CHAPTER VII ASSEMBLING THE MOTORSIn the present stage of model aeroplane building, rubber strand motors satisfy every demand. Models have been flown for more than 2,500 feet by the force of these twisted strands, and doubtless their efficiency will be still further increased. Such motive power is besides very easily obtained and applied. Careful tests have shown that more energy may be stored up in twisted rubber strands than in the same weight of springs of steel or any other metal.In gauging the strength of your motor, much depends upon whether your model is to rise from the ground or be launched from the hand. In the model tournaments in England, the flying machines are almost invariably thrown across the starting line, while in America they are required to rise unaided. It is obviously unfair, therefore, to compare the distance records of the two countries.A Metal Motor AnchorageA Metal Motor AnchorageIt requires a comparatively powerful motor to raise a model from the ground, whereas a lighter motor would be sufficient to propel it through the air. Many models, capable of flights of several hundred feet when thrown will refuse to rise, while, on the other hand, some models which rise well enough have poor distance qualities.It should be borne in mind that the length of the motor, speaking broadly, controls the distance qualities, and its diameter the speed of the model aeroplane. A long slender motor, capable of from five hundred to one thousand turns which will revolve the propellers for thirty seconds or more, should insure a flight of several hundred feet. As you increase the number of strands of rubber, building up the diameter of the motor, you cut down the number of turns and therefore its duration, although you increase its speed.A motor capable of one thousand turns must be about forty inches in length and consist of but six, or at most eight, of these strands. A model which may be driven by this motor, it will be found, must be very light. A model aeroplane weighing upwards of one pound, on the other hand, will require motors composed of fourteen strands or more to raise it from the ground. It is a very simple matter, of course, to add strands of rubber until your motor develops sufficient energy for the work it is expected to do.The length and diameter of your motor, again, has a direct influence on the height of the flight. Too much power tends to raise the aeroplane higher than necessary above the ground. Since it requires more energy to drive a model aeroplane upward than along a horizontal direction, this is obviously a waste of energy.If it is desired to fly the model as far as possible, it must be kept close to the ground. In the case of weight-lifting contests, the problem of altitude is, of course, entirely different. Overwinding is even worse than underwinding, since it shortens the life of the motor.Try out your aeroplane with ten strands on each motor and increase them later. The motor, as previously explained, is formed by looping the rubber strands loosely between the hooks, just as zephyr is wound on a skein. Keep the strands very loose and fasten them to the hooks by tying with a strand of rubber. In winding, do not turn the propeller after the rubber has a double row of knots for its entire length. Such a motor should take up from three hundred to five hundred turns, perhaps more. Do not keep the elastic wound up too long before starting your flight. The strain is great and it quickly wears out.A Metal Motor AnchorageA Metal Motor AnchorageThe rubber strands should not be allowed to come in contact with any metal parts of the model. The copper that is often used for wiring is especially injurious and tends to decompose the rubber. The hooks of both the propeller and motor anchorage should be covered with a piece of rubber tubing. This serves a double purpose. With this protection, the rubber when tightly twisted is in no danger of being cut by the wire or of taking up the oxides which quickly eat through it.A notable model possessing unusual stability. Built by W.S. Howell, Jr.A notable model possessing unusual stability. Built by W.S. Howell, Jr.Front view of model built by W.S. Howell, Jr.Front view of model built by W.S. Howell, Jr.It requires an expert to pick out the best quality of rubber. If the strands be examined under a magnifying glass, it will be found that the edges of fresh rubber of the best quality are clean-cut, whereas the cheaper rubber, and that which is worn, has commenced to granulate, giving the edges a ragged appearance.A simple test is to stretch the rubber over a ruler. A good rubber, in first-class condition, will stretch about seven times its length, and on being released instantly spring back to its original size. The same rubber should stretch to ten times its length without breaking.There is a great difference of opinion among the most successful model builders as to the best shape of rubber strands. Some prefer the flat, band rubber, while others are obtaining satisfactory results with rubber cut in square strands. The strand used by the English model builders is seldom more than one-sixteenth of an inch square, while in America one-eighth of an inch strand is commonly used.Experiments have been made with a single strand of rubber one-fourth of an inch square, but the results have not been satisfactory. One theory is that the corners of the square rubber tend to cut into one another and quickly wear out, and that a perfectly round strand would be the more efficient. At present there are no such strands on the market. It is argued by some that the square strand in twisting must be turned on itself further than the flat strand, and is therefore placed under an unnecessary strain. After all, the advantage of one form over another is fractional, and an extra strand added to the motor will balance any possible defects.Figures have been prepared giving the exact relation of the size of rubber to the number of turns, although such statistics are elastic. The problem may be worked out with your own motor. Differences of temperature will be quickly noted. The rules prepared by V. E. Johnson, M.A., an English authority on aviation, are as follows: The motive power is doubled by increasing the number of rubber strands one-half; by doubling the number of strands, the motive power is increased more than two times; and the tripling of the strands increases the motive power seven times. As regards the number of turns the same authority states that the doubling of the number of strands diminishes the number of turns by one-third to one-half.A Metal SkidA Metal SkidIt is also found that each strand will have doubled knots of 310 turns; four strands, 440; sixteen strands at 200; and eight at 210. This is working with strands one-sixteenth of an inch square. As a rule, rubber should not be turned after the second row of knots is formed. And by the way, you will find that the rubber, after being tightly twisted, tends to stick together, and should be carefully separated after a flight so that the air can reach all surfaces.According to the experiments made by Mr. Johnson, one pound of rubber may be made to store up 320 foot pounds of energy, while one pound of steel, in the form of springs, will only store up 65 pounds.In the early model aeroplanes much valuable energy was lost through friction. There has been a marked improvement in the construction of the propellers, axles, and bearings. Friction has been reduced to practically nothing. It is possible, of course, to drive a propeller with the shaft turning in a hole drilled at random through a stick, with a glass bead for a washer. It is very important, however, that the axle should turn exactly at right angles, and to hold it in position requires careful adjustment. To meet the demands of model aeroplane builders, several shaft mechanisms have been prepared, even to a very complete arrangement of miniature ball bearings.The model builder who cannot avail himself of these parts can, nevertheless, imitate their action with reasonable fidelity. The axle attached to the propeller should be heavy enough to resist bending in ordinary wear and tear. A bicycle spoke is just the thing. When you have decided upon this axle, procure a piece of metal tubing in which the axle will turn freely, without binding or rattling about. The tubing should then be passed through the frame supporting the propeller exactly at right angles, and extend out at either side about half an inch. To fasten it securely in position, glue and if necessary drive small wedges,—a match or toothpick,—about it.Several metal washers should be strung on the axle between the upper edge of the shaft and the propeller. These may be punched from a sheet of metal. A section of this tube may also be inserted part way in the propeller, and washers introduced where they meet. The second tube will insure smooth action.The projecting tube will serve also to remove the propeller far enough from the frame to prevent its striking. By freely oiling these parts, the propeller may be made to turn very freely.An ingenious adjustment of aileronsAn ingenious adjustment of aileronsTuning up the model for a flight.Tuning up the model for a flight.In bending the axle into a hook for holding the rubber strands of the motor, care must be taken to keep the ends of the strands on a line with the axle. After turning the wire into a hook, bend back the shank to the proper angle. It will be seen that if the motor carries the axle about from side to side, the friction will be considerably increased. Over this hook, slip a piece of rubber tubing before attaching the strands of rubber, since the metal is likely to cut and wear the motor. It will be found a good plan to tie the strands together just below the hook to keep them from slipping off. And, by the way, do not keep your motor wound up any longer than you can help before a flight, since the strain on the rubber in this position is very great.As motors have increased in power and distance qualities, the process of winding up has become a serious problem. The simple method of turning the propeller by hand takes too long, and a slip with a powerful motor may give one an ugly cut. An ordinary machine drill will do the work much more quickly. Some drills are geared so that a single turn of the wheel will give you ten revolutions of the propeller.To arrange your motor for winding with a drill, run the axle through the propellers and turn in the form of a closed hook. A small hook should then be fixed to the end of the drill, which may be inserted in this loop. Some boys use a double hook on the propeller, detach the strands of rubber, wind them up, and then attach them to the propeller.A very simple and ingenious method of winding up has been adopted in the remarkable model constructed by Mr. Mungokee. The motor is anchored by running the wire holding the strands through the supporting stick of the base, and bending the end into a hook which, as the rubber pulls, is held securely in a second hole at the side.Showing Construction And Mounting Of Propeller And Axle.Showing Construction And Mounting Of Propeller And Axle.To wind up, it is only necessary to draw out this hook, attach it to the winding drill and turn. When wound up, the pull of the motor will obviously hold the end of the hook firmly in the hole, making it impossible for it to turn. This does away with extra hooks and the trouble of hooking up the motor when once it has been wound.The life of your rubber motor may be lengthened by careful winding. As long as you wind up by turning the propeller by hand, it is safe to turn it as fast as you can, since the process is slow at best. In case the turning is done with a machine drill or some similar geared wheel, there is danger at some points of winding too fast.It is safe to wind as quickly as you can until the first row of knots has formed in the rubber strands, but at the moment the double strands begin to appear the winding should proceed very slowly. You will find that if you wind very quickly the double knots will appear in tight groups or bunches, and that only after considerable winding do these begin to spread out evenly. This puts the rubber under a severe and unnecessary strain and shortens its life.The simplest way of locking the propellers when once wound up is to thrust a piece of cane or reed through the hooks. The twist of the motor will hold it tightly in position, so that you can carry your model about, even shake it vigorously without danger of dislodging it. If you have twin propellers, use a strip long enough to pass through both hooks. Remove the strip just before starting. Be careful, of course, that your axles have not been thrown out of plumb.It will be found very convenient to equip your model with a single clasp for holding the propellers after they have been wound up, which may be easily released. It is awkward to keep them from slipping. An effective break may be made by attaching two strips of reed or cane, such as you use for skids, to either side of the motor base, so that the free ends will pass between the propeller blades and the frame, thus locking them fast.These bands should spring outward and be held in position by rubber bands running from one to the other. To release the propellers, simply pinch the two free ends together, and the propellers will be freed at the same instant. Do not keep your motor wound up a moment longer than you can help. It is very trying to the rubber to be held in this tightly-twisted position.In mounting your propeller, it is well to make the support for the bearing of the propeller axle as long as possible. An axle turning in a shaft one inch in length will meet with much less resistance than in a half-inch shaft, and with a good motor an inch-and-a-half shaft is still better. The rear stick of your motor base, which often holds the propeller axle, is usually made as thin as possible and rarely gives you more than a half-inch support.It is a good plan to lengthen the shaft by attaching a block of wood to the frame and passing the axle through it. Cut from a strip one-half an inch square a piece one inch in length, or whatever seems necessary. This may be mortised slightly into the stick and glued at right angles.An excellent monoplane capable of long flights.An excellent monoplane capable of long flights.Long-distance model built by Percy Pierce.Long-distance model built by Percy Pierce.Now drill a hole through the stick, with the grain, and the stick of your motor base and pass the tube holding the propeller shaft through both. To make this look shipshape, round off the edges. A great advantage of this stick is that it enables you to mount the propeller as far as you like from the frame, thus preventing it from striking.Showing An Excellent Way Of Fastening The Propellers To The Framework.Showing An Excellent Way Of Fastening The Propellers To The Framework.In mounting the propellers above or below the frame, you will need similar supports. The blocks should measure half an inch in width by one and a half inches square and should be cut with the grain of the wood running lengthwise. The hole for the propeller shaft is drilled near the top, and the block is securely fastened to the frame.It will be found a good plan to mortise the frame slightly in order to make the joint perfectly rigid, even in the face of a bad smash-up. Many boys merely glue the stick in position and bind it securely to the motor base with fine strong thread, and paint it with glue or shellac to hold it in position. These blocks may be fastened either above or below the frame or at the sides.In mounting the propellers, bear in mind that a position above the planes tends to drive the aeroplane downward, while the thrust exerted below tends to throw the aeroplane upward. The builders of model aeroplanes differ as much as to the best position of the propellers as the designers of man-carrying machines. Excellent models have been built with the propellers in either position. It is obviously impossible to lay down a rule for all models, since the properties of the planes vary so widely.A very simple and efficient support for the propeller shaft may be made of metal to correspond to the motor anchorage. Procure a sheet of heavy tin—a piece of sheet aluminum is still better—one-half inch in width and three inches in length. Now mark off a one-half inch, one inch, two inches, and two and one-half inches, and bend over the ends at right angles, as shown in the accompanying drawing.This support may be nailed or screwed rigidly to the end of the motor base, and a hole for the shaft of the propeller drilled through the two uprights. The propeller must be mounted so that the blades will, of course, be free of the base. The size of the support may be altered to suit the frame. In case you are using a heavy propeller, say an inch blade, the metal must be heavy enough to resist the pull of the propeller.The forward ends of the motors may be held by a cross piece cut from a sheet of aluminum six inches in width and two inches in depth, which is bound rigidly to the end of the motor base with shoemaker's thread. Aluminum suitable for this purpose costs about fifteen cents a square foot, and is soft enough to be cut with heavy shears.An ingenious motor anchorage of metal construction has been hit upon by the builders of model aeroplanes in France. We are all familiar with the difficulty of raising the hook, holding the rubber bands, high enough above the main frame, or fusilage, to be perfectly free. Instead of attaching a wooden block, the French boys bend a piece of tin, or some such metal, very simply into a support for the hook.You will need a sheet of metal heavy enough to withstand the full force of the motor when wound up. The tin used in cans, as a rule, is not heavy enough. For each support you will need a rectangle of tin or metal measuring three by one and one-half inches. Parallel to the longer base, draw a line one-quarter of an inch above. From the center, erect a long rectangle one-quarter of an inch wide, extending to the opposite side. Now connect the ends of the line above the base with the points at which the upright rectangle intersects the top line, round off the edges neatly and cut away this triangle. Four holes should be cut or punched in the tin, as indicated in the drawing.Now bend the tin on the two upright lines until the two sides are parallel. This support is fitted to the end of a motor base and secured by driving nails through the three holes at the base covering the wood. The end of the hook which holds the rubber strands of the motor should be passed through the opening at the end, bent over and fastened into position with a drop or two of solder. Such a support adds practically nothing to the weight of the frame, and obviously anchors the motor rigidly.Model built by Rutledge Barry, winner of spectacular flight contest.Model built by Rutledge Barry, winner of spectacular flight contest.A model by Percy Pierce, winner of the indoor long-distance record.A model by Percy Pierce, winner of the indoor long-distance record.The efficiency of a rubber-strand motor may be considerably increased by careful adjustment. If the strands first be wound rather loosely, as a rope is formed, and strung between the propeller hook and the motor anchorage, you will find that about thirty per cent. more rubber may be added without increasing the length and that a five to ten per cent. increase in the number of effective turns may be gained as well. By increasing the amount of rubber, you will, of course, add accordingly to the power of the motor. It is safe to say that the efficiency of your motor is increased upwards of twenty-five per cent. by this adjustment. The credit of this ingenious arrangement is due to Mr. W. Howell, Jr.It will be well to experiment with a short-strand motor, using a single strand of rubber for the test. Let us assume that your motor is twelve inches in length, thus making a double strand twenty-four inches long. First knot this, string it between the two hooks and turn it, counting the revolutions until the first row of double knots begins to appear. Note the number of turns.Now untie the strand and, holding one end, twist it until the lines of the edges make a continuous loose spiral throughout its entire length. The easiest way of twisting them is to lay them on a flat surface and rub with the palm of the hand.Now bring the two ends together and let the strands twist and wriggle until they come to rest. Fasten the ends and measure the double twisted strand. You will find that it measures less than ten inches.To prepare a strand for a twelve-inch motor, you must therefore begin with a piece of rubber fully thirty inches in length. It is clear, therefore, that the new plan enables you to gain considerably more rubber length for length. Now string your twisted rubber on the hooks of your motor so that to wind up you must turn against the twisted strand. You will find that a number of turns are required before the rubber strands are untwisted and lie parallel, which is pure gain. Count the number of turns up to the time the first line of the double knots appears, and you will find that it is about five per cent. greater than in the case of the single strands.The power exerted by your motor is meanwhile increased in direct proportion to the amount of rubber added. Still another advantage of this adjustment lies in the fact that such a motor will unwind to the first turn. In preparing a multiple-strand rubber, each strand must, of course, be twisted in the same direction and exactly the same number of times before being installed.The builders of model aeroplanes may profit from the experience of the automobile tire manufacturers in studying the properties of the rubber used for motors. Rubber is at best comparatively short-lived. It suffers a surface deterioration on being exposed to the air, which in time affects the entire mass.This process of decay goes on fastest in very warm weather and in very bright sunlight. It is believed that sea air and the rarified air of the mountains are bad for rubber. On the other hand, a very low temperature, as you may perhaps have discovered, robs the rubber of much of its elasticity.It will pay you to take some trouble to protect the rubber strands as far as possible. Lay them away in a can or jar in some cool, dry and dark place when they are not in use. Some boys cover the rubber with powdered chalk. When the surface of the rubber begins to granulate, its best days are over. Rubber is originally white in color, while the refining process gives it the familiar gray tone.The Para rubber is generally considered the best of the many kinds now on the market. As a rule, any oil or grease tends to decay the rubber, as any motorist can tell you. This is particularly unfortunate for the aviator, since the efficiency of the rubber motor is increased by slightly lubricating the strands. Many boys prefer to chance injuring their motors in order to gain the advantage of the oiled strands.The strands thus prepared slide smoothly on one another and do not grip each other even when tightly wound. The simplest preparation for greasing the strands is a solution of ordinary soap and water. A few drops poured over the strands will suffice. When your motor unwinds, be careful to keep your face out of range, since a few drops might be flung into your eyes. Several preparations for lubricating the motors have been placed upon the market.The direction flights may be controlled very easily by winding the motor. If you care to fly your model in circles or spirals, the simplest plan for influencing its direction is to give different power to your propellers. It often happens that a model must be in a restricted place, perhaps a straight-away flight is out of the question.The model may be deflected to the right or left by the use of vertical propellers, but they require delicate adjustment, and a gust of wind may destroy their effect. By winding up one double the number of turns of the other, a circular flight is assured. To gauge the diameter of the circle merely alter the relation of the number of turns. You will soon find that you can control the diameter of the circle with remarkable accuracy.A Motor AnchorageA Motor Anchorage
CHAPTER VII ASSEMBLING THE MOTORSIn the present stage of model aeroplane building, rubber strand motors satisfy every demand. Models have been flown for more than 2,500 feet by the force of these twisted strands, and doubtless their efficiency will be still further increased. Such motive power is besides very easily obtained and applied. Careful tests have shown that more energy may be stored up in twisted rubber strands than in the same weight of springs of steel or any other metal.In gauging the strength of your motor, much depends upon whether your model is to rise from the ground or be launched from the hand. In the model tournaments in England, the flying machines are almost invariably thrown across the starting line, while in America they are required to rise unaided. It is obviously unfair, therefore, to compare the distance records of the two countries.A Metal Motor AnchorageA Metal Motor AnchorageIt requires a comparatively powerful motor to raise a model from the ground, whereas a lighter motor would be sufficient to propel it through the air. Many models, capable of flights of several hundred feet when thrown will refuse to rise, while, on the other hand, some models which rise well enough have poor distance qualities.It should be borne in mind that the length of the motor, speaking broadly, controls the distance qualities, and its diameter the speed of the model aeroplane. A long slender motor, capable of from five hundred to one thousand turns which will revolve the propellers for thirty seconds or more, should insure a flight of several hundred feet. As you increase the number of strands of rubber, building up the diameter of the motor, you cut down the number of turns and therefore its duration, although you increase its speed.A motor capable of one thousand turns must be about forty inches in length and consist of but six, or at most eight, of these strands. A model which may be driven by this motor, it will be found, must be very light. A model aeroplane weighing upwards of one pound, on the other hand, will require motors composed of fourteen strands or more to raise it from the ground. It is a very simple matter, of course, to add strands of rubber until your motor develops sufficient energy for the work it is expected to do.The length and diameter of your motor, again, has a direct influence on the height of the flight. Too much power tends to raise the aeroplane higher than necessary above the ground. Since it requires more energy to drive a model aeroplane upward than along a horizontal direction, this is obviously a waste of energy.If it is desired to fly the model as far as possible, it must be kept close to the ground. In the case of weight-lifting contests, the problem of altitude is, of course, entirely different. Overwinding is even worse than underwinding, since it shortens the life of the motor.Try out your aeroplane with ten strands on each motor and increase them later. The motor, as previously explained, is formed by looping the rubber strands loosely between the hooks, just as zephyr is wound on a skein. Keep the strands very loose and fasten them to the hooks by tying with a strand of rubber. In winding, do not turn the propeller after the rubber has a double row of knots for its entire length. Such a motor should take up from three hundred to five hundred turns, perhaps more. Do not keep the elastic wound up too long before starting your flight. The strain is great and it quickly wears out.A Metal Motor AnchorageA Metal Motor AnchorageThe rubber strands should not be allowed to come in contact with any metal parts of the model. The copper that is often used for wiring is especially injurious and tends to decompose the rubber. The hooks of both the propeller and motor anchorage should be covered with a piece of rubber tubing. This serves a double purpose. With this protection, the rubber when tightly twisted is in no danger of being cut by the wire or of taking up the oxides which quickly eat through it.A notable model possessing unusual stability. Built by W.S. Howell, Jr.A notable model possessing unusual stability. Built by W.S. Howell, Jr.Front view of model built by W.S. Howell, Jr.Front view of model built by W.S. Howell, Jr.It requires an expert to pick out the best quality of rubber. If the strands be examined under a magnifying glass, it will be found that the edges of fresh rubber of the best quality are clean-cut, whereas the cheaper rubber, and that which is worn, has commenced to granulate, giving the edges a ragged appearance.A simple test is to stretch the rubber over a ruler. A good rubber, in first-class condition, will stretch about seven times its length, and on being released instantly spring back to its original size. The same rubber should stretch to ten times its length without breaking.There is a great difference of opinion among the most successful model builders as to the best shape of rubber strands. Some prefer the flat, band rubber, while others are obtaining satisfactory results with rubber cut in square strands. The strand used by the English model builders is seldom more than one-sixteenth of an inch square, while in America one-eighth of an inch strand is commonly used.Experiments have been made with a single strand of rubber one-fourth of an inch square, but the results have not been satisfactory. One theory is that the corners of the square rubber tend to cut into one another and quickly wear out, and that a perfectly round strand would be the more efficient. At present there are no such strands on the market. It is argued by some that the square strand in twisting must be turned on itself further than the flat strand, and is therefore placed under an unnecessary strain. After all, the advantage of one form over another is fractional, and an extra strand added to the motor will balance any possible defects.Figures have been prepared giving the exact relation of the size of rubber to the number of turns, although such statistics are elastic. The problem may be worked out with your own motor. Differences of temperature will be quickly noted. The rules prepared by V. E. Johnson, M.A., an English authority on aviation, are as follows: The motive power is doubled by increasing the number of rubber strands one-half; by doubling the number of strands, the motive power is increased more than two times; and the tripling of the strands increases the motive power seven times. As regards the number of turns the same authority states that the doubling of the number of strands diminishes the number of turns by one-third to one-half.A Metal SkidA Metal SkidIt is also found that each strand will have doubled knots of 310 turns; four strands, 440; sixteen strands at 200; and eight at 210. This is working with strands one-sixteenth of an inch square. As a rule, rubber should not be turned after the second row of knots is formed. And by the way, you will find that the rubber, after being tightly twisted, tends to stick together, and should be carefully separated after a flight so that the air can reach all surfaces.According to the experiments made by Mr. Johnson, one pound of rubber may be made to store up 320 foot pounds of energy, while one pound of steel, in the form of springs, will only store up 65 pounds.In the early model aeroplanes much valuable energy was lost through friction. There has been a marked improvement in the construction of the propellers, axles, and bearings. Friction has been reduced to practically nothing. It is possible, of course, to drive a propeller with the shaft turning in a hole drilled at random through a stick, with a glass bead for a washer. It is very important, however, that the axle should turn exactly at right angles, and to hold it in position requires careful adjustment. To meet the demands of model aeroplane builders, several shaft mechanisms have been prepared, even to a very complete arrangement of miniature ball bearings.The model builder who cannot avail himself of these parts can, nevertheless, imitate their action with reasonable fidelity. The axle attached to the propeller should be heavy enough to resist bending in ordinary wear and tear. A bicycle spoke is just the thing. When you have decided upon this axle, procure a piece of metal tubing in which the axle will turn freely, without binding or rattling about. The tubing should then be passed through the frame supporting the propeller exactly at right angles, and extend out at either side about half an inch. To fasten it securely in position, glue and if necessary drive small wedges,—a match or toothpick,—about it.Several metal washers should be strung on the axle between the upper edge of the shaft and the propeller. These may be punched from a sheet of metal. A section of this tube may also be inserted part way in the propeller, and washers introduced where they meet. The second tube will insure smooth action.The projecting tube will serve also to remove the propeller far enough from the frame to prevent its striking. By freely oiling these parts, the propeller may be made to turn very freely.An ingenious adjustment of aileronsAn ingenious adjustment of aileronsTuning up the model for a flight.Tuning up the model for a flight.In bending the axle into a hook for holding the rubber strands of the motor, care must be taken to keep the ends of the strands on a line with the axle. After turning the wire into a hook, bend back the shank to the proper angle. It will be seen that if the motor carries the axle about from side to side, the friction will be considerably increased. Over this hook, slip a piece of rubber tubing before attaching the strands of rubber, since the metal is likely to cut and wear the motor. It will be found a good plan to tie the strands together just below the hook to keep them from slipping off. And, by the way, do not keep your motor wound up any longer than you can help before a flight, since the strain on the rubber in this position is very great.As motors have increased in power and distance qualities, the process of winding up has become a serious problem. The simple method of turning the propeller by hand takes too long, and a slip with a powerful motor may give one an ugly cut. An ordinary machine drill will do the work much more quickly. Some drills are geared so that a single turn of the wheel will give you ten revolutions of the propeller.To arrange your motor for winding with a drill, run the axle through the propellers and turn in the form of a closed hook. A small hook should then be fixed to the end of the drill, which may be inserted in this loop. Some boys use a double hook on the propeller, detach the strands of rubber, wind them up, and then attach them to the propeller.A very simple and ingenious method of winding up has been adopted in the remarkable model constructed by Mr. Mungokee. The motor is anchored by running the wire holding the strands through the supporting stick of the base, and bending the end into a hook which, as the rubber pulls, is held securely in a second hole at the side.Showing Construction And Mounting Of Propeller And Axle.Showing Construction And Mounting Of Propeller And Axle.To wind up, it is only necessary to draw out this hook, attach it to the winding drill and turn. When wound up, the pull of the motor will obviously hold the end of the hook firmly in the hole, making it impossible for it to turn. This does away with extra hooks and the trouble of hooking up the motor when once it has been wound.The life of your rubber motor may be lengthened by careful winding. As long as you wind up by turning the propeller by hand, it is safe to turn it as fast as you can, since the process is slow at best. In case the turning is done with a machine drill or some similar geared wheel, there is danger at some points of winding too fast.It is safe to wind as quickly as you can until the first row of knots has formed in the rubber strands, but at the moment the double strands begin to appear the winding should proceed very slowly. You will find that if you wind very quickly the double knots will appear in tight groups or bunches, and that only after considerable winding do these begin to spread out evenly. This puts the rubber under a severe and unnecessary strain and shortens its life.The simplest way of locking the propellers when once wound up is to thrust a piece of cane or reed through the hooks. The twist of the motor will hold it tightly in position, so that you can carry your model about, even shake it vigorously without danger of dislodging it. If you have twin propellers, use a strip long enough to pass through both hooks. Remove the strip just before starting. Be careful, of course, that your axles have not been thrown out of plumb.It will be found very convenient to equip your model with a single clasp for holding the propellers after they have been wound up, which may be easily released. It is awkward to keep them from slipping. An effective break may be made by attaching two strips of reed or cane, such as you use for skids, to either side of the motor base, so that the free ends will pass between the propeller blades and the frame, thus locking them fast.These bands should spring outward and be held in position by rubber bands running from one to the other. To release the propellers, simply pinch the two free ends together, and the propellers will be freed at the same instant. Do not keep your motor wound up a moment longer than you can help. It is very trying to the rubber to be held in this tightly-twisted position.In mounting your propeller, it is well to make the support for the bearing of the propeller axle as long as possible. An axle turning in a shaft one inch in length will meet with much less resistance than in a half-inch shaft, and with a good motor an inch-and-a-half shaft is still better. The rear stick of your motor base, which often holds the propeller axle, is usually made as thin as possible and rarely gives you more than a half-inch support.It is a good plan to lengthen the shaft by attaching a block of wood to the frame and passing the axle through it. Cut from a strip one-half an inch square a piece one inch in length, or whatever seems necessary. This may be mortised slightly into the stick and glued at right angles.An excellent monoplane capable of long flights.An excellent monoplane capable of long flights.Long-distance model built by Percy Pierce.Long-distance model built by Percy Pierce.Now drill a hole through the stick, with the grain, and the stick of your motor base and pass the tube holding the propeller shaft through both. To make this look shipshape, round off the edges. A great advantage of this stick is that it enables you to mount the propeller as far as you like from the frame, thus preventing it from striking.Showing An Excellent Way Of Fastening The Propellers To The Framework.Showing An Excellent Way Of Fastening The Propellers To The Framework.In mounting the propellers above or below the frame, you will need similar supports. The blocks should measure half an inch in width by one and a half inches square and should be cut with the grain of the wood running lengthwise. The hole for the propeller shaft is drilled near the top, and the block is securely fastened to the frame.It will be found a good plan to mortise the frame slightly in order to make the joint perfectly rigid, even in the face of a bad smash-up. Many boys merely glue the stick in position and bind it securely to the motor base with fine strong thread, and paint it with glue or shellac to hold it in position. These blocks may be fastened either above or below the frame or at the sides.In mounting the propellers, bear in mind that a position above the planes tends to drive the aeroplane downward, while the thrust exerted below tends to throw the aeroplane upward. The builders of model aeroplanes differ as much as to the best position of the propellers as the designers of man-carrying machines. Excellent models have been built with the propellers in either position. It is obviously impossible to lay down a rule for all models, since the properties of the planes vary so widely.A very simple and efficient support for the propeller shaft may be made of metal to correspond to the motor anchorage. Procure a sheet of heavy tin—a piece of sheet aluminum is still better—one-half inch in width and three inches in length. Now mark off a one-half inch, one inch, two inches, and two and one-half inches, and bend over the ends at right angles, as shown in the accompanying drawing.This support may be nailed or screwed rigidly to the end of the motor base, and a hole for the shaft of the propeller drilled through the two uprights. The propeller must be mounted so that the blades will, of course, be free of the base. The size of the support may be altered to suit the frame. In case you are using a heavy propeller, say an inch blade, the metal must be heavy enough to resist the pull of the propeller.The forward ends of the motors may be held by a cross piece cut from a sheet of aluminum six inches in width and two inches in depth, which is bound rigidly to the end of the motor base with shoemaker's thread. Aluminum suitable for this purpose costs about fifteen cents a square foot, and is soft enough to be cut with heavy shears.An ingenious motor anchorage of metal construction has been hit upon by the builders of model aeroplanes in France. We are all familiar with the difficulty of raising the hook, holding the rubber bands, high enough above the main frame, or fusilage, to be perfectly free. Instead of attaching a wooden block, the French boys bend a piece of tin, or some such metal, very simply into a support for the hook.You will need a sheet of metal heavy enough to withstand the full force of the motor when wound up. The tin used in cans, as a rule, is not heavy enough. For each support you will need a rectangle of tin or metal measuring three by one and one-half inches. Parallel to the longer base, draw a line one-quarter of an inch above. From the center, erect a long rectangle one-quarter of an inch wide, extending to the opposite side. Now connect the ends of the line above the base with the points at which the upright rectangle intersects the top line, round off the edges neatly and cut away this triangle. Four holes should be cut or punched in the tin, as indicated in the drawing.Now bend the tin on the two upright lines until the two sides are parallel. This support is fitted to the end of a motor base and secured by driving nails through the three holes at the base covering the wood. The end of the hook which holds the rubber strands of the motor should be passed through the opening at the end, bent over and fastened into position with a drop or two of solder. Such a support adds practically nothing to the weight of the frame, and obviously anchors the motor rigidly.Model built by Rutledge Barry, winner of spectacular flight contest.Model built by Rutledge Barry, winner of spectacular flight contest.A model by Percy Pierce, winner of the indoor long-distance record.A model by Percy Pierce, winner of the indoor long-distance record.The efficiency of a rubber-strand motor may be considerably increased by careful adjustment. If the strands first be wound rather loosely, as a rope is formed, and strung between the propeller hook and the motor anchorage, you will find that about thirty per cent. more rubber may be added without increasing the length and that a five to ten per cent. increase in the number of effective turns may be gained as well. By increasing the amount of rubber, you will, of course, add accordingly to the power of the motor. It is safe to say that the efficiency of your motor is increased upwards of twenty-five per cent. by this adjustment. The credit of this ingenious arrangement is due to Mr. W. Howell, Jr.It will be well to experiment with a short-strand motor, using a single strand of rubber for the test. Let us assume that your motor is twelve inches in length, thus making a double strand twenty-four inches long. First knot this, string it between the two hooks and turn it, counting the revolutions until the first row of double knots begins to appear. Note the number of turns.Now untie the strand and, holding one end, twist it until the lines of the edges make a continuous loose spiral throughout its entire length. The easiest way of twisting them is to lay them on a flat surface and rub with the palm of the hand.Now bring the two ends together and let the strands twist and wriggle until they come to rest. Fasten the ends and measure the double twisted strand. You will find that it measures less than ten inches.To prepare a strand for a twelve-inch motor, you must therefore begin with a piece of rubber fully thirty inches in length. It is clear, therefore, that the new plan enables you to gain considerably more rubber length for length. Now string your twisted rubber on the hooks of your motor so that to wind up you must turn against the twisted strand. You will find that a number of turns are required before the rubber strands are untwisted and lie parallel, which is pure gain. Count the number of turns up to the time the first line of the double knots appears, and you will find that it is about five per cent. greater than in the case of the single strands.The power exerted by your motor is meanwhile increased in direct proportion to the amount of rubber added. Still another advantage of this adjustment lies in the fact that such a motor will unwind to the first turn. In preparing a multiple-strand rubber, each strand must, of course, be twisted in the same direction and exactly the same number of times before being installed.The builders of model aeroplanes may profit from the experience of the automobile tire manufacturers in studying the properties of the rubber used for motors. Rubber is at best comparatively short-lived. It suffers a surface deterioration on being exposed to the air, which in time affects the entire mass.This process of decay goes on fastest in very warm weather and in very bright sunlight. It is believed that sea air and the rarified air of the mountains are bad for rubber. On the other hand, a very low temperature, as you may perhaps have discovered, robs the rubber of much of its elasticity.It will pay you to take some trouble to protect the rubber strands as far as possible. Lay them away in a can or jar in some cool, dry and dark place when they are not in use. Some boys cover the rubber with powdered chalk. When the surface of the rubber begins to granulate, its best days are over. Rubber is originally white in color, while the refining process gives it the familiar gray tone.The Para rubber is generally considered the best of the many kinds now on the market. As a rule, any oil or grease tends to decay the rubber, as any motorist can tell you. This is particularly unfortunate for the aviator, since the efficiency of the rubber motor is increased by slightly lubricating the strands. Many boys prefer to chance injuring their motors in order to gain the advantage of the oiled strands.The strands thus prepared slide smoothly on one another and do not grip each other even when tightly wound. The simplest preparation for greasing the strands is a solution of ordinary soap and water. A few drops poured over the strands will suffice. When your motor unwinds, be careful to keep your face out of range, since a few drops might be flung into your eyes. Several preparations for lubricating the motors have been placed upon the market.The direction flights may be controlled very easily by winding the motor. If you care to fly your model in circles or spirals, the simplest plan for influencing its direction is to give different power to your propellers. It often happens that a model must be in a restricted place, perhaps a straight-away flight is out of the question.The model may be deflected to the right or left by the use of vertical propellers, but they require delicate adjustment, and a gust of wind may destroy their effect. By winding up one double the number of turns of the other, a circular flight is assured. To gauge the diameter of the circle merely alter the relation of the number of turns. You will soon find that you can control the diameter of the circle with remarkable accuracy.A Motor AnchorageA Motor Anchorage
CHAPTER VII ASSEMBLING THE MOTORSIn the present stage of model aeroplane building, rubber strand motors satisfy every demand. Models have been flown for more than 2,500 feet by the force of these twisted strands, and doubtless their efficiency will be still further increased. Such motive power is besides very easily obtained and applied. Careful tests have shown that more energy may be stored up in twisted rubber strands than in the same weight of springs of steel or any other metal.In gauging the strength of your motor, much depends upon whether your model is to rise from the ground or be launched from the hand. In the model tournaments in England, the flying machines are almost invariably thrown across the starting line, while in America they are required to rise unaided. It is obviously unfair, therefore, to compare the distance records of the two countries.A Metal Motor AnchorageA Metal Motor AnchorageIt requires a comparatively powerful motor to raise a model from the ground, whereas a lighter motor would be sufficient to propel it through the air. Many models, capable of flights of several hundred feet when thrown will refuse to rise, while, on the other hand, some models which rise well enough have poor distance qualities.It should be borne in mind that the length of the motor, speaking broadly, controls the distance qualities, and its diameter the speed of the model aeroplane. A long slender motor, capable of from five hundred to one thousand turns which will revolve the propellers for thirty seconds or more, should insure a flight of several hundred feet. As you increase the number of strands of rubber, building up the diameter of the motor, you cut down the number of turns and therefore its duration, although you increase its speed.A motor capable of one thousand turns must be about forty inches in length and consist of but six, or at most eight, of these strands. A model which may be driven by this motor, it will be found, must be very light. A model aeroplane weighing upwards of one pound, on the other hand, will require motors composed of fourteen strands or more to raise it from the ground. It is a very simple matter, of course, to add strands of rubber until your motor develops sufficient energy for the work it is expected to do.The length and diameter of your motor, again, has a direct influence on the height of the flight. Too much power tends to raise the aeroplane higher than necessary above the ground. Since it requires more energy to drive a model aeroplane upward than along a horizontal direction, this is obviously a waste of energy.If it is desired to fly the model as far as possible, it must be kept close to the ground. In the case of weight-lifting contests, the problem of altitude is, of course, entirely different. Overwinding is even worse than underwinding, since it shortens the life of the motor.Try out your aeroplane with ten strands on each motor and increase them later. The motor, as previously explained, is formed by looping the rubber strands loosely between the hooks, just as zephyr is wound on a skein. Keep the strands very loose and fasten them to the hooks by tying with a strand of rubber. In winding, do not turn the propeller after the rubber has a double row of knots for its entire length. Such a motor should take up from three hundred to five hundred turns, perhaps more. Do not keep the elastic wound up too long before starting your flight. The strain is great and it quickly wears out.A Metal Motor AnchorageA Metal Motor AnchorageThe rubber strands should not be allowed to come in contact with any metal parts of the model. The copper that is often used for wiring is especially injurious and tends to decompose the rubber. The hooks of both the propeller and motor anchorage should be covered with a piece of rubber tubing. This serves a double purpose. With this protection, the rubber when tightly twisted is in no danger of being cut by the wire or of taking up the oxides which quickly eat through it.A notable model possessing unusual stability. Built by W.S. Howell, Jr.A notable model possessing unusual stability. Built by W.S. Howell, Jr.Front view of model built by W.S. Howell, Jr.Front view of model built by W.S. Howell, Jr.It requires an expert to pick out the best quality of rubber. If the strands be examined under a magnifying glass, it will be found that the edges of fresh rubber of the best quality are clean-cut, whereas the cheaper rubber, and that which is worn, has commenced to granulate, giving the edges a ragged appearance.A simple test is to stretch the rubber over a ruler. A good rubber, in first-class condition, will stretch about seven times its length, and on being released instantly spring back to its original size. The same rubber should stretch to ten times its length without breaking.There is a great difference of opinion among the most successful model builders as to the best shape of rubber strands. Some prefer the flat, band rubber, while others are obtaining satisfactory results with rubber cut in square strands. The strand used by the English model builders is seldom more than one-sixteenth of an inch square, while in America one-eighth of an inch strand is commonly used.Experiments have been made with a single strand of rubber one-fourth of an inch square, but the results have not been satisfactory. One theory is that the corners of the square rubber tend to cut into one another and quickly wear out, and that a perfectly round strand would be the more efficient. At present there are no such strands on the market. It is argued by some that the square strand in twisting must be turned on itself further than the flat strand, and is therefore placed under an unnecessary strain. After all, the advantage of one form over another is fractional, and an extra strand added to the motor will balance any possible defects.Figures have been prepared giving the exact relation of the size of rubber to the number of turns, although such statistics are elastic. The problem may be worked out with your own motor. Differences of temperature will be quickly noted. The rules prepared by V. E. Johnson, M.A., an English authority on aviation, are as follows: The motive power is doubled by increasing the number of rubber strands one-half; by doubling the number of strands, the motive power is increased more than two times; and the tripling of the strands increases the motive power seven times. As regards the number of turns the same authority states that the doubling of the number of strands diminishes the number of turns by one-third to one-half.A Metal SkidA Metal SkidIt is also found that each strand will have doubled knots of 310 turns; four strands, 440; sixteen strands at 200; and eight at 210. This is working with strands one-sixteenth of an inch square. As a rule, rubber should not be turned after the second row of knots is formed. And by the way, you will find that the rubber, after being tightly twisted, tends to stick together, and should be carefully separated after a flight so that the air can reach all surfaces.According to the experiments made by Mr. Johnson, one pound of rubber may be made to store up 320 foot pounds of energy, while one pound of steel, in the form of springs, will only store up 65 pounds.In the early model aeroplanes much valuable energy was lost through friction. There has been a marked improvement in the construction of the propellers, axles, and bearings. Friction has been reduced to practically nothing. It is possible, of course, to drive a propeller with the shaft turning in a hole drilled at random through a stick, with a glass bead for a washer. It is very important, however, that the axle should turn exactly at right angles, and to hold it in position requires careful adjustment. To meet the demands of model aeroplane builders, several shaft mechanisms have been prepared, even to a very complete arrangement of miniature ball bearings.The model builder who cannot avail himself of these parts can, nevertheless, imitate their action with reasonable fidelity. The axle attached to the propeller should be heavy enough to resist bending in ordinary wear and tear. A bicycle spoke is just the thing. When you have decided upon this axle, procure a piece of metal tubing in which the axle will turn freely, without binding or rattling about. The tubing should then be passed through the frame supporting the propeller exactly at right angles, and extend out at either side about half an inch. To fasten it securely in position, glue and if necessary drive small wedges,—a match or toothpick,—about it.Several metal washers should be strung on the axle between the upper edge of the shaft and the propeller. These may be punched from a sheet of metal. A section of this tube may also be inserted part way in the propeller, and washers introduced where they meet. The second tube will insure smooth action.The projecting tube will serve also to remove the propeller far enough from the frame to prevent its striking. By freely oiling these parts, the propeller may be made to turn very freely.An ingenious adjustment of aileronsAn ingenious adjustment of aileronsTuning up the model for a flight.Tuning up the model for a flight.In bending the axle into a hook for holding the rubber strands of the motor, care must be taken to keep the ends of the strands on a line with the axle. After turning the wire into a hook, bend back the shank to the proper angle. It will be seen that if the motor carries the axle about from side to side, the friction will be considerably increased. Over this hook, slip a piece of rubber tubing before attaching the strands of rubber, since the metal is likely to cut and wear the motor. It will be found a good plan to tie the strands together just below the hook to keep them from slipping off. And, by the way, do not keep your motor wound up any longer than you can help before a flight, since the strain on the rubber in this position is very great.As motors have increased in power and distance qualities, the process of winding up has become a serious problem. The simple method of turning the propeller by hand takes too long, and a slip with a powerful motor may give one an ugly cut. An ordinary machine drill will do the work much more quickly. Some drills are geared so that a single turn of the wheel will give you ten revolutions of the propeller.To arrange your motor for winding with a drill, run the axle through the propellers and turn in the form of a closed hook. A small hook should then be fixed to the end of the drill, which may be inserted in this loop. Some boys use a double hook on the propeller, detach the strands of rubber, wind them up, and then attach them to the propeller.A very simple and ingenious method of winding up has been adopted in the remarkable model constructed by Mr. Mungokee. The motor is anchored by running the wire holding the strands through the supporting stick of the base, and bending the end into a hook which, as the rubber pulls, is held securely in a second hole at the side.Showing Construction And Mounting Of Propeller And Axle.Showing Construction And Mounting Of Propeller And Axle.To wind up, it is only necessary to draw out this hook, attach it to the winding drill and turn. When wound up, the pull of the motor will obviously hold the end of the hook firmly in the hole, making it impossible for it to turn. This does away with extra hooks and the trouble of hooking up the motor when once it has been wound.The life of your rubber motor may be lengthened by careful winding. As long as you wind up by turning the propeller by hand, it is safe to turn it as fast as you can, since the process is slow at best. In case the turning is done with a machine drill or some similar geared wheel, there is danger at some points of winding too fast.It is safe to wind as quickly as you can until the first row of knots has formed in the rubber strands, but at the moment the double strands begin to appear the winding should proceed very slowly. You will find that if you wind very quickly the double knots will appear in tight groups or bunches, and that only after considerable winding do these begin to spread out evenly. This puts the rubber under a severe and unnecessary strain and shortens its life.The simplest way of locking the propellers when once wound up is to thrust a piece of cane or reed through the hooks. The twist of the motor will hold it tightly in position, so that you can carry your model about, even shake it vigorously without danger of dislodging it. If you have twin propellers, use a strip long enough to pass through both hooks. Remove the strip just before starting. Be careful, of course, that your axles have not been thrown out of plumb.It will be found very convenient to equip your model with a single clasp for holding the propellers after they have been wound up, which may be easily released. It is awkward to keep them from slipping. An effective break may be made by attaching two strips of reed or cane, such as you use for skids, to either side of the motor base, so that the free ends will pass between the propeller blades and the frame, thus locking them fast.These bands should spring outward and be held in position by rubber bands running from one to the other. To release the propellers, simply pinch the two free ends together, and the propellers will be freed at the same instant. Do not keep your motor wound up a moment longer than you can help. It is very trying to the rubber to be held in this tightly-twisted position.In mounting your propeller, it is well to make the support for the bearing of the propeller axle as long as possible. An axle turning in a shaft one inch in length will meet with much less resistance than in a half-inch shaft, and with a good motor an inch-and-a-half shaft is still better. The rear stick of your motor base, which often holds the propeller axle, is usually made as thin as possible and rarely gives you more than a half-inch support.It is a good plan to lengthen the shaft by attaching a block of wood to the frame and passing the axle through it. Cut from a strip one-half an inch square a piece one inch in length, or whatever seems necessary. This may be mortised slightly into the stick and glued at right angles.An excellent monoplane capable of long flights.An excellent monoplane capable of long flights.Long-distance model built by Percy Pierce.Long-distance model built by Percy Pierce.Now drill a hole through the stick, with the grain, and the stick of your motor base and pass the tube holding the propeller shaft through both. To make this look shipshape, round off the edges. A great advantage of this stick is that it enables you to mount the propeller as far as you like from the frame, thus preventing it from striking.Showing An Excellent Way Of Fastening The Propellers To The Framework.Showing An Excellent Way Of Fastening The Propellers To The Framework.In mounting the propellers above or below the frame, you will need similar supports. The blocks should measure half an inch in width by one and a half inches square and should be cut with the grain of the wood running lengthwise. The hole for the propeller shaft is drilled near the top, and the block is securely fastened to the frame.It will be found a good plan to mortise the frame slightly in order to make the joint perfectly rigid, even in the face of a bad smash-up. Many boys merely glue the stick in position and bind it securely to the motor base with fine strong thread, and paint it with glue or shellac to hold it in position. These blocks may be fastened either above or below the frame or at the sides.In mounting the propellers, bear in mind that a position above the planes tends to drive the aeroplane downward, while the thrust exerted below tends to throw the aeroplane upward. The builders of model aeroplanes differ as much as to the best position of the propellers as the designers of man-carrying machines. Excellent models have been built with the propellers in either position. It is obviously impossible to lay down a rule for all models, since the properties of the planes vary so widely.A very simple and efficient support for the propeller shaft may be made of metal to correspond to the motor anchorage. Procure a sheet of heavy tin—a piece of sheet aluminum is still better—one-half inch in width and three inches in length. Now mark off a one-half inch, one inch, two inches, and two and one-half inches, and bend over the ends at right angles, as shown in the accompanying drawing.This support may be nailed or screwed rigidly to the end of the motor base, and a hole for the shaft of the propeller drilled through the two uprights. The propeller must be mounted so that the blades will, of course, be free of the base. The size of the support may be altered to suit the frame. In case you are using a heavy propeller, say an inch blade, the metal must be heavy enough to resist the pull of the propeller.The forward ends of the motors may be held by a cross piece cut from a sheet of aluminum six inches in width and two inches in depth, which is bound rigidly to the end of the motor base with shoemaker's thread. Aluminum suitable for this purpose costs about fifteen cents a square foot, and is soft enough to be cut with heavy shears.An ingenious motor anchorage of metal construction has been hit upon by the builders of model aeroplanes in France. We are all familiar with the difficulty of raising the hook, holding the rubber bands, high enough above the main frame, or fusilage, to be perfectly free. Instead of attaching a wooden block, the French boys bend a piece of tin, or some such metal, very simply into a support for the hook.You will need a sheet of metal heavy enough to withstand the full force of the motor when wound up. The tin used in cans, as a rule, is not heavy enough. For each support you will need a rectangle of tin or metal measuring three by one and one-half inches. Parallel to the longer base, draw a line one-quarter of an inch above. From the center, erect a long rectangle one-quarter of an inch wide, extending to the opposite side. Now connect the ends of the line above the base with the points at which the upright rectangle intersects the top line, round off the edges neatly and cut away this triangle. Four holes should be cut or punched in the tin, as indicated in the drawing.Now bend the tin on the two upright lines until the two sides are parallel. This support is fitted to the end of a motor base and secured by driving nails through the three holes at the base covering the wood. The end of the hook which holds the rubber strands of the motor should be passed through the opening at the end, bent over and fastened into position with a drop or two of solder. Such a support adds practically nothing to the weight of the frame, and obviously anchors the motor rigidly.Model built by Rutledge Barry, winner of spectacular flight contest.Model built by Rutledge Barry, winner of spectacular flight contest.A model by Percy Pierce, winner of the indoor long-distance record.A model by Percy Pierce, winner of the indoor long-distance record.The efficiency of a rubber-strand motor may be considerably increased by careful adjustment. If the strands first be wound rather loosely, as a rope is formed, and strung between the propeller hook and the motor anchorage, you will find that about thirty per cent. more rubber may be added without increasing the length and that a five to ten per cent. increase in the number of effective turns may be gained as well. By increasing the amount of rubber, you will, of course, add accordingly to the power of the motor. It is safe to say that the efficiency of your motor is increased upwards of twenty-five per cent. by this adjustment. The credit of this ingenious arrangement is due to Mr. W. Howell, Jr.It will be well to experiment with a short-strand motor, using a single strand of rubber for the test. Let us assume that your motor is twelve inches in length, thus making a double strand twenty-four inches long. First knot this, string it between the two hooks and turn it, counting the revolutions until the first row of double knots begins to appear. Note the number of turns.Now untie the strand and, holding one end, twist it until the lines of the edges make a continuous loose spiral throughout its entire length. The easiest way of twisting them is to lay them on a flat surface and rub with the palm of the hand.Now bring the two ends together and let the strands twist and wriggle until they come to rest. Fasten the ends and measure the double twisted strand. You will find that it measures less than ten inches.To prepare a strand for a twelve-inch motor, you must therefore begin with a piece of rubber fully thirty inches in length. It is clear, therefore, that the new plan enables you to gain considerably more rubber length for length. Now string your twisted rubber on the hooks of your motor so that to wind up you must turn against the twisted strand. You will find that a number of turns are required before the rubber strands are untwisted and lie parallel, which is pure gain. Count the number of turns up to the time the first line of the double knots appears, and you will find that it is about five per cent. greater than in the case of the single strands.The power exerted by your motor is meanwhile increased in direct proportion to the amount of rubber added. Still another advantage of this adjustment lies in the fact that such a motor will unwind to the first turn. In preparing a multiple-strand rubber, each strand must, of course, be twisted in the same direction and exactly the same number of times before being installed.The builders of model aeroplanes may profit from the experience of the automobile tire manufacturers in studying the properties of the rubber used for motors. Rubber is at best comparatively short-lived. It suffers a surface deterioration on being exposed to the air, which in time affects the entire mass.This process of decay goes on fastest in very warm weather and in very bright sunlight. It is believed that sea air and the rarified air of the mountains are bad for rubber. On the other hand, a very low temperature, as you may perhaps have discovered, robs the rubber of much of its elasticity.It will pay you to take some trouble to protect the rubber strands as far as possible. Lay them away in a can or jar in some cool, dry and dark place when they are not in use. Some boys cover the rubber with powdered chalk. When the surface of the rubber begins to granulate, its best days are over. Rubber is originally white in color, while the refining process gives it the familiar gray tone.The Para rubber is generally considered the best of the many kinds now on the market. As a rule, any oil or grease tends to decay the rubber, as any motorist can tell you. This is particularly unfortunate for the aviator, since the efficiency of the rubber motor is increased by slightly lubricating the strands. Many boys prefer to chance injuring their motors in order to gain the advantage of the oiled strands.The strands thus prepared slide smoothly on one another and do not grip each other even when tightly wound. The simplest preparation for greasing the strands is a solution of ordinary soap and water. A few drops poured over the strands will suffice. When your motor unwinds, be careful to keep your face out of range, since a few drops might be flung into your eyes. Several preparations for lubricating the motors have been placed upon the market.The direction flights may be controlled very easily by winding the motor. If you care to fly your model in circles or spirals, the simplest plan for influencing its direction is to give different power to your propellers. It often happens that a model must be in a restricted place, perhaps a straight-away flight is out of the question.The model may be deflected to the right or left by the use of vertical propellers, but they require delicate adjustment, and a gust of wind may destroy their effect. By winding up one double the number of turns of the other, a circular flight is assured. To gauge the diameter of the circle merely alter the relation of the number of turns. You will soon find that you can control the diameter of the circle with remarkable accuracy.A Motor AnchorageA Motor Anchorage
In the present stage of model aeroplane building, rubber strand motors satisfy every demand. Models have been flown for more than 2,500 feet by the force of these twisted strands, and doubtless their efficiency will be still further increased. Such motive power is besides very easily obtained and applied. Careful tests have shown that more energy may be stored up in twisted rubber strands than in the same weight of springs of steel or any other metal.
In gauging the strength of your motor, much depends upon whether your model is to rise from the ground or be launched from the hand. In the model tournaments in England, the flying machines are almost invariably thrown across the starting line, while in America they are required to rise unaided. It is obviously unfair, therefore, to compare the distance records of the two countries.
A Metal Motor AnchorageA Metal Motor Anchorage
A Metal Motor Anchorage
It requires a comparatively powerful motor to raise a model from the ground, whereas a lighter motor would be sufficient to propel it through the air. Many models, capable of flights of several hundred feet when thrown will refuse to rise, while, on the other hand, some models which rise well enough have poor distance qualities.
It should be borne in mind that the length of the motor, speaking broadly, controls the distance qualities, and its diameter the speed of the model aeroplane. A long slender motor, capable of from five hundred to one thousand turns which will revolve the propellers for thirty seconds or more, should insure a flight of several hundred feet. As you increase the number of strands of rubber, building up the diameter of the motor, you cut down the number of turns and therefore its duration, although you increase its speed.
A motor capable of one thousand turns must be about forty inches in length and consist of but six, or at most eight, of these strands. A model which may be driven by this motor, it will be found, must be very light. A model aeroplane weighing upwards of one pound, on the other hand, will require motors composed of fourteen strands or more to raise it from the ground. It is a very simple matter, of course, to add strands of rubber until your motor develops sufficient energy for the work it is expected to do.
The length and diameter of your motor, again, has a direct influence on the height of the flight. Too much power tends to raise the aeroplane higher than necessary above the ground. Since it requires more energy to drive a model aeroplane upward than along a horizontal direction, this is obviously a waste of energy.
If it is desired to fly the model as far as possible, it must be kept close to the ground. In the case of weight-lifting contests, the problem of altitude is, of course, entirely different. Overwinding is even worse than underwinding, since it shortens the life of the motor.
Try out your aeroplane with ten strands on each motor and increase them later. The motor, as previously explained, is formed by looping the rubber strands loosely between the hooks, just as zephyr is wound on a skein. Keep the strands very loose and fasten them to the hooks by tying with a strand of rubber. In winding, do not turn the propeller after the rubber has a double row of knots for its entire length. Such a motor should take up from three hundred to five hundred turns, perhaps more. Do not keep the elastic wound up too long before starting your flight. The strain is great and it quickly wears out.
A Metal Motor AnchorageA Metal Motor Anchorage
A Metal Motor Anchorage
The rubber strands should not be allowed to come in contact with any metal parts of the model. The copper that is often used for wiring is especially injurious and tends to decompose the rubber. The hooks of both the propeller and motor anchorage should be covered with a piece of rubber tubing. This serves a double purpose. With this protection, the rubber when tightly twisted is in no danger of being cut by the wire or of taking up the oxides which quickly eat through it.
A notable model possessing unusual stability. Built by W.S. Howell, Jr.A notable model possessing unusual stability. Built by W.S. Howell, Jr.
A notable model possessing unusual stability. Built by W.S. Howell, Jr.
Front view of model built by W.S. Howell, Jr.Front view of model built by W.S. Howell, Jr.
Front view of model built by W.S. Howell, Jr.
It requires an expert to pick out the best quality of rubber. If the strands be examined under a magnifying glass, it will be found that the edges of fresh rubber of the best quality are clean-cut, whereas the cheaper rubber, and that which is worn, has commenced to granulate, giving the edges a ragged appearance.
A simple test is to stretch the rubber over a ruler. A good rubber, in first-class condition, will stretch about seven times its length, and on being released instantly spring back to its original size. The same rubber should stretch to ten times its length without breaking.
There is a great difference of opinion among the most successful model builders as to the best shape of rubber strands. Some prefer the flat, band rubber, while others are obtaining satisfactory results with rubber cut in square strands. The strand used by the English model builders is seldom more than one-sixteenth of an inch square, while in America one-eighth of an inch strand is commonly used.
Experiments have been made with a single strand of rubber one-fourth of an inch square, but the results have not been satisfactory. One theory is that the corners of the square rubber tend to cut into one another and quickly wear out, and that a perfectly round strand would be the more efficient. At present there are no such strands on the market. It is argued by some that the square strand in twisting must be turned on itself further than the flat strand, and is therefore placed under an unnecessary strain. After all, the advantage of one form over another is fractional, and an extra strand added to the motor will balance any possible defects.
Figures have been prepared giving the exact relation of the size of rubber to the number of turns, although such statistics are elastic. The problem may be worked out with your own motor. Differences of temperature will be quickly noted. The rules prepared by V. E. Johnson, M.A., an English authority on aviation, are as follows: The motive power is doubled by increasing the number of rubber strands one-half; by doubling the number of strands, the motive power is increased more than two times; and the tripling of the strands increases the motive power seven times. As regards the number of turns the same authority states that the doubling of the number of strands diminishes the number of turns by one-third to one-half.
A Metal SkidA Metal Skid
A Metal Skid
It is also found that each strand will have doubled knots of 310 turns; four strands, 440; sixteen strands at 200; and eight at 210. This is working with strands one-sixteenth of an inch square. As a rule, rubber should not be turned after the second row of knots is formed. And by the way, you will find that the rubber, after being tightly twisted, tends to stick together, and should be carefully separated after a flight so that the air can reach all surfaces.
According to the experiments made by Mr. Johnson, one pound of rubber may be made to store up 320 foot pounds of energy, while one pound of steel, in the form of springs, will only store up 65 pounds.
In the early model aeroplanes much valuable energy was lost through friction. There has been a marked improvement in the construction of the propellers, axles, and bearings. Friction has been reduced to practically nothing. It is possible, of course, to drive a propeller with the shaft turning in a hole drilled at random through a stick, with a glass bead for a washer. It is very important, however, that the axle should turn exactly at right angles, and to hold it in position requires careful adjustment. To meet the demands of model aeroplane builders, several shaft mechanisms have been prepared, even to a very complete arrangement of miniature ball bearings.
The model builder who cannot avail himself of these parts can, nevertheless, imitate their action with reasonable fidelity. The axle attached to the propeller should be heavy enough to resist bending in ordinary wear and tear. A bicycle spoke is just the thing. When you have decided upon this axle, procure a piece of metal tubing in which the axle will turn freely, without binding or rattling about. The tubing should then be passed through the frame supporting the propeller exactly at right angles, and extend out at either side about half an inch. To fasten it securely in position, glue and if necessary drive small wedges,—a match or toothpick,—about it.
Several metal washers should be strung on the axle between the upper edge of the shaft and the propeller. These may be punched from a sheet of metal. A section of this tube may also be inserted part way in the propeller, and washers introduced where they meet. The second tube will insure smooth action.
The projecting tube will serve also to remove the propeller far enough from the frame to prevent its striking. By freely oiling these parts, the propeller may be made to turn very freely.
An ingenious adjustment of aileronsAn ingenious adjustment of ailerons
An ingenious adjustment of ailerons
Tuning up the model for a flight.Tuning up the model for a flight.
Tuning up the model for a flight.
In bending the axle into a hook for holding the rubber strands of the motor, care must be taken to keep the ends of the strands on a line with the axle. After turning the wire into a hook, bend back the shank to the proper angle. It will be seen that if the motor carries the axle about from side to side, the friction will be considerably increased. Over this hook, slip a piece of rubber tubing before attaching the strands of rubber, since the metal is likely to cut and wear the motor. It will be found a good plan to tie the strands together just below the hook to keep them from slipping off. And, by the way, do not keep your motor wound up any longer than you can help before a flight, since the strain on the rubber in this position is very great.
As motors have increased in power and distance qualities, the process of winding up has become a serious problem. The simple method of turning the propeller by hand takes too long, and a slip with a powerful motor may give one an ugly cut. An ordinary machine drill will do the work much more quickly. Some drills are geared so that a single turn of the wheel will give you ten revolutions of the propeller.
To arrange your motor for winding with a drill, run the axle through the propellers and turn in the form of a closed hook. A small hook should then be fixed to the end of the drill, which may be inserted in this loop. Some boys use a double hook on the propeller, detach the strands of rubber, wind them up, and then attach them to the propeller.
A very simple and ingenious method of winding up has been adopted in the remarkable model constructed by Mr. Mungokee. The motor is anchored by running the wire holding the strands through the supporting stick of the base, and bending the end into a hook which, as the rubber pulls, is held securely in a second hole at the side.
Showing Construction And Mounting Of Propeller And Axle.Showing Construction And Mounting Of Propeller And Axle.
Showing Construction And Mounting Of Propeller And Axle.
To wind up, it is only necessary to draw out this hook, attach it to the winding drill and turn. When wound up, the pull of the motor will obviously hold the end of the hook firmly in the hole, making it impossible for it to turn. This does away with extra hooks and the trouble of hooking up the motor when once it has been wound.
The life of your rubber motor may be lengthened by careful winding. As long as you wind up by turning the propeller by hand, it is safe to turn it as fast as you can, since the process is slow at best. In case the turning is done with a machine drill or some similar geared wheel, there is danger at some points of winding too fast.
It is safe to wind as quickly as you can until the first row of knots has formed in the rubber strands, but at the moment the double strands begin to appear the winding should proceed very slowly. You will find that if you wind very quickly the double knots will appear in tight groups or bunches, and that only after considerable winding do these begin to spread out evenly. This puts the rubber under a severe and unnecessary strain and shortens its life.
The simplest way of locking the propellers when once wound up is to thrust a piece of cane or reed through the hooks. The twist of the motor will hold it tightly in position, so that you can carry your model about, even shake it vigorously without danger of dislodging it. If you have twin propellers, use a strip long enough to pass through both hooks. Remove the strip just before starting. Be careful, of course, that your axles have not been thrown out of plumb.
It will be found very convenient to equip your model with a single clasp for holding the propellers after they have been wound up, which may be easily released. It is awkward to keep them from slipping. An effective break may be made by attaching two strips of reed or cane, such as you use for skids, to either side of the motor base, so that the free ends will pass between the propeller blades and the frame, thus locking them fast.
These bands should spring outward and be held in position by rubber bands running from one to the other. To release the propellers, simply pinch the two free ends together, and the propellers will be freed at the same instant. Do not keep your motor wound up a moment longer than you can help. It is very trying to the rubber to be held in this tightly-twisted position.
In mounting your propeller, it is well to make the support for the bearing of the propeller axle as long as possible. An axle turning in a shaft one inch in length will meet with much less resistance than in a half-inch shaft, and with a good motor an inch-and-a-half shaft is still better. The rear stick of your motor base, which often holds the propeller axle, is usually made as thin as possible and rarely gives you more than a half-inch support.
It is a good plan to lengthen the shaft by attaching a block of wood to the frame and passing the axle through it. Cut from a strip one-half an inch square a piece one inch in length, or whatever seems necessary. This may be mortised slightly into the stick and glued at right angles.
An excellent monoplane capable of long flights.An excellent monoplane capable of long flights.
An excellent monoplane capable of long flights.
Long-distance model built by Percy Pierce.Long-distance model built by Percy Pierce.
Long-distance model built by Percy Pierce.
Now drill a hole through the stick, with the grain, and the stick of your motor base and pass the tube holding the propeller shaft through both. To make this look shipshape, round off the edges. A great advantage of this stick is that it enables you to mount the propeller as far as you like from the frame, thus preventing it from striking.
Showing An Excellent Way Of Fastening The Propellers To The Framework.Showing An Excellent Way Of Fastening The Propellers To The Framework.
Showing An Excellent Way Of Fastening The Propellers To The Framework.
In mounting the propellers above or below the frame, you will need similar supports. The blocks should measure half an inch in width by one and a half inches square and should be cut with the grain of the wood running lengthwise. The hole for the propeller shaft is drilled near the top, and the block is securely fastened to the frame.
It will be found a good plan to mortise the frame slightly in order to make the joint perfectly rigid, even in the face of a bad smash-up. Many boys merely glue the stick in position and bind it securely to the motor base with fine strong thread, and paint it with glue or shellac to hold it in position. These blocks may be fastened either above or below the frame or at the sides.
In mounting the propellers, bear in mind that a position above the planes tends to drive the aeroplane downward, while the thrust exerted below tends to throw the aeroplane upward. The builders of model aeroplanes differ as much as to the best position of the propellers as the designers of man-carrying machines. Excellent models have been built with the propellers in either position. It is obviously impossible to lay down a rule for all models, since the properties of the planes vary so widely.
A very simple and efficient support for the propeller shaft may be made of metal to correspond to the motor anchorage. Procure a sheet of heavy tin—a piece of sheet aluminum is still better—one-half inch in width and three inches in length. Now mark off a one-half inch, one inch, two inches, and two and one-half inches, and bend over the ends at right angles, as shown in the accompanying drawing.
This support may be nailed or screwed rigidly to the end of the motor base, and a hole for the shaft of the propeller drilled through the two uprights. The propeller must be mounted so that the blades will, of course, be free of the base. The size of the support may be altered to suit the frame. In case you are using a heavy propeller, say an inch blade, the metal must be heavy enough to resist the pull of the propeller.
The forward ends of the motors may be held by a cross piece cut from a sheet of aluminum six inches in width and two inches in depth, which is bound rigidly to the end of the motor base with shoemaker's thread. Aluminum suitable for this purpose costs about fifteen cents a square foot, and is soft enough to be cut with heavy shears.
An ingenious motor anchorage of metal construction has been hit upon by the builders of model aeroplanes in France. We are all familiar with the difficulty of raising the hook, holding the rubber bands, high enough above the main frame, or fusilage, to be perfectly free. Instead of attaching a wooden block, the French boys bend a piece of tin, or some such metal, very simply into a support for the hook.
You will need a sheet of metal heavy enough to withstand the full force of the motor when wound up. The tin used in cans, as a rule, is not heavy enough. For each support you will need a rectangle of tin or metal measuring three by one and one-half inches. Parallel to the longer base, draw a line one-quarter of an inch above. From the center, erect a long rectangle one-quarter of an inch wide, extending to the opposite side. Now connect the ends of the line above the base with the points at which the upright rectangle intersects the top line, round off the edges neatly and cut away this triangle. Four holes should be cut or punched in the tin, as indicated in the drawing.
Now bend the tin on the two upright lines until the two sides are parallel. This support is fitted to the end of a motor base and secured by driving nails through the three holes at the base covering the wood. The end of the hook which holds the rubber strands of the motor should be passed through the opening at the end, bent over and fastened into position with a drop or two of solder. Such a support adds practically nothing to the weight of the frame, and obviously anchors the motor rigidly.
Model built by Rutledge Barry, winner of spectacular flight contest.Model built by Rutledge Barry, winner of spectacular flight contest.
Model built by Rutledge Barry, winner of spectacular flight contest.
A model by Percy Pierce, winner of the indoor long-distance record.A model by Percy Pierce, winner of the indoor long-distance record.
A model by Percy Pierce, winner of the indoor long-distance record.
The efficiency of a rubber-strand motor may be considerably increased by careful adjustment. If the strands first be wound rather loosely, as a rope is formed, and strung between the propeller hook and the motor anchorage, you will find that about thirty per cent. more rubber may be added without increasing the length and that a five to ten per cent. increase in the number of effective turns may be gained as well. By increasing the amount of rubber, you will, of course, add accordingly to the power of the motor. It is safe to say that the efficiency of your motor is increased upwards of twenty-five per cent. by this adjustment. The credit of this ingenious arrangement is due to Mr. W. Howell, Jr.
It will be well to experiment with a short-strand motor, using a single strand of rubber for the test. Let us assume that your motor is twelve inches in length, thus making a double strand twenty-four inches long. First knot this, string it between the two hooks and turn it, counting the revolutions until the first row of double knots begins to appear. Note the number of turns.
Now untie the strand and, holding one end, twist it until the lines of the edges make a continuous loose spiral throughout its entire length. The easiest way of twisting them is to lay them on a flat surface and rub with the palm of the hand.
Now bring the two ends together and let the strands twist and wriggle until they come to rest. Fasten the ends and measure the double twisted strand. You will find that it measures less than ten inches.
To prepare a strand for a twelve-inch motor, you must therefore begin with a piece of rubber fully thirty inches in length. It is clear, therefore, that the new plan enables you to gain considerably more rubber length for length. Now string your twisted rubber on the hooks of your motor so that to wind up you must turn against the twisted strand. You will find that a number of turns are required before the rubber strands are untwisted and lie parallel, which is pure gain. Count the number of turns up to the time the first line of the double knots appears, and you will find that it is about five per cent. greater than in the case of the single strands.
The power exerted by your motor is meanwhile increased in direct proportion to the amount of rubber added. Still another advantage of this adjustment lies in the fact that such a motor will unwind to the first turn. In preparing a multiple-strand rubber, each strand must, of course, be twisted in the same direction and exactly the same number of times before being installed.
The builders of model aeroplanes may profit from the experience of the automobile tire manufacturers in studying the properties of the rubber used for motors. Rubber is at best comparatively short-lived. It suffers a surface deterioration on being exposed to the air, which in time affects the entire mass.
This process of decay goes on fastest in very warm weather and in very bright sunlight. It is believed that sea air and the rarified air of the mountains are bad for rubber. On the other hand, a very low temperature, as you may perhaps have discovered, robs the rubber of much of its elasticity.
It will pay you to take some trouble to protect the rubber strands as far as possible. Lay them away in a can or jar in some cool, dry and dark place when they are not in use. Some boys cover the rubber with powdered chalk. When the surface of the rubber begins to granulate, its best days are over. Rubber is originally white in color, while the refining process gives it the familiar gray tone.
The Para rubber is generally considered the best of the many kinds now on the market. As a rule, any oil or grease tends to decay the rubber, as any motorist can tell you. This is particularly unfortunate for the aviator, since the efficiency of the rubber motor is increased by slightly lubricating the strands. Many boys prefer to chance injuring their motors in order to gain the advantage of the oiled strands.
The strands thus prepared slide smoothly on one another and do not grip each other even when tightly wound. The simplest preparation for greasing the strands is a solution of ordinary soap and water. A few drops poured over the strands will suffice. When your motor unwinds, be careful to keep your face out of range, since a few drops might be flung into your eyes. Several preparations for lubricating the motors have been placed upon the market.
The direction flights may be controlled very easily by winding the motor. If you care to fly your model in circles or spirals, the simplest plan for influencing its direction is to give different power to your propellers. It often happens that a model must be in a restricted place, perhaps a straight-away flight is out of the question.
The model may be deflected to the right or left by the use of vertical propellers, but they require delicate adjustment, and a gust of wind may destroy their effect. By winding up one double the number of turns of the other, a circular flight is assured. To gauge the diameter of the circle merely alter the relation of the number of turns. You will soon find that you can control the diameter of the circle with remarkable accuracy.
A Motor AnchorageA Motor Anchorage
A Motor Anchorage