Self-propelling air devices must be of the lightest possible weight and yet they must have strength. There will be no attempt to give a great variety of model aeroplanes; but a few can be discussed, perhaps three or four. The first is a little practice model that has been of great service to me, both for study and for instruction to others. It is small and will not fly far. I can wind it up and turn it loose in a schoolroom. It hits rather hard sometimes but nothing has happened to it beyond a broken propeller, and the rubber bands that are used to tie the planes to the spine have been broken.

Model Aeroplanes 220

Fig. 220.

In Fig. 220 the model is shown in two views, the plan and side elevation. The planes are made of 1/16" birch veneer, but other woods, will do. The small fore plane is bent at quite a sharp angle and was shaped as shown in Fig. 221. Steam the plane thoroly over the teakettle and place it under pressure until dry and it will remain so bent. The plane is also tilted up a little by means of a small wedge.

The spine is made of spruce and is 1/4"x1/4"x12". The large plane has about 1/8" camber and is bent as shown in Fig. 222. Lay a strip as thick as the desired camber on a board that you can nail brads into. Steam the veneer for the plane and lay in the 1/8" strip in this case about one-third the distance back from the front edge, bend down until the edge touches the board underneath the strip and drive brads in slanting so as to hold it down. The brads can be bent down a little after they are driven in. By using brads on both sides the veneer can be held down until dry. The outline can be cut away before or after the bending. The decoration of course is not essential, but it is interesting to beautify it a little. The anchor block for the propeller shaft is of wood 1/4"x1"x1" and is glued and nailed with brads to the rear end of the spine. A piece of tin 3/8" wide is bent about the top of the anchor block, f, Fig. 223. The hole in the wood should be larger than the propeller shaft while the hole in the tin should make a good fit. In this way the bearing is on the tin instead of the wood, and reduces the friction to a minimum. After the tin is on, the block should be wound with linen thread and coated with glue or shellac.

Model Aeroplanes 221Model Aeroplanes 222

Figs. 221, 222.

Model Aeroplanes 223

Fig. 223.

The propeller shaft is made from a bicycle spoke, Fig. 223; two of these can be purchased for a nickel. The long nut, shown at b, is cut with a metal saw in two places, giving small nuts c and d; c is used on the inside and d on the outside of the propeller. The spoke is then cut off long enough to pass thru the propeller, a glass bead as a washer, and the anchor block, with room for a good hook on the end for the attachment of the rubber motor. The propeller will be discussed further in the next chapter; the only thing to be mentioned here is the size of the blank from which it is made, which is 1/2"xl"x4". Another piece of the spoke is bent as in Fig. 224, and is inserted in the fore end of the spine and bent still further into shape like Fig. 225. This gives the other anchor hook for the rubber motor. One other piece is the small keel shown in the side view. A groove is made in the under side of the spine and the keel set in with glue.

Model Aeroplanes 224Model Aeroplanes 225

Figs. 224, 225.

I am using four rounds of 1/16" rubber string for the motor. That makes eight strands. Six do very well. This is a very useful little model but it will not fly over fifty feet, or mine has not, but the fact that it does not fly far, gives you opportunity to study its start, its landing, and its flight. The long distance models are out of observation range so soon that we miss the chance to diagnose their crazy symptoms, if they have any, and most of them have some.

At the beginning of model aeroplane making, everyone seemed to try to see how much surface could be exposed in the planes, now the best models are those with as narrow planes as it is possible to use and still support the air craft. The reason is obvious - there is so much skin friction on broad surfaces. At the beginning, many were inclined to scoff at the rubber band motor, but since flights have been made considerably over a half mile, with this same power, it seems good enough for anybody. Most of the long distance flyers have long framework so as to accommodate long strands of rubber, which allow much increase in the winding up of the motor.

Model Aeroplanes 226Model Aeroplanes 227

Fig. 226.

A Good Model. A simple and effective model is shown in Fig. 226. Lay out a light framework, as shown in Fig. 227. It is the combination of a tailless kite and a triangular box-kite. Three long sticks, a, b, c, are used for the triangular portion and three cross-sticks, d, e, f, are for the wing supports. A vertical post, g, about 1/4"x3/8"x8" is used in the center of the rear (the wide part), to stiffen the frame and give an anchorage for the propeller shaft. Four light braces, h, i, j, and k, make it possible to use lighter material than one would suspect for the entire framework. In a model 3' long, a, b, and c, need not be larger than 3/16" square, but there must be no split or uneven places in a stick so small. The braces 1/8"x3/16" would be plenty large. The two upper pieces, b, c, should be flattened on the inside of the front end so as to make them join together, terminating in a point. The lower spine, a, should be flattened on the upper side for the same reason. All three should be glued and lashed together with linen thread. A triangular block, l, should be placed about 4" back from the front end with a strong cup-hook screwed in the side toward the rear, on which the ring of the rubber motor is attached. The block, l, must be well secured to the triangular framework with glue and thread. The cross-piece, d, is 30" long and is bowed upward as is shown by Fig. 228. Piece e is 24" long, 5" in front of d, and both are 3/16"x1/4". 1/8"x3/16" will be heavy enough for f, and this should be bowed much more than d, and e. It will be necessary to steam this piece a little. Chinese rice tissue will be good for covering. Cover the underside of the two planes, and the underside of the triangular framework which is similar to the hull of a boat, and acts as a keel. Test out well as a glider. Put more and less curve to bows, and experiment for poise of model. A small piece of tin on each side of the support will give a good bearing for the propeller shaft. The hole in the wood should be a trifle larger than the shaft. String is run from both ends of d and e to the front end of the framework but is not attached to f.