Fig. 485
Fig. 486
When the wood is supple, twist it as in Fig. 484. This sounds easier to do than it really is, the difficulty being to get the twist on one side exactly equal to the twist on the other. For this reason the tin propellers are more satisfactory to make. However suppose the correct twist has been given, the next thing to do is to sand-paper the wooden propeller carefully and file a groove around the middle at A; now wrap a piece of wire, A C, tightly around the propeller in this central groove, and put on the head, B. The propeller is now ready to be fastened to the glider shown in Fig. 480.
To fasten Propeller to Glider. Cut a piece of tin to the pattern shown in Fig. 485, bend along the dotted line; make a hole at F for axle, B C, to go through. Bend portion E round the front end of the glider, keep it in its place by bending it with thread coated with glue; portion F with the hole is bent down at right angles as shown in Fig. 486. Now pass axle, A C, through hole F, bend end C into a hook. Put screw-eye D in the rod about one-third of length of rod from the other end (see Fig. 486). Fasten strands of elastic from hook C to D. It is best really to have a hook at D so that the elastic can be slipped over. The strands should be just loose enough to remain taut when unwound. When the propeller is in position the planes will probably have to be readjusted. The tin propeller can be attached in a similar way. These propellers will do for almost any simple design of aeroplanes.
When the motor is wound up for flight, the number of turns to give to the propeller will depend upon the strength and number of the elastic strands used. About a hundred turns is a usual number. Throw the motor forward in a slightly downward direction; because it is a glider it will tend to follow a gentle curve to the ground at first, but the whirling propeller will tend to carry it forward and upward. The first attempts may be failures, but these models are well worth many trials.
The Hawk Aeroplane (Fig. 487) is a common flying toy worked as the above by elastic. Cut two blocks of wood, A, A´; make holes in them as shown. Into the square holes fix and glue two square rods C. Through A´ bore a hole for the piece of cane, B B´, to pass through. F is a wire spindle with a hook at one end for elastic; it passes through the hole in block A´, through two beads, and through a piece of cork, F, into which it must be fixed. K is a piece of cane bent as in diagram, passing through a hole in cork, H. The bend is more permanent if the cane is held to the spout of a boiling kettle; the ends of K should be slightly warped in opposite directions. Into block A another wire hook is fixed and bands of elastic are passed over this hook and the opposite one, as in the diagram; the more bands the better.
The cane B B´ is bent round at each end and fastened to the wooden rods, C C, by thread. The cane, K K, is fastened by thread as in the diagram; the thread can pass through a hole in the cork. Spaces T, T, T, T are covered with thin tissue paper gummed to thread and cane by means of overlapping edges. The model is wound up and set going like the previous one. Care must be taken to have it properly balanced, and it must be made as light as possible; the blocks A, A´ may very well be cut from cork. Light bamboo cane can be used for posts, C C. At its best, however, the Hawk Aeroplane is not so good a flyer as the first model described.
