Fig. 87 shows the general design of the A- shaped gliding plane or aeroplane. This is composed of main frame pieces A, A, running fore and aft, joined at their rear ends by a cross bar B, the ends of which project out slightly beyond their juncture with the side bars A, A. These projecting ends have holes drilled therein to receive the shafts a, a, of the propeller D, D. A main plane E is mounted transversely across this frame at its rear end, while at its forward end is a small plane, called the elevator. The pointed end of the frame has on each side a turnbuckle G, for the purpose of winding up the shaft, and thus twisting the propeller, although this is usually dispensed with, and the propeller itself is turned to give sufficient twist to the rubber for this purpose. THE POWER FOR MODEL AEROPLANES.--One end of the rubber is attached to the hook of the shaft C, and the other end to the hook or to the turnbuckle G, if it should be so equipped. The rubbers are twisted in opposite directions, to correspond with the twist of the propeller blades, and when the propellers are permitted to turn, their grip on the air will cause the model to shoot forwardly, until the rubbers are untwisted, when the machine will gradually glide to the ground. MAKING THE PROPELLER.--These should have the pitch uniform on both ends, and a simple little device can be made to hold the twisted blade after it has been steamed and bent. Birch and holly are good woods for the blades. The strips should be made thin and then boiled, or, what is better still, should be placed in a deep pan, and held on a grid above the water, so they will be thoroughly steamed. They are then taken out and bent by hand, or secured between a form specially prepared for the purpose. The device shown in Fig. 88 shows a base board which has in the center a pair of parallel pins A, A, slightly separated from each other. _Fig. 88. Making the Propeller._ At each end of the base board is a pair of holes C, D, drilled in at an angle, the angles being the pitch desired for the ends of the propeller. In one of these holes a pin E is placed, so the pins at the opposite ends project in different directions, and the tips of the propeller are held against the ends of these pins, while the middle of the propeller is held between the parallel pins A, A. The two holes, at the two angles at the ends of the board, are for the purpose of making right and left hand propellers, as it is desirable to use two propellers with the A-shaped model. Two propellers with the deltoid model are not so necessary. After the twist is made and the blade properly secured in position it should be allowed to thoroughly dry, and afterwards, if it is coated with shellac, will not untwist, as it is the changing character of the atmosphere which usually causes the twisted strips to change their positions. Shellac prevents the moist atmosphere from affecting them.