THE BOYS’ BOOK OF
MODEL AEROPLANES

Launching the Airship.

THE BOYS’ BOOK OF
MODEL AEROPLANES

HOW TO BUILD AND FLY
THEM: WITH THE STORY OF
THE EVOLUTION OF THE
FLYING MACHINE

BY

FRANCIS A. COLLINS

ILLUSTRATED WITH MANY
PHOTOGRAPHS AND DIAGRAMS
BY THE AUTHOR

LONDON
EVELEIGH NASH
1912

TO
ARNOLD MILLER COLLINS
(Aged Ten)

THAN WHOM NO COLLABORATOR COULD
HAVE BEEN MORE ENTHUSIASTIC

CONTENTS

PART I

MODELS: HOW TO BUILD AND FLY THEM

LIST OF ILLUSTRATIONS

PART I

MODELS: HOW TO BUILD
AND FLY THEM

THE BOYS’ BOOK OF
MODEL AEROPLANES

CHAPTER I

THE NEW SPORT FOR BOYS

IN the boy’s calendar nowadays the aëroplane season comes in with sledding and runs all through skating, marble, top, kite-flying, and bicycle time. The delights of all the old games seem to be found in this marvelous new toy. The fun in throwing a top cannot compare with that of launching an aëroplane, while kite-flying is a very poor substitute for the actual conquest of the air. To watch one of these fascinating little ships of the air, which you have fashioned and built with your own hands, actually rise from the earth and soar aloft with a swallow’s swiftness, is perhaps the greatest boy’s sport in the world. Certainly no new game or toy has ever taken such hold of the boy’s imagination, and in so short a time enrolled such an army of enthusiasts.

Throughout the country to-day upward of ten thousand boy aviators are struggling with the problem of the air-ship. Among these junior aëronauts the record for height and that for distance in flying are matters of quite as lively interest as among the grown-ups. The great contests of aviators here and abroad are watched with intelligent interest. Let a new form of aëroplane, a biplane or monoplane, appear, and it is quickly reproduced by scores of models and its virtues put to an actual test. If a new wing or new plan for insuring stability is invented, a new thought in the steering-device, or some new application of power, it is instantly the subject of earnest discussion among the junior aëronauts the country over.

Nor are junior aëronauts merely imitators. The mystery of the problems of the air, the fascination of a new world of conquest, make a strong appeal to the American temperament. With thousands of bright boys working with might and main to build air-ships which will actually fly, there is certain to be real progress. Thousands of different models have been designed and put to actual test. This army of inventors, ranging in age from twelve to eighteen years, some of whom will be the aviators of the future, cannot fail to do great service, as time goes on, in the actual conquest of the air.

Within a few months this army of inventors has become organized into clubs, and a regular program of tournaments has been arranged. The junior aëro clubs are found in connection with many schools, both public and private; they are made features of the Young Men’s Christian Association amusements, or they become identified with various neighborhoods. Tournaments are arranged between clubs of different cities or States, while an international tournament is even planned between the United States and Great Britain.

The junior aëro world has its prizes, which are scarcely less coveted than the rewards for actual flight. Some fifty medals have been distributed this year among the members of the New York Junior Aëro Club. Many elaborate trophies will be contended for during 1910 by the junior aëronauts of the country. A handsome silver cup of special design has been presented by Mr. A. Leo Stevens, and a second by Mr. Sidney Bowman, while similar trophies are offered by Commodore Marshall, O. Chanute, and others.

The toy aëroplane is not limited to any one season, as one’s sled, kite, or skates. In the winter months the tests of flight may be carried out in any large room or hall. There is even an advantage in holding such a tournament in a large school-room, riding-academy, or armory, since there is no baffling wind to contend with. Already definite rules have been laid down for conducting these tests and for making official records of flights. It is possible, therefore, to compare the records made in different cities or countries with one another.

A Junior Aëroclub with Its Instructor in One of the New York Public Schools.

The junior aëro tournaments are likely to be the most thrilling experience in a boy’s life. The feats which the world has watched with such breathless interest at aviation meets at Rheims, Pau, or Los Angeles are reproduced in miniature in these boys’ contests without loss of enthusiasm. The weeks or months of preparation in scores of little workshops are now put to an actual test. The model air-ship, which has cost so many anxious and delightful hours in the building, is to spread its wings with scores of similar air-craft. The superiority of the monoplane or biplane forms is to be tested without fear or favor.

For the young inventors, even for the mere layman in such matters, the scene is extremely animated. On every hand one sees the inventors tuning up their air-craft for the final test. There are lively discussions in progress over the marvelous little toys. The layman hears a new language spoken with perfect confidence about him. The boys have already made the picturesque vocabulary of the world of aviation their own. The discussion ranges over monoplanes and biplanes, cellular types, and flexed planes, or of rigid and lateral braces. To hear a crowd of these enthusiasts shout their comments as the air-ships fly about is in itself an education in advanced aëronautics.

Directly the floor is cleared, the judges take their position, and the junior sky-pilot toes the mark, air-ship in hand. “One, two, three,” shouts the starter, and with a whir the graceful air-craft is launched. The flutter of the tiny propeller suggests the sudden rise of a covey of partridges. The little craft, at once so graceful and frail, defies all the accepted laws of gravitation. It darts ahead in long, undulating curves as it floats over the invisible air-currents. As in the aëroplanes of larger size, the length of the flight is dependent almost wholly on the motive power. As the little engine slows down, the craft wavers, and then in a long curve, for it can do nothing ungraceful, it glides to rest, skidding along the floor like a bird reluctant to leave the sky.

When the time comes for the races between the air-craft, enthusiasm runs high. Naturally these contests are the most popular features of the tournament. A line of inventors, with their air-craft, usually six at a time, take their positions at the starting-line. Each air-craft has been tuned to its highest powers. The labor of weeks, the study of air-craft problems, the elaboration of pet inventive schemes, are represented in the shining model. And the problem before the young inventors is most baffling. There are few models to work from, the science is still so young, and the inventor may well feel himself something of a Columbus in launching his frail craft upon this uncharted sea.

At the signal half a dozen propellers are instantly released, a whirring as of innumerable light wings fills the air. The curious flock of mechanical birds rises and falls, dipping in long, graceful curves as they struggle toward the goal. Some graceful little craft perfectly reproducing to the last detail the famous Wright machine shoulders along beside a glistening monoplane which resembles a great hawk with wings outspread. The next craft is perhaps a complicated arrangement of planes of no registered type, while the craft made familiar by the photographs of the famous aviators are reproduced.

The thrill of an aëroplane race is a sensation peculiarly its own. It seems so astonishing that the graceful little craft should remain aloft at all, that they are a never-failing delight to the eye. The varying fortunes of the race, the temporary lead gained by one craft, to be lost the next moment to another, which a second later itself falls behind, and the final heat between the survivors in the race as they approach the goal, are enough to drive the average boy crazy with delight.

A Young Inventor in His Workshop.

Boys Comparing Models.

The rules for these contests are rigidly observed. Each air-craft is sent aloft by its inventor or owner. The start must be made from a mark, and of course each aëroplane must toe the mark. There must be three judges for each event. One stands at the starting-line and gives the word of command for the start of the race or flight, as the case may be. A second judge stands midway down the course, and the third at or near the finishing-line. Each young aviator winds up his craft, adjusts the power with his own hands, and sets the rudder for the flight.

The miniature air-craft must act in flight exactly the same as the great working air-craft which carry men aloft. A toy air-ship must make its flight in a horizontal position, and if it turns over in flight, even though it flies farther and faster than any other, it is disqualified. The craft must also fly in a reasonably straight line toward the goal, and should it be deflected for any reason and go off at a tangent, the flight, no matter how successful otherwise, will not be counted. In case of a collision between air-craft, the race is repeated. The responsibility for adjusting the power, arranging the steering-gear, and giving direction to the flight at the start is entirely in the hands of the young engineer himself.

In measuring the length of the flights, again, the point at which the air-ship first touches the ground is fixed arbitrarily as the end. Often the little craft merely grazes the ground to rise and skid for many feet, but in the official count this secondary flight is not considered. First and last, no one but the owner of the little craft is permitted to touch it. The grace with which the ship lands is also taken into consideration in granting the prizes. Each boy is permitted three trials. As in the regular aviation world, these records rarely stand for more than a few days at a time.

These air-ships are driven by ropes of rubber bands which are turned on themselves until they are tightly knotted, when in unwinding they serve to drive the propeller around some hundreds of times. The rubber is so light that it adds little to the weight of the craft. The motor is of course a makeshift and at best only serves to keep the propeller in motion for a fraction of a minute. Experiments have been made in driving the propeller with compressed air, which is carried in an aluminium rod fastened beneath the planes. But the force of thousands of youthful inventive geniuses is certain to bring forth some new motive power.

It is characteristic of the American boy that our young aviators should feel themselves disgraced to fly a model not of their own make. As a result, miniature craft of amazing ingenuity and workmanship are being turned out by the amateur aviators all over the country. The materials employed, such as rattan, bamboo, or light lath, and the silk for covering the planes, or the wires for bracing the frame, cost but a few pennies. Toy aviation is one of the most democratic of sports.

CHAPTER II

WHY THE AEROPLANE FLIES

THE aviator must venture in his frail craft upon an unknown and uncharted sea. The great problem is to ride the shifting air currents and keep the machine right side up. Although we cannot see the air currents, we know that they are constantly ebbing and flowing, piling themselves in great heaps, or slipping away in giddy vortices. There is much beautiful scenery, high mountain peaks, deep valleys, and level plains formed by these ever shifting air currents through which the aviator must steer his course blindly as best he may. A great bank of whirling clouds driven before the wind shows how rough and tumbling a sea he must navigate.

The air being a much thinner medium than water is, of course, far more unstable and baffling. Its supporting power is not only very small but constantly varies. The flying machine which will navigate successfully in a perfectly quiet atmosphere may be unseaworthy, or rather, unairworthy, when a wind springs up, or the shifting of the wind may spoil all the air pilot’s plans. To add to his troubles, the aviator must move among air currents which change and change again in a moment’s time. As we study the difficulties of air navigation we will appreciate, more than ever, the wonderful patience, skill, and daring of the successful aviators.

The action of the air currents had first to be carefully studied before flight became possible. Although the air is invisible we now know exactly how the air currents act upon the wings or planes. When a plane surface, such as the wing of an aëroplane, moves horizontally through the air, the air is caught for a moment underneath it and is pressed down slightly and a moment later slips out again from under the other edges at the sides and back. It is this air under pressure which yields a slight support.

It has been proven by many experiments that this supporting power varies with the shape of the plane or surface driven horizontally through the air. A long narrow surface driven sideways gains much more support from the air than the same area in the form of a square or any other shape. In other words, a square surface ten feet square containing 100 square feet will not travel as far as a surface twenty feet long and five feet wide.

The explanation is very simple. As the square surface moves along, the air is momentarily compressed under the front edge, but instantly slips off at the back and sides. As the broad surface of the rectangular plane cuts the air, however, few of the air currents can escape at the sides while the most of them are crowded together and held in place until they slip off at the back. The supporting power of the plane is therefore in direct proportion to the length of the front or, as it is called, the entering edge of the plane.

Here we find one of the secrets of the flight of birds. The spread between the tips of their outstretched wings is much greater than the width of the wings themselves. It also explains why the Wright model, for instance, should be so oddly shaped and should move sideways like a crab. If you study the models of the successful monoplanes with this in mind they have a new meaning. The law of the proportion of the entering edge is very important in designing an aëroplane.

It is so important for the air to be confined as long as possible beneath the gliding plane that many devices have been tried to hold it. Some planes are built with a slight edge running around the sides and back, on the under surface, to hem in the air. Some of the biplanes are built with closed sides, the cellular form they are called, to keep the air from slipping away. The box kite is constructed with this in view. The builder of model aëroplanes will find, however, that the slight edge formed by turning the cloth over the frame of the plane is sufficient to hold the air.

The flight of a kite, by the way, appears a very simple matter once this law is understood. The air currents strike the kite at an angle and are deflected or carrom off at exactly the same angle. A line drawn through the middle of this angle, exactly bisecting it, will give you the direction of the force exerted by the wind. Meanwhile the kite string holds the plane rigidly in position. As the kite darts from side to side it is merely obeying this law and adjusting itself so that its surface will stand at right angles to this thrust of the wind. An aëroplane is simply a kite which makes its own wind or air currents.

The kite is, of course, balanced against the wind currents and kept more or less stable by its cord, but an aëroplane must balance itself. The secret of insuring stability was discovered only after years of experience with gliders in actual flights.

The stability of the aëroplane depends upon the proper adjustment of the pressure of the air on the machine. There is, of course, a center of pressure, just as there is a center of gravity in every aëroplane of whatever form or size. It may be laid down as a general rule that a plane traveling horizontally in a quiet atmosphere is kept horizontal and stable by making the centers of pressure and gravity coincide.

The air currents, as we pointed out, are never entirely at rest but are constantly tilting the plane about. Hold a sheet of stiff paper horizontally and let it fall. It will flutter to the ground or perhaps be twirled away, indicating the presence of a number of unexpected air currents. The aëroplane which would remain stable in a perfectly quiet atmosphere must overcome all these twists and turns. The problem of stability has not yet of course been solved. Having reached this stage in the evolution of the aëroplane the aviator next began to experiment by bending his wings or planes and throwing out lateral or stability planes to help him keep his balance.

It was now found that a very little tilting of the planes upward or downward would serve to right the machine when it leaned over. The secret, like so many others, was gained by watching the flights of birds. You have perhaps seen a great albatross or sea gull soar without the slightest effort and apparently without motion. Look more closely and you will see that the tips of the broad wings move slightly from time to time, while the main body of the wings remains rigid, which is the great secret of stability in flight.

The ends of the planes were next made flexible, very slightly so, and arranged so that they might be moved up and down or flexed at will. The flights made with this adjustment were at once brought under control. New planes were added before and behind, and it was found that the machine could be kept from darting up and down just as well as tilting over at the ends. The aëroplane was now ready for the installation of the motor.

The best curve for the wing of an aëroplane is an irregular curve drawn above the horizontal line. It is not a perfect arc of a circle but reaches its greatest height about one third back of the front edge, with the rest of the line slightly flattened. It is much the same line as is formed by some waves just before they break. The plane thus shaped is driven with the blunt or entering edge forward or against the wind. In building the large aëroplanes this curve is worked out with great accuracy, but the builder of model airships may carry the line in his eye.

As the air strikes the entering edge of this surface it is driven underneath and held there for a moment before it can escape from beneath this hollow. The support of the air is therefore greater than in the case of a flat plane, or in fact, any other form. The air which passes over the top of the entering edge, meanwhile, glides or slips off at a slight upward angle, thus forming a partial vacuum over the greater part of the upper surface. This vacuum, in turn, tends to pull the plane slightly upward thus acting in the same direction as the air which is compressed beneath it.

The planes thus constructed are, besides, much more easily controlled than those of any other shape. When the entering edge of this plane is raised the pressure of the air beneath is increased and the pull of the partial vacuum combines with it to make it rise. The difficult problem of getting the aëroplane aloft was largely solved by this curve. Once aloft, such an airship answers her helm much better than any other form.

This curve is accountable for many of the movements of aëroplanes which seem so mysterious to the mere layman. When an aëroplane turns, its outer end rises, and the more rapid is its flight the greater is this tilt. It must be remembered that the end is moving more rapidly and the increased speed causes the plane to lift. Many photographs of aëroplanes show them balanced at precarious angles while making a turn. If the plane is tilted too high the air currents slip out from beneath, no vacuum is developed above, and it quickly loses speed. On the other hand, if it be inclined downward it soon loses the supporting power of the air and plunges down.

The First Glider Weighted at the Front.

At every stage of this development the aviators are indebted to the birds for information. The successful aëroplanes have great width compared to their depth, they gain stability by flexing the tips of the wings, and their planes are arched upward and forward exactly as are the wings of a bird. The aviator arranges his center of gravity after the same general model, below the planes and well forward. He places his engine forward, just as the bird has its strongest muscles in the chest, and he builds his frame of hollow tubes like the bones of a bird.

CHAPTER III

HOW TO BUILD A “GLIDER”

THE simplest form of heavier-than-air machine is the stiff card or letter which you may spin across the room. If you give it just the right twirl it will glide on a level for many feet. There are many ways besides of folding a sheet of stiff paper which will convert it into a surprisingly clever little airship. With a little practice these gliders may be made to fly ten or twenty times their own length, which would be a very creditable flight for the best aëroplane models.

There is no better way to begin the construction of a model aëroplane than by study and experiment with these paper ships. The most famous aëronauts of the day, the Wright brothers, Curtiss, Herring, and many others, have spent years working with gliders before attempting to build or fly an aëroplane. It is in this way that they discovered what form of wing would support the greatest weight, whether the passenger should stand up or lie down, how to place the propeller and the rudder, and hundreds of other details which have made possible the actual conquests of the air.

Following in their footsteps, or rather their flights, the amateur aëronaut should first build and fly only gliders or aëroplanes without means of self-propulsion. The simplest form of glider may be made by cutting a broad oval from a sheet of stiff letter-paper and creasing it down the middle. The experiment may be made more interesting, however, by cutting out the plane like the outstretched wings of a bird, as suggested in the accompanying illustration. Try as you may, this sheet will not fly. Now add a trifling weight to the front of the plane. This may be done by fastening one or more paper clips to the edge, pasting a match or a toothpick, or by dropping a little tallow or sealing-wax.

At first you will underestimate the weight your little airship will carry. Add more weight in the same way, and test its gliding powers until the little airship will glide gracefully across the floor. Keep the length of these models under six inches. If you increase it beyond this, the model loses steadiness and flutters about ineffectively.

An interesting model may be made by folding a sheet of stiff paper in an arrow-like form. The idea is to form a series of planes which will support the weight of the tiny craft and, at the same time, enable it to fly or dart in a straight line. It will be found that the vertical surfaces lend stability and keep the ship moving in a straight line. You will soon learn, in this way, more of the principles of aëroplane construction than mere reading from books can teach you. Be careful, meanwhile, to remember just how you have launched the various forms of models, whether you have thrown them with an upward or downward motion, and how hard a push you have given them. The skill you acquire in this way will be valuable later on when you come to launch your regular model aëroplane.

Dowel Strips of Different Sizes.

We are now ready to begin the construction of the frames of aëroplane models. The first model will be merely a glider. The frame and wings or planes of an aëroplane are built much the same as a kite. The idea in all such work is to combine the greatest possible strength or stability with extreme lightness. Remember, however, that the aëroplane during its flights is racked and shaken by its motor, and is likely to land with a bump. The materials used must be stronger than in the case of an ordinary kite, the joints more securely formed, and the entire structure braced in every possible way.

The best materials for constructing these gliders or aëroplanes are very cheap and easily obtained. At almost any hardware-store you will find a variety of “dowel-sticks,” which seem especially made for this work. They are smooth, round sticks a yard in length and of a variety of diameter. The sticks three sixteenths of an inch in diameter will be found most serviceable, while the larger sticks are just the thing for the backbones of your aëroplane. These sticks will not split at the ends and may be readily worked. They cost one cent apiece.

Some boys find that the reed or cane suits their purpose better than the dowel-sticks, since it is more flexible and a trifle lighter. The cane is easy to work when you wish to build planes with curved lines. It can be readily shaped to any desired form by first wetting it and allowing it to dry after working. Care must be taken in using it, since the ends are likely to split. Bundles of this cane may be bought at most hardware-stores or in department-stores. Enough material for constructing a model may be bought for a few cents.

The lightest of all available materials is bamboo. It is difficult to procure, however, and requires more working up than the others. The best plan is to buy a stick of bamboo, a dry piece, and split it into strips of the desired length and thickness. The grain is so straight that there is practically no waste material as in ordinary wood. The strips may be readily planed or sandpapered. The wood is extremely light and strong enough for all practical purposes of the model aëroplane builder. An old bamboo fishing-pole may answer your purpose.

The first gliders constructed should be of the monoplane form, that is, with a single surface. The biplane or multiplane models will come later. Meanwhile, one is not losing time in working only on these simple models, for the experience is valuable and nothing is lost, since when the frame is properly constructed the motor and propeller may be added. The work throughout is extremely simple, and there are no problems of which the average ingenious American boy need be afraid.

DIAGRAM FOR PLAN OF THE AËROPLANE ON PAGE 58.
DIAGRAM—SHOWN IN PERSPECTIVE.
Plate A.

To construct the model shown in Plate A first make two frames of dowel-sticks, bamboo, or reed, or, if these be lacking, of light lath, the smaller frame 8½ by 19½ and the larger one 10½ by 36½ inches. Care must be taken to have the sides of the rectangle exactly the same length and the joints closely and neatly finished. Some boys prefer to lay one stick over another, then wrap the joint tightly with thin but strong linen thread, and over this brush a coat of thin glue, without using any brads or nails.

In kite-building, to be sure, it would be enough to lay the strips over one another and fasten roughly with a tack. Nor did the lengths of the stick, when covered with paper, make much if any difference. The aëroplane, it must be remembered, travels edgewise, and, having no guiding string, is at the mercy of every gust of wind. If the frames are carelessly proportioned it will not travel true, but is likely to be deflected. Imagine a boat whose sides are not exactly uniform trying to travel in a straight line. It would be lopsided, and would roll and pitch under the most favorable conditions. Now an aëroplane, since it travels in so thin a medium as air, is far more sensitive than a boat, and it becomes lopsided if its proportions be in the least inaccurate. Only the greatest care in construction will produce an air craft which will fly true and straight.

It makes little or no difference in a kite if the ends project a little and the joints be carelessly made. Not only must your aëroplane be perfectly proportioned, but it must be finished like a piece of fine furniture. The question of friction is a very important one in the heavier-than-air machine. You cannot be too careful to round off every corner and smooth every exposed surface. If you have opportunity to see a regular aëroplane, a Wright or Curtiss model, you will find that every part of the machine has been sandpapered and varnished with the greatest care. This is not done for the sake of appearances, but because it has been found that the wind striking against the rough piece of wood meets an appreciable amount of resistance, whereas it slips past a polished surface with little or no friction. Your aëroplane should be finished like a violin.

A Coil of Cane or Reed.

In building these planes be careful to compare the lengths of the corresponding sides throughout. If you prefer to use brads for fastening the joints do so. The dowel-stick and bamboo will take the brads with little danger of splitting. When thoroughly dry, cut away the glue which has squeezed out, round off the ends, and sandpaper with fine sand or emery-paper. If you use brads it will not be necessary to place the joints in a vise while drying. Should your strips split, bore the holes with a fine awl. Some boys after drilling the holes merely tie and glue the sticks together, using no nails whatever.

Now cut three dowel-strips 34 inches long and slightly sharpen their ends, so that when brought together they will form a prism whose base is about one fourth their length. Next bend a strong piece of wire into a hook—a hair-pin will answer for small models—and fasten it in the apex of the prism, with the hook inside. The projecting end of wire should then be bent over, and the three dowel-sticks glued and tied tightly together.

At the open end of the prism next fasten two strips from end to end, leaving the third side of the triangle open. Now fasten your two planes on the open side of the prism, slightly mortising the sticks and gluing and nailing them securely in position. To further strengthen the prism, join the three sides at the middle with three sticks, forming a complete triangle. The prism thus braced will be found as strong as a heavy central stick, besides being much lighter and providing an excellent base for the propeller. A strong stick about half an inch square should be tied and glued across the middle of the triangle at the base of the prism to support the motor.

The frame once complete, sandpapered and varnished, it is ready to be covered. At first this may be done with some smooth paper. Almost any thin material, muslin or linen, will answer for the purpose, although white silk makes the most finished-looking model. Such scraps as may be found in the family piece-bag will answer every purpose. In sewing the cloth over the frame the advice of some big sister, aunt, or the mother may well be taken. The idea is to fasten the cloth smoothly and neatly over the frame, keeping the surface free from creases or wrinkles of any kind. Boys are likely to be awkward with the needle. The cloth may also be glued over the frames. When complete cover the planes with a thin solution of paraffin dissolved in benzine.

In attaching the planes or wings to the central axis of the model, the larger stick or backbone may be mortised neatly, so that the sides of the frame will be sunk in flush with the upper surface. A fairly good glider may be made, however, by merely nailing down the frames against this backbone. The distance between the two planes is a complicated problem, but the beginner had better at first imitate the model shown in the accompanying illustration. If the two supporting planes be too far apart or too near together, the glider will fall. The amateur must experiment by changing their position on the central axis until he hits the right proportion. He will be able later to carry this proportion in his eye, and the experience will prove invaluable. Until you have hit upon the proper position, fasten them to the backbone with rubber bands. These permit you to slide the planes back and forth without the trouble of nailing.

Aëroplanes, unlike kites, fly best in a perfectly quiet atmosphere. If you make your trial flights out of doors, select a quiet day. A room, a barn, or any large interior will be found better. In launching your glider, hold it from beneath, so that it balances, and throw it forward with a swift, steady movement of the arm. A little practice will make you very expert.

Splitting a Bamboo Fish-Pole.

You will now find yourself fitted to reproduce any of the simpler forms of monoplane models, several of which are here illustrated. An interesting model is made by attaching U-shaped wings to a central axis. In making these curved planes the reed will be found useful. Other effective gliders are made with triangular wings fixed at a variety of angles. Remember that the model must be absolutely symmetrical. In attaching the frames to the central axis, always make the joints as smooth and rigid as possible.

The weighting of the glider will be found to be a very important detail. As a rule the gliders require a considerable weight at the front. The exact position of the weight can only be determined by experiment. The simplest way is to wire a nail or a piece of metal to the edge of the frame. If your glider does not balance perfectly, which is likely to be the case, this fault can be largely remedied by weighting it. The tendency of the glider is likely to be upward, and the weight serves to keep it on an even keel. When your model glides steadily through the air, without rolling or pitching, you have constructed a well-balanced frame. It will then be time to take up the problem of propulsion.

CHAPTER IV

BUILDING THE MOTOR

A WELL-CONSTRUCTED glider alone makes a fascinating toy, but once the motor has been installed it seems almost alive. Your little craft will now be ready for new conquests. It will imitate the flights of the famous aviators, contending with the same problems, perhaps meeting similar accidents.

The motor is the most interesting, as it is the most important, detail of the aëroplane. Although it is possible to buy the propellers for the motor, it is advisable that every boy should work out this problem for himself. An effective motor is easy to build, and costs practically nothing. The length of your propeller-blades should be equal to about one third the width of your largest plane. For this you will need six strips of some light wood, such as pine or ash, although a cigar-box wood, if the grain be straight, will answer. Cut the strips to measure about half an inch in width and one eighth of an inch thick. (See Plate B.)

THE PROPELLER BEFORE CUTTING DOWN.
Plate B.

The strips should be covered with a thin glue and laid one on top of another, and a very thin nail be carefully driven through the little pile at the exact center between the two ends. While the glue is still soft, turn the sticks on the axis formed by the nail, so that they make a double fan, spacing the outer edges about one quarter of an inch apart. Be certain that the fan is regular, and then give the nail a final rap to tighten its hold and keep all the glued surfaces together, and set away to dry. If you can prop up the ends it will be better to put a flat-iron or other weight on each end to make the strips glue together tighter.

The thrust or propelling power depends as much upon the curves of the propeller as upon the force with which the motor is driven. If the propeller be too flat, it will not take hold of the air, while if the pitch or angle of the curve be too sharp, it will simply bore holes in the air and create a vacuum which is useless. The pitch should be about one in twelve; that is, if the propeller-blade be twelve inches long, the curve should be one inch high.

When the glue is thoroughly dry and hard the projecting step-like edges may be cut away. A flat chisel or an ordinary pen-knife will do the work. Be careful to keep the ends uniform, since much depends upon the balance. Cut away the wood until the blades are one eighth of an inch or less in thickness, and round off the corners. The propeller should then be sandpapered perfectly smooth and varnished. You will be delighted to find how professional and shipshape the finished propeller will be.

Now carefully remove the nail fastening the pieces, and you will find, of course, that it marks the exact center and forms a perfect axis. Should you need to enlarge this hole, do not attempt to bore it, since this may split the wood, but burn it out, using a nail heated over a gas-flame. Now insert a stiff wire in this hole—a hat-pin will answer—and fasten it by clenching it at the back tight to the propeller, and fill up the hole with glue. The photographs of the propellers of various models will give you an excellent idea of the proper curve.

Aviators differ as to the proper position for the propellers in toy aëroplanes. Here is a problem you must work out for yourself. Some believe that the propeller placed in front of the planes gets a firmer grip on the air, since when the propeller is at the stern the planes make many disturbing currents, just as a steamship churns the water in its wake. Others argue that by placing this propelling force at the rear of the planes the craft is made more steady. At any rate, excellent flights may be made with either arrangement.

In connecting up your propeller with the motor it is very important that the shaft should turn freely and that the bearings offer the least possible resistance. If you have built your aëroplane from the drawing (see [Plate A]), now drill a hole exactly in the center of the stick which crosses the triangle at the rear of the frame. This hole will come on a line with the apex of the prism, or exactly in the center of the triangle. When the turning of the motor pulls the ends of the frame together, the strain will therefore be exactly distributed among the three sides or braces.

The propeller must be kept clear of the frame and must never touch or scrape against it. First a thin strip of metal, drilled to take the axle or hat-pin, should be nailed over the hole in the crosspiece. A sheet of aluminium such as is used for name-plates is just the thing. Now on the propeller-wire or axis string a smooth, symmetrical glass bead, and pass the axle through the metal strip and the crosspiece. This will give you an excellent substitute for ball-bearings. The end of the wire should then be turned into a hook well inside the frame. The propeller should be mounted so carefully that it will turn freely without friction and without wabbling from side to side.

The simplest and most effective motor is formed by connecting the two hooks with many turns of a long, thin strand of rubber, which can be bought by the yard or pound. The thinner strands of rubber will exert more force than the heavy bands, and red rubber is more durable than any other. The bands should be looped loosely between the two hooks, just as you would wind a skein of zephyr—over the hook on the propeller-“shaft,” then around the hook at the other end, then down over the propeller-shaft hook, and so on. If the hooks be three feet apart the combined strands should form a band one inch or more in diameter. If you cannot buy the rubber in this form, a number of two-inch rubber bands, such as you buy by the box at the stationer’s, may be lopped chain fashion together to form a continuous rope from hook to hook.

To store up energy for the flight, simply turn your propeller round and round until the rope of rubber bands is tightly knotted. You can readily tell when it is sufficiently wound and the danger-point is reached, which comes when the pull of the rubber grows too strong for your frame. The average motor should be turned about one hundred and fifty times. When the propeller is released the rubber bands in unwinding will give you back almost exactly the same number of revolutions, less perhaps one or two, which represents the loss through friction.

Model Constructed from Diagram, Plate A.

If the propeller simply buzzes around, coming to rest in a few seconds, without raising your aëroplane, it is probably too small for the weight of the aëroplane. When fully wound up the propeller should run for about ten seconds. On the other hand, if the propeller be too large, it will quickly twist the aëroplane out of its course and drive it to earth. It is well to try out your motor thoroughly to make sure of its running smoothly before attempting any actual flights.

Do not yield to the temptation of trying your wings, however, until the skids have been attached. Most of the regular full-size aëroplanes run on ordinary bicycle wheels, although the Wrights use runners like a sleigh. These skids or runners enable the machine to run along the ground with the least possible friction and greatly assist in rising. In the models of aëroplanes the skids serve a double purpose in protecting the machine when it alights.

A serviceable skid may be made by building a triangle of thin strips and attaching it to the frame with the broad side downward, as shown in the accompanying drawing. Skids made of reed curving down from the main body of the aëroplane will also serve to take up the shock. There are many ways of constructing these skids, and a study of the models here illustrated will give many suggestions. If you intend to have your aëroplane start from the ground, the front skids should be somewhat longer than those in the rear to give it the proper lift.

The friction of the skids is greatly reduced by mounting them on wheels. Small metal wheels may be borrowed from toy automobiles, or small disks of wood or cork will answer for the purpose. A very simple axis may be formed by running a long hat-pin through the uprights of the skids. The photographs of the best models will be found full of suggestions. You will need at least three skids to form a tripod for your aëroplane. It makes little difference if you use one leg in front, or two.

It is very important that the frame should be properly braced to withstand the strain brought upon it. In the glider this bracing is less important, but the action of the motor changes the situation. The rapid movement of the propellers wracks the entire frame, and the impact on landing is naturally greater when the weight is increased. A thin copper wire, No. 32, 34, or 36, should be used, which will be found strong and flexible, while adding little to the weight. After constructing your aëroplane go over it carefully and cut away the wood wherever it may be lightened, and then strengthen it by bracing. Wherever a joint may be strengthened or a strut or a plane be made more rigid by bracing, do not spare the wire.

The accompanying drawing, with the photographs of models, will indicate how these braces may best be applied. To begin with, braces should be run, wherever possible, from the corners of the planes to the central frame and the skids. In the monoplane forms you will find it worth while to add posts or perpendiculars to the upper side of the frame and run wire braces diagonally to the ends of the planes. The extreme ends of the planes should also be connected.

Splitting the Cigar Box Cover to Build the Propeller.

No matter how carefully you have constructed your aëroplane, you will find the planes have a tendency to sag and become wrinkled. These braces give you the opportunity to pull them taut and hold them in this position. This is commonly called “tuning up” the aëroplane. It will be found convenient to fasten small rings to the ends of the braces whenever they may be slipped over the ends of the frame to save the trouble of winding. The more perfectly your aëroplane is tuned up, the greater will be its speed and distance qualities.

THE DIAGRAM OF A MONOPLANE.
Planes measure 20 inches by 8 inches. The motor base is 36 inches in length.
Plate C.

An excellent monoplane for the beginner is shown in drawing. (Plate C.) It is very simple and easily adjusted, and when well tuned up will fly upward of two hundred feet. The two planes are built separately in the proportion indicated. The frame consists of a central stick supported by triangular skids. An ordinary hat-pin run through the supports near the ground serves as an axle for wooden disks or wheels. The front skids are made somewhat higher to give the front planes the proper angle of elevation.

The bracing of the planes is simple but effective, and should be copied carefully, particularly the double bracing in the rear, using ordinary wire for the purpose. A double support is used for the axle of the propeller, an excellent idea, which keeps the shaft rigidly in place. It is formed by fastening two blocks drilled to hold the axle to the bottom of the main frame. The planes are held taut by wires running from the corners to a post at the middle of the plane. The front plane is hinged at its rear edge, and may be tilted by pulling back a piece of whalebone fastened at its center, which is tacked to the top of the frame. The rudder turns on a triangular frame attached to the top of the rear plane. A string passes through the rear end of the rudder to the rear edge of the plane, forming a triangle, which makes it possible to adjust the rudder-plane and fix it rigidly in position.

After you have built one or two models you will find yourself confronted by a bewildering number of schemes for constructing new forms. It will be found a very simple matter to use stiff wire for many parts of your model instead of wood or reed. In building rounded planes the wire will be a convenience. The wire may be attached to the wooden frame by embedding it in the wood and binding it fast. And, by the way, you can get a surprising effect by painting your wooden frame with silver paint, as the Wrights do. To all appearance you will have an aluminium frame.

An aëroplane to be considered shipshape must be even more perfect in every detail than the finest racing yacht. Go over your model, scrutinize every detail; if after taking every precaution, your planes do not fit like the sails of a racing yacht, cover them with a thin solution of paraffin. On hardening, this will hold the material perfectly smooth, so that the planes will offer a perfect lifting surface.

The amateur aëronaut must be prepared for disappointments. An aëroplane is one of the crankiest crafts in the world to manage. It may twist and turn, plunge in and out, up and down, apparently without the least excuse. There is always, however, a good reason somewhere for its behavior. As you learn its ways, which, after all, are very simple, the flights will be longer, swiftier, and steadier. There is no toy in the world which so quickly repays one for patience and perseverance.

CHAPTER V

FINE POINTS OF CONSTRUCTION

A GREAT many experiments have been made to find whether the flat or curved wings give the best support, and how sharply the curve should be drawn. The wings of birds are curved slightly upward, and in the end, after all the experiments, it has been found that this curve is just the right one. All forms of aëroplanes will fly more swiftly and steadily if the planes be slightly bowed or flexed. After you have built your aëroplane with flat wings it will repay you to replace them with flexed planes, and you will find that the experience in building models will make this construction very simple.

The lighter and more flexible materials, such as bamboo or cane, are best for the curved planes. After you have decided upon the dimensions of the wings cut the pieces for the ends slightly longer than the width of your planes. These pieces may then be bent by steaming them over a kettle of boiling water and bending to the desired curve. When dry they will hold their shape remarkably well. Another plan is to use a flexible strip and pull the ends together by a strong thread or wire until the wood is bowed to just the right curve. A corset steel or whalebone may readily be curved in the same way. It is a common mistake to curve the plane too sharply, when the resistance offered to the air will be greater than that with the flat plane.

A plane two or three feet in width cannot be held in shape merely by curving the end pieces. A series of ribs must be added at equal distances, each having, of course, exactly the same upward curve. The ribs may be fastened to the sides of the planes with small brads or simply with glue or wire. The covering should then be drawn down. A very smooth covering may be made of rice-paper. Cut the sheets the proper size and lay them for a few minutes between moistened cloths. Now stretch the paper carefully over the frame and glue in position. When dry the paper will contract and leave a smooth, taut surface like the head of a drum.

Much depends upon the curve of the plane. A wing whose curve is not a perfect arc of a circle, but which is rounded just back of the front edge and flattened at the rear, will be found to offer the least resistance to the air. The best plan is to study the curves in the aëroplanes or models and imitate them. Different models require different planes. It is a problem which each young aëronaut must work out for himself.

A Model Aëroplane Built from the Drawing ([Plate C], Chap. IV).

The question of rudders or guiding planes is very important. It is too much to expect of even the best model that it will fly in an unswerving line. Any simple vertical plane which may be turned from side to side and held in position will act as a rudder. There is great difference of opinion as to the proper size and position of these guiding surfaces. It is argued by some aviators that the rudder should be placed above the plane, where the air is undisturbed, while others believe that the partial vacuum created above the wings in flight makes the propeller ineffective. Still others argue that a rudder placed back of the planes affords a leverage, and is therefore more effective. Try a rudder in each position. It is impossible to lay down a law for all models.

The larger models should be equipped with twin propellers. In building these the greatest care should be taken to have them exactly the same size, weight, and pitch. Twin propellers should, as a rule, be placed at the front of the machine, that is, they should pull and not push the planes. If by any accident the motor of one should fail, the second propeller will continue to keep the aëroplane afloat and break its fall on descending. With the propellers at the stern of the little airship, the failure of one would cause the plane to pitch downward, and the remaining propeller would drive it down to possible disaster.

In winding up the two motors, care should be taken to give both the same number of turns. The aëroplane may be launched by holding a propeller in either hand and releasing simultaneously. The double motor insures a steadier as well as a longer flight. Always turn the propellers in opposite directions. In flying they must spin around either toward each other or away from each other. If they turn the same way they will give the model a torque which no rudder could possibly overcome.

The efficiency of your motor depends more upon its length than its diameter. In constructing the motor-base, especially for the larger models, arrange to have the strands of rubber bands extend the entire length of your aëroplane, and if necessary, project well forward of the front plane. Such a motor in unwinding will exert a more sustained force. The shorter strands of greater diameter will unwind much more quickly and give very short flights.

With a little experience you will soon learn to gauge your motor to the needs of your air-ship. It is, of course, absolutely necessary that the force exerted by the motor should be sufficient to keep your aëroplane in rapid motion, but it is easy to make it too powerful. If it were possible to attach a “governor” to your motor, this would not matter so much. But since this is practically out of the question, the motor itself must be very nicely proportioned to the demand made upon it. You will soon be able to judge between the steady whir of a good motor, and the buzz of a propeller which races. There is a distinct note for each.

The motor is, at present, the great problem of the model aëroplane. The rubber bands are, at best, only a make-shift. It is practically out of the question to get a flight of more than fifteen seconds in this way, so that the distance is limited to a little more than two hundred feet. It is doubtless only a question of time before a much more efficient form of motor will be invented. Very probably, some amateur aviator will be the first to apply a new means of propulsion, which would be an important achievement indeed.

The simplest form of motor after the rubber bands would seem to be some form of metal spring which could be wound up. Long before the days of automobiles, as we now know them, wagons were built with motors of springs, and some surprising runs were obtained. The spring lends itself to many forms of construction, and is not expensive. It will be necessary to control its action in some way, however, to prevent it from racing and running down in almost no time, like the too heavy rubber motors. It might be found interesting to experiment with the spring to be found in the ordinary roller-shade. The weight of these springs is not too great to be carried by a good aëroplane model, which, of course, is a great factor in their favor.

Detail of Rudder and Propeller of Model Built from Drawing ([Plate C]).

A number of experiments have been made in France to equip aëroplane models with compressed-air motors. The compressed air is carried in a hollow tube in much the same position as the rubber bands. Many believe that the motor problem, for the toy aëroplane will be solved in this way. A number of interesting models have also been equipped with clock-work motors. A small movement, such as may be borrowed from some mechanical toys, will run for a minute or more. What glorious flights would be possible if our models could be kept aloft—say five times as long as at present. When you feel that you thoroughly understand your model, borrow the clock work from some old toy and make the experiment. It is possible to buy motors for model aëroplanes. The smallest of these develops one half horsepower, weighs seven pounds and will run for fifteen minutes.

The best covering for the wings still remains largely an open question. Although your model will make successful flights with almost any kind of covering, you will find that its stability will be increased and the flight lengthened by a little attention to this detail. According to the Wright Brothers, the most successful covering is the one which offers the greatest resistance to the air. The pressure of the air upward under the planes tends to force its way through the meshes of even the finest cloth. The addition of a coat of varnish will prevent this leakage. A light parchment will also be found effective. It will be well to experiment with a variety of coverings.

A very light, serviceable frame may be made for your motor-base by using hollow shafts or sticks. Procure a very thin, light wood, such as is used for veneering, and after cutting it carefully into strips, glue them together to form a hollow shaft about an inch square. Although the shell may be only one sixteenth of an inch thick, the frame will be found strong enough for all practical purposes. A hollow frame of this kind will save several ounces of weight.

The builder of aëroplane models will find a good friend in aluminium. It is strong enough for all purposes of the model air-ship and, even when used freely, adds almost nothing to the weight. The metal costs ninety cents a pound, but it is so light that, at this rate, it will be found a very cheap material. Comparatively thick pieces may be used for braces or for angles, thus making the frame absolutely rigid, while adding but a fraction of an ounce to the weight. The metal, being comparatively soft, is easily worked, and simple castings may be made at little expense.

Many builders of aëroplanes waste time and ingenuity quite unnecessarily in constructing sets of wheels for carrying their models. The time would be better employed in looking to your planes. The amount of friction saved by attaching wheels, even good ones, to your model, is after all very trifling. Should the wheels jam or stick, which is likely to be the case with such small models, they are worse than skids, and besides, add appreciably to the weight. A light skid is better than a clumsy wheel. If your model fails to rise from the ground, the fault is not at all likely to be in the skids, but in the thrust or lifting-surface.

An excellent plan for guiding the flights is to add square frames of soft lead wire to the front or cutting-edge of your front planes. Bend a piece of wire to form three sides of a square, each two or three inches long, and fasten the loose ends to the plane. By bending these up or down, the center of gravity may be altered at a touch. If your model goes askew, you may bend one of these up and the other down, until you get the desired balance.

In actual practice, the soaring- or floating-planes seem to add greater stability to the model and effect to a marked degree the length of the flight. It is difficult to tell exactly why. The planes in passing may create an eddy in the air, a following wave, as it were, which tends to retard the flight, while the floating-plane smoothes this out. In any event, here is an experiment well worth trying.

CHAPTER VI

SIMPLE MONOPLANE MODELS

OF the variety of aëroplanes, there seems to be no end. Nature offers a bewildering variety of models in the innumerable birds and insects, which may be accepted as successful monoplanes. These, in turn, may be copied and modified indefinitely. The science of aviation is still so young that there is ample opportunity for invention and discovery for all, and every new trial adds something to our information, and carries the science a step nearer perfection.

It will be found an excellent plan to build, once and for all, a strong well proportioned motor base, and mount a powerful motor and well modeled propeller. A variety of planes may then be tested out by attaching them to this. The motor base will answer for practically all monoplane forms and many biplane models as well. Such a frame should be about three feet in length and carry one or better two motors, placed side by side.

There is as much danger in providing too much lifting-surface in your aëroplane as too little. This fault is well illustrated in an exceedingly clever French model ([Plate I]). Although the model is well constructed, and appears ship-shape at first glance, it nevertheless has far too much surface and will not fly well. If the depth of the wings were reduced fully one half, it would have a much better chance.

The best lifting-planes are those which present a broad front or entering edge, but with comparatively little depth. The successful flying-machines, whether monoplanes or biplanes, use these very wide but shallow planes forward. The theory is of course that the air is caught for an instant beneath the plane and before it has a chance to slip off the sides, the wing has caught its very slight supporting power and moved on to new and undisturbed air.

With this rule in mind examine the model’s front plane once more. It will be seen that, as the air is caught under this broad surface, it will try to escape in all directions and set up currents of air. Instantly the broad plane loses its balance and tilts to one side or the other. No weighting of the plane can overcome this. If the plane were forced through the air at a very high speed a steady flight might be possible, but it is useless to try to overcome this tendency to tip and wabble.

The planes again are badly designed. A perfectly straight front or entering edge gives the best results. A certain stability is gained by curving the front plane slightly, this will be discussed later, but there is no excuse for the semicircle described in this case. Every inch of surface cut away from the front edge of the plane directly reduces its lifting power. The arrow like form of the rear plane does not matter because this is a stability plane, not a lifting plane. In this case the rear plane is twice the size it should be.

PLATE I. A Clever Folding Model. The Wings Are Broader than Need Be.

The propeller of this model is much too small, even if the size of the planes was correct. It is well placed however at the front of the model where it may turn in undisturbed air. The passage of these large planes, or any planes for that matter, is likely to cut up the air just as a ship churns the water into a wake behind it and the propeller does not work effectively in these eddies. The motor seems powerful and well braced, although it might be made even longer by carrying it to the extreme rear.

Several very useful ideas may be borrowed from the construction of the frame of this model. It is made entirely of metal, so jointed that it may be folded up into very compact form like an umbrella. The amateur model builder should not attempt anything so complicated, but an old umbrella frame may be used with good results in building a rigid frame. Use the steel rod of the umbrella as a backbone, and cut away the ribs you do not need. The others may be bent into various shapes to form the front or sides of the planes, the skids or braces. Such a construction is light and perfectly rigid.

A very effective monoplane may be made by curving the front and rear edges of the forward plane, while keeping the rear or stability plane rectangular in shape ([Plate 2]). The curve of this model may be imitated to advantage, as well as the general proportions. Such a plane is less likely to be deflected by air currents than a straight entering-edge and insures longer and steadier flights. Should you be troubled by your model twisting from side to side in flight try curving the front edge of the forward plane.

This model is one of the easiest to make and is an excellent one for beginners. Build the two planes separately making the larger one about thirty inches in width and ten inches in depth, and the second one fifteen inches in width and ten inches in depth. The curved sticks may be worked up by using bamboo or dowel-sticks, soaking them in water and fastening them in a bowed position while damp and leaving them to dry. It may be found a good plan to use a heavier stick for the rear edge of the plane to gain stability.

A single stick about one half an inch in diameter may be used for the backbone. It will be found an excellent plan to attach the planes lightly to the main frame so that they may be adjusted before fixing them finally in position. Place them in the position shown in the accompanying photograph, and move them up and down until the flights are all that you expect, when they may be fastened for good and all. The bracing of this model is excellent and may be safely imitated. It enables one to tune up either plane and fix them rigidly in position. The propeller is very properly placed forward although it appears to be rather small. It is unnecessary to bother with any vertical rudder for this model since the curve of the front plane insures a reasonably straight flight.

A popular French model which may be easily imitated consists of curved planes both front and rear ([Plate 3]). The curve of the planes is too complicated to be carried out in wood, but may be readily formed by bending a stiff wire to the desired shape. The front plane should be about twelve inches in width and four inches in depth. The rear should be about half this size and of the same form. The planes may be readily mounted on a small dowel stick. A small propeller and a motor a foot in length will answer. A small semi-circular fin should be set below the rear plane to act as rudder. First cover the frames with a stiff paper and after you have succeeded in adjusting it, this may be replaced by cloth. The model will not fly far, or very steadily, but it is interesting to practice with. The balance of the model is open to criticism; for the center of gravity appears to be too far forward.

PLATE II.

A Model Aëroplane Worth Imitating.

The simplest of all models to build, and not the least interesting, is the small paper monoplane ([Plate 4]). The planes which are slightly curved are formed of a stiff card which will hold its shape when bent into position. These may be attached to the main stick by inserting an edge into a groove in the stick and glueing in place. It is not well to construct these more than six inches in width over all.

One of the simplest monoplanes to construct is formed of a broad rectangular forward plane with a fan-shaped stability-plane at the rear ([Plate 5]). This is a French model which is said to have flown long distances; that is to say, 300 feet or more. It has several very interesting features. In the first place the combined area of its planes is doubtless greater than that of any other model here described. The vertical rudder which looks very shipshape and effective is very easy to build and the frame illustrates several new principles.

The frame or motor-base may be made of heavy dowel sticks or light lath as indicated in the photograph. It will be found simpler to avoid tapering the frame at the rear by merely constructing a stout rectangular base with a length two and one half times its width. The forward plane is slightly bowed or flexed. It will be found a good plan to construct the frame for the base and then bow a light strip at either end against the edge. By fastening the covering to these curved strips a smooth curved surface may be obtained.

The rear stability-plane may be stretched over a fan-shaped frame of strips or lath which is in turn fastened to the motor-base. Another plan is to attach the front and rear edges of the plane, the rear one being slightly longer, and stretch the covering over these leaving the sides free as in the photograph of the accompanying model. The vertical rudder is very simple, consisting of a piece of dowel stick sunk in the rear frame to which a rectangular piece of cloth is attached the front corner being pulled taut.

The spread of the planes appears to be considerably greater than needs be. Since the front plane is flexed it may be reduced one third or even one half in depth without reducing its lifting quality; although in this case it should be placed nearer the stability plane. This reduction would, of course, make an important saving in the weight of the craft. So large a model calls for two propellers which will prove more effective at the front rather than the rear of the machine. It might be well to carry the motors further back than has been done in this model thus gaining additional power.

Since the model is expected to rise unaided from the ground the question of the skids is very important. The design followed in the model is excellent. The front of the frame is supported by legs consisting of inverted triangles built of dowel sticks attached to the frame. The axle connecting the two runs on small wheels, such as may be borrowed from a toy automobile. The rear of the frame rests on a simple skid made of curved reed. These supports place the model at an angle which should enable it to rise easily without loss of power. There is a great deal of satisfaction in working on so large a model, the parts may be made stronger and there is less likelihood of its getting out of order.

Now turn from these broad planes to the rather slight model ([Plate 6]), and the faults of its proportion are at once obvious. The front plane is much too far back for stability. Such a model will glide fairly well, and, if the motor be powerful it will rise quickly, but a steady horizontal flight is out of the question. The size of the planes seems perilously small, and yet if they be well shaped and spaced they will prove large enough. This is just the sort of model a beginner is likely to make, and therefore serves a very useful purpose in pointing a lesson.

PLATE III.

An Ingenious French Model Made of Umbrella Wire.

It is not without its good points. The front plane has been carefully flexed and attached to the motor frame at a good angle. An interesting experiment has also been made in carrying the edges of the front plane a trifle behind the rear edge, thus making for stability. The vertical rudder above the rear stability-plane is well placed, although it appears rather small. The skids upon which the model rests and the proportion of the front to the rear elevation are excellent. It is a first rate plan in building such a model to attach the front plane temporarily to the motor-base, and move it back and forth in the trial flights until the best spacing has been found.

CHAPTER VII

ELABORATING THE MONOPLANE

IT is surprising to find how far the pure monoplane form has been developed by the builders of model aëroplanes. It is no exaggeration to say that they have carried some principles of construction even further than the builders of the large man-carrying monoplanes. Since a model is so easily built, and costs so little, it is of course possible to experiment with all sorts of new forms. A great many of these will doubtless prove to be all wrong, but some are certain to be valuable discoveries. In future years, when the aëroplane has been perfected and perhaps plays an important part in commerce, sport and warfare it will probably be possible to trace back many of its improvements to the model aëroplanes designed, built and flown by American boys of to-day.

A beautiful model of a pure monoplane form carefully elaborated is shown in [Plate 7]. In this case increased stability is obtained by throwing out additional planes both to the front and rear. It may appear at first glance that these stability-planes are very small compared with the broad soaring-plane, but they have not proved so in flight. It will be remembered that the elevating-plane of the Wright machine is very small compared with the spread of the main wings. There is besides a great advantage in placing the stability plane well forward since it makes it possible to build an unusually long motor-base and install longer and more powerful motors.

The main plane is one of the best examples of construction work to be found among all these models. It is well proportioned and the curve has been skilfully drawn. The plane is made unusually rigid by a series of supports or braces run both horizontally and vertically. Such a plane calls for considerable time and patience, but it will well repay the builder by the long and steady flights it insures for the model. In adding ribs to a large plane of this kind a convenient material may be prepared by splitting up thin wooden plates or dishes, such as you buy at the grocers for a penny. The strips obtained in this way may be easily glued or tied to the edge of the plane and shaped as desired.

A long, straight flight is insured for this model by equipping it with three vertical rudders or guiding-planes. The first rudder is well placed above the front plane. The second performs a good service beneath the main plane, while the third is carried unusually far back behind the propellers. The problem whether a rudder is more effective above or below the planes is very ingeniously solved in this case by placing them in both positions. An interesting principle is involved in placing the rear rudder. By fixing it far behind the center of gravity of the model a considerable leverage is obtained, and a small, light rudder becomes more effective in this position than a much larger plane placed forward. These rudders are built so that they may be easily turned from side to side and fixed rigidly at any angle.

PLATE IV.

One of the Simplest of Aëroplanes to Construct.

Still another interesting feature of this model is the design of the skids. The model is supported at an angle which enables it to rise easily. These skids are besides arranged with shock-absorbers, simply constructed with elastic bands, which enable them to take up the shock on landing and thus protects the machine. This is an interesting field of experiment and a little care in building these skids will save many a smash-up.

It cannot be too often stated, that the supporting power of the planes depends far more upon their shape than their size. A remarkably effective model may be made with planes, which are little more than blades ([Plate 8]). The planes, in this case, are made of white wood, slightly curved. The front or entering edge is very sharp, while, at the rear, a thin strip of shellaced silk is glued, thus forming a good soaring blade. The front plane is a counterpart of the first, except that it is smaller. The only stability plane is a thin, knife-like strip placed vertically just before the rear plane. The model is mounted on skids. It is driven by a small propeller placed far back of the center of gravity. It is probably the easiest as it is the smallest of all models to construct, and will fly for more than three hundred feet.

In building this model it will be found a good plan to bend the strips of wood for the planes by steaming them over a kettle. Allow the steam to play on the under or concave side of the plane. When dry the plane will retain its shape. The front or entering edge should be trimmed away to a sharp line and sand-papered perfectly smooth. The front corners of the planes should be slightly rounded while the rear edges are kept straight. The forward plane should be tilted slightly upward to enable it to rise, but at an angle of less than thirty degrees. The secret of the remarkable flights of this model probably lies in the smoothness of its planes and the absence of irregular parts which offer a resistance to the air.

An interesting field of experiment, as yet almost untouched, lies in the triangular, or narrow-prowed forms of aëroplanes ([Plate 9]). The theory of this model is, that a triangle entering the air end-wise, will meet with less resistance than when presenting a broad, entering edge. The model is, frankly, an experiment, although it has been found to have unexpected stability, and flies well. Its central planes, joined at right angles, is supported by two, lateral, stability-planes, radiating backward from the front of the model. The aëroplane is drawn, not pushed, through the air, by double propellers, and is steered by an angular guiding-plane at the rear. The planes are mounted upon a triangular frame, which runs on wheels, two being set forward and one aft. The planes, taking advantage of the dihedral angle, seem to rest upon the air, which makes for stability. In actual practice, however, the planes in this particular model have been found to be too narrow. The question naturally arises as to the effect of reversing this model and turning the dihedral angle of the central plane, into a tent effect. As a matter of actual experience, the model flies almost equally well upside down.

In many of the early attempts to build aëroplanes the wings or planes were tilted sharply upward from the center thus forming what is known as a dihedral angle. This form served to lower the center of gravity and, it was thought, made for stability. The Wright Brothers found that this plan, although it lowered the center of gravity, caused it to move from side to side like a pendulum, and therefore abandoned it in favor of the flat curved wing which have been so generally imitated. Now this model returns to the old principle of the dihedral model, but treats it in a new way. By building the model with three planes, each with the dihedral angle, the center of gravity has been lowered and, at the same time, the oscillation has been greatly reduced.

PLATE V.

Too Large for Beginners, but Will Make Long Flights.

The narrow-prowed form of this model is also very interesting and its principle may well be copied. All of the successful monoplanes aloft to-day, the Bleriot, Santos Dumont, Antoinette and others are driven with their larger or soaring planes forward and their smaller stability-planes in the rear. The day may come when these machines will be reversed. The model before us may point the way to a great improvement in the building of air-craft. It is an important principle for the builder of model aëroplanes to bear in mind.

In the present state of model aëroplane building, the longest flights are made with an adaptation of the monoplane forms. An excellent model is shown in [Plate 10]. The dihedral, or V shape of the planes gives them greater supporting power than others in the horizontal position. The stability plane beneath is particularly recommended, since it utilizes the frame already in position and does not add to the weight of the model. The rear of this plane, which is hinged, is easily adjusted.

The planes of this model are especially interesting. They are made of silk, laid over frames of dowel sticks, and each pair is held tightly together by the simple device of connecting them with elastic bands, attached to clasps. The wires running to the corners of the planes, are fastened to small brass rings which may be slipped over the sticks or posts in the center of the frame, which makes them very simple to adjust. It will be noticed that the rear part of each plane swings freely, and is kept in place only by corset steels, used as ribs, which are sewn into the cloth. These floating or soaring blades, as they are sometimes called, insure longer flights.

With such a model there is little danger of building a too powerful motor. By increasing the size of the wings, and careful weighting, a surprising amount of power may be applied to such a model without rendering it unstable. This is of course a great advantage in such a model, since it lends itself to longer flights and the installation of comparatively heavy motors. When you find yourself with a model of this design in good working order, experiment by binding the wings or planes at the middle to form an arched surface like the wings of a sea gull. The flying radius of some of these models has been increased fully fifty per cent by this simple expedient.

An interesting modification of this form ([Plate 11]) is provided with rigid wings, and is driven by a single propeller. The very simple but effective method of bracing the wings, may be studied to advantage. The skids are well designed. In still another type of this general monoplane form ([Plate 12]) the propeller is placed in front of the planes, and the rubber motor runs below the main bar. The wheels supporting this model are particularly well made.

A very serviceable, little monoplane form may be made by making the rear upper plane adjustable (Plates [13]-[14]). The front plane is V-shaped and is unusually stable for so light a model. By tilting the rear plane up or down, a good level flight may be obtained. The frame, in this case, is made of wire. The propeller is placed well behind the rear plane, thus bringing the center of gravity well forward to balance the angle of the rear plane. The blades of the propeller are made of twisted wood, which is not to be recommended, since it is likely to lose its shape.

In Plates [15]-[16] we have a well thought out little monoplane, which well repays study. The propeller is set forward of the lifting plane which is the larger of the wings. The rear plane may be tilted up or down. The rudder, which is also adjustable, is set below it. The arrangement of skids is excellent, enabling it to rise from the ground with little loss of friction. The method of flexing the front plane may well be imitated.

Model shown in Plate V. Ready for a Flight.

A good working idea of the aëroplane is clearly shown by the builder of the biplane with triangular wings ([Plate 17]). His model is not successful and will not fly, yet it embodies several good features. The biplane form of the lifting plane is excellent in itself as we have seen in earlier models. The spacing of the two planes is good, and the bracing of the model throughout is well planned. The triangle does not make a good soaring plane even when its broad side is made the entering edge. The triangle serves well enough however for the rear stability plane. The chief fault of the model is that it is much too large. The motor although well proportioned is much too weak to propel so large a frame.

An interesting variation from the common type of aëroplane is made by varying the angle of the sides of the planes ([Fig. 18]). Here is a well constructed model, and, with a single exception, fairly well proportioned. The mistake, and it is likely to prove a serious one, is in the size of the vertical rudders. They are well placed above the main plane, but their size is likely to defeat the purpose for which they were designed and knock the model off its course rather than keep it steady. It is a question again if one of these rudders would not serve the purpose better than two and thus minimize weight and resistance.

The best point of this model is the ingenious method of enlarging the surface of the planes without increasing the size of the planes or adding to their weight. This is done by cutting the covering of the planes at an angle and keeping the entire surface taut by bracing. It is of course very important that the cloth should be held tight without wrinkling. The plan of having the wings taper slightly outward is good. Such a model combines more lifting surface with less weight than any other model of this general group.

CHAPTER VIII

BUILDING A BIPLANE

EVERY one knows, of course, that the box-kite flies better than a plane surface, and many believe that the box or cellular type of aëroplane has a similar advantage over the monoplane. The enclosed end keeps the air from slipping off the edges of the plane, and makes for stability. There is all the difference in the world, or rather in the air, between an actual flight and the movement of a model aëroplane. The aviator, by flexing his planes, and adjusting his rudders fore and aft, may balance his craft to suit the air currents. In the model aëroplane, the adjustment must be made before starting once and for all. Several interesting principles are involved in the cellular or box form of aëroplanes which will well repay study (Plates [19]-[20]).

In disturbed air, which is of course the usual condition of the atmosphere, the cellular model is likely to be deflected, and since the elevating plane or planes cannot be adjusted, it will soon fall off its course. Such models are easy to construct, and any one who has built a monoplane will have little difficulty with them. No attempt is made to flex the planes. The cellular type must be equipped with a lifting-plane forward, which may be easily adjusted to any angle, and held in position. It is indispensable that you have two propellers placed aft behind the main plane. The model may be made much more effective by adding a third stability-plane or rudder at the rear. It may be either vertical or horizontal and should be easily adjusted. The models illustrated, herewith, are very simple forms and clearly indicate the necessary frame work. It will be found that these models require considerable ballast, skilfully distributed.

PLATE VI.

A Model with Both Good and Bad Features.

In building these cellular forms select some light lath for the frame rather than dowel sticks. It will be necessary to join many of these together at right angles, and the curved stick will be found difficult to work. For each box cut four sticks the desired width, and eight sticks the depth of your plane. The box should be almost exactly square so that all these shorter sticks should be the same length. Now build your box by nailing and glueing these sticks together, taking great pains to have it symmetrical. Should a single one of these sticks be too long or too short it will throw the entire frame out of plumb and make it next to impossible to get a straight flight.

In most of these models the front or rear stability-planes are made exactly like the larger frame only much smaller. When the frames are completed and thoroughly dry and smooth, stretch the cloth covering tightly over them by drawing it lengthwise, all the way around. By using a single piece of cloth it will be found easier to pull it together and hold it tight and smooth. It will be found a good plan to touch the outer edges of the frame you are covering with glue just before covering. When the glue dries the cloth will thus be held firmly in position. The cloth may be fastened to the outer edges by glueing or sewing.

A simple but effective plan for mounting the stability-planes is suggested by the models here illustrated. The frame of the motor-base may be made the width of the smaller frame and fastened between the two sticks. It should be left free so that it may be tilted up or down and fixed in any position. If the rear stability-plane is to serve as rudder it should of course be mounted vertically so that it may be turned to right or left. Be sure to make your frame sufficiently strong and rigid. A light frame which will vibrate when the motor turns or is shaken by the wind will be found very troublesome indeed.

The cylindrical forms of planes ([Plate 21]) carries the foregoing principles a step further. A surprising degree of stability is obtained by thus enclosing the air, and by throwing out several lateral stability-planes fore and aft. The models may be constructed of heavy wire, ordinary umbrella wire will answer the purpose, and may be readily bent. The planes in the accompanying model are merely suggestive. The broad planes placed forward, well above the diameter, promise well, but the rear wings appear unstable and small for the other surface. The forward or lifting-plane is again, much too narrow. The cylindrical form is equipped with a double propeller, one before and the other in the rear, both mounted on a bar, which forms the exact axis of the cylinder. This adjustment will give you a very pleasant surprise. The vibration and torque of the two propellers seem to equalize one another, and the thrust is much more steady than in the case of a single screw. The thrust is not only double, in this way, but the gain for stability is surprising. The model should be mounted on skids to assist it in rising, and to take up the force of the impact on landing.

The double propeller, mounted on the same shaft, may be used successfully in many models. A very simple monoplane form ([Plate 22]) may be equipped in this way. If two or more planes be mounted between the propellers, an astonishing soaring quality may be had. It is an excellent plan to fasten the planes to the frame at first by rubber bands, so that they may be pushed up or down readily, and adjusted and weighted to suit the conditions.

There is danger in this form, however, that the plane will turn completely over in its flight, although this will have little effect upon the thrust or direction. The model is exceedingly simple to make. The propellers should not be too large, not more than twice the diameter of the planes at most. The two propellers must, of course, be turned in opposite directions, to correct the twisting tendency.

PLATE VII.

A Good Example of Careful Designing and Workmanship.

Should you construct a motor-base of this kind with propellers at either end it will be found interesting to experiment by attaching planes of different shapes and sizes. It requires very little surface to keep such a monoplane afloat. Instead of the circular and elliptical plane placed lengthwise, as in the accompanying model, try the effect of larger circles and broader ellipses, placing the latter sideways. This may be varied by using small rectangular planes with the corners rounded off. Sooner or later you will hit upon a shape of plane and a spacing which will give you good, steady flights of surprising length.

It has been suggested that a good motor-base be built with double propellers and the various forms of planes tested out upon it. Let us carry this idea further and, now that we have had some experience in building aëroplane models, construct a quadruple motor-base; that is a motor-base with four strands of rubber bands and four propellers, two forward and two aft. The four would of course have to be very nicely balanced. The two sets of propellers if carefully set up would tend to correct one another, as we have seen in the cylindrical and other double propellers thus giving a very steady flight. The increased speed of such a motor would carry any good model at a much higher rate of speed than any of the present forms.

There is a very simple rule to be remembered in building all biplanes, regarding the spacing of the planes. The distance between the super-imposed planes should always be equal to the width of the planes themselves. A beautiful model ([Plate 23]) is here reproduced, to show how not to space your planes. In all other respects the model is excellent. The planes themselves are beautifully constructed and scientifically curved. It is interesting to note, in this case, that the front and rear sets of planes would be much too far apart were they flat surfaces, but being flexed as they are, their supporting power is greatly increased. By placing them so far apart, a longer and more powerful motor may be used. The rudders, both fore and aft, are adjustable, and appear very effective and shipshape.

The method of tuning up the planes in this model is especially to be recommended. From a post, placed at the center of the planes, wires are run to the corners which holds the frame perfectly taut. For the main frame, or backbone, a metal tube has been used which greatly adds to the appearance of the model. This aluminium tubing may be bought cheaply and will serve admirably for this purpose.

The most popular of all models, among amateur aëronauts in America, at least, is the Wright machine (Plates [24]-[25]). The opinion is ventured that this is due more to the attractiveness of its lines and the pride we all take in its wonderful achievements, than to its actual flying ability as a model. The most perfect of these models will rarely fly more than a hundred feet. They will be found exceedingly difficult to weight and adjust so that they will maintain their course in a disturbed air current.

The planes of these models are usually made separate from the motor base. The shafts of the propellers, with the rubber motors and skids, are built up in a single piece. This plan has the advantage of making the planes adjustable so that they may move backward or forward as desired. The model leaves the ground from a base, much the same as the rail used by the large Wright machines. Some models are even started by the propulsion of a rubber band attached to the frame, which is pulled back and released, like the old-fashioned sling shot.

PLATE VIII.

An Effective Model with Wooden Wings.

CHAPTER IX

COMBINING MONOPLANE AND BIPLANE FORMS

ALTHOUGH the regular biplane form is exceedingly difficult to manage in small models, there is great advantage in combining it with the monoplane forms ([Plate 26]). The biplane makes an excellent lifting plane, and when the model combines with it a broad monoplane for stability, surprisingly long flights may be made. The model here illustrated has flown 218 feet 6 inches.

Despite its size, the model is exceedingly light. It is made almost entirely of dowel sticks braced with piano wire. Still another advantage of the biplane form is the action of the supporting surface when it comes to descend. The model settles easily to the ground, in contrast to many monoplane models which come down with a dislocating shock. The skids of this model are simple and effective. In a model of this form it is obviously best to have the propellers drive rather than pull it.

An ingenious young aëronaut has reversed the above order and placed his biplane in the rear, using the monoplane for lifting ([Plate 27]). His model is unusually large, having a spread of four feet. The biplane is square, with lateral stability planes on either side. The elevating planes appear small in proportion, but they serve to keep the craft on an even keel. The most striking feature of this model is its extreme lightness. Although unusually large, it weighs but nine ounces. The frame, except for the braces is built of reed. The planes are covered with parchment. The model is driven by two rather small propellers. The position of the propellers will appear, at first glance, to be rather low, but it must be remembered that the extreme lightness of the model brings the center of gravity very far down. The model has flown more than two hundred feet.

PLATE IX.

An Interesting Experiment Along New Lines.

The stability of the models thus combining the monoplane and biplane forms comes as a surprise. Both the models in question rise easily from the ground, which is more than can be said of many aëroplanes big or little, and once aloft maintain a steady horizontal flight, which is still more unusual. An interesting field of experiment is suggested by these combinations. These successful experiments have been made with perfectly flat planes. Suppose now we try them out with flexed planes. If the stability thus gained may be combined with the increased soaring quality of the curved plane, we may be on the way to making some remarkable flights. In the summer of 1909 a number of boys built and flew model aëroplanes in New York, when many interesting and well constructed models were brought out, and the longest flight was only sixty feet. Less than one year later the same boys succeeded in flying their machines for more than two hundred feet. The new models were no larger, the motors no more powerful, but the machine had become more shipshape and efficient. It is reasonable to suppose that each year will bring a similar advance.

CHAPTER X

FAULTS AND HOW TO MEND THEM

YOUR model, perhaps a beautiful one, finished in every part, may twist and tip about as soon as it is launched and quickly dart to the ground. The fault is likely to be in the propeller, being too large for the size and weight of the machine. This may be remedied by adding a weight to the front of the machine, by wiring on a nut or piece of metal. Should this fail to steady the aëroplane, the propeller must be cut down.

When your propeller is too small the machine will not rise from the ground, or, if launched in the air, will quickly flutter to earth. If the model on leaving your hand, with the propeller in full motion, fails to keep its position from the very start, the blade should be made larger. There is no use in wasting time and patience over the machine as it is.

Many a beginner, with mistaken zeal, constructs a too powerful motor. The power in this case turns the propeller too swiftly for it to grasp the air. It merely bores a hole in the air and exerts little propelling force. An ordinary motor when wound up one hundred and fifty turns should take about ten seconds, perhaps a trifle longer, to unwind. It is a good plan to time it before chancing a flight.

Bad bracing is another frequent source of trouble. The planes should be absolutely rigid. Test your model by winding up your motor and letting it run down while keeping the aëroplane suspended, by holding it loosely in one hand. If the motor racks the machine, that is, if the little ship is all a-flutter and the planes tremble visibly, the entire frame needs tuning up. It is impossible for an aëroplane to hold its course if the planes are in the least wabbly. The braces should be taut. A loose string or wire incidentally offers as much resistance to the air as a wooden post.

The flight of your model aëroplane should be horizontal, with little or no wave-motion. Your craft at first may rise to a considerable height, say fifteen or twenty feet, then plunge downward, right itself, and again ascend, and repeat this rather violent wave-motion until it strikes the ground. To overcome this, look carefully to the angle or lift of your front plane or planes and to the weighting.

The explanation is very simple. As the aëroplane soars upward, the air is compressed beneath the planes, and this continues until the surface balances, tilts forward, and the downward flight commences. Your planes should be so inclined that the center of air-pressure comes about one third of the distance back from the front edge. The center of gravity of each plane, however, should come slightly in front of the center of pressure. After all, the best plan is to proceed by the rule of thumb, and tilt your planes little by little, and add or lessen the weight in one place or another, until the flight is horizontal and stable.

If your aëroplane does not rise from the ground, but merely slides along, the trouble is likely to be in your lifting plane. Tilt it a trifle and try again. The simplest way to do this is to make the front skids higher than those at the back. If the front skids are too high, the plane will shoot up in the air and come down within a few feet.

The most carefully constructed model is likely to go awry in the early flights. The propeller seems to exert a twist or torque, as it is called, which sends it to the right or left, or up or down, even in a perfectly undisturbed atmosphere. It is assumed that your model is symmetrical. An aëroplane not properly balanced, which is larger on one side than the other, or in which the motor is not exactly centered, cannot, of course, be expected to fly straight. However, to be on the safe side, go all over the machine again. Measure its planes to see that the propeller is in the center. Hold it up in front of you right abeam, and test with your eye if the parts be properly balanced.

If it still flies badly askew, flex the planes by bending the ends up or down very slightly by tightening or loosening the wire braces running to the corners. At the same time add a little weight to counteract the tipping tendency. A nut or key may be wired on the edge which persists in turning up. It may require much more weight than you imagine. The difference should begin to show at once. Even after a model appears to work fairly well as a glider, the addition of the motor may so change the center of gravity that it will “cut up” dreadfully.

It will be well to leave your planes loose so that they may be shifted back and forth and not fasten them till you have tried out the motor. If you followed the plan suggested of fastening the plane to the central frame by crossing rubber bands over it, you can easily adjust them. If the model tends to fly upward at a sharp angle, slide the front plane forward an inch, and try another flight. There is an adjustment somewhere which will give the model the steady, horizontal flight you are after.

Some models will refuse to rise and swing around in an abrupt circle the moment the motor is turned on. This may be caused by the propeller being much too small for the motor. After looking over all the photographs of the models shown in these pages you will gain an idea of the proper proportion, and be able to tell offhand if the propeller is out of proportion. A small propeller revolving very rapidly, or racing, is likely to give the model a torque, even if it be otherwise well proportioned. Don’t try to remedy this with rudder surfaces, but change your propeller, or your motor, or both.

PLATE X.

An Excellent Monoplane Capable of Long Flights.

When your aëroplane turns in long, even curves to one side or the other, look to your rudder surface. Turn it to one side or the other, just as you would in steering a boat. It is, of course, obvious that it must be kept rigidly in position. If a slight turn of the rudder does not straighten out the flight, you probably need more guiding surface, and the rudder must be enlarged. If the model still continues to turn away from a straight line, tilting as it does so, try a little weight at the end of the plane which rises.

The commonest of all accidents to aëroplane models is the smashing up of the skids on landing. A model will frequently rise to a height of fifteen or twenty feet, and the shock of a fall from such an elevation is likely to work havoc in the underbody. There is no reason, however, why your model should not come down as lightly as a bird from the crest of the flight wave. The model, when properly proportioned, weighted, or balanced, will settle down gradually and not pitch violently. It is these quick darts to earth which cause the worst disasters.

A model should have sufficient supporting surface to break its fall when the motor runs down, at any reasonable elevation. If the model aëroplane falls all in a heap, as soon as the motor slows down, it will be well to look to this and perhaps increase the size of your planes. As a general rule, the biplanes or the models in which the double planes have been used, either for lifting or soaring planes, will settle down more gradually. The lateral planes, whatever their position, also lend valuable support when the critical time comes in the descent. Your model is not perfect until it falls easily at the end of the flight.

Detail of Model Shown in Plate X.

Under perfect condition, in absolutely undisturbed air, an aëroplane may be made to come down so lightly that no bones, even the smallest, will be broken. A gust of wind, however, may ruin all your calculations and bring the aëroplane down with a dislocating shock. The skids must be designed to meet extreme conditions, the worst that can possibly befall. It has been pointed out that these skids or supports should be high enough to give the propeller clearance so that the propeller blades will not touch the ground. By using a light flexible cane for the purpose, and bending them under, a spring may be formed which will take up the shock of a violent landing. Some builders go further and rig up the skids with braces of rubber bands to increase this cushion effect. A variety of constructions are shown in the photographs of the various models. Your skids should enable your model to withstand any ordinary shock of landing, without breakage of any kind.

The life of your motor can be greatly increased by careful handling. The rubber strands are likely to be worn away against the hooks at either end. The wire used for the hooks should be as heavy as possible to keep it from cutting through. Be careful that the wire which comes in contact with the rubber is perfectly smooth and flawless. A little roughness or a spur on the wire will soon cut through the rubber. It is a good plan to slip a piece of rubber tubing tightly over the hook and loop the rubber bands of your motor over this cushion.

The first break in the rubber bands is likely to come near the center of the strand. A number of loose ends appear. The broken ends should be knotted neatly and the loose ends cut away. If the strands come in contact with any part of the motor base, a breaking will quickly follow, and your strands soon become covered with a fringe of loose ends. Be careful to tie up all loose ends and trim them away, since the ends in twisting serve to break other strands. Although the finer strands of rubber give the greater thrust, do not buy them too small, since they are easily broken.

PLATE XI.

A Well Thought Out Monoplane.

The length of your motor base beyond the front plane should be carefully calculated. It is very easy, of course, to run your shaft too far forward. The center of gravity is easily shifted in this way, and your model soon becomes unmanageable. An aëroplane with this fault will not rise, but merely pitches forward under the thrusts of the motor. It is almost useless to attempt to balance this by weighting the machine. The front plane should be placed further forward, and if the lifting surface does not seem sufficient, cut away the front of your motor base, once for all. A too short motor base, on the other hand, will cause your model to shoot upward at a sharp angle, and waste much valuable propelling power before it rights itself and takes a regular horizontal flight.

In the model aëroplane there is only one point where friction affects the flight, namely, along the propeller shaft. One can hardly be too careful in the construction of the axle. The thrust of the rubber at best, is limited, and this power must be exerted without loss of any kind. A faulty propeller shaft will use up a surprising amount of energy. Your rubber motor should unwind to within one or two turns.

Bear in mind that one of four things is likely to be responsible for your trouble. The planes may not be properly placed on the frame, they may not be properly flexed, they are not set at the proper angle of elevation, or your motor is at fault. Watch these points, and you will soon have your machine under perfect control. In the extremely complicated models it is often difficult to locate the fault. Build your model so that these parts may be adjusted in a moment without taking apart. After you have built an aëroplane model, even a very simple one, the pictures of other aëroplanes will have a new meaning for you. Every new model you see will give you some new idea. A number of the most successful aëroplane models in the country are shown in the accompanying photographs. Study these carefully, and you will learn more from them of practical aëroplane construction than from any amount of reading.

PART II

THE HISTORY AND SCIENCE OF
AVIATION

CHAPTER I

THE FIRST FLYING MACHINES

THE conquest of the air was not won by a happy accident of invention. Long before man learned to fly the science of aviation had to be created by investigation and experiment. At first with very crude attempts, a great many flying machines had to be built, and many lives sacrificed in flying them. The exact nature of the invisible air currents and the action of wings and planes, were to be learned before the delicate mechanism of the modern aëroplane was possible. Probably no other great invention has required such long and patient preparation.

In many ways the aëroplane is therefore a greater achievement than the steam engine or the steamboat. When Watt turned from watching his tea kettle to build his engine, he applied mechanical principles which had long been in actual use, and there were many experienced mechanics to help him. Robert Fulton, again, when he set up his engine, found the science of boat-building highly developed. The aviator had no such advantage. He must first of all build a craft which would keep afloat in the most unstable of mediums. A motive power had to be applied to suit these conditions, and the two must be so attuned that they would work perfectly together when the least slip would mean instant disaster. As we learn to realize these difficulties we will appreciate more than ever how marvellous a creation is the modern aëroplane.

PLATE XII.

A Good Example of Tilted Planes.

Man has thought much about flying from the earliest times. The open air has always seemed the natural highway, and flying machines were invented hundreds of years before anyone dreamed of steamengines or steamboats. The ancient Greeks long ago spun wonderful tales of the mythical Daedalus and Icarus and their flight to the sun and back again. The first practical aviator seems to have been a Greek named Achytas, and we are told he invented a dove of wood propelled by heated air. There is another ancient record of a brass fly which made a short flight, so that we may be sure that even the ancients had their own ideas about heavier-than-air machines.

As far as we may judge from these quaint old records the early aviators attempted to fly with wings which they flapped about them in imitation of birds. About the year 67 A. D., during the reign of the Emperor Nero, an aviator named “Simon the Magician” made a public flight before a Roman crowd. According to the record, “He rose into the air through the assistance of demons. But St. Peter having offered a prayer, the action of the demons ceased and the magician was crushed in a fall and perished instantly.” The end of the account, which sounds very probable indeed, is the first aëronautical smash-up on record.

Even in these early days the interest in aëronautics appears to have been widespread. It is recorded that a British king named Baldud succeeded in flying over the city of Trinovante, but unfortunately fell and, landing on a temple, was instantly killed. In the eleventh century a Benedictine monk built a pair of wings modelled upon the poet Ovid’s description of those used by Daedalus, which was apparently a very uncertain model. The aviator jumped from a high tower against the wind, and, according to the record, sailed for 125 feet, when he fell and broke both his legs. That he should have attempted to fly against the wind, by the way, indicates some knowledge of aircraft.

If we may trust the rude folklore of the Middle Ages, the glider form of airship which anticipated the modern aëroplane was used with some success a thousand years ago. An inventor named Oliver of Malmesburg, built a glider and soared for 370 feet, which would be a creditable record for such a craft even in our day. A hundred years later a Saracen attempted to fly in the same way and was killed by a fall. The number of men who have given their lives to the cause of aviation in all these centuries of experiment must be considerable.

Meanwhile the kite and balloon had long been in use in China. There is no reason to doubt that kites were well understood and even put to practical use in time of war as early as 300 B. C. A Chinese general, Han Sin, is said to have actually signalled by kites to a beleaguered city that he was outside the walls and expected to lend assistance. And a French missionary visiting China in 1694 reported that he had seen the records of the coronation of the Emperor Fo Kien in 1306 which described the balloon ascensions that formed part of the ceremony.

The fifteenth century was the most active period in aëronautical experiments before our own. A number of intelligent minds worked at the problem and notable progress was made, although all fell short of flying. Even in the light of our present knowledge of aëronautics we must admire the thorough, scientific way the aviators went about their work five centuries ago. Many of their discoveries have been of great assistance to our modern aviators. Had these investigators possessed our modern machinery, of which they knew little or nothing, it is, very likely they would actually have flown.

One of the greatest of these investigators was Leonardo da Vinci, famous as architect and engineer as well as painter and sculptor. To begin at the beginning of the subject, he dissected the bodies of many birds and made careful, technical drawings to illustrate the theory of the action of wings. These drawings and descriptions are still preserved, and even to-day repay careful study. He also calculated with great detail the amount of force which would be necessary to drive such machines. Plans were prepared for flying machines of the heavier than air form to be driven by wings, and even by screw propellers, which was looking far into the future.

PLATE XIII.

A Serviceable Form Made of Wire.

Among all these early experiments the best record of actual flight was made by Batitta Dante, a brother of the great Italian poet. In 1456 Dante flew in a glider of his own construction for more than 800 feet at Perugia in Italy and a few years later he succeeded in flying in the same glider over Lake Trasimene. The glides made by the Wright Brothers while perfecting their machines seldom reached this length.

For several centuries it was believed that a lifting screw, if one could be built, would supply enough lifting power to support a heavier than air machine. Da Vinci experimented along this line for many years and even built a number of models with paper screws. This form of flying machine is called the helicopter. The plan was then abandoned for nearly five centuries and revived in our own century. The record of all the aviators and their experiments would fill many volumes.