“ In other words, if the motor of a large machine were started and the aeroplane launched without a pilot, would its chances of flight be as good, in proportion to its size, as those of our best model aeroplanes? A model aeroplane which flies 300 feet performs as remarkable a feat as would a large machine flying, unguided, a mile or more. The progress in the construction of model aeroplanes, in brief, already deserves serious scientific consideration. ”

“ Watch the successful model as it gains its altitude, settles down to a horizontal flight, is perhaps knocked off its course by a cross current, and steadies itself with a graceful curve and proceeds on its way.
All these problems must be anticipated. The young aviator must ingeniously arrange his planes and ballast in advance. The regular sky pilot, on the other hand, meets the problems of the air as he encounters them, by flexing his wings against disturbing currents or by banking to maintain an even keel at a turn. ”

“ CHAPTER I MODEL AEROPLANES OF 1911 For the average boy there is no more stirring music than the brisk, whirring note of his model aeroplane. Let the propellers spin steadily for ten glorious seconds, and the journey spans a couple hundred feet or more. Double the time and the flight becomes a triumph. Out of the ingenuity of thousands of boy aviators, the world over, has come a surprising development of the model aeroplane. The experimental stage is passed. Any bright boy may now build a model aeroplane which is certain to give results. ”

“ It is only when an aeroplane is held fast that its propellers kick up such a fuss and blow your hat off. The aeroplane propeller's work is much the same as that of a steamship, although the air through which it travels has many tricks not yet understood. The density of the air compares to that of water as one to eight hundred, but the friction encountered by the air propellers is much greater than 1-800th that of water. It may be laid down as a general rule, however, that the driving force of an aeroplane propeller varies as the square of the number of revolutions per minute. ”

“ A Motor Anchorage
CHAPTER VIII DIRECTIONAL CONTROL The unerring flight of birds is, of course, the model for the builders of heavier-than-air machines. Much of the birds' skill in directing their motive power remains a mystery to us, but we are learning to analyze and, in a measure, imitate them. The builder of model aeroplanes again must not alone imitate the methods of the birds; he must make their system of maintaining stability automatic. A study of a variety of successful models shows that there is great difference of opinion as to the best plan for stabilizing the aeroplane. ”

“ The tipping of a car running on a single track, or of a ship at sea, is of course very much like the rolling of an aeroplane in flight; and it would seem that such a stabilizing device might solve the problem. The gyroscope has a serious disadvantage, however. Since it revolves at enormous speed any breakage would tend to throw the detached part to one side with dangerous force. In the case of the gyroscope used to steady ships at sea this force would be sufficient to send a piece of metal through the hull. On so delicate a craft as an aeroplane such an accident might readily prove disastrous. ”

“ The success of a glider depends more upon its modeling and finish of its planes than in the case of the model aeroplane. It must gain as much support as possible from the air, since it has no motive power to keep it aloft. Its head resistance must also be cut down. The ordinary cloth-covered planes, which serve well enough for an ordinary model aeroplane, will not carry a glider far. The planes must, therefore, be of metal or wood, or when built-up planes are used they must be of the most careful workmanship. ”

“ Like the famous designers and pilots of man-carrying craft this younger generation of designers give their names to their machines. Our young designers, as a rule, confine themselves to developing a particular type of machine. A comparison of the models of the same builder for a year or more will usually show that the same general form and arrangement of the planes remain the same.
The Percy Pierce model, which borrows the name of its designer, is probably the best known of these model aeroplanes. ”

“ It is very little more trouble to build two motors than one, and the model thus equipped will not only travel much further, but will insure much more stable flights. A common trouble in model building has been the lack of stability. Your model has been likely to capsize, even under favorable conditions, spoiling the flight, while a chance gust of wind would knock it out of its course in spite of everything you could do. To overcome this tendency, the surface of the planes might be increased, but this added to the weight of the model, thus cutting down the length of the flights. ”

“ During the past year practically all of the biplane forms have been abandoned by model builders. As a result of wide experiments, it has been found that the monoplane exerts more sustension per unit of surface than any two or three-plane machines. In theory, it is, of course, possible to increase the sustained force by setting one plane above another, but in practice it has been found that the planes must be set so far apart that the arrangement is impracticable. ”

“ Storing energy for a long distance flight
CHAPTER V THEORY AND PRACTICE OF PLANE CONSTRUCTION THE planes of your model aeroplane need no longer be a blind experiment whose merits or defects may only be learned by actual test. The science of wing-building is much better understood to-day than a year ago. Without going into the complicated equations dealing with aspect ratio, pressure, and gravity, it is important that one bear in mind a few definite rules in designing even the simplest planes. A great many useless experiments may be avoided. ”

“ In the collapsible skid we find one of the most interesting novelties of the year. This ingenious mechanism, which is very easy to adjust, and which is placed under the front of the model on rising from the ground, is drawn into a horizontal position extending out before the machine and acts as a buffer, an aerial cow-catcher. Any simple form of skid may be adjusted in this way. The upper end or ends are merely fastened to the motor base so that they will swing easily back and forth. ”

“ The formula which obliges one to solve a complicated problem in algebra or calculus to know where to cut off a stick is obviously absurd in the case of small models. These formulas which may be found in technical books on aviation seem to savor too much of certain school books to be brought in for the builder of model aeroplanes. A good rule to remember is that the thrust should equal the weight of the machine. ”

“ What may be called the 1911 type of model aeroplane looks every inch a racer. Every unnecessary stick and string has been cut away. When skids are used they are of the lightest possible material and the simplest construction. The miniature rubber-tired wheels, with ball bearings, which made many of last year's models so attractive, are rarely used. The plane surface has been reduced fully one half. One great secret of success is in the cutting down of weight. When your propeller has but half the work to do, the length of the flight is, of course, greatly increased. ”

“ The stability of a model is greater when its course is downward than when in a horizontal flight. In this position, the center of pressure is much less likely to shift, and the pole of gravity has rather a steadying effect. For this reason a glider thrown from an elevation travels much more evenly than a power-driven machine. Try reversing your planes.
Why is it that my aeroplane sails all right, but when I increase the power of my motor it falls off and darts about until it reaches the ground? ”

“ A great advance will be made in aviation with the appearance of some practical contrivance for securing automatic stability. The aeroplane as it stands to-day shows a wonderful advance in the improvement of its general lines, and the mechanical perfection of its parts, but the question of stability remains practically the same as it was when the Wright Brothers made their first flights. The machine has been brought under a remarkable control, but only as it is directed by the practised hand of the sky pilot. ”

“ Man has learned to fly. More than 1,000 aeroplanes have been built which have successfully risen above the earth. It is estimated that these aeroplanes have flown in all more than 250,000 miles, or a distance equal to ten times the circumference of the earth. But no machine has yet been made which will fly alone, without the skilful manipulation of planes and rudders. The model aeroplane which soars gracefully aloft, suiting itself to the varying air conditions, perhaps comes nearest to the automatic flying machine. ”

“ Much has been learned about motors. It has been found that the rubber motor is capable of great development. Since a flight of one-half a mile may be made by twisted bands of rubber, the average model builder may be content to let clock work and miniature gasoline engines take care of themselves. By building and flying thousands of models, we have found what form of rubber strand is best, just how heavy the strands should be, and the most efficient point of winding. ”

“ Since the length of model aeroplane flights has been increased ten times, their improvement is comparable to that of the large man-carrying machines. The science has become more exact, and the chance of failure reduced, until to-day successful flights are within the reach of all.
In the preparation of this volume thanks are due to the New York Model Aero Club, to Mr. Edward Durrant, Percy Pierce, Cecil Peoli, W. S. Howells, Jr., and to the young gentlemen whose models are illustrated herewith, who, singly and collectively, are doing much for the development of the science in America. ”

“ It has been found in experiments of man-carrying machines that an increase in the speed of a flight would often render an ordinarily steady machine unstable. It is argued by some authorities that the air is churned up, as it were, by the forward planes, and that the rear wing, therefore, rocks just as will a boat in rough water. If your model flies well at a certain speed, you had better stick to the motor, and try a larger plane. ”

“ The model should, moreover, rest upon skids at as low an angle as possible.
In starting off, the planes will thus exert their maximum lift, or nearly so. If the narrow planes be elevated too much, the center of pressure will come nearer the rear than the front edge, and tend to force the aeroplane downward, or, as the phrase is, make it "sit on its tail." As long as a plane is traveling horizontally, or at low angles, its rear portion exerts very little sustaining power and may be cut away.
A plane with a high aspect ratio is much more stable in flight than a surface of greater depth. ”

“ The best American models, on the other hand, would be outdistanced in an English meet, but their flights would show them to have far greater automatic stability than their English rivals. It is extremely interesting to speculate whether the American or English types of model aeroplanes will survive, and which is contributing more to the solving of the great mysteries of aviation, but, after all, it is a question which only time can answer. ”

“ The propellers of a model aeroplane are subject to more wear and tear than those of a regular passenger-carrying machine. At the end of every flight, they face a possible catastrophe. In the search for some durable form of screw, a number of interesting discoveries have been made. One builder has succeeded in coating a wooden propeller with bronze by subjecting it to an electroplating process, but this is much too complicated for the amateur. The lighter metals, aluminum and magnalium, naturally suggest themselves for the purpose. ”

“ Let an aviator suddenly run into a hot or a cold strait of air and the pressure upon his planes will instantly change. The effect of temperature must be taken into consideration by any one flying model aeroplanes. It may happen that a draft of cool or of hot air, by changing the pressure on the planes, will throw a model aeroplane out of balance and mar an otherwise promising flight. A difference of a few degrees of temperature will often affect a very sensitive model. The only way to combat this is of course to build your model with the greatest possible stability. ”

“ 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. ”

“ The silk wheel is not recommended for the beginner; but for one who is anxious to finish his model to the last detail as attractively as possible, they form an interesting feature.
Ping-pong balls make serviceable skids. Since they are carefully rounded, they will turn easily. To mount them, drill a hole for the wire shaft or axle, taking great care to have it pass through opposite points of the sphere. The wire may then be bent above it and attached to the skid. The celluloid turning on the wire axle produces practically no friction, and the ball offers very little resistance to the air. ”

“ In flying model aeroplanes the performance of a machine will often vary unaccountably from day to day. With the same motor and winding, the model will fly much higher and more freely at different seasons of the year. It is well to bear in mind that in the summer months the heat causes a low density. The pressure exerted by the atmosphere is therefore correspondingly small; the model, or for that matter a large machine, travels much faster. A dry day also tends to cause low density. ”

“ The sticks used for the motor base are hollow, being built up of a light veneer one-sixteenth of an inch thick. The joints are so cleverly arranged that they would deceive the average eye. The main sticks of the frame are joined by a series of trusses of the same delicate construction which form an exceptionally rigid base of amazing lightness. Every detail of the model shows the same delicacy of construction. The planes are built up of thin strips of bamboo covered with Japanese silk on both surfaces, the curve being drawn perfectly. ”

“ It is believed by many aviators that the problem of automatic stability will be solved by some form of the gyroscope. A great many experiments are being made with various forms of the gyroscope, although no machine has as yet been actually fitted and flown with such a device. The general principle of the gyroscope is very simple. It consists of a wheel which is made to revolve at very high speed. When such a wheel turns fast enough it will remain in a fixed position. Every one is familiar for instance with the gyroscope top. ”

“ Even in the open country the presence of a deep valley or other depression will so affect the density of the atmosphere that an aeroplane is likely to be drawn down from its course. These areas are known among aviators as "pockets," and are often large enough to swallow up a large man-carrying craft, at times with disastrous effects. The chance of your model aeroplane running into such a pocket is of course considerable. ”

“ It is well to remember that in increasing the width of your propeller blade you add to the skin friction.
Some designers carry the curve of the propeller blade to the center of the axle, while others leave the center blank. It is argued by the former that the longer the blade the greater is the thrust. Others believe that the blade exerts little or no thrust near the center and is weakened by being cut away too much. The builder of model aeroplanes has one great advantage over the designer of passenger-carrying craft. The model does not have to carry fuel. ”

“ On one hand it is argued that the forward propeller, or tractor as it is called, works in undisturbed air and is therefore more efficient. Most of the large passenger-carrying aeroplanes are driven by tractors. Others argue that the propeller churns up the air and that the planes would therefore balance themselves against the gusts thus set in motion, which makes their flight unstable besides requiring additional power. Practically all of the successful model aeroplanes this year are driven by propellers. ”

“ The beginner who is constructing his first model will find a small machine by far the most satisfactory. The more experienced model builder, on the other hand, will find that so simple a model will enable him to try out new theories quickly and cheaply. A simple Bleriot form, one foot in length, driven tail foremost is recommended. Many successful model builders keep such a model constantly in their workshops. ”

“ If more power is put on, they argue, it will only tend to send the machine up in the air and will not increase its speed. This is probably true in a measure of model aeroplanes as well. When you have found the speed at which your aeroplane flies best do not change the number of rubber bands of your motor or the number of turns in winding.
Do the tails of birds serve as rudders to guide them in flying?
It is an open question. Some aviators who have made very careful observations of birds in flight deny that the tails have anything to do with their direction. ”

“ One or more machines are almost always aloft. It is as thrilling as a three-ringed circus.
CHAPTER III PARLOR AVIATION A model glider, or aeroplane without a motor, will be found perhaps as entertaining a toy as the power-driven machine. It is much simpler, of course, to build and adjust a successful glider even than the most elementary model aeroplane. With the problem of the motor and propeller removed, the cost of construction besides is reduced to practically nothing. Here is excellent entertainment for those who have not the time or patience for model building. ”

“ Our amateur aviators are attacking one great problem of aviation which the pilots of man-carrying crafts are perhaps neglecting. Model aeroplanes are built to maintain their equilibrium in the air automatically. They must not only rise from the ground, prepared for a long flight, but must be contrived to resist all manner of baffling air currents aloft. ”