CHAPTER XI FUSELAGE (BODY) CONSTRUCTION.

CHAPTER XI FUSELAGE (BODY) CONSTRUCTION.Purpose of Fuselage. The fuselage of a monoplane or tractor biplane is the backbone of the machine. It forms a means of connecting the tail surfaces to the main wing surfaces, carries the motor, fuel and pilot, and transmits the weight of these items to the wings and chassis. With the exception of the wing structure, the fuselage is the most important single item in the construction of the aeroplane. Fig. 1 shows a typical arrangement of a two-place biplane fuselage equipped with a water-cooled motor. The motor E, propeller Y, and radiator R are placed in the front of the fuselage, and considerably in advance of the wings W and D. Immediately behind the motor is the passenger's seat A and the fuel tank F. The pilot's seat B is placed behind the trailing edge of the wings and is behind the passenger's seat. The cockpit openings G and H are cut in the fuselage top for the passenger and pilot respectively. The rear extension of the fuselage carries the control surfaces, L being the vertical fin, M the rudder, O the fixed tail or stabilizer, and P the elevator.Resistance. To reduce the resistance in flight, the fuselage is of as perfect streamline form as possible, the fuselage being deepest at a point about one-third from the front. From this point it tapers out gradually to the rear. With the motors now in use it is only possible to approximate the ideal streamline form owing to the front area of the radiator and to the size of the motor. Again, the projection of the pilot's head above the fuselage adds considerably to the resistance. The wind shields I disturb the flow of air. The connections to the tail surfaces and to the chassis members K also add to the total resistance. An arched "turtle deck" J is generally provided, of such a shape that the pilot's head is effectively "streamlined," the taper of this deck allowing the disturbed air to close in gradually at the rear. The flat area presented by the radiator R is probably the greatest single source of resistance, and for this reason the radiator is sometimes placed at the side of the fuselage, or in some other position that will allow of a better front end outline. An example of this construction is shown by Fig. 2 in which the radiator R is placed behind and above the motor E. The front fuselage end Z can now be made of a more suitable streamline form.Figs. 1-2-3. Fuselage and Motor Arrangement of Tractor Biplanes.Figs. 1-2-3. Fuselage and Motor Arrangement of Tractor Biplanes.Fig. 3 is a view of the front end of a typical fuselage in which an air-cooled rotary type of motor is installed. Since the diameter of this type of motor is seldom much less than three feet, it is necessary to have a very great diameter in the extreme front. The motor housing or "cowl" marked E has a diameter "d" which should smoothly blend into the outline of the fuselage at "b." In the older types of construction there was often a very considerable break in the outline at this point, especially in cases where the circular cowl was abruptly connected to a square fuselage. A break of this sort greatly increases the head resistance. A "spinner" or propeller cap marked Z in Fig. 3 is an aid in reducing the resistance offered by the motor cowl and also reduces the resistance of the inner, and ineffective, portion of the propeller blades. The cap in any case is smaller than the cowl opening in order that cooling air be admitted to the enclosed cylinders.Distribution of Loads. Returning to Fig. 1, we note that the weight of the fuselage, pilot, passenger, fuel, control surfaces and motor are carried to the upper wing W by the "cabane" strut members C-C and stays, the lower wing being connected directly into the sides of the fuselage. Continuations of the cabane members on the interior of the fuselage inter-connect the upper and lower wings (shown in dotted lines). The interplane stays in connection with the cabane members bind the wings and fuselage into a unit. A vertical line "CP" passes through the center of pressure of both wings, and approximately through the center of gravity of the machine. In other Words, the machine is nearly balanced on the center of pressure line. The turning moments of weights behind the CP must approximately balance the opposite turning moments of the masses located in front of the CP. The exact relation between the center of pressure and the center of gravity will be taken up later.Variable loads such as the passenger, gasoline and oil, are placed as nearly as possible on the center of pressure line, so that variation in the weight will not affect the balance. In the figure, the passenger's seat A, and the fuel tank F are on the CP line, or nearly so. Thus, a reduction in the weight of the fuel will not affect the "trim" of the machine, nor will a wide variation in the weight of the passenger produce any such effect. As shown, the passenger's seat is placed directly on the top of the fuel tank, an arrangement widely used by European constructors. In the majority of American machines the fuel tank is placed at the top of the fuselage instead of in the position illustrated. As the pilot is considered as a constant weight, his location does not affect the balance.When at rest on the ground, the weight of the rear end of the fuselage is supported by the tail skid N. The length of this skid must be such that the tail surfaces are kept well clear of the ground. The center of the chassis wheel Q is placed in front of the center of gravity so that the weight of the machine will cause the tail skid to bear on the ground when the machine is at rest. If the wheel were behind the center of gravity, the machine would "stand on its nose" when making a landing. The wheels must be located so that the tendency to "nose over" is as small as possible, and yet must not be set so far forward that they will cause an excessive load on the tail skid. With too much load on the skid, the tail will not come up, except after fast and prolonged running, and heavy stresses will be set up in the framework due to the tail bumping over the ground at high speed. The skids should not be dragged further than absolutely necessary, especially on rough ground. With proper weight and wheel adjustment, the tail should come up in a short run. The wheel adjustment will be taken up under the head of "Chassis."Position in Flight. In normal horizontal flight, the center line of thrust CT is horizontal or nearly so. This line of thrust passes through the center of the motor crankshaft and propeller. In an upward climb, the CT is inclined at the angle of climb, and since the CT indicates the line of flight, the streamline curves of the body should be laid out so that the axis of least body resistance will coincide with the line of thrust. When flying horizontally at the normal speed, the body must present the minimum of resistance and the wings must be at the most efficient angle of incidence. In climbing, or flying at a very low speed, the tail must necessarily be depressed to gain a large angle of wing incidence, and hence the body resistance will be comparatively high owing to the angle of the body with the flight line. It is best to have the least resistance of the fuselage coincide with the normal horizontal flight speed. This condition at once establishes the angle of the wings in regard to the fuselage center line.Center Line of Resistance. The center line of thrust should pass through the center of total head resistance as nearly as possible. The total resistance referred to is composed of the wing drag, body and chassis resistances. In an ordinary military type of aeroplane this line is located approximately at one-third of the gap from the bottom wing. Owing to variations in the drag of the Wings at different angles, this point varies under different flying conditions, and again, it is affected by the form and size of the fuselage and chassis. The exact location of the center of resistance involves the computation of all of the resistance producing items.In addition to passing through the center of resistance, the center line of thrust should pass slightly below the center of gravity of the machine. In this position the pull of the motor tends to hold the head up, but in-case of motor failure the machine immediately tends to head-dive and thus to increase its speed. The tendency to dive with a dead motor automatically overcomes the tendency to "stall" or to lose headway. With the centerline of thrust determined, and with given motor dimensions, the fuselage position can be located at once in regard to the wings. This is good enough for a preliminary layout, but must be modified in the final design. As before explained, the centerline of thrust is located at a point between the two wings, approximately one-third of the gap from the lower wing.In machines having a span of 35 feet and over, it is a trifle less than one-third the gap, while in small speed scouts it is generally a trifle over one-third. This rule checks very closely with the data obtained from 22 standard machines. Thus, in a machine having a 6-foot gap, the propeller centerline will be located about 2 feet above the lower wing. The top of the fuselage (measured under the stabilizer surface) is from 5 to 8 inches above the center line of thrust. At the motor end, the height of the fuselage above the CT is controlled by a number of factors, either by the type of motor, or by the arrangements made for access to the motor parts. In a number of European machines, the motor sits well above the top of the fuselage, this always being the case when a six-cylinder, vertical water-cooled motor is used. With an air-cooled type, the top is governed by the cowl diameter.Motor Compartment. The space occupied by the motor and its accessories is known as the "motor compartment," and in monoplane and tractor biplane fuselage it is located in the extreme front of the body. The interior arrangement varies with different types of motors and makes of machines. With rotary cylinder motors, the "compartment" is often nothing but a metal cowl, while with large water-cooled motors it occupies a considerable portion of the body. Water-cooled motors are generally covered with automobile type hoods, these usually being provided with "gilled" openings for ventilation. Owing to the heat generated in the motor, some sort of ventilation is imperative at this point. Whatever the type, the compartment is always cut off from the rest of the fuselage by a fireproof metal partition to guard against fire reaching the passenger or fuel tanks. The fuel and oil should always be separated from the motor by substantial partitions since a single carbureter "pop" may cause serious trouble.Fig. 4. Mounting and Cowls for Rotary Cylinder Motors. Courtesy "Flight."Fig. 4. Mounting and Cowls for Rotary Cylinder Motors. Courtesy "Flight."Accessibility is a most important feature in the design of the motor end, and hence the hood should be of the hinged automobile type so that it can be easily raised for inspection or repairs. In the Curtis JN4-B Military Training Tractor, the cylinder heads and valve mechanism project slightly above the top of the hood so that these parts are amply cooled and are entirely accessible. Access to the carbureter can be had through a small hand-hole in the side of the hood. The radiator in this Curtiss model is located in the extreme front end of the fuselage—automobile fashion. The propeller shaft passes through a central opening in the radiator. In Fig. 6 the vertical motor E is set down low in the frame, the upper part of the fuselage F ending at H. The engine bearer B, which carries the motor, forms the top part of the fuselage at this point. The engine is thus in the clear and access can easily be had to every part of the motor. The radiator is in front of the motor at R. When in flight the motor is covered by a sheet metal hood similar to the folding hood used on automobiles. This type is used in the Martin, Sturtevant, and several European machines.Fig. 5. Motor Compartment of a Curtiss Tractor Biplane Using a Front Type Radiator.Fig. 5. Motor Compartment of a Curtiss Tractor Biplane Using a Front Type Radiator. Note the Two Exhaust Pipes Which Carry the Gases Over the Top of the Wings.Fig. 7 is a very common front end arrangement used with side radiators. The top fuselage member F is brought down in a very low curve, leaving the greater part of the motor projecting above the fuselage. At the extreme front, the upper fuselage member F joins the engine bearer B, the connection being made with a pressed steel plate. The radiator R is shown at the side of the fuselage. The cylinders are not usually covered when in flight. In the front view it will be noted that the radiators are arranged on either side of the fuselage. A side view of the H. and M. Farman Fighter is shown by Fig. 10. This is a very efficient French machine which has seen much active service in the war. The front end is much like that shown in Fig. 7 except that a spinner cap is fitted to the propeller boss. A "V" type motor allows of the radiator being mounted between the two rows of cylinders, and in a position where it will cause the least possible head resistance.Figs. 6-7. Various Motor Arrangements, and Radiator Locations.Figs. 6-7. Various Motor Arrangements, and Radiator Locations.Fig. 10. A Type of H. and M. Farman Tractor Fighting Biplane.Fig. 10. A Type of H. and M. Farman Tractor Fighting Biplane. This Machine Uses a "V". Type Motor, with the Radiator in the Valve Alley. The Gunner and the Machine Gun Are Mounted in the Rear Cock-pit. It Will Be Noted That the Body Is Raised Well Above the Lower Wing So that the Gun Field Is Increased. The Pilot Is Well Ahead of the Entering Edge of the Lower Wing. Courtesy of "Aerial Age."The fuselage is of excellent streamline form and shows careful study in regard to the arrangement of the power plant. Unlike the majority of machines, the fuselage is raised well above the bottom wing, this being done evidently to increase the range of the gun in the rear cockpit. The increased height allows the gun to shoot over the top plane at a fairly small angle, and the height above the ground permits the use of a very large and efficient propeller without having an excessively high chassis. At the rear the fuselage tapers down to a very thin knife edge and therefore produces little disturbance.Fig. 11. Radiator Mounted at Leading Edge of Upper Wing.Fig. 11. Radiator Mounted at Leading Edge of Upper Wing. This Type Is Used with the Sturtevant and Lawson Aeroplanes and Is Very Effective Because of the Improved Circulation.Fig. 11 shows a Sturtevant Training Biplane in which the radiator is mounted at the front edge of the upper plane. This arrangement was originally introduced by the Sturtevant Company in their steel biplanes and has proved a very efficient type for cooling, although the radiator must affect the lift of the top plane to a very considerable extent.Pilot and Passenger Compartments. These compartments contain the seats, controls, and instruments, and in the military types contain the gun mounts and ammunition. In some battle-planes, the passenger or "observer" occupies the rear seat, as this position gives a wider range of fire against rear or side attacks. This arrangement is true of the H. and M. Farman machine just illustrated and described. In the large German "Gotha" the gunner occupies the rear position and fires through, or above, a tunnel built through the rear end of the fuselage. In some forms of training machines, the pilot and passenger sit side by side instead of in tandem, as this arrangement allows better communication between the pilot and student, and permits the former to keep better watch over the movements of the student. A notable example of this type is the Burgess Primary Trainer. A side-by-side machine must have a very wide fuselage and therefore presents more head resistance than one with the seats arranged in tandem, but with proper attention to the streamline form this can be reduced so that the loss is not as serious as would be imagined from a view of the layout.The seats may be of several types, (a) the aluminum "bucket" type similar to, but lighter than, the bucket seats used in racing automobiles; (b) the woven wicker seat used in many types of German machines, or (c) the modified chair form with wooden side rails and tightly stretched leather back and bottom. Whatever the type, they should be made as comfortable as possible, since the operation of a heavy machine is trying enough without adding additional discomfort in the form of flimsy hard seats. In the older machines the seats were nothing more than perches on which the pilot balanced himself precariously and in intense discomfort. A few pounds added in the form of a comfortable seat is material well spent since it is a great factor in the efficient operation of the machine. Wicker seats are light, yielding and comfortable, and can be made as strong or stronger than the other types. It seems strange that they have not been more widely adopted in this country.All seats should be slightly tilted back so that the pilot can lean back in a comfortable position, with a certain portion of his weight against the back of the seat. Sitting in a rigid vertical position is very tiring, and is especially so when flying in rough weather, or on long reconnaissance trips. The backs of the seats should be high and head rests should be provided so that the pilot's head can be comfortably supported against the pressure of the wind. If these head rests are "streamlined" by a long, tapering, projecting cone running back along the top of the fuselage, the resistance can be considerably reduced. This arrangement was first introduced in the Gordon-Bennett Deperdussin and has been followed in many modern machines. In the Deperdussin, the pilot's head was exposed directly to the full blast of the propeller slipstream and a head support was certainly needed. Small, transparent wind shields are now fastened to the front edge of the cockpit openings which to a certain extent shield the pilot from the terrific wind pressure. These are quite low and present little resistance at high speeds.Fig. 12. Hall-Scott Motor and Side Type Radiator Mounting on a Typical Tractor.Fig. 12. Hall-Scott Motor and Side Type Radiator Mounting on a Typical Tractor.A heavy leather covered pad, or roll, should be run entirely around the edge of the cockpit opening as a protection to the pilot in case of an accident or hard landing. The roll should be at least 3 1/2" in diameter and should be filled with horse hair. All sharp edges in the cockpit should be similarly guarded so that in the event of the pilot being thrown out of his seat, he will not be cut or bruised. Each seat should be provided with an improved safety strap that will securely hold the pilot in his seat, and yet must be arranged so that it can be quickly and easily released in an emergency. In flight the occupants must be securely strapped in place to prevent being thrown out during rapid maneuvers or in rough weather. Buckles should be substantial and well sewed and riveted to the fabric so that there will be no danger of their being torn out. The straps must be arranged so that they will not interfere with the free movement of the pilot, and so that they will not become entangled with the controls. It is best to copy the sets approved by the government as these are the result of long continued experiment and use.Fig. 13. Deperdussin Monoplane with Monocoque Body. Note the Streamline Form of the Body and the Spinner Cap at the Root of the Propeller.Fig. 13. Deperdussin Monoplane with Monocoque Body. Note the Streamline Form of the Body and the Spinner Cap at the Root of the Propeller.Care must be taken to have the seats located at the correct height from the floor so that the legs will not become cramped. In the majority of machines, the vertical rudder is operated by the feet. Unless the seat is at the proper height, the pilot will be in a strained position as he cannot shift around nor take his feet from the rudder bar. Either the rudder bar or the seat should be adjustable for different lengths of legs. Usually the adjustment is made in the rudder bar since it is not usually advisable to shift the seats owing to the necessity of having the pilot's weight in a fixed position. In some old types of monoplanes, the pilot sat on a small pad placed on the floor of the fuselage. Needless to say, this was a horribly uncomfortable position to be in, but as the flights of that time were of short duration it did not matter much. If the feet could be removed occasionally from the rudder bar the matter of seat position would not be of so much importance, but to sit flat on the floor, with the legs straight out, for a couple of hours is a terrible strain and has undoubtedly caused many accidents through cramps.As both the passenger and the fuel are varying weights, the fuel tank seat idea is good. This allows both of these items to be placed at the center of gravity of the machine where weight variation will have no effect on the balance of the plane. In this position, however, the fuel must be pumped up to a higher auxiliary tank since the main tank would be too far below the carbureter for gravity feed.The flooring of the cockpits can be either of veneer, or can be built up of small spruce slats about 1/2" x 1/2", the slats being spaced about 1/2" apart. The latter floor is specified by the government for seaplane use, and is very light and desirable. The floor is placed only at points where it will be stepped on. Observation holes are cut in the floor on a line with the edge of the seats so that the occupants can view the ground without looking over the edge of the fuselage. The observation port holes are about 9 inches in diameter. Glass should never be used in the cockpits except for the instrument covers, unless it is of the non-splintering "triplex" laminated type of glass. The use of inflammable celluloid should also be avoided as being even more dangerous than the glass. The triplex glass is built up of two or more layers of glass, which are cemented together with a celluloid film applied under heavy pressure. This form of construction is very strong, and while it can be broken, it will not fly apart in the form of splinters.All instruments should be placed directly in front of the pilot so that he can take observations without turning his head. Usually all of the instruments, with the exception of the compass, are mounted on a single "instrument board" placed in front of the pilot and directly under the forward edge of the cockpit opening. The compass can be placed on the floor as in American machines, or inserted in the upper wing as in some European machines. The motor control apparatus is placed where it can be reached conveniently from the seat. Oil gages, gasoline gages, and revolution counters are generally placed on the instrument board where they can be easily observed. If a wireless set is carried, the switches are placed on, or near, the instrument board. Owing to the uses to which the different machines are put it is impossible to give a list of instruments that would be suitable for every machine. The simplest machine should have the following instruments:Altimeterfor measuring altitude.Clockof special aeroplane type.Incidence indicator.Air speed indicatorsfor measuring the speed of the machine relative to the air.Gasoline, oil and pressure gagesfor determining amount of fuel.Instruments for Navy and Army machines are of course more complete. In the specifications for Army Hydroaeroplanes (twin motor type 1916) the following instruments are specified:Aneroid Barometer.Graduated in feet, and reading from sea-level to 12,000 feet.Compasses.One in each cockpit. To be of the Sperry Gyroscopic type with an elastic suspension and properly damped. Shall be attached to, and synchronized with, the ground drift indicator.Ground Drift Indicator.Located in observer's cockpit. For noting drift due to side winds. See illustration on page 244.Clock.Special aeroplane type, built to resist vibration. Located in pilot's cockpit.Fig. 14. Aeroplane Compass of the McCreagh-Osborn Type. (Sperry)Fig. 14. Aeroplane Compass of the McCreagh-Osborn Type. (Sperry)Gasoline Supply Gage.To indicate the amount of fuel in gravity service tank at all attitudes of flight, and shall be visible from pilot's seat. A gage in the main tank will also be desirable that will register the approaching exhaustion of fuel. This indicator should register when 75% of the fuel in the main tank is exhausted, and then record the remainder continuously.Air Speed Indicator.One in pilot's cockpit.Angle of Incidence Indicator.Sperry type. To be located in pilot's cockpit.Inclinometer.For measuring angle of inclination of longitudinal axis of machine. In pilot's cockpit, and placed on instrument board in the vicinity of tachometers.Bank Indicator.For indicating the proper amount of bank on turns. In pilot's cockpit.Map Board.One revolving map board placed in pilot's cockpit.Map Desk.One folding map desk in observer's cockpit.Fig. 15. Sperry Ground Drift Indicator.Fig. 15. Sperry Ground Drift Indicator.Tachometers.For measuring speed of motors in revolutions per minute. Pilot's cockpit.Self-Starter Switch.For operating self-starter. On instrument board in pilot's cockpit.Among the other accessories specified in the cockpit for the above machines are a Pyrene fire extinguisher; a 2-gallon water breaker; a speaking tube for communication between the pilot and observer (1" to 1 1/8"); a flashlight signal for speaking tube; and a tool kit. The weight of the tool kit shall not exceed 11 lbs.Fig. 16. Cock-pit of a "London and Provincial" Biplane.Fig. 16. Cock-pit of a "London and Provincial" Biplane. Control Lever in Foreground and Instrument Board Under Cowl. Courtesy of "Flight."General Proportions of the Fuselage. The total length of the fuselage depends upon the type of power plant, upon the span or chord of the wings, and upon the arrangement of the tail surfaces. The rear end of the fuselage should be far enough away from the wings to insure that the rear surfaces are not unduly affected by the "down-wash" or the "wake-stream" of the wings. A very short fuselage gives a short lever arm to the control surfaces, hence these surfaces must be very large with a short body. With the stabilizer surface close to the wings, the "damping" effect is slight, that is, the surface does not effectively kill or "damp down" oscillations. Large tail surfaces are heavy, difficult to brace, and cause a very considerable amount of head resistance. The extra weight of a long fuselage is generally offset by the increased weight caused by the large tail area of the short body type.When machines are crated and shipped at frequent intervals, a very long fuselage is objectionable unless it is built in two sections. It also requires much storage space and a very long hangar. Machines for private use must often be sacrificed from the efficiency standpoint in order to keep the dimensions within reasonable limits. An aeroplane requiring an enormous hangar has certainly no attraction for the average man. Every effort must be made to condense the overall dimensions or to arrange the extremities so that they can be easily dismounted. Exhibition flyers require specially portable machines since they ship them nearly every day, and the expense of handling a long awkward fuselage may alone determine the choice of a plane. It is usually best to divide the body at a point just to the rear of the pilot's seat, although many flyers look upon a two-part body with disfavor unless they can be shown that the joint connections are as strong as the rest of the fuselage.Fig. 19. Fuselage Dimension Chart for Two Place Aeroplane Fuselage.Fig. 19. Fuselage Dimension Chart for Two Place Aeroplane Fuselage. Upper Diagram Is the Water Cooled Type and the Lower Figure Applies to a Machine with a Rotating Air Cooled Motor. See Table of Dimensions on Page 248.As a guide in the choice of fuselage proportions, a set of diagrams and a table are attached which gives the general overall dimensions of several prominent makes of machines. The letters in the diagram refer to the letters heading the columns in the tables so that the general dimensions of any part can be readily determined. I do not claim that these dimensions should be followed religiously in every case, but they show what has been done in the past and will at least suggest the limits within which a new machine can be built.Fig. 20. Fuselage Dimension DiagramsFig. 20. Fuselage Dimension Diagrams Giving the Principal Dimensions of Speed Scout Machines. Upper Figure Shows Typical Scout with Water Cooled Motor (Curtiss), While Lower Diagram Shows an Arrangement Common with Rotary Air Cooled Motors (Nieuport)Table BIPLANE FUSELAGE (Large Reconnaissance and Battle Planes)Fig. 19 gives the outline and dimension letters for two-place machines of what is known as the "Reconnaissance Type." Both water-cooled and air-cooled motor equipments are shown, the top machine being of the water-cooled type while the lower figure shows a typical two-place machine with a rotary air-cooled motor. Underneath this side elevation is a front view of the fuselage, and a section taken through the point of greatest depth. As shown, the fuselage is of square cross-section, but the dimension B applies equally to the diameter of a circular cross-section. Dimension C gives the height of the curved upper deck, or "turtle deck" of the fuselage. Dimension D shows the extreme length extending in front of the leading edge of the lower wing, and T shows the length of the rear portion back of the leading edge of the lower wing, the leading edge being taken as a base of measurement. The location of the deepest section, measured from the extreme front of the fuselage, is given by E, the depth at this point being indicated by B. The extreme width is shown by I. In the machine shown, side radiators are used, the blunt front end dimensioned by G and K being the dimension of the front engine plate. When front radiators are used, the dimensions G and K also apply to the size of the radiator. The amount of advance, or the distance of the chassis wheel center from the leading edge is given by S, and the distance of the wheel center below the leading edge is given by R. V is the length of the engine projecting above the fuselage top. The passenger or observer is indicated by 1 and the pilot by 2. The top plane is 3 and the bottom plane 4. The engine is located by 5, and the top fuselage-rail, or "longeron," by 7. Turtle deck is 6.BIPLANE FUSELAGE TABLE (Speed Scouts)* Round monocoque body, dimensions (B) and (F) measured from outer diameter or top of circleFig. 20 gives the diagrams of speed scout machines, both of the air-cooled and water-cooled types. These are the small, fast, single seat machines so much used in the European war for repelling air attacks and for guarding the larger and slower bombing and observation machines. The upper drawing shows a Curtiss Speed Scout equipped with a "V" type water-cooled motor and a circular front radiator. While the front of the body is circular, it gradually fades out into a square cross-section at the rear. The lower machine is a Nieuport speed scout equipped with a rotating cylinder air-cooled motor. In this scout, the diameter of the motor cowl is given by dimension K. Body is of square cross-section. It will also be noted that the chord of the lower plane is less than that of the upper plane and that the deep body almost entirely fills the gap between the two wings.Fig. 21. Curtiss J N 4-B Fuselage Boxed for Shipment.Fig. 21. Curtiss J N 4-B Fuselage Boxed for Shipment.With some of the later speed scouts, the body entirely fills the gap between the wings and the top plane is fastened directly to the top members of the fuselage. This makes windows necessary in the sides of the fuselage. When vertical water-cooled motors are used on speed scouts, the front view is entirely cut off, for these are very large motors and project above the fuselage for a considerable distance. This obstruction is avoided in the Curtiss speed scout shown, by the use of a "V" type motor. It will be noted that these two scouts, especially the Nieuport, are of excellent stream line form, a very important item with such high speed machines. The propeller of later Nieuports is provided with a conical spinner cap which evidently reduces the head resistance to a considerable extent. The different portions of the machine are indicated by the same figures as in the case of the reconnaissance machine.

Purpose of Fuselage. The fuselage of a monoplane or tractor biplane is the backbone of the machine. It forms a means of connecting the tail surfaces to the main wing surfaces, carries the motor, fuel and pilot, and transmits the weight of these items to the wings and chassis. With the exception of the wing structure, the fuselage is the most important single item in the construction of the aeroplane. Fig. 1 shows a typical arrangement of a two-place biplane fuselage equipped with a water-cooled motor. The motor E, propeller Y, and radiator R are placed in the front of the fuselage, and considerably in advance of the wings W and D. Immediately behind the motor is the passenger's seat A and the fuel tank F. The pilot's seat B is placed behind the trailing edge of the wings and is behind the passenger's seat. The cockpit openings G and H are cut in the fuselage top for the passenger and pilot respectively. The rear extension of the fuselage carries the control surfaces, L being the vertical fin, M the rudder, O the fixed tail or stabilizer, and P the elevator.

Resistance. To reduce the resistance in flight, the fuselage is of as perfect streamline form as possible, the fuselage being deepest at a point about one-third from the front. From this point it tapers out gradually to the rear. With the motors now in use it is only possible to approximate the ideal streamline form owing to the front area of the radiator and to the size of the motor. Again, the projection of the pilot's head above the fuselage adds considerably to the resistance. The wind shields I disturb the flow of air. The connections to the tail surfaces and to the chassis members K also add to the total resistance. An arched "turtle deck" J is generally provided, of such a shape that the pilot's head is effectively "streamlined," the taper of this deck allowing the disturbed air to close in gradually at the rear. The flat area presented by the radiator R is probably the greatest single source of resistance, and for this reason the radiator is sometimes placed at the side of the fuselage, or in some other position that will allow of a better front end outline. An example of this construction is shown by Fig. 2 in which the radiator R is placed behind and above the motor E. The front fuselage end Z can now be made of a more suitable streamline form.

Figs. 1-2-3. Fuselage and Motor Arrangement of Tractor Biplanes.Figs. 1-2-3. Fuselage and Motor Arrangement of Tractor Biplanes.

Figs. 1-2-3. Fuselage and Motor Arrangement of Tractor Biplanes.

Fig. 3 is a view of the front end of a typical fuselage in which an air-cooled rotary type of motor is installed. Since the diameter of this type of motor is seldom much less than three feet, it is necessary to have a very great diameter in the extreme front. The motor housing or "cowl" marked E has a diameter "d" which should smoothly blend into the outline of the fuselage at "b." In the older types of construction there was often a very considerable break in the outline at this point, especially in cases where the circular cowl was abruptly connected to a square fuselage. A break of this sort greatly increases the head resistance. A "spinner" or propeller cap marked Z in Fig. 3 is an aid in reducing the resistance offered by the motor cowl and also reduces the resistance of the inner, and ineffective, portion of the propeller blades. The cap in any case is smaller than the cowl opening in order that cooling air be admitted to the enclosed cylinders.

Distribution of Loads. Returning to Fig. 1, we note that the weight of the fuselage, pilot, passenger, fuel, control surfaces and motor are carried to the upper wing W by the "cabane" strut members C-C and stays, the lower wing being connected directly into the sides of the fuselage. Continuations of the cabane members on the interior of the fuselage inter-connect the upper and lower wings (shown in dotted lines). The interplane stays in connection with the cabane members bind the wings and fuselage into a unit. A vertical line "CP" passes through the center of pressure of both wings, and approximately through the center of gravity of the machine. In other Words, the machine is nearly balanced on the center of pressure line. The turning moments of weights behind the CP must approximately balance the opposite turning moments of the masses located in front of the CP. The exact relation between the center of pressure and the center of gravity will be taken up later.

Variable loads such as the passenger, gasoline and oil, are placed as nearly as possible on the center of pressure line, so that variation in the weight will not affect the balance. In the figure, the passenger's seat A, and the fuel tank F are on the CP line, or nearly so. Thus, a reduction in the weight of the fuel will not affect the "trim" of the machine, nor will a wide variation in the weight of the passenger produce any such effect. As shown, the passenger's seat is placed directly on the top of the fuel tank, an arrangement widely used by European constructors. In the majority of American machines the fuel tank is placed at the top of the fuselage instead of in the position illustrated. As the pilot is considered as a constant weight, his location does not affect the balance.

When at rest on the ground, the weight of the rear end of the fuselage is supported by the tail skid N. The length of this skid must be such that the tail surfaces are kept well clear of the ground. The center of the chassis wheel Q is placed in front of the center of gravity so that the weight of the machine will cause the tail skid to bear on the ground when the machine is at rest. If the wheel were behind the center of gravity, the machine would "stand on its nose" when making a landing. The wheels must be located so that the tendency to "nose over" is as small as possible, and yet must not be set so far forward that they will cause an excessive load on the tail skid. With too much load on the skid, the tail will not come up, except after fast and prolonged running, and heavy stresses will be set up in the framework due to the tail bumping over the ground at high speed. The skids should not be dragged further than absolutely necessary, especially on rough ground. With proper weight and wheel adjustment, the tail should come up in a short run. The wheel adjustment will be taken up under the head of "Chassis."

Position in Flight. In normal horizontal flight, the center line of thrust CT is horizontal or nearly so. This line of thrust passes through the center of the motor crankshaft and propeller. In an upward climb, the CT is inclined at the angle of climb, and since the CT indicates the line of flight, the streamline curves of the body should be laid out so that the axis of least body resistance will coincide with the line of thrust. When flying horizontally at the normal speed, the body must present the minimum of resistance and the wings must be at the most efficient angle of incidence. In climbing, or flying at a very low speed, the tail must necessarily be depressed to gain a large angle of wing incidence, and hence the body resistance will be comparatively high owing to the angle of the body with the flight line. It is best to have the least resistance of the fuselage coincide with the normal horizontal flight speed. This condition at once establishes the angle of the wings in regard to the fuselage center line.

Center Line of Resistance. The center line of thrust should pass through the center of total head resistance as nearly as possible. The total resistance referred to is composed of the wing drag, body and chassis resistances. In an ordinary military type of aeroplane this line is located approximately at one-third of the gap from the bottom wing. Owing to variations in the drag of the Wings at different angles, this point varies under different flying conditions, and again, it is affected by the form and size of the fuselage and chassis. The exact location of the center of resistance involves the computation of all of the resistance producing items.

In addition to passing through the center of resistance, the center line of thrust should pass slightly below the center of gravity of the machine. In this position the pull of the motor tends to hold the head up, but in-case of motor failure the machine immediately tends to head-dive and thus to increase its speed. The tendency to dive with a dead motor automatically overcomes the tendency to "stall" or to lose headway. With the centerline of thrust determined, and with given motor dimensions, the fuselage position can be located at once in regard to the wings. This is good enough for a preliminary layout, but must be modified in the final design. As before explained, the centerline of thrust is located at a point between the two wings, approximately one-third of the gap from the lower wing.

In machines having a span of 35 feet and over, it is a trifle less than one-third the gap, while in small speed scouts it is generally a trifle over one-third. This rule checks very closely with the data obtained from 22 standard machines. Thus, in a machine having a 6-foot gap, the propeller centerline will be located about 2 feet above the lower wing. The top of the fuselage (measured under the stabilizer surface) is from 5 to 8 inches above the center line of thrust. At the motor end, the height of the fuselage above the CT is controlled by a number of factors, either by the type of motor, or by the arrangements made for access to the motor parts. In a number of European machines, the motor sits well above the top of the fuselage, this always being the case when a six-cylinder, vertical water-cooled motor is used. With an air-cooled type, the top is governed by the cowl diameter.

Motor Compartment. The space occupied by the motor and its accessories is known as the "motor compartment," and in monoplane and tractor biplane fuselage it is located in the extreme front of the body. The interior arrangement varies with different types of motors and makes of machines. With rotary cylinder motors, the "compartment" is often nothing but a metal cowl, while with large water-cooled motors it occupies a considerable portion of the body. Water-cooled motors are generally covered with automobile type hoods, these usually being provided with "gilled" openings for ventilation. Owing to the heat generated in the motor, some sort of ventilation is imperative at this point. Whatever the type, the compartment is always cut off from the rest of the fuselage by a fireproof metal partition to guard against fire reaching the passenger or fuel tanks. The fuel and oil should always be separated from the motor by substantial partitions since a single carbureter "pop" may cause serious trouble.

Fig. 4. Mounting and Cowls for Rotary Cylinder Motors. Courtesy "Flight."Fig. 4. Mounting and Cowls for Rotary Cylinder Motors. Courtesy "Flight."

Fig. 4. Mounting and Cowls for Rotary Cylinder Motors. Courtesy "Flight."

Accessibility is a most important feature in the design of the motor end, and hence the hood should be of the hinged automobile type so that it can be easily raised for inspection or repairs. In the Curtis JN4-B Military Training Tractor, the cylinder heads and valve mechanism project slightly above the top of the hood so that these parts are amply cooled and are entirely accessible. Access to the carbureter can be had through a small hand-hole in the side of the hood. The radiator in this Curtiss model is located in the extreme front end of the fuselage—automobile fashion. The propeller shaft passes through a central opening in the radiator. In Fig. 6 the vertical motor E is set down low in the frame, the upper part of the fuselage F ending at H. The engine bearer B, which carries the motor, forms the top part of the fuselage at this point. The engine is thus in the clear and access can easily be had to every part of the motor. The radiator is in front of the motor at R. When in flight the motor is covered by a sheet metal hood similar to the folding hood used on automobiles. This type is used in the Martin, Sturtevant, and several European machines.

Fig. 5. Motor Compartment of a Curtiss Tractor Biplane Using a Front Type Radiator.Fig. 5. Motor Compartment of a Curtiss Tractor Biplane Using a Front Type Radiator. Note the Two Exhaust Pipes Which Carry the Gases Over the Top of the Wings.

Fig. 5. Motor Compartment of a Curtiss Tractor Biplane Using a Front Type Radiator. Note the Two Exhaust Pipes Which Carry the Gases Over the Top of the Wings.

Fig. 7 is a very common front end arrangement used with side radiators. The top fuselage member F is brought down in a very low curve, leaving the greater part of the motor projecting above the fuselage. At the extreme front, the upper fuselage member F joins the engine bearer B, the connection being made with a pressed steel plate. The radiator R is shown at the side of the fuselage. The cylinders are not usually covered when in flight. In the front view it will be noted that the radiators are arranged on either side of the fuselage. A side view of the H. and M. Farman Fighter is shown by Fig. 10. This is a very efficient French machine which has seen much active service in the war. The front end is much like that shown in Fig. 7 except that a spinner cap is fitted to the propeller boss. A "V" type motor allows of the radiator being mounted between the two rows of cylinders, and in a position where it will cause the least possible head resistance.

Figs. 6-7. Various Motor Arrangements, and Radiator Locations.Figs. 6-7. Various Motor Arrangements, and Radiator Locations.Fig. 10. A Type of H. and M. Farman Tractor Fighting Biplane.Fig. 10. A Type of H. and M. Farman Tractor Fighting Biplane. This Machine Uses a "V". Type Motor, with the Radiator in the Valve Alley. The Gunner and the Machine Gun Are Mounted in the Rear Cock-pit. It Will Be Noted That the Body Is Raised Well Above the Lower Wing So that the Gun Field Is Increased. The Pilot Is Well Ahead of the Entering Edge of the Lower Wing. Courtesy of "Aerial Age."

Figs. 6-7. Various Motor Arrangements, and Radiator Locations.Figs. 6-7. Various Motor Arrangements, and Radiator Locations.

Figs. 6-7. Various Motor Arrangements, and Radiator Locations.

Fig. 10. A Type of H. and M. Farman Tractor Fighting Biplane.Fig. 10. A Type of H. and M. Farman Tractor Fighting Biplane. This Machine Uses a "V". Type Motor, with the Radiator in the Valve Alley. The Gunner and the Machine Gun Are Mounted in the Rear Cock-pit. It Will Be Noted That the Body Is Raised Well Above the Lower Wing So that the Gun Field Is Increased. The Pilot Is Well Ahead of the Entering Edge of the Lower Wing. Courtesy of "Aerial Age."

Fig. 10. A Type of H. and M. Farman Tractor Fighting Biplane. This Machine Uses a "V". Type Motor, with the Radiator in the Valve Alley. The Gunner and the Machine Gun Are Mounted in the Rear Cock-pit. It Will Be Noted That the Body Is Raised Well Above the Lower Wing So that the Gun Field Is Increased. The Pilot Is Well Ahead of the Entering Edge of the Lower Wing. Courtesy of "Aerial Age."

The fuselage is of excellent streamline form and shows careful study in regard to the arrangement of the power plant. Unlike the majority of machines, the fuselage is raised well above the bottom wing, this being done evidently to increase the range of the gun in the rear cockpit. The increased height allows the gun to shoot over the top plane at a fairly small angle, and the height above the ground permits the use of a very large and efficient propeller without having an excessively high chassis. At the rear the fuselage tapers down to a very thin knife edge and therefore produces little disturbance.

Fig. 11. Radiator Mounted at Leading Edge of Upper Wing.Fig. 11. Radiator Mounted at Leading Edge of Upper Wing. This Type Is Used with the Sturtevant and Lawson Aeroplanes and Is Very Effective Because of the Improved Circulation.

Fig. 11. Radiator Mounted at Leading Edge of Upper Wing. This Type Is Used with the Sturtevant and Lawson Aeroplanes and Is Very Effective Because of the Improved Circulation.

Fig. 11 shows a Sturtevant Training Biplane in which the radiator is mounted at the front edge of the upper plane. This arrangement was originally introduced by the Sturtevant Company in their steel biplanes and has proved a very efficient type for cooling, although the radiator must affect the lift of the top plane to a very considerable extent.

Pilot and Passenger Compartments. These compartments contain the seats, controls, and instruments, and in the military types contain the gun mounts and ammunition. In some battle-planes, the passenger or "observer" occupies the rear seat, as this position gives a wider range of fire against rear or side attacks. This arrangement is true of the H. and M. Farman machine just illustrated and described. In the large German "Gotha" the gunner occupies the rear position and fires through, or above, a tunnel built through the rear end of the fuselage. In some forms of training machines, the pilot and passenger sit side by side instead of in tandem, as this arrangement allows better communication between the pilot and student, and permits the former to keep better watch over the movements of the student. A notable example of this type is the Burgess Primary Trainer. A side-by-side machine must have a very wide fuselage and therefore presents more head resistance than one with the seats arranged in tandem, but with proper attention to the streamline form this can be reduced so that the loss is not as serious as would be imagined from a view of the layout.

The seats may be of several types, (a) the aluminum "bucket" type similar to, but lighter than, the bucket seats used in racing automobiles; (b) the woven wicker seat used in many types of German machines, or (c) the modified chair form with wooden side rails and tightly stretched leather back and bottom. Whatever the type, they should be made as comfortable as possible, since the operation of a heavy machine is trying enough without adding additional discomfort in the form of flimsy hard seats. In the older machines the seats were nothing more than perches on which the pilot balanced himself precariously and in intense discomfort. A few pounds added in the form of a comfortable seat is material well spent since it is a great factor in the efficient operation of the machine. Wicker seats are light, yielding and comfortable, and can be made as strong or stronger than the other types. It seems strange that they have not been more widely adopted in this country.

All seats should be slightly tilted back so that the pilot can lean back in a comfortable position, with a certain portion of his weight against the back of the seat. Sitting in a rigid vertical position is very tiring, and is especially so when flying in rough weather, or on long reconnaissance trips. The backs of the seats should be high and head rests should be provided so that the pilot's head can be comfortably supported against the pressure of the wind. If these head rests are "streamlined" by a long, tapering, projecting cone running back along the top of the fuselage, the resistance can be considerably reduced. This arrangement was first introduced in the Gordon-Bennett Deperdussin and has been followed in many modern machines. In the Deperdussin, the pilot's head was exposed directly to the full blast of the propeller slipstream and a head support was certainly needed. Small, transparent wind shields are now fastened to the front edge of the cockpit openings which to a certain extent shield the pilot from the terrific wind pressure. These are quite low and present little resistance at high speeds.

Fig. 12. Hall-Scott Motor and Side Type Radiator Mounting on a Typical Tractor.Fig. 12. Hall-Scott Motor and Side Type Radiator Mounting on a Typical Tractor.

Fig. 12. Hall-Scott Motor and Side Type Radiator Mounting on a Typical Tractor.

A heavy leather covered pad, or roll, should be run entirely around the edge of the cockpit opening as a protection to the pilot in case of an accident or hard landing. The roll should be at least 3 1/2" in diameter and should be filled with horse hair. All sharp edges in the cockpit should be similarly guarded so that in the event of the pilot being thrown out of his seat, he will not be cut or bruised. Each seat should be provided with an improved safety strap that will securely hold the pilot in his seat, and yet must be arranged so that it can be quickly and easily released in an emergency. In flight the occupants must be securely strapped in place to prevent being thrown out during rapid maneuvers or in rough weather. Buckles should be substantial and well sewed and riveted to the fabric so that there will be no danger of their being torn out. The straps must be arranged so that they will not interfere with the free movement of the pilot, and so that they will not become entangled with the controls. It is best to copy the sets approved by the government as these are the result of long continued experiment and use.

Fig. 13. Deperdussin Monoplane with Monocoque Body. Note the Streamline Form of the Body and the Spinner Cap at the Root of the Propeller.Fig. 13. Deperdussin Monoplane with Monocoque Body. Note the Streamline Form of the Body and the Spinner Cap at the Root of the Propeller.

Fig. 13. Deperdussin Monoplane with Monocoque Body. Note the Streamline Form of the Body and the Spinner Cap at the Root of the Propeller.

Care must be taken to have the seats located at the correct height from the floor so that the legs will not become cramped. In the majority of machines, the vertical rudder is operated by the feet. Unless the seat is at the proper height, the pilot will be in a strained position as he cannot shift around nor take his feet from the rudder bar. Either the rudder bar or the seat should be adjustable for different lengths of legs. Usually the adjustment is made in the rudder bar since it is not usually advisable to shift the seats owing to the necessity of having the pilot's weight in a fixed position. In some old types of monoplanes, the pilot sat on a small pad placed on the floor of the fuselage. Needless to say, this was a horribly uncomfortable position to be in, but as the flights of that time were of short duration it did not matter much. If the feet could be removed occasionally from the rudder bar the matter of seat position would not be of so much importance, but to sit flat on the floor, with the legs straight out, for a couple of hours is a terrible strain and has undoubtedly caused many accidents through cramps.

As both the passenger and the fuel are varying weights, the fuel tank seat idea is good. This allows both of these items to be placed at the center of gravity of the machine where weight variation will have no effect on the balance of the plane. In this position, however, the fuel must be pumped up to a higher auxiliary tank since the main tank would be too far below the carbureter for gravity feed.

The flooring of the cockpits can be either of veneer, or can be built up of small spruce slats about 1/2" x 1/2", the slats being spaced about 1/2" apart. The latter floor is specified by the government for seaplane use, and is very light and desirable. The floor is placed only at points where it will be stepped on. Observation holes are cut in the floor on a line with the edge of the seats so that the occupants can view the ground without looking over the edge of the fuselage. The observation port holes are about 9 inches in diameter. Glass should never be used in the cockpits except for the instrument covers, unless it is of the non-splintering "triplex" laminated type of glass. The use of inflammable celluloid should also be avoided as being even more dangerous than the glass. The triplex glass is built up of two or more layers of glass, which are cemented together with a celluloid film applied under heavy pressure. This form of construction is very strong, and while it can be broken, it will not fly apart in the form of splinters.

All instruments should be placed directly in front of the pilot so that he can take observations without turning his head. Usually all of the instruments, with the exception of the compass, are mounted on a single "instrument board" placed in front of the pilot and directly under the forward edge of the cockpit opening. The compass can be placed on the floor as in American machines, or inserted in the upper wing as in some European machines. The motor control apparatus is placed where it can be reached conveniently from the seat. Oil gages, gasoline gages, and revolution counters are generally placed on the instrument board where they can be easily observed. If a wireless set is carried, the switches are placed on, or near, the instrument board. Owing to the uses to which the different machines are put it is impossible to give a list of instruments that would be suitable for every machine. The simplest machine should have the following instruments:

for measuring altitude.

of special aeroplane type.

Incidence indicator.

for measuring the speed of the machine relative to the air.

for determining amount of fuel.

Instruments for Navy and Army machines are of course more complete. In the specifications for Army Hydroaeroplanes (twin motor type 1916) the following instruments are specified:

Graduated in feet, and reading from sea-level to 12,000 feet.

One in each cockpit. To be of the Sperry Gyroscopic type with an elastic suspension and properly damped. Shall be attached to, and synchronized with, the ground drift indicator.

Located in observer's cockpit. For noting drift due to side winds. See illustration on page 244.

Special aeroplane type, built to resist vibration. Located in pilot's cockpit.

Fig. 14. Aeroplane Compass of the McCreagh-Osborn Type. (Sperry)Fig. 14. Aeroplane Compass of the McCreagh-Osborn Type. (Sperry)

Fig. 14. Aeroplane Compass of the McCreagh-Osborn Type. (Sperry)

To indicate the amount of fuel in gravity service tank at all attitudes of flight, and shall be visible from pilot's seat. A gage in the main tank will also be desirable that will register the approaching exhaustion of fuel. This indicator should register when 75% of the fuel in the main tank is exhausted, and then record the remainder continuously.

One in pilot's cockpit.

Sperry type. To be located in pilot's cockpit.

For measuring angle of inclination of longitudinal axis of machine. In pilot's cockpit, and placed on instrument board in the vicinity of tachometers.

For indicating the proper amount of bank on turns. In pilot's cockpit.

One revolving map board placed in pilot's cockpit.

One folding map desk in observer's cockpit.

Fig. 15. Sperry Ground Drift Indicator.Fig. 15. Sperry Ground Drift Indicator.

Fig. 15. Sperry Ground Drift Indicator.

For measuring speed of motors in revolutions per minute. Pilot's cockpit.

For operating self-starter. On instrument board in pilot's cockpit.

Among the other accessories specified in the cockpit for the above machines are a Pyrene fire extinguisher; a 2-gallon water breaker; a speaking tube for communication between the pilot and observer (1" to 1 1/8"); a flashlight signal for speaking tube; and a tool kit. The weight of the tool kit shall not exceed 11 lbs.

Fig. 16. Cock-pit of a "London and Provincial" Biplane.Fig. 16. Cock-pit of a "London and Provincial" Biplane. Control Lever in Foreground and Instrument Board Under Cowl. Courtesy of "Flight."

Fig. 16. Cock-pit of a "London and Provincial" Biplane. Control Lever in Foreground and Instrument Board Under Cowl. Courtesy of "Flight."

General Proportions of the Fuselage. The total length of the fuselage depends upon the type of power plant, upon the span or chord of the wings, and upon the arrangement of the tail surfaces. The rear end of the fuselage should be far enough away from the wings to insure that the rear surfaces are not unduly affected by the "down-wash" or the "wake-stream" of the wings. A very short fuselage gives a short lever arm to the control surfaces, hence these surfaces must be very large with a short body. With the stabilizer surface close to the wings, the "damping" effect is slight, that is, the surface does not effectively kill or "damp down" oscillations. Large tail surfaces are heavy, difficult to brace, and cause a very considerable amount of head resistance. The extra weight of a long fuselage is generally offset by the increased weight caused by the large tail area of the short body type.

When machines are crated and shipped at frequent intervals, a very long fuselage is objectionable unless it is built in two sections. It also requires much storage space and a very long hangar. Machines for private use must often be sacrificed from the efficiency standpoint in order to keep the dimensions within reasonable limits. An aeroplane requiring an enormous hangar has certainly no attraction for the average man. Every effort must be made to condense the overall dimensions or to arrange the extremities so that they can be easily dismounted. Exhibition flyers require specially portable machines since they ship them nearly every day, and the expense of handling a long awkward fuselage may alone determine the choice of a plane. It is usually best to divide the body at a point just to the rear of the pilot's seat, although many flyers look upon a two-part body with disfavor unless they can be shown that the joint connections are as strong as the rest of the fuselage.

Fig. 19. Fuselage Dimension Chart for Two Place Aeroplane Fuselage.Fig. 19. Fuselage Dimension Chart for Two Place Aeroplane Fuselage. Upper Diagram Is the Water Cooled Type and the Lower Figure Applies to a Machine with a Rotating Air Cooled Motor. See Table of Dimensions on Page 248.

Fig. 19. Fuselage Dimension Chart for Two Place Aeroplane Fuselage. Upper Diagram Is the Water Cooled Type and the Lower Figure Applies to a Machine with a Rotating Air Cooled Motor. See Table of Dimensions on Page 248.

As a guide in the choice of fuselage proportions, a set of diagrams and a table are attached which gives the general overall dimensions of several prominent makes of machines. The letters in the diagram refer to the letters heading the columns in the tables so that the general dimensions of any part can be readily determined. I do not claim that these dimensions should be followed religiously in every case, but they show what has been done in the past and will at least suggest the limits within which a new machine can be built.

Fig. 20. Fuselage Dimension DiagramsFig. 20. Fuselage Dimension Diagrams Giving the Principal Dimensions of Speed Scout Machines. Upper Figure Shows Typical Scout with Water Cooled Motor (Curtiss), While Lower Diagram Shows an Arrangement Common with Rotary Air Cooled Motors (Nieuport)Table BIPLANE FUSELAGE (Large Reconnaissance and Battle Planes)

Fig. 20. Fuselage Dimension Diagrams Giving the Principal Dimensions of Speed Scout Machines. Upper Figure Shows Typical Scout with Water Cooled Motor (Curtiss), While Lower Diagram Shows an Arrangement Common with Rotary Air Cooled Motors (Nieuport)

Table BIPLANE FUSELAGE (Large Reconnaissance and Battle Planes)

Fig. 19 gives the outline and dimension letters for two-place machines of what is known as the "Reconnaissance Type." Both water-cooled and air-cooled motor equipments are shown, the top machine being of the water-cooled type while the lower figure shows a typical two-place machine with a rotary air-cooled motor. Underneath this side elevation is a front view of the fuselage, and a section taken through the point of greatest depth. As shown, the fuselage is of square cross-section, but the dimension B applies equally to the diameter of a circular cross-section. Dimension C gives the height of the curved upper deck, or "turtle deck" of the fuselage. Dimension D shows the extreme length extending in front of the leading edge of the lower wing, and T shows the length of the rear portion back of the leading edge of the lower wing, the leading edge being taken as a base of measurement. The location of the deepest section, measured from the extreme front of the fuselage, is given by E, the depth at this point being indicated by B. The extreme width is shown by I. In the machine shown, side radiators are used, the blunt front end dimensioned by G and K being the dimension of the front engine plate. When front radiators are used, the dimensions G and K also apply to the size of the radiator. The amount of advance, or the distance of the chassis wheel center from the leading edge is given by S, and the distance of the wheel center below the leading edge is given by R. V is the length of the engine projecting above the fuselage top. The passenger or observer is indicated by 1 and the pilot by 2. The top plane is 3 and the bottom plane 4. The engine is located by 5, and the top fuselage-rail, or "longeron," by 7. Turtle deck is 6.

BIPLANE FUSELAGE TABLE (Speed Scouts)* Round monocoque body, dimensions (B) and (F) measured from outer diameter or top of circle

* Round monocoque body, dimensions (B) and (F) measured from outer diameter or top of circle

Fig. 20 gives the diagrams of speed scout machines, both of the air-cooled and water-cooled types. These are the small, fast, single seat machines so much used in the European war for repelling air attacks and for guarding the larger and slower bombing and observation machines. The upper drawing shows a Curtiss Speed Scout equipped with a "V" type water-cooled motor and a circular front radiator. While the front of the body is circular, it gradually fades out into a square cross-section at the rear. The lower machine is a Nieuport speed scout equipped with a rotating cylinder air-cooled motor. In this scout, the diameter of the motor cowl is given by dimension K. Body is of square cross-section. It will also be noted that the chord of the lower plane is less than that of the upper plane and that the deep body almost entirely fills the gap between the two wings.

Fig. 21. Curtiss J N 4-B Fuselage Boxed for Shipment.Fig. 21. Curtiss J N 4-B Fuselage Boxed for Shipment.

Fig. 21. Curtiss J N 4-B Fuselage Boxed for Shipment.

With some of the later speed scouts, the body entirely fills the gap between the wings and the top plane is fastened directly to the top members of the fuselage. This makes windows necessary in the sides of the fuselage. When vertical water-cooled motors are used on speed scouts, the front view is entirely cut off, for these are very large motors and project above the fuselage for a considerable distance. This obstruction is avoided in the Curtiss speed scout shown, by the use of a "V" type motor. It will be noted that these two scouts, especially the Nieuport, are of excellent stream line form, a very important item with such high speed machines. The propeller of later Nieuports is provided with a conical spinner cap which evidently reduces the head resistance to a considerable extent. The different portions of the machine are indicated by the same figures as in the case of the reconnaissance machine.

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