MODEL AEROPLANES.
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.
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.
Figs. 221, 222. [↑]
Fig. 223. [↑]
The spine is made of spruce and is ¼” × ¼” × 12”. The large plane has about ⅛” 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 ⅛” 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 ¼” × 1” × 1” and is glued and nailed with brads to the rear end of the spine. A piece of tin ⅜” 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.
Figs. 224, 225. [↑]
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 ½” × 1” × 4”. 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.
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.
Fig. 226. [↑]
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.
Figs. 227, 228. [↑]
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 ¼” × ⅜” × 8” 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 ⅛” × 3/16” 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” × ¼”. ⅛” × 3/16” 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.
Fig. 229. [↑]
When long models are made with single spine, they need some simple wire supports to prevent springing up or down, and from left to right. [Fig. 229] is 4’ long and the spine is only ¼” × ¼” at the small end ¼” × ⅜” at the larger end. A little 1/16” oak veneer cut in strips 3/16” wide would be very serviceable for the purpose of support in trussing the long spine. It should stand 2” above and below the spine, and the same amount for the right and left brace, [Fig. 230]. The wires for these should extend about a foot on each side of these posts, and be attached to the spine with little tin anchors, as shown in [Fig. 230], a.
Figs. 230, 231, 232. [↑]
The propeller shaft bearing is of metal and is lashed to the cross-piece, called the base, [Fig. 231]. It is not necessary to have two points of bearing for the shaft. The metal is about 1/16” × ¼” × 1”, bent as in [Fig. 232], and lashed to the under side of the base. The planes are similar to those in the next model. 1” × 1½” × 7½” propeller blanks are used. Try about fourteen strands of 1/16” string rubber for each motor, seven rounds.
Fig. 233. [↑]
My favorite model aeroplane is shown in [Fig. 233]. It had made some very pretty flights when it took a notion to glide into a young man’s bicycle as he was riding by. Well, there was no improvement on the aeroplane when the chain and spokes of the bicycle were thru with it.
Figs. 234, 235, 236, 237. [↑]
The framework is light and is spread well at the rear. The two spines are 3/16” × ¼” × 33” and they come together at the forward end, the vertical section being ¼”. Nine inches back from the front end is a cross-piece that is just under ⅛” in thickness, ¼” wide and 2½” long. The cross-piece is on the upper side of the spines, and is fastened by a small ¼” brad, is lashed with thread and coated with glue or shellac. The other cross-piece is 1” forward from the rear end, is of the same dimensions in cross-section as the forward piece, but is 8” long and is secured in the same manner as the other, see [Fig. 234]. The framework is further stiffened by two fine wires that run diagonally from the ends of one cross-piece to the ends of the other. They are secured to the inside vertical face of the spines by means of small pieces of tin that have two small holes, one at each end, the one receives a ¼” brad that is driven into the spine, while the wire is attached to the other hole. The little pieces of tin are about 3/16” × ½” and are lashed to the spine in addition to the fastening by the small brad. This kind of fastening prevents slipping, also the cutting into the wood, either of which would destroy the efficiency of the wire. In order to increase the tension of the wire, a small turn-buckle is inserted, [Fig. 235].
Fig. 238. [↑]
Figs. 239, 240. [↑]
Fig. 241. [↑]
The bearings for the propeller shafts are lashed to the outside face of the rear end of each spine, [Fig. 236]. The bearing is a piece of brass 1/16” × ¼” × 1”, and is bent to a right angle at the middle. A small hole is drilled for a brad into the side of the spine and the other hole is drilled to receive the propeller shaft, which is 1/16” steel wire. The shaft is bent into a hook after it passes thru the bearing. To prevent the rubber of the motor from touching the steel wire, which is injurious to the rubber, a small rubber hose is slipped over the hook. In this model, the propellers are pieces of veneer steamed and pressed into the spiral shape. The propeller shaft then is bent around the center of the propeller, has two little washers between this and the bearing, after which comes the covered hook, see [Fig. 237]. A piece of tin ½” wide and 1¼” long is folded about the propeller before the shaft is bent around. The shaft is soldered to the tin, the tin being secured by two small brads and shellac. A small tin rudder with a small fold in its upper portion may be slipped over the back cross-piece, [Fig. 238]. The fore plane is made of very thin spruce, shaped like [Fig. 239], and is bent up almost like a butterfly’s wings, [Fig. 240]. The wood is less than 1/16” thick. A double hook as anchors for the double motors, is bent and secured about the fore end of the framework. The hooks are covered with the rubber hose, the same as the propeller shaft, [Fig. 241].
Fig. 242. [↑]
The large plane is 4½” in the widest place and is 20” long. It is the shape of [Fig. 242] in outline, the straight side being to the rear. The outline of the plane is a steel or brass spring wire 1/16” diameter and is spliced at the center of the long sides, being soldered at this point. The ends of the wire lap over an inch or more. There are but two ribs which are 5½” from the outer ends. The ribs have a slight curve upward, most of it being near the free edge of the plane, [Fig. 243]. The ends of the ribs are bent at a right angle and are soldered to the outside framework of wire. The cover of the plane is made of prepared silk and is made ¼” larger all around than the size of the outline of the wire frame. A ¼” hem is then turned which gives strength to the edge. The cover is now over cast with needle and thread to the framework, stretching fairly tight.
Fig. 243. [↑]
The framework of the large plane is not secured directly to the wooden framework of the model, but is soldered to wire loops that in turn lie flat on top of the spines of the frame, [Fig. 242], a, a. This gives opportunity to tie with string so as to try out the model. If it is too far forward, it can be slipped back and vice versa; when the correct position is located, it is permanently wired to the wooden framework. The fore plane is attached by means of rubber string. This is known as the Mann monoplane, and is a commercial product.
The propellers will be further discussed in the next chapter.