They may be divided into four classes:
A. Small models of large machines, made for the purposes of construction.
B. Small models of large machines made for the purpose of flying as kites.
D. Self-propelling models.
It will be seen at a glance that this chapter should be expanded into a book by itself. Mr. Collins has written an excellent book, "The Second Book of Model Aeroplanes", on the subject, and I hope the readers of this book will look it up, as it will be worth while. In dealing with the subject in this chapter we can not go into it very deeply and not many plans can be given, but we will try to touch here and there some of the important features of construction.
I have grouped the model aeroplanes into four divisions, but before we proceed it will be well to notice the various classes of large machines. There is the monoplane or one plane type; the biplane or two planes, one above the other; and the multiplanes in which several planes are used. The first two have survived, and form the very large percentage of all that are attempted these days. I should like to make clear that I do not recommend, even discourage, any attempt at gliders large enough to carry the maker, and the aeroplane in which a motor engine is to be placed. There is too much danger connected with them, and our lives and limbs are too precious a gift to be trifled with in such unnecessary ventures. The little models, however, are harmless and yet are very fascinating, even when there is no thought of their embodiment in a large machine.
In group A, where the worker seeks to imitate a large machine in miniature, the joy of the undertaking lies in the processes involving very accurate work and nicety of finish. There is a fascination for young people in the making of things in miniature. The models made in group A are usually larger than in group D, as the pieces of the framework need a little more material to work to advantage, while in D, the parts must be kept light. Weight is not so much of an item in group A.
The photograph of the Curtis model, Fig. 207, has a clock spring works in it, but it is of no service. This is a very fine piece of work and has been admired bv many. Outside of the clock works the model is all handmade. Little turn buckles for tightening the guy wires were made, as well as the little metal attachments to which the ends of the guy wires are attached. The silk covering was stretched and oiled on the frame.
An equally well made model is shown in Fig. 208. In this monoplane all the curving of ribs and trussing of frame were very accurately done. It will be recognized that this is a very excellent piece of work and the outlines of the planes are very beautiful and well proportioned. The planes are supported at the outer ends by careful adjustment of wires above and below the wings. Notice the two little braces above the center of the framework to which the guy wires are attached. Turn-buckles are used on this model also. The horizontal and vertical planes to the rear of the model, but to the front in the picture, were ideas original with the maker, altho I have seen pictures similar to this since.
Some make up these models in good shape for the purpose of using them as attractions in show windows. Merchants will sometimes give a rental for a good model. Very often when used as a display, an electric motor is installed in them so as to run the propellers.
In group B, the models are made to fly as kites. It is possible to gain much knowledge about the motor driven models by patient study on the aeroplane kite. The kite flying side will not help so much as the gliding. When the aeroplane kite is well up, if the string is allowed considerable slack, the model will glide if well balanced and if the planes are tilted properly. Balance will be necessary both to right and left and fore and aft. It is very interesting to get such a model pulled well up in the air and have a release that will cut the kite line. The punk method is good, only that we would like to have better control of just the time for cutting loose. The punk has this advantage however, that not knowing just when it will cut loose you are held in happy suspense, just as you wait for a bite on your fish line.
Another simple releasing device can be used: hooks are placed on the kite at each point of attachment of the bridle, and on the end of each string of the bridle is tied a small ring, which is to be hooked on the hook of the kite. The hooks must bend back and downward and must he stiff enough not to bend. Of course the kite line will have to be kept quite taut until time for release, when, if the line is slackened suddenly, the rings drop off, thus releasing the kite line. If it glides well some interesting things will develop. There will be swoops and glides, and loop the loops and all sorts of gyrations before it reaches the ground. If one is going to make a model just to fly in the air without the maneuvering, but to look like an aeroplane in the air, it should have the bridle placed so as to cause the kite to stay as near the horizontal as possible. In order to do this, the upper loop of the bridle should be shortened or the lower one lengthened as on a tailless or any other kite. On the tailless kite one can shift the bridle so as to make the kite stay nearly over head, in fact I have had them pass the zenith and dive over to the other side, and that well up in the air. A propeller that is turned by the breeze will help considerably in giving it a realistic touch. Fig. 99 is very good for aeroplane kites. The side wings can be extended and modified, as in Fig. 209, or the cross-pieces can be bowed up, as in Fig. 210. The bridle should be attached only in two places.
Figs. 209, 210, 211, 212, 213, 214, 215.
A biplane is shown Fig. 211, one with bowed cross-pieces in Fig. 212, and one with bent up tips on the upper plane in Fig. 213. The folded paper glider made by the children soars excellently; try an aeroplane kite on that plan, Fig. 214. Another modification of Fig. 214 is the bird aeroplane kite, Fig. 215. In this a plane is placed about half way from front to back. The ends of the wings get their curve from the back stick, a piece of heavy reed, and the outline of the bird is also of reed. By drawing the shape on a board the reed can be bent to the shape. The reed should be wet and tacks should be driven at each side to keep the shape until dry. This kite, if well made, should glide for a very long distance.
It would take too much space to go into details with each design, but the drawings I think will be sufficient for most readers who may be planning these models, especially where framework and finished kite are both given.