each direction for stretch. Small eyelets should be put along the sides and rear edges an inch apart for the lacing. At the front edge, the cloth is tacked directly to the beam, the edge being taken well under and around to the back. Strong fish line is good material for the lacing.After the cloth is laced on, it must be tacked down to the small ribs. For this purpose, use upholstery tacks as they have big cup-shaped heads which grip the cloth and do not tear out. As an extra precaution a strip of heavy tape must be run over each rib under the tack heads. All the control members are covered on both sides, the edges being folded under and held by tacks.Making the Propeller. If the completed biplane is to fly properly and also have sufficient speed to make it safe, considerable care must be devoted to the design and making of the propeller. Every aeroplane has a safe speed, usually referred to in technical parlance as itscritical speed. In the case of the Curtiss biplane under consideration, this speed is about 40 miles an hour. By speeding up the motor considerably, it may be able to make 42 to 43 miles an hour in a calm, such a condition representing the only true measure of an aeroplane's ability in this direction, while on the other hand, it would not be safe to let its speed with relation to the wind (not to the ground) fall much below 35 miles an hour. At any slower rate of travel, its dynamic stability would be precarious and the machine would be likely to dive to the ground unexpectedly. The reasons for this have been explained more in detail under the heading of "The Internal Work of the Wind."The necessity of making the propeller need not discourage the ambitious builder—if he can spare the time to do it right, it will be excellent experience. If not, propellers designed for driving a machine of this size can be purchased ready to mount from any one of quite a number of manufacturers. But as the outlay required will be at least $50, doubtless most experimenters will prefer to undertake this part of the work as well as that of building the framework and main cell, particularly as more than 90 per cent of the sum mentioned is represented by labor. The cost of the material required is insignificant by comparison.True-Screw Design. First it will be necessary to design the propeller to meet the requirements of the biplane itself. As this is a matter that has already been gone into in considerable detail under the appropriate heading, no further explanation of propeller characteristics or of the technical terms employed, should be needed here. We will assume that the biplane is to have a speed of 40 miles per hour in still air with the motor running at 1,200 r.p.m. With this data, it will not be difficult to calculate the correct pitch of the propeller to give that result. Thus40 X 5,280 X 100 / 60 X 1,200 X 85 = 3.45or in round numbers a pitch of 3 1/2 feet. 40 (the speed in miles per hour) times 5,280 (feet per mile) divided by 00 (minutes in an hour) gives the speed of the aeroplane in feet per minute. Dividing this by 1,200 (revolutions per minute) gives the number of feet the aeroplane is to advance per revolution of the propeller. The "100/85" part of the equation represents the efficiency of the propeller which can safely be figured on,i.e., 85 per cent, or an allowance for slip of 15 per cent. Forty miles an hour is the maximum speed to be expected, while the r.p.m. rate of the engine should be that at which it operates to the best advantage.The merits of thetrue-screwandvariable-pitchpropellers have already been dwelt upon. The former is not only more simple to build, but experience has shown that, as generally employed, it gives better efficiency. Hence, the propeller under consideration will, be of the true-screw type. Its pitch has already been calculated as 3 1/2 feet. For a machine of this size and power, it should be 6 feet in diameter. Having worked out the pitch and decided upon the diameter, the next and most important thing is to calculate the pitch angle. It will be evident that no two points on the blade will travel through the air at the same speed. Obviously, a point near the tip of the propeller moves faster than one near the hub, just as in rounding a curve, the outer wheel of an automobile has to travel faster than the inner, because it has to travel farther to cover the same ground. For instance, taking the dimensions of the propeller in question it will be seen that its tips will be traveling through the air at close to 4.3 miles per minute, that is,6 X π X 1200 / 5,280 = 4.28in which 6, the diameter of the propeller in feet, times π gives the circumference of the circle which is traveled by the blade tips 1,200 times per minute; this divided by the number of feet per mile gives the miles per minute covered. On the other hand, a point on the blade but 6 inches from the hub will turn at only approximately 3,500 feet per minute. Therefore, if every part of the blade is to advance through the air equally, the inner part must be set at a greater angle than the outer part. Each part of the blade must be set at such an angle that at each revolution it will move forward through the air a distance equal to the pitch. This is known as the pitch angle. The pitch divided by the circumference of the circle described by any part of the blade, will give a quantity known as the tangent of an angle for that particular part. The angle corresponding to that tangent may most easily be found by referring to a book of trigonometric tables.Table II. Propeller Blade DataFor example, take that part of the blade of a 3 1/2-foot pitch propeller which is 6 inches from the center of the hub. Then3.5 X 12 / 6 X 2 π = 1.1141 tangent of 48 degrees 5 minutesin which 3.5 X 12 reduces the pitch to inches, while 6 X 2π is the circumference of the circle described by the point 6 inches from the hub. However, in order to give the propeller blade a proper hold on the air, it must be set at a greater angle than these figures would indicate. That is, it must be given an angle of incidence similar to that given to every one of the supporting planes of the machine. This additional angle ranges from 2 degrees 30 minutes, to 4 degrees, depending upon the speed at which the particular part of the blade travels; the greater the speed, the less the angle. This does not apply to that part of the blade near the hub as the latter is depended upon solely for strength and is not expected to add to the effective thrust of the propeller.Table II shows the complete set of figures for a blade of 3 1/2-foot pitch, the angles being worked out for sections of the blade 3 inches apart.These angles are employed in Fig. 21, which shows one blade of the propeller and its cross sections.It should be understood that these calculations apply only to the type of propeller known as thetrue screw, as distinguished from thevariable pitch. The design of the latter is a matter of personal skill and experience in its making which is hardly capable of expression in any mathematical formula. There are said to be only about three men in this country who know how to make a proper variable-pitch propeller, and it naturally is without advantage when made otherwise.Fig. 21. Details of Propeller Construction, Curtiss BiplaneFig. 21. Details of Propeller Construction, Curtiss BiplaneShaping the Blades. Like the ribs, the propeller is made up of a number of laminations of boards finished true and securely glued, afterward being cut to the proper shape, though this process, of course, involves far more skill than in the former case. Spruce is the strongest wood for its weight, but it is soft and cracks easily. Maple, on the other hand, is tough and hard, so that it will be an advantage to alternate the layers of these woods with an extra maple board, in order to make both outside strips of the harder wood, so as to form a good backing for the steel flanges at the hub, the rear layer extending the full length of the thin rear edges of the blades. Other woods may be employed and frequently are used by propeller manufacturers, such as mahogany (not the grained wood used for furniture, but a cheaper grade which is much stronger), walnut, alternate spruce and whitewood, and others.The boards should be selected with the greatest care so as to insure their being perfectly clear,i.e., absolutely free of knots, cross-grained streaks, or similar flaws, which would impair their strength and render them difficult to work smoothly. They should measure 6 inches wide by 6 feet 1 inch in length. Their surfaces must be finished perfectly true, so that they will come together uniformly all over the area on which they bear on one another, and the various pieces must be glued together with the most painstaking care. Have the glue hot, so that it will spread evenly, and see that it is of a uniform consistency, in order that it may be smoothly applied to every bit of the surface. They must then be clamped together under as much pressure as it is possible to apply to them with the means at hand, the rib press already described in detail forming an excellent tool for this purpose. Tighten up the nuts evenly a little at a time, avoiding the application of excessive or uneven pressure at one point, continuing the gradual tightening up process until it can not be carried any farther. This is to prevent the boards from assuming a curve in drying fast. Allow at least twenty-four hours for drying, during which period the laminated block should be kept in a cool, dry place at as even a temperature as possible.Before undertaking the remainder of the work, all of which must be carried out by hand, with the exception of cutting the block to the outline of the propeller, which may be done with a band saw, a set of templates or gauges should be made from the drawings. These will be necessary as guides for finishing the propeller accurately. Draw the sections out full size on sheets of cardboard or tin and cut out along the curves, finally dividing each sheet into two parts, one for the upper side and one for the lower. Care must be taken to get the sides of the template square, and when they are used, the propeller should be laid on a perfectly true and flat block. Each template should be marked as it is finished, to indicate what part of the blade it is a gauge for. The work of cutting the laminated block down to the lines represented by the templates is carried out with the aid of the plane, spoke shave, and gouge. After the firstroughing outto approximate the curvature of the finished propeller is completed, the cuts taken should be very fine, as it will be an easy matter to go too deep, thus spoiling the block and necessitating a new start with fresh material. For finishing, pieces of broken glass are employed to scrape the wood to a smooth surface, followed by coarse and finally by fine sandpaper.Mounting. The hub should be of the same diameter as the flange on the engine crank shaft to which the flywheel was bolted, and should have its bolt holes drilled to correspond. To strengthen the hub, light steel plates of the same diameter are screwed to it, front and back, and the bolt holes drilled right through the metal and wood. This method of fastening is recommended where it is possible to substitute the propeller for the flywheel formerly on the engine, it being common practice to omit the use of the flywheel altogether. The writer does not recommend this, however, as the advantages of smoother running and more reliable operation gained by the use of a flywheel in addition to the propeller far more than offset any disadvantage represented by its weight. It will be noted that the Wright motors have always been equipped with a flywheel of ample size and weight and this is undoubtedly responsible, in some measure at least, for the fact that the Wright biplanes fly with considerably less power than is ordinarily employed for machines of the same size. If the motor selected be equipped with an unusually heavy flywheel, and particularly where the wheel is of comparatively small diameter, making it less effective as a balancer, it may be replaced with one of lighter weight and larger diameter. It may be possible to attach it by keying to the forward end of the crank shaft, thus leaving the flange from which the flywheel was taken free for mounting the propeller. An ordinary belt pulley will serve excellently as the new flywheel, as most of its weight is centered in its rim, but as the common cast-iron belt pulley of commerce is seldom intended to run at any such speed as that of an automobile motor, it should be examined carefully for flaws. Otherwise, there will be danger of its blunting with disastrous results under the influence of centrifugal force. Its diameter should not exceed 16 inches in order to keep its peripheral speed within reasonable limits. Where the mounting of the motor permits of its use, a wood pulley 18 to 20 inches in diameter with a steel band about 1/8 to 1/4-inch thick, shrunk on its periphery, may be employed. Most builders will ridicule the idea of a flywheel other than the propeller itself. "You do not need it; so why carry the extra weight?" will be their query. It is not absolutely necessary, but it is an advantage.In case the flywheel of the engine selected is keyed to the crank shaft, or in case it is not possible to mount both the flywheel and the propeller on different ends of the crank shaft, some other expedient rather than that of bolting to the flange must be adopted. In such a case, the original flywheel, where practical to retain it, may be drilled and tapped and the propeller attached directly to it. Where the flywheel can not be kept, it will usually be found practical to cut off its rim and bolt the propeller either to the web or spokes, or to the flywheel hub, if it be cut down to the latter.The drawing. Fig. 21, shows the rear or concave side of the propeller. From the viewpoint of a man standing in its wind and facing forward, it turns to the left, or anti-clockwise. On many of the propellers now on the market, the curved edge is designed to go first. This type may have greater advantages over that described, but the straight front edge propeller is easier for the amateur to make.Mounting the Engine. Having completed the propeller, the next step is the mounting of the engine. Reference to the types available to the amateur aeroplane builder has already been made. There are a number of motors now on the market that have been designed specially for this purpose and not a few of them are of considerable merit. Their cost ranges from about $250 up to $2,500, but it may be possible to pick up a comparatively light-weight automobile motor second hand which will serve all purposes and which will cost far less than the cheapest aeronautic motor on the market. It must be capable of developing 30 actual horse-power at 1,000 to 1,200 r.p.m. and must not exceed 400 pounds complete with all accessories, such as the radiator and piping, magneto, water, oil, etc. Considerable weight may be saved on an automobile motor by removing the exhaust manifold and substituting a lighter flywheel for the one originally on the engine—or omitting it altogether, as just mentioned. A light-weight aeronautic radiator should be used in preference to the usual automobile radiator.When placing the engine in position on the ash beams forming its bed or support, it must be borne in mind that the complete machine, with the operator in the aviator's seat, is designed to balance on a point about 1 1/2 feet back of the front edge of the main planes. As the operator and the motor represent much the larger part of the total weight, the balance may easily be regulated by moving them slightly forward or backward, as may be required. It will be necessary, of course, to place the engine far enough back in any case to permit the propeller blades to clear the planes. The actual installation of the engine itself will be an easy matter for anyone who has had any experience in either automobile or marine gasoline motor work. It is designed to be bolted to the two engine beams in the same manner as on the side members of the frame of an automobile, or the engine bed in a boat. Just in front of the engine is the best place for the gasoline tank, which should be cylindrical with tapering ends, to cut down its wind resistance. If the designer is not anxious to carry out points as fine as this, a light copper cylindrical tank may be purchased from stock. It should hold at least ten gallons of gasoline. In front of the tank is the radiator.Controls. The controls may be located to conform to the builder's own ideas of accessibility and convenience. Usually the switch is placed on the steering column, and it may be of the ordinaryknifevariety, or one of the special switches made for this purpose, as taste may dictate. The throttle control and spark advance may either be in the form of pedals, working against springs, or of small levers working on a notched sector, at the side of the seat. The complete control, levers, and sector may be purchased ready to mount whenever desired, as they are made in this form for both automobile and marine work. This likewise applies to the wheel, which it would not pay the amateur to attempt to make.Another pedal should work a brake on the front wheel, the brake shoe consisting of a strip of sheet steel, fastened at one end to the fore part of the skid and pressed against the wheel by a bamboo rod directly connected with the brake pedal. An emergency brake can also be made by loosely bolting a stout bar of steel on the skid near its rear end; one end of this bar is connected to a lever near the seat, so that when this lever is pulled back the other end of the bar tends to dig into the ground. As making a landing is one of the most difficult feats for the amateur aviator to master and sufficient space for a long run after alighting is not always available, these brakes will be found a very important feature of the machine.Fig. 22. Method of Starting the Engine of an AeroplaneFig. 22. Method of Starting the Engine of an AeroplaneThe engine is started by swinging the propeller, and this is an operation requiring far more caution than cranking an automobile motor. Both hands should be placed on the same blade. Fig. 22, and the latter should always be pulled downward—never upward. With the switch off, first turn the propeller over several times to fill the cylinders with gas, leaving it just ahead of dead center of one of the cylinders, and with one blade extending upward and to the left at a 45-degree angle. After closing the switch, take the left blade with both hands and swing it downward sharply, getting out of the way of the following blade as quickly as possible.Tests. The first thing to be done after the propeller is finished and mounted on the engine is to test the combination, or power plant of the biplane, for speed and thrust, or pulling power. From these two quantities it will be easy to figure the power that the engine is delivering. The only instruments necessary are a spring balance reading to 300 pounds or over; a revolution counter, such as may be procured at any machinist's supply house for a dollar or two; and a watch. One end of the spring balance is fastened to the front end of the skid and the other to a heavy stake firmly driven in the ground a few feet back. The wheels of the biplane should be set on smooth boards so that they will not offer any resistance to the forward thrust. When the engine is started the spring balance will give a direct reading of the pull of the propeller.With one observer noting the thrust, another should check the number of revolutions the engine is turning per minute. To do this, a small hole should previously have been countersunk in the hub of the propeller to receive the conical rubber tip of the revolution counter. The observer stands behind the propeller, watch in one hand and revolution counter in the other. At the beginning of the minute period, the counter is pressed firmly against the hub, and quickly withdrawn at the end of the minute. A stop watch is naturally an advantage for the purpose. The horse-power is figured as follows, assuming, for example, a thrust of 250 pounds at 1,200 r.p.m.250 X 1200 X 3.5 X 100 / 33.000 X 85 = 37 h. p.As before, the "100/85" allows for the slip and represents the efficiency of the propeller; 33,000 is the number of foot pounds per minute or the equivalent of one horse-power, and 3.5 is the pitch of the propeller.Assembling the Biplane. Assembling the machine complete requires more space than is available in the average workshop. However, it is possible to assemble the sections of the planes in a comparatively small room, carrying the work far enough to make sure that everything will go together properly when the time comes for complete assembly at the testing ground. In this case, it is preferable to assemble the end sections first, standing them away when complete to make room for the central section, on which the running gear and outriggers are to be built up.The builder will have decided by this time whether he will make his machine on the regular plan, with one main rib between each section, or on the quick-detachable plan, which has two main ribs on either side of the central section, as previously explained.It is desirable to be able to assemble two sections at once and this should be possible anywhere as it requires a space only about 6 by 13 feet. Two wood 2X4's, about 12 feet long, should be nailed down on the blocks on the floor; make these level and parallel to each other at a distance of 3 feet 6 inches on centers, one being 3 inches higher than the other. Strips of wood should be nailed on them, so as to hold the main beams of the frame in place while assembling.The two front and two rear beam sections are laid in place and joined with the sheet-steel sleeves, the flanges of the sleeves on the inner side of the beams. Then through the sleeves in the front beams, which are, of course, those on the higher bed, drill the holes for the strut socket bolts (1/4 inch). The holes for the outer ones go through the projecting ends of the beams; those for the inner ones are half in each of the two abutting beams. At the end where the central section joins on, a short length of wood of the same section may be inserted in the sleeve while drilling the hole. An assistant should hold the beams firmly together while the holes are being drilled.Now lay in place the three main ribs belonging to the two sections under construction and fasten them at the front ends by putting in place the strut sockets for which the holes have been drilled, with a turnbuckle plate under each socket, Fig. 16. The strut socket bolt passes through the main rib and the beam. The bed on which the assembling is being done, should be cut when sufficiently under the joints to leave room for the projecting bolt ends. Set the ribs square with the front beams, then arrange the rear beams so that their joints come exactly under the ribs; clamp the ribs down and drill a true, vertical hole through the rib beam, holding the two sections of the beam together as before. Then put the rear strut sockets in place, using the angle washers previously described, above and below the rib.When the quick-detachable plan is followed, the ribs at the inner ends of the double section, where they join the central section, should be bolted on an inch from the ends of the beam, using 1/4-inch stove bolts instead of the socket bolts. The sleeves should be slotted, so that they can slide off without removing these bolts, as the sleeves and ribs which occupy the position over the joints of the beams, belong to the central section.The sections should now be strung up with the diagonal truss wires which will make them rigid enough to stand handling. The wires are attached at each end to the flange bolts of the sleeves. Either one or two turnbuckles may be used on each wire, as already explained; if but one turnbuckle be used, the other end of the wire may be conveniently attached to a strip of sheet steel bent double and drilled for the bolt, like the sheet-steel slip of a turnbuckle. The attachment, of whatever nature, should be put between the end and the flange of the sleeve, not between the two flanges.Three or four ribs can be used on each section; four are preferable on sections of full 6-foot length. They are, of course, evenly spaced on centers. At the front ends, they are attached to the beam by wood screws through their flattened ferrules. The attachment to the rear beam is made with a slip of sheet steel measuring 1/2 by 3 inches, bent over the rib and fastened to the beam at each side with a wood screw. A long wire nail is driven through the rib itself on the beam.Four double sections should be built up in this manner, the right and left upper and the right and left lower sections. Uppers and lowers are alike except for the inversion of the sockets in the upper sections. Rights and lefts differ in that the outer beams are long enough to fill up the sleeves, not leaving room for another beam to join on.Inserting the struts in their sockets between the upper and lower sections of the same side will now form either of the two sides of the machine complete. Care should be taken to get the rear struts the proper length with respect to the front ones to bring the upper and lower planes parallel. The distance from the top of the lower front beam to the top of the upper front beam should be the same as the distance between the rows of bracing holes in the upper and lower main ribs just above and below the rear struts—about 4 feet 6 inches. It should hardly be necessary to mention that the thick edges of the struts come to the front—they are fish-shaped and a fish is thicker at the head than at the tail.The truss wires may now be strung on in each square of the struts, beams, and main ribs, using turnbuckles as previously described. The wires should be taut enough to sing a low note when plucked between the thumb and forefinger. If the construction is carried out properly, the framework will stand square and true with an even tension on all the wires. It is permissible for the struts to slant backward a little as seen from the side, but all should be perfectly in line.For adjusting the turnbuckles, the builder should make for himself a handy little tool usually termed a nipple wrench. It is simply a strip of steel 1 1/2 by 1/2 by 3/32 inches, with a notch cut in the middle of the long sides to fit the flattened ends of the turnbuckle nipples. This is much handier than the pliers and does not burr up the nipples.It has been assumed in this description of the assembling that the builder is working in a limited space; if, on the contrary, he has room enough to set up the whole frame at once, the work will be much simpler. In this case, the construction bed should be 30 feet long. First build up the upper plane complete, standing it against the wall when finished; then build the lower plane, put the struts in their sockets, and lay on the upper plane complete.Returning to the plan of assembly by sections, after the side sections or wings of the machine have been completed, the struts may be taken out and the sections laid aside. The middle section, to which the running gear and outriggers will be attached, is now to be built up in the same way. If the builder is following the plan in which there is one main rib between each section, it will be necessary to take off the four inner main ribs from the sections already completed, to be used at the ends of the central section. The plan drawing of the complete machine shows that the ribs of the central section are cut off just back of the rear beam to make room for the propeller. This is necessary in order to set the motor far enough forward to balance the machine properly. The small ribs in this section have the same curve but are cut off 10 inches shorter at their rear ends, and the stumps are smoothed down for ferrules like those for the other small ribs. In the plan which has one main rib between each section, the main rib on each side of the central section must be left full length. In the quick-detachable plan with two main ribs on each side of the central section, the inner ones, which really belong to this section, are cut off short like the small ribs.In the drawing of the complete machine, the distance between the struts which carry the engine bed is shown as 2 feet. This is only approximate, as the distance must be varied to suit the motor employed. By this time, the builder will have decided what engine he is going to use—or can get—and should drill the holes for the sockets of these struts with due respect to the width of the engine's supporting feet or lugs, remembering that the engine bed beams go on the inside of the struts. In the drawing of the running gear. Fig. 17, the distance between the engine-bed struts has been designatedA. The distances,B, on each side are, of course, approximately (6'— 2*A*), whateverAmay be.VIEW OF THE FRENCH AVIATION GROUNDS SHOWING THE HANGARS RANGED ALONG THE EDGES OF THE FIELDVIEW OF THE FRENCH AVIATION GROUNDS SHOWING THE HANGARS RANGED ALONG THE EDGES OF THE FIELDThis Photograph Protected By International CopyrightEXAMINATION PAPERBUILDING AND FLYING ANAEROPLANEPART IRead Carefully: Place your name and full address at the head of the paper. Any cheap, light paper like the sample previously sent you may be used. Do not crowd your work, but arrange it neatly and legibly.Do not copy the answers from the Instruction Paper; use your own words so that we may be sure that you understand the subject.What type of machine, biplane or monoplane, makes the best glider and why?Give the dimensions of a glider which will support a man's weight.In a glider which has no rudder, how is the machine controlled?Give carefully the details of the start in making a glide.In what direction relative to the wind should a glide be made? Justify your answer.How must the stability and balance of a glider in flight be controlled?State the proper conditions for a successful glide.Give the essential characteristics of a Curtiss aeroplane, defining the various parts.Describe briefly the details of construction of the main supporting surfaces of a Curtiss.Draw a diagram of the assembled planes showing how the struts and cross wires are placed to give the required rigidity.Give the details of the running gear of the Curtiss.What is the office of the Curtiss ailerons and how are they controlled from the operator's seat? Draw sketch.Describe the details of the front and rear outriggers.What type of propeller is advised for the Curtiss? Give the details of its construction.Describe carefully the manner in which a propeller should move through the air in order to give the maximum propulsion.What determines the exact location of the motor in the aeroplane?Give correct method of starting the motor when ready for a flight.What tests should be conducted before a flight is undertaken?After completing the work, add and sign the following statement:I hereby certify that the above work is entirely my own.(Signed)
Main Planes and Struts. It is preferable to begin with the construction of the main planes and their struts and truss wires, the ribs already described being the first step.
The main beams offer no special difficulties. They are ovals 1 1/4 by 1 5/8 inches, all 6 feet long except the eight end ones, which are 6 feet 2 inches. The beams of the central section should be of ash, or should be thicker than the others. In the latter case, they must be tapered at the ends so that the clamping sleeves will fit and the additional wood must be all on the lower side, so that the rib will not be thrown out of alignment. The spruce used for the other beams should be reasonably clear and straight grained, but a small knot or two does not matter, provided it does not come near the ends of the beam. The beams may be cut to the oval shape by the sawmill or planed down by hand.
"Fish-shaped" or "stream-line" section, as it is more commonly termed, is used for the struts, Fig. 15. It is questionable whether this makes any material difference in the wind resistance, but it is common practice to follow it in order to minimize this factor. It is more important that the struts be larger at their centers than at the ends, as this strengthens them considerably. At their ends the struts have ferrules of the 1-inch brass or steel tubing, and fit into the sockets which clamp the ribs and beams together. The material is spruce but the four central struts which carry the engine bed should either be ash or of larger size, say 1 1/4 by 3 inches.
Care Necessary to Get Planes Parallel. The front struts must be longer than the rear ones by the thickness of a main rib at the point where the rear strut bolt passes through it, less the thickness of the rib ferrule through which the bolt of the front strut must pass. However, the first distance is not really the actual thickness of the rib, but the distance between the top of the rear beam and the bottom of the strut socket. In the drawings the difference in length between the front and rear struts is given as 2 inches, but it is preferable for the builder to leave the rear struts rather long and then measure the actual distance when assembling, cutting the struts to fit. The ends of the struts should also be countersunk enough to clear the head of the socket bolt.
One of the items which the builder can not well escape buying in finished form is the strut sockets. These are cup-shaped affairs of pressed steel which sell at 20 cents each. Sixteen of them will be required for the main frame, and a dozen more can advantageously be used in the front and rear controls, though for this purpose they are not absolutely necessary. They can also be obtained in a larger oval size suitable for the four central struts that carry the engine bed, as well as in the standard 1-inch size. The bolts which project through the bottom of the sockets are ordinary 1/4-inch stove bolts, with their heads brazed to the sockets.
For the rear struts, where the bolt must pass through the slanting main rib, it is advisable to make angle washers to put under the socket and also between the beam and rib. These washers are made by sawing up a piece of heavy brass tubing, or a bar with a 1/4-inch hole drilled in its center, the saw cuts being taken alternately at right angles and at 60 degrees to the axis of the tube.
The sleeves which clamp together the ends of the beams are made of sheet steel of about 20 gauge. The steel is cut out on the pattern given in the drawing, Fig. 16, and the 3/16-inch bolt holes drilled in the flanges. The flanges are bent over by clamping the sheet in a vise along the bending line and then beating down with a hammer. Then the sleeves can be bent into shape around a stray end of the beam wood. The holes for the strut socket bolts should not be drilled until ready to assemble. Ordinarily, 3/16-inch stove bolts will do to clamp the flanges together.
Having reached this stage, the amateur builder must now supply himself with turnbuckles. As already mentioned, these may either be purchased or made by hand. It is permissible to use either one or two turnbuckles on each wire. One is really sufficient, but two—one at each end—add but little weight and give greater leeway in making adjustments. As there are about 115 wires in the machine which need turnbuckles, the number required will be either 115 or 230, depending upon the plan which is followed. Those of the turnbuckles to be used on the front and rear controls and the ailerons, about one-fifth of the total number, may be of lighter stock than those employed on wires which carry part of the weight of the machine.
Making Turnbuckles for the Truss Wires. On the supposition that the builder will make his own turnbuckles, a simple form is described here. As will be seen from Fig. 16, the turnbuckles are simply bicycle spokes, with the nipple caught in a loop of sheet steel and the end of the spoke itself twisted into an eye to which the truss wire can be attached. The sheet steel used should be 18 or 16 gauge, and may be cut to pattern with a heavy pair of tin snips. The spokes should be 3/32 inch over the threaded portion. The eye should be twisted up tight and brazed so that it can not come apart. The hole in the middle of each strip is, of course, drilled the same size as the spoke nipple. The holes in the ends are 3/16 inch.
In the original Curtiss machines, the turnbuckles were strung on the socket bolts one after another, sometimes making a pack of them half an inch thick. A much neater construction is shown in the drawings, in which the bolt pierces a single plate with lugs to which to make the turnbuckles fast by riveting. The plates are of different shapes, with two, three, or four lugs, according to the places where they are to be used. They are cut from steel stock 3/32 inch thick, with 1/4-inch holes for the socket bolts and 3/16 inch, or other convenient size, for the rivets that fasten on the turnbuckles.
The relative merits of cable and piano wire for trussing have not been thoroughly threshed out. Each has its advantages and disadvantages. Most of the well-known builders use cable; yet if the difference between 1,000 feet of cable at 2 1/4 cents per foot (the price for 500-foot spools), and 8 pounds of piano wire at 70 cents a pound, looks considerable to the amateur builder, let him by all means use the wire. The cable, if used, should be the 3/32-inch size, which will stand a load of 800 pounds; piano wire should be 24 gauge, tested to 745 pounds. It should be noted that there is a special series of gauges for piano wire, known as the music wire gauge, in which the size of the wire increases with the gauge numbers, instead of the contrary, as is usual with machinery wire gauges.
One by no means unimportant advantage of the piano wire is that it is much easier to fasten into the turnbuckles. A small sleeve or ferrule, a 1/4-inch length of 1/8-inch tubing, is first strung on the wire. The end of the wire is then passed through the turnbuckle eye, bent up, thrust through the sleeve, and again bent down. When the machine is taken apart, the wire is not disconnected from the eye, but instead the turnbuckle spoke is unscrewed from the nipple. The shape of the sheet-steel loop should be such as to hold the latter in place. Cable, on the other hand, must be cut with about 2 inches to spare. After being threaded through the turnbuckle eye, the end is wound back tightly on itself and then soldered, to make certain that it can not loosen.
With a supply of turnbuckles and cable or piano wire at hand, the builder may go ahead with the main box-like structure or cell, which should be completed except for the cloth covering, and in proper alignment, before taking up the construction of the running gear and controls.
Running Gear. The running gear of the machine is built of seamless steel tubing, those parts which carry the weight of the machine direct being of 3/4-inch outside diameter, 16-gauge tubing, while the others are 5/8-inch outside diameter, either 18 or 20 gauge. About 25 feet of the heavy and 45 feet of the light tubing will be required, in lengths as follows: Heavy, four 3-foot, three 4-foot; light, one 6-foot, two 4-foot 6-inch, and seven 4-foot pieces. Referring to Fig. 17, two diagonal braces from the rear beam to the engine bed, the V-shaped piece under the front engine bed struts and all of the rear frame except the horizontal piece from wheel to wheel, are of heavy tubing. The horizontal in the rear frame, diagonals from the rear wheels and the rear end of the skid to the front beam, the two horizontals between the front and rear beam, and the forward V are of light tubing.
Fig. 17. Details of Curtiss Running GearFig. 17. Details of Curtiss Running Gear
Fig. 17. Details of Curtiss Running Gear
Three ash beams are used in the running gear. Two of these run diagonally from the rear end of the engine bed to the front wheel. These are about 10 feet long and 1 by 1 3/4 inches section. The third, which on rough ground acts as a skid, is 8 1/2 feet long and about 2 inches square. Between the joints where the tubing frames are attached to it, the upper corners may be beveled off with a spoke shave an inch or more down each side. The beams are attached to the front wheel with strips of steel stock 1 1/2 inches wide and 1/8 inch thick. The engine bed beams are also ash about 1 by 1 3/4 inches section. Their rear ends are bolted to the middle of the rear engine bed struts and the front ends may be 1/2 inch higher.
SCENE AT AVIATION MEET AT ROUEN, FRANCE, SHOWING AN ANTOINETTE MONOPLANE MAKING A TURNSCENE AT AVIATION MEET AT ROUEN, FRANCE, SHOWING AN ANTOINETTE MONOPLANE MAKING A TURNThis Photograph Protected By International Copyright
SCENE AT AVIATION MEET AT ROUEN, FRANCE, SHOWING AN ANTOINETTE MONOPLANE MAKING A TURNThis Photograph Protected By International Copyright
A FRENCH MONOPLANE TRAVELLING SIXTY-FIVE MILES AN HOURA FRENCH MONOPLANE TRAVELLING SIXTY-FIVE MILES AN HOURThis Photograph Protected By International Copyright
A FRENCH MONOPLANE TRAVELLING SIXTY-FIVE MILES AN HOURThis Photograph Protected By International Copyright
The wheels are usually 20 by 2 inches, and of the bicycle type, but heavier and wider in the hub; the tires are single tube. These wheels, complete with tires, cost about $10 each. This size is used on the standard Curtiss machines, but novice operators, whose landings are not quite as gentle as they might be, find them easily broken. Therefore, it may be more economical in the end to pay a little more and get heavier tires—at least to start with.
For working the tubing into shape, a plumber's blow torch is almost indispensable—most automobilists will already possess one of these. The oval, flat variety, holding about one pint, is very handy and packs away easily, but on steady work requires filling somewhat too frequently. With a dozen bricks a shield can be built in front of the torch to protect the flame and concentrate the heat. Whenever it is to be flattened and bent, the tubing should be brought to a bright red or yellow heat. Screwing the vise down on it will then flatten it quickly without hammer marks. Where the bend is to be made in the middle of the piece, however, it may be necessary to resort to the hammer and anvil.
It is convenient to start with the framework under the rear beam. This may be drawn accurately to full size on the workshop floor, and the tubes bent to fit the drawing. With this framework once in place, a definite starting point for the remainder of the running gear is established. Here and in all other places, when boring through wood, the holes should be drilled out full, and larger washers should be placed under the bolt head and nut. All nuts should be provided with some sort of locking device The perspective drawing. Fig. 17, should show the general arrangement clearly enough to enable the builder to finish the running gear.
Outriggers. Both the front and rear control members, or "outriggers" as they are termed, Fig. 12, may be conveniently built up on the central section of the main frame, which, it is assumed, has now been fitted with the running gear.
The horizontal rudder, or "elevator," is a biplane structure like the main cell of the machine, but with fewer struts; it is carried in front of the main planes on twoA-shaped frames. The vertical rudder, at the rear, is split along the middle and straddles a fixed horizontal plane, ortail. This also is carried on twoA-shaped frames. Lateral stability is controlled by two auxiliary planes or ailerons, one at each side of the machine and carried on the two outer front struts. These three control units—elevator,tailandrudder, andailerons—will now be taken up separately and their construction, location on the machine, and operation will be described.
Fig. 18. Details of Rudders and Ailerons, Curtiss BiplaneFig. 18. Details of Rudders and Ailerons, Curtiss Biplane
Fig. 18. Details of Rudders and Ailerons, Curtiss Biplane
Horizonal Rudder or Elevator. The two planes of the elevator are 2 feet wide by 5 feet 8 inches long and are spaced 2 feet apart, being held in this position by ten struts. The frames of the planes are built of spruce sticks 1/2 by 1 inch, each plane having two sticks the full length and five evenly spaced crosspieces or ribs. These are joined together with squares of X-sheet tin, as shown in the detailed drawing, Fig. 18. With a little experimenting, paper patterns can be made from which the tin pieces can be cut out. The sticks are then nailed through the tin with 3/4-inch brads.
It is convenient to draw the frames out accurately on a smooth wood floor and then work over this drawing. The first few brads will hold the sticks in place. When all the brads have been driven, a little drop of solder should be run in around the head of each one. This is a tedious job. One must be careful to use no more solder than necessary as it increases the weight very rapidly. Two pounds of wire solder should be sufficient for all the control members which are built in this way. When the top side is soldered, pry the frame loose from the floor with a screwdriver and turn it over. Then the projecting points of the brads must be clinched and the soldering repeated.
At this stage, the two frames should be covered on both sides with the prepared cloth used for covering the main planes. The method of preparing this cloth is detailed a little farther along.
The struts, so-called, to continue the analogy with the main planes, are turned sticks of spruce 3/8 inch in diameter. They are fitted at each end with ferrules of thin 3/8-inch brass, or steel tubing, driven on tight. Instead of using sockets, the struts are held at each end, simply by a long wood screw driven through the tin and wood of the plane frame and into the strut. These screws also hold the turnbuckles for the truss wires. For trussing purposes, the elevator is regarded as consisting of two sections only, the intermediate struts being disregarded.
The turnbuckles and wire used here and in the other control members may well be of lighter stock than those used in the main planes. Piano wire, No. 18, or 1/16-inch cable is amply strong. The sheet steel may be about 22 gauge, instead of 16, and the bicycle spokes smaller in proportion. No turnbuckle plates are necessary. The screws running into the struts may be passed directly through the eyes of the turnbuckles, where they would have been attached to the turnbuckle plate. In order to secure a square and neat structure, those struts which have turnbuckles at their ends should be made a trifle shorter than the others.
At each end, the elevator has anX-shaped frame of 1/4-inch steel tubing; at the intersection of theX's are pivots on which the elevator is supported. EachXis made of two tubes, bent into a y and flattened and brazed together at the points. The ends of theX's are flattened and bent over so that the screws which hold the struts in place may pass through them.
Fig. 19. Curtiss Biplane Ready for FlightFig. 19. Curtiss Biplane Ready for Flight
Fig. 19. Curtiss Biplane Ready for Flight
To the front middle strut is attached an extension which acts as a lever for operating the elevator. This is a stick of spruce 3/4 inch in diameter and 3 feet 3 inches long. At its upper end it has a ferrule of steel tubing, flattened at the end. The lower part of the stick may be fastened to the strut by wrapping the tube with friction tape, or by improvising a couple of sheet steel clamps. The upper end of the stick is braced by a 1/4-inch steel tube, extending to the top of the rear middle strut, and held by the same screw as the strut. This extension lever is connected to the steering column by a bamboo rod, 1 inch in diameter and about 10 feet long, provided with flattened ferrules of steel tubing at each end. Each ferrule should be held on by a 1/8-inch stove bolt passing through it.
Front and Rear Outrigger Frames. Both the front elevator and the tail and rudder at the rear, are carried, as mentioned above, each on a pair ofA-shaped frames, similar to one another, except that those in the rear are longer than those in the front. Both are made of spruce of about the same section as used for the struts of the main frame. These pieces may either be full length, or they may be jointed at the intersection of the crosspieces, the ends being clamped in a sheet-steel sleeve, just like that used on the beams of the main frame. In this case, it is advisable to run a 1/8-inch stove bolt through each of the ends.
Fig. 20. Details of Outriggers and Front Elevating Planes as Seen from Driver's SeatFig. 20. Details of Outriggers and Front Elevating Planes as Seen from Driver's Seat
Fig. 20. Details of Outriggers and Front Elevating Planes as Seen from Driver's Seat
The crosspieces of theA-frames are spruce of the same section, or a little smaller. At their ends may be used strut sockets like those of the main frame; or, if it is desired to save this expense, they may be fastened by strips of 1/16-inch steel stock with through bolts.
The front outrigger has, besides the two A-frames, a rather complicated arrangement of struts designed to brace the front wheel against the shocks of landing. This arrangement does not appear very plain in a plan or elevation, and may best be understood by reference to the photograph, Fig. 19, and the perspective drawing, Fig. 20. Fig. 20 is a view from the driver's seat. The elevator is seen in front, theA-frames at each side, and at the bottom the two diagonal beams to the engine bed and the skid.
Reference to this drawing will show the two diagonals run from the front wheel up and back to the top of the main frame, and two more from the wheel forward to the short crosspieces near the apexes of theA-frame: there is also a vertical strut which intersects two horizontal pieces running between the ends of the longer crosspieces of theA-frames. Altogether, there are five attachments on each side of the front wheel, through which the axle bolt must pass, viz, the connections to the skid, to one of the diagonals to the engine bed, to one of the rear diagonals, to one of the front diagonals, and to one side of the fork carrying the vertical strut. Of these the skid attachments should be on the inside closest to the wheel, and the engine bed diagonals next.
The four additional diagonals running to the front wheel may be spruce of the same section used in theA-frames, or turned one inch round. At each end they have flattened ferrules of steel tubing. The beams of theA-frames have similar ferrules at the ends where they attach to the main frames. These attachments should be made on the socket bolts of the struts on either side of the middle 6-foot section and on the outer side of the main beams—not between the beam and the socket itself.
It is possible, of course, to make all theA-frames and diagonal braces of bamboo, if desired, the qualities of this material already having been referred to. Bamboo rods for this purpose should be between 1 and 1 1/4 inches in diameter. Where ferrules are fitted on the ends, the hole of the bamboo should be plugged with wood glued in place.
Generally, in the construction of the outrigger frames, the builder can use his own discretion to a considerable extent. There tire innumerable details which can be varied—far too many to consider even a part of the possibilities in this connection. If the builder runs across any detail which he does not see mentioned here, he may safely assume that any workmanlike job will suffice. Often, the method may be adapted to the materials on hand. The diagonal wires from the crosspieces of the A-frames to the struts should be crossed.
Rudder and Tail Construction. The frame for the rudder and tail are constructed in much the same way as those for the elevator, Fig. 18. Spruce sticks 1 by 1/2 inch are used throughout, except for the piece at the back edge of the rudder and the long middle piece across the tail; these should be 1 1/2 by 1/2 inch. This long middle piece of the tail is laid across on top of the rest of the framework. When the cloth is put on, this makes the upper surface slightly convex while the lower surface remains flat. The ends of this piece should be reinforced with sheet steel, fairly heavy and drilled for 1/4-inch bolts, attaching the tail to theA-frames.
The rudder is hung from two posts extending above and below the tail. These posts may be set in cast aluminum sockets, such as may be obtained from any supply house for 20 cents apiece. The posts need not be more than 3/4 inch in diameter. At their outer ends, they should have ferrules of steel tubing, and the turnbuckles or other attachments for the truss wires should be attached by a wood screw running into the end of each. From these posts the rudder may be hung on any light hinges the builder may find convenient, or on hinges improvised from screw eyes or eye bolts, with a bolt passing through the eyes of each.
In steering, the rudder is controlled by a steering wheel carried on a hinged post in front of the pilot. This post should be ash about 1 by 1 1/4 inches. It hinges at the bottom on a steel tube of 1/2-inch diameter which passes through it and is supported at the ends on diagonal beams to the engine bed. Two diagonals of lighter tubing may be put in to hold the posts centered between the two beams.
The post is, of course, upright, and the hub of the wheel is horizontal. The wheel may be conveniently mounted on a piece of tubing of the same size as the hub hole, run through the post and held by a comparatively small bolt, which passes through it and has a big washer on either end. The wheel is preferably of the motor-boat variety with a groove around the rim for the steering cable.
The rear edge of the tail should be about 1 inch lower than the front. To make the rudder post stand approximately vertical, wedge-shaped pieces of wood may be set under the sockets.
The steering connections should be of flexible cables of steel such as are made for this purpose. There should be a double pulley on the post just under the wheel, and the cables should be led off the post just at the hinge at the bottom, so that swinging the post will not affect them. The cable is then carried under the lower main plane and out the lower beams of theA-frames. It is attached to the rudder at the back edge; snap hooks should be used for easy disconnection in packing. Perhaps the best way of guiding the cable, instead of using pulleys, is to run it through short pieces of tubing lashed to the beams with friction tape. The tubing can be bent without flattening by first filling it with melted lead, which, after the bending, can be melted out again.
Ailerons for Lateral Stability. The framework of the ailerons is made in the same way as that for the elevator, tail, and rudder, Fig. 18. The pieces around the edges should be 1 1/2 by 1/2 inch, as also the long strip laid over the top of the ribs. The ribs should be 1/2 by 3/4 inch. Each aileron has two holes, one for the strut to pass through, and the other for the diagonal truss wires at their intersection. The back edge also has a notch in it to clear the fore and aft wires. Each aileron is hung on four strips of soft steel about 1/2 by 3/16 inch, twisted so that one end is at right angles to the other. These are arranged one on each side of the strut which passes through the aileron, and one at each end. Bolts through the struts carry three of them and the outer one is trussed by wires to each end of the outer strut.
A frame of 1/4-inch steel tubing fits around the aviator's shoulders and is hinged to the seat, so that he can move it by leaning from one side to the other. This is connected by flexible cable to the rear edges of the ailerons, so that when the aviator leans to the left, he will raise the left and lower the right aileron. The upper edges of the ailerons are directly connected to each other by a cable running along the upper front beam, so that they must always move together.
Covering of the Planes. Mention has already been made of the fact, in the general description of the machine, that light sail cloth, as employed on the Wright machines, may be used for the planes or wings. As a matter of fact, many different materials may be successfully employed, the selection depending upon the builder himself and his financial resources. About 55 square yards of material will be required, and in comparing prices always compare the width as this may vary from 28 to 55 inches. Rubberized silk which is used on the standard Curtiss machines is the most expensive covering, its cost running up to something like two hundred dollars. There are also several good aero fabrics on the market which sell at 60 cents a square yard, as well as a number of brands of varnish for the cloth—most of them, however, quite expensive. The most economical method is to employ a strong linen cloth coated with shellac, which will be found very satisfactory.
The covering of the frames with the cloth may well be postponed until after the engine has been installed and tested, thus avoiding the splashing of oil and dirt which the fabric is apt to receive during this operation. The wire to which the cloth is laced, must be strung along the rear ends of the ribs of each plane. The wires pass through holes in the ends of the small ribs and are attached to the main ribs with turnbuckles. At the ends of the planes the main ribs must be braced against the pull of the wire by a piece of 1/4-inch tubing running from the end of the rib diagonally up to the rear beam. Both turnbuckles and tube are fastened with one wood screw running into the end of the rib.
The cloth should be cut to fit the panels between the main ribs and hemmed up, allowing at least an inch in each direction for stretch. Small eyelets should be put along the sides and rear edges an inch apart for the lacing. At the front edge, the cloth is tacked directly to the beam, the edge being taken well under and around to the back. Strong fish line is good material for the lacing.
After the cloth is laced on, it must be tacked down to the small ribs. For this purpose, use upholstery tacks as they have big cup-shaped heads which grip the cloth and do not tear out. As an extra precaution a strip of heavy tape must be run over each rib under the tack heads. All the control members are covered on both sides, the edges being folded under and held by tacks.
Making the Propeller. If the completed biplane is to fly properly and also have sufficient speed to make it safe, considerable care must be devoted to the design and making of the propeller. Every aeroplane has a safe speed, usually referred to in technical parlance as itscritical speed. In the case of the Curtiss biplane under consideration, this speed is about 40 miles an hour. By speeding up the motor considerably, it may be able to make 42 to 43 miles an hour in a calm, such a condition representing the only true measure of an aeroplane's ability in this direction, while on the other hand, it would not be safe to let its speed with relation to the wind (not to the ground) fall much below 35 miles an hour. At any slower rate of travel, its dynamic stability would be precarious and the machine would be likely to dive to the ground unexpectedly. The reasons for this have been explained more in detail under the heading of "The Internal Work of the Wind."
The necessity of making the propeller need not discourage the ambitious builder—if he can spare the time to do it right, it will be excellent experience. If not, propellers designed for driving a machine of this size can be purchased ready to mount from any one of quite a number of manufacturers. But as the outlay required will be at least $50, doubtless most experimenters will prefer to undertake this part of the work as well as that of building the framework and main cell, particularly as more than 90 per cent of the sum mentioned is represented by labor. The cost of the material required is insignificant by comparison.
True-Screw Design. First it will be necessary to design the propeller to meet the requirements of the biplane itself. As this is a matter that has already been gone into in considerable detail under the appropriate heading, no further explanation of propeller characteristics or of the technical terms employed, should be needed here. We will assume that the biplane is to have a speed of 40 miles per hour in still air with the motor running at 1,200 r.p.m. With this data, it will not be difficult to calculate the correct pitch of the propeller to give that result. Thus
40 X 5,280 X 100 / 60 X 1,200 X 85 = 3.45
or in round numbers a pitch of 3 1/2 feet. 40 (the speed in miles per hour) times 5,280 (feet per mile) divided by 00 (minutes in an hour) gives the speed of the aeroplane in feet per minute. Dividing this by 1,200 (revolutions per minute) gives the number of feet the aeroplane is to advance per revolution of the propeller. The "100/85" part of the equation represents the efficiency of the propeller which can safely be figured on,i.e., 85 per cent, or an allowance for slip of 15 per cent. Forty miles an hour is the maximum speed to be expected, while the r.p.m. rate of the engine should be that at which it operates to the best advantage.
The merits of thetrue-screwandvariable-pitchpropellers have already been dwelt upon. The former is not only more simple to build, but experience has shown that, as generally employed, it gives better efficiency. Hence, the propeller under consideration will, be of the true-screw type. Its pitch has already been calculated as 3 1/2 feet. For a machine of this size and power, it should be 6 feet in diameter. Having worked out the pitch and decided upon the diameter, the next and most important thing is to calculate the pitch angle. It will be evident that no two points on the blade will travel through the air at the same speed. Obviously, a point near the tip of the propeller moves faster than one near the hub, just as in rounding a curve, the outer wheel of an automobile has to travel faster than the inner, because it has to travel farther to cover the same ground. For instance, taking the dimensions of the propeller in question it will be seen that its tips will be traveling through the air at close to 4.3 miles per minute, that is,
6 X π X 1200 / 5,280 = 4.28
in which 6, the diameter of the propeller in feet, times π gives the circumference of the circle which is traveled by the blade tips 1,200 times per minute; this divided by the number of feet per mile gives the miles per minute covered. On the other hand, a point on the blade but 6 inches from the hub will turn at only approximately 3,500 feet per minute. Therefore, if every part of the blade is to advance through the air equally, the inner part must be set at a greater angle than the outer part. Each part of the blade must be set at such an angle that at each revolution it will move forward through the air a distance equal to the pitch. This is known as the pitch angle. The pitch divided by the circumference of the circle described by any part of the blade, will give a quantity known as the tangent of an angle for that particular part. The angle corresponding to that tangent may most easily be found by referring to a book of trigonometric tables.
Table II. Propeller Blade Data
For example, take that part of the blade of a 3 1/2-foot pitch propeller which is 6 inches from the center of the hub. Then
3.5 X 12 / 6 X 2 π = 1.1141 tangent of 48 degrees 5 minutes
in which 3.5 X 12 reduces the pitch to inches, while 6 X 2π is the circumference of the circle described by the point 6 inches from the hub. However, in order to give the propeller blade a proper hold on the air, it must be set at a greater angle than these figures would indicate. That is, it must be given an angle of incidence similar to that given to every one of the supporting planes of the machine. This additional angle ranges from 2 degrees 30 minutes, to 4 degrees, depending upon the speed at which the particular part of the blade travels; the greater the speed, the less the angle. This does not apply to that part of the blade near the hub as the latter is depended upon solely for strength and is not expected to add to the effective thrust of the propeller.
Table II shows the complete set of figures for a blade of 3 1/2-foot pitch, the angles being worked out for sections of the blade 3 inches apart.
These angles are employed in Fig. 21, which shows one blade of the propeller and its cross sections.
It should be understood that these calculations apply only to the type of propeller known as thetrue screw, as distinguished from thevariable pitch. The design of the latter is a matter of personal skill and experience in its making which is hardly capable of expression in any mathematical formula. There are said to be only about three men in this country who know how to make a proper variable-pitch propeller, and it naturally is without advantage when made otherwise.
Fig. 21. Details of Propeller Construction, Curtiss BiplaneFig. 21. Details of Propeller Construction, Curtiss Biplane
Fig. 21. Details of Propeller Construction, Curtiss Biplane
Shaping the Blades. Like the ribs, the propeller is made up of a number of laminations of boards finished true and securely glued, afterward being cut to the proper shape, though this process, of course, involves far more skill than in the former case. Spruce is the strongest wood for its weight, but it is soft and cracks easily. Maple, on the other hand, is tough and hard, so that it will be an advantage to alternate the layers of these woods with an extra maple board, in order to make both outside strips of the harder wood, so as to form a good backing for the steel flanges at the hub, the rear layer extending the full length of the thin rear edges of the blades. Other woods may be employed and frequently are used by propeller manufacturers, such as mahogany (not the grained wood used for furniture, but a cheaper grade which is much stronger), walnut, alternate spruce and whitewood, and others.
The boards should be selected with the greatest care so as to insure their being perfectly clear,i.e., absolutely free of knots, cross-grained streaks, or similar flaws, which would impair their strength and render them difficult to work smoothly. They should measure 6 inches wide by 6 feet 1 inch in length. Their surfaces must be finished perfectly true, so that they will come together uniformly all over the area on which they bear on one another, and the various pieces must be glued together with the most painstaking care. Have the glue hot, so that it will spread evenly, and see that it is of a uniform consistency, in order that it may be smoothly applied to every bit of the surface. They must then be clamped together under as much pressure as it is possible to apply to them with the means at hand, the rib press already described in detail forming an excellent tool for this purpose. Tighten up the nuts evenly a little at a time, avoiding the application of excessive or uneven pressure at one point, continuing the gradual tightening up process until it can not be carried any farther. This is to prevent the boards from assuming a curve in drying fast. Allow at least twenty-four hours for drying, during which period the laminated block should be kept in a cool, dry place at as even a temperature as possible.
Before undertaking the remainder of the work, all of which must be carried out by hand, with the exception of cutting the block to the outline of the propeller, which may be done with a band saw, a set of templates or gauges should be made from the drawings. These will be necessary as guides for finishing the propeller accurately. Draw the sections out full size on sheets of cardboard or tin and cut out along the curves, finally dividing each sheet into two parts, one for the upper side and one for the lower. Care must be taken to get the sides of the template square, and when they are used, the propeller should be laid on a perfectly true and flat block. Each template should be marked as it is finished, to indicate what part of the blade it is a gauge for. The work of cutting the laminated block down to the lines represented by the templates is carried out with the aid of the plane, spoke shave, and gouge. After the firstroughing outto approximate the curvature of the finished propeller is completed, the cuts taken should be very fine, as it will be an easy matter to go too deep, thus spoiling the block and necessitating a new start with fresh material. For finishing, pieces of broken glass are employed to scrape the wood to a smooth surface, followed by coarse and finally by fine sandpaper.
Mounting. The hub should be of the same diameter as the flange on the engine crank shaft to which the flywheel was bolted, and should have its bolt holes drilled to correspond. To strengthen the hub, light steel plates of the same diameter are screwed to it, front and back, and the bolt holes drilled right through the metal and wood. This method of fastening is recommended where it is possible to substitute the propeller for the flywheel formerly on the engine, it being common practice to omit the use of the flywheel altogether. The writer does not recommend this, however, as the advantages of smoother running and more reliable operation gained by the use of a flywheel in addition to the propeller far more than offset any disadvantage represented by its weight. It will be noted that the Wright motors have always been equipped with a flywheel of ample size and weight and this is undoubtedly responsible, in some measure at least, for the fact that the Wright biplanes fly with considerably less power than is ordinarily employed for machines of the same size. If the motor selected be equipped with an unusually heavy flywheel, and particularly where the wheel is of comparatively small diameter, making it less effective as a balancer, it may be replaced with one of lighter weight and larger diameter. It may be possible to attach it by keying to the forward end of the crank shaft, thus leaving the flange from which the flywheel was taken free for mounting the propeller. An ordinary belt pulley will serve excellently as the new flywheel, as most of its weight is centered in its rim, but as the common cast-iron belt pulley of commerce is seldom intended to run at any such speed as that of an automobile motor, it should be examined carefully for flaws. Otherwise, there will be danger of its blunting with disastrous results under the influence of centrifugal force. Its diameter should not exceed 16 inches in order to keep its peripheral speed within reasonable limits. Where the mounting of the motor permits of its use, a wood pulley 18 to 20 inches in diameter with a steel band about 1/8 to 1/4-inch thick, shrunk on its periphery, may be employed. Most builders will ridicule the idea of a flywheel other than the propeller itself. "You do not need it; so why carry the extra weight?" will be their query. It is not absolutely necessary, but it is an advantage.
In case the flywheel of the engine selected is keyed to the crank shaft, or in case it is not possible to mount both the flywheel and the propeller on different ends of the crank shaft, some other expedient rather than that of bolting to the flange must be adopted. In such a case, the original flywheel, where practical to retain it, may be drilled and tapped and the propeller attached directly to it. Where the flywheel can not be kept, it will usually be found practical to cut off its rim and bolt the propeller either to the web or spokes, or to the flywheel hub, if it be cut down to the latter.
The drawing. Fig. 21, shows the rear or concave side of the propeller. From the viewpoint of a man standing in its wind and facing forward, it turns to the left, or anti-clockwise. On many of the propellers now on the market, the curved edge is designed to go first. This type may have greater advantages over that described, but the straight front edge propeller is easier for the amateur to make.
Mounting the Engine. Having completed the propeller, the next step is the mounting of the engine. Reference to the types available to the amateur aeroplane builder has already been made. There are a number of motors now on the market that have been designed specially for this purpose and not a few of them are of considerable merit. Their cost ranges from about $250 up to $2,500, but it may be possible to pick up a comparatively light-weight automobile motor second hand which will serve all purposes and which will cost far less than the cheapest aeronautic motor on the market. It must be capable of developing 30 actual horse-power at 1,000 to 1,200 r.p.m. and must not exceed 400 pounds complete with all accessories, such as the radiator and piping, magneto, water, oil, etc. Considerable weight may be saved on an automobile motor by removing the exhaust manifold and substituting a lighter flywheel for the one originally on the engine—or omitting it altogether, as just mentioned. A light-weight aeronautic radiator should be used in preference to the usual automobile radiator.
When placing the engine in position on the ash beams forming its bed or support, it must be borne in mind that the complete machine, with the operator in the aviator's seat, is designed to balance on a point about 1 1/2 feet back of the front edge of the main planes. As the operator and the motor represent much the larger part of the total weight, the balance may easily be regulated by moving them slightly forward or backward, as may be required. It will be necessary, of course, to place the engine far enough back in any case to permit the propeller blades to clear the planes. The actual installation of the engine itself will be an easy matter for anyone who has had any experience in either automobile or marine gasoline motor work. It is designed to be bolted to the two engine beams in the same manner as on the side members of the frame of an automobile, or the engine bed in a boat. Just in front of the engine is the best place for the gasoline tank, which should be cylindrical with tapering ends, to cut down its wind resistance. If the designer is not anxious to carry out points as fine as this, a light copper cylindrical tank may be purchased from stock. It should hold at least ten gallons of gasoline. In front of the tank is the radiator.
Controls. The controls may be located to conform to the builder's own ideas of accessibility and convenience. Usually the switch is placed on the steering column, and it may be of the ordinaryknifevariety, or one of the special switches made for this purpose, as taste may dictate. The throttle control and spark advance may either be in the form of pedals, working against springs, or of small levers working on a notched sector, at the side of the seat. The complete control, levers, and sector may be purchased ready to mount whenever desired, as they are made in this form for both automobile and marine work. This likewise applies to the wheel, which it would not pay the amateur to attempt to make.
Another pedal should work a brake on the front wheel, the brake shoe consisting of a strip of sheet steel, fastened at one end to the fore part of the skid and pressed against the wheel by a bamboo rod directly connected with the brake pedal. An emergency brake can also be made by loosely bolting a stout bar of steel on the skid near its rear end; one end of this bar is connected to a lever near the seat, so that when this lever is pulled back the other end of the bar tends to dig into the ground. As making a landing is one of the most difficult feats for the amateur aviator to master and sufficient space for a long run after alighting is not always available, these brakes will be found a very important feature of the machine.
Fig. 22. Method of Starting the Engine of an AeroplaneFig. 22. Method of Starting the Engine of an Aeroplane
Fig. 22. Method of Starting the Engine of an Aeroplane
The engine is started by swinging the propeller, and this is an operation requiring far more caution than cranking an automobile motor. Both hands should be placed on the same blade. Fig. 22, and the latter should always be pulled downward—never upward. With the switch off, first turn the propeller over several times to fill the cylinders with gas, leaving it just ahead of dead center of one of the cylinders, and with one blade extending upward and to the left at a 45-degree angle. After closing the switch, take the left blade with both hands and swing it downward sharply, getting out of the way of the following blade as quickly as possible.
Tests. The first thing to be done after the propeller is finished and mounted on the engine is to test the combination, or power plant of the biplane, for speed and thrust, or pulling power. From these two quantities it will be easy to figure the power that the engine is delivering. The only instruments necessary are a spring balance reading to 300 pounds or over; a revolution counter, such as may be procured at any machinist's supply house for a dollar or two; and a watch. One end of the spring balance is fastened to the front end of the skid and the other to a heavy stake firmly driven in the ground a few feet back. The wheels of the biplane should be set on smooth boards so that they will not offer any resistance to the forward thrust. When the engine is started the spring balance will give a direct reading of the pull of the propeller.
With one observer noting the thrust, another should check the number of revolutions the engine is turning per minute. To do this, a small hole should previously have been countersunk in the hub of the propeller to receive the conical rubber tip of the revolution counter. The observer stands behind the propeller, watch in one hand and revolution counter in the other. At the beginning of the minute period, the counter is pressed firmly against the hub, and quickly withdrawn at the end of the minute. A stop watch is naturally an advantage for the purpose. The horse-power is figured as follows, assuming, for example, a thrust of 250 pounds at 1,200 r.p.m.
250 X 1200 X 3.5 X 100 / 33.000 X 85 = 37 h. p.
As before, the "100/85" allows for the slip and represents the efficiency of the propeller; 33,000 is the number of foot pounds per minute or the equivalent of one horse-power, and 3.5 is the pitch of the propeller.
Assembling the Biplane. Assembling the machine complete requires more space than is available in the average workshop. However, it is possible to assemble the sections of the planes in a comparatively small room, carrying the work far enough to make sure that everything will go together properly when the time comes for complete assembly at the testing ground. In this case, it is preferable to assemble the end sections first, standing them away when complete to make room for the central section, on which the running gear and outriggers are to be built up.
The builder will have decided by this time whether he will make his machine on the regular plan, with one main rib between each section, or on the quick-detachable plan, which has two main ribs on either side of the central section, as previously explained.
It is desirable to be able to assemble two sections at once and this should be possible anywhere as it requires a space only about 6 by 13 feet. Two wood 2X4's, about 12 feet long, should be nailed down on the blocks on the floor; make these level and parallel to each other at a distance of 3 feet 6 inches on centers, one being 3 inches higher than the other. Strips of wood should be nailed on them, so as to hold the main beams of the frame in place while assembling.
The two front and two rear beam sections are laid in place and joined with the sheet-steel sleeves, the flanges of the sleeves on the inner side of the beams. Then through the sleeves in the front beams, which are, of course, those on the higher bed, drill the holes for the strut socket bolts (1/4 inch). The holes for the outer ones go through the projecting ends of the beams; those for the inner ones are half in each of the two abutting beams. At the end where the central section joins on, a short length of wood of the same section may be inserted in the sleeve while drilling the hole. An assistant should hold the beams firmly together while the holes are being drilled.
Now lay in place the three main ribs belonging to the two sections under construction and fasten them at the front ends by putting in place the strut sockets for which the holes have been drilled, with a turnbuckle plate under each socket, Fig. 16. The strut socket bolt passes through the main rib and the beam. The bed on which the assembling is being done, should be cut when sufficiently under the joints to leave room for the projecting bolt ends. Set the ribs square with the front beams, then arrange the rear beams so that their joints come exactly under the ribs; clamp the ribs down and drill a true, vertical hole through the rib beam, holding the two sections of the beam together as before. Then put the rear strut sockets in place, using the angle washers previously described, above and below the rib.
When the quick-detachable plan is followed, the ribs at the inner ends of the double section, where they join the central section, should be bolted on an inch from the ends of the beam, using 1/4-inch stove bolts instead of the socket bolts. The sleeves should be slotted, so that they can slide off without removing these bolts, as the sleeves and ribs which occupy the position over the joints of the beams, belong to the central section.
The sections should now be strung up with the diagonal truss wires which will make them rigid enough to stand handling. The wires are attached at each end to the flange bolts of the sleeves. Either one or two turnbuckles may be used on each wire, as already explained; if but one turnbuckle be used, the other end of the wire may be conveniently attached to a strip of sheet steel bent double and drilled for the bolt, like the sheet-steel slip of a turnbuckle. The attachment, of whatever nature, should be put between the end and the flange of the sleeve, not between the two flanges.
Three or four ribs can be used on each section; four are preferable on sections of full 6-foot length. They are, of course, evenly spaced on centers. At the front ends, they are attached to the beam by wood screws through their flattened ferrules. The attachment to the rear beam is made with a slip of sheet steel measuring 1/2 by 3 inches, bent over the rib and fastened to the beam at each side with a wood screw. A long wire nail is driven through the rib itself on the beam.
Four double sections should be built up in this manner, the right and left upper and the right and left lower sections. Uppers and lowers are alike except for the inversion of the sockets in the upper sections. Rights and lefts differ in that the outer beams are long enough to fill up the sleeves, not leaving room for another beam to join on.
Inserting the struts in their sockets between the upper and lower sections of the same side will now form either of the two sides of the machine complete. Care should be taken to get the rear struts the proper length with respect to the front ones to bring the upper and lower planes parallel. The distance from the top of the lower front beam to the top of the upper front beam should be the same as the distance between the rows of bracing holes in the upper and lower main ribs just above and below the rear struts—about 4 feet 6 inches. It should hardly be necessary to mention that the thick edges of the struts come to the front—they are fish-shaped and a fish is thicker at the head than at the tail.
The truss wires may now be strung on in each square of the struts, beams, and main ribs, using turnbuckles as previously described. The wires should be taut enough to sing a low note when plucked between the thumb and forefinger. If the construction is carried out properly, the framework will stand square and true with an even tension on all the wires. It is permissible for the struts to slant backward a little as seen from the side, but all should be perfectly in line.
For adjusting the turnbuckles, the builder should make for himself a handy little tool usually termed a nipple wrench. It is simply a strip of steel 1 1/2 by 1/2 by 3/32 inches, with a notch cut in the middle of the long sides to fit the flattened ends of the turnbuckle nipples. This is much handier than the pliers and does not burr up the nipples.
It has been assumed in this description of the assembling that the builder is working in a limited space; if, on the contrary, he has room enough to set up the whole frame at once, the work will be much simpler. In this case, the construction bed should be 30 feet long. First build up the upper plane complete, standing it against the wall when finished; then build the lower plane, put the struts in their sockets, and lay on the upper plane complete.
Returning to the plan of assembly by sections, after the side sections or wings of the machine have been completed, the struts may be taken out and the sections laid aside. The middle section, to which the running gear and outriggers will be attached, is now to be built up in the same way. If the builder is following the plan in which there is one main rib between each section, it will be necessary to take off the four inner main ribs from the sections already completed, to be used at the ends of the central section. The plan drawing of the complete machine shows that the ribs of the central section are cut off just back of the rear beam to make room for the propeller. This is necessary in order to set the motor far enough forward to balance the machine properly. The small ribs in this section have the same curve but are cut off 10 inches shorter at their rear ends, and the stumps are smoothed down for ferrules like those for the other small ribs. In the plan which has one main rib between each section, the main rib on each side of the central section must be left full length. In the quick-detachable plan with two main ribs on each side of the central section, the inner ones, which really belong to this section, are cut off short like the small ribs.
In the drawing of the complete machine, the distance between the struts which carry the engine bed is shown as 2 feet. This is only approximate, as the distance must be varied to suit the motor employed. By this time, the builder will have decided what engine he is going to use—or can get—and should drill the holes for the sockets of these struts with due respect to the width of the engine's supporting feet or lugs, remembering that the engine bed beams go on the inside of the struts. In the drawing of the running gear. Fig. 17, the distance between the engine-bed struts has been designatedA. The distances,B, on each side are, of course, approximately (6'— 2*A*), whateverAmay be.
VIEW OF THE FRENCH AVIATION GROUNDS SHOWING THE HANGARS RANGED ALONG THE EDGES OF THE FIELDVIEW OF THE FRENCH AVIATION GROUNDS SHOWING THE HANGARS RANGED ALONG THE EDGES OF THE FIELDThis Photograph Protected By International Copyright
VIEW OF THE FRENCH AVIATION GROUNDS SHOWING THE HANGARS RANGED ALONG THE EDGES OF THE FIELDThis Photograph Protected By International Copyright
EXAMINATION PAPER
EXAMINATION PAPER
BUILDING AND FLYING ANAEROPLANE
BUILDING AND FLYING AN
AEROPLANE
PART I
PART I
Read Carefully: Place your name and full address at the head of the paper. Any cheap, light paper like the sample previously sent you may be used. Do not crowd your work, but arrange it neatly and legibly.Do not copy the answers from the Instruction Paper; use your own words so that we may be sure that you understand the subject.
What type of machine, biplane or monoplane, makes the best glider and why?
Give the dimensions of a glider which will support a man's weight.
In a glider which has no rudder, how is the machine controlled?
Give carefully the details of the start in making a glide.
In what direction relative to the wind should a glide be made? Justify your answer.
How must the stability and balance of a glider in flight be controlled?
State the proper conditions for a successful glide.
Give the essential characteristics of a Curtiss aeroplane, defining the various parts.
Describe briefly the details of construction of the main supporting surfaces of a Curtiss.
Draw a diagram of the assembled planes showing how the struts and cross wires are placed to give the required rigidity.
Give the details of the running gear of the Curtiss.
What is the office of the Curtiss ailerons and how are they controlled from the operator's seat? Draw sketch.
Describe the details of the front and rear outriggers.
What type of propeller is advised for the Curtiss? Give the details of its construction.
Describe carefully the manner in which a propeller should move through the air in order to give the maximum propulsion.
What determines the exact location of the motor in the aeroplane?
Give correct method of starting the motor when ready for a flight.
What tests should be conducted before a flight is undertaken?
After completing the work, add and sign the following statement:
I hereby certify that the above work is entirely my own.
(Signed)