ioo OUR PHYSICAL WORLD 



propeller between the holes and included in the loop of wire will 

 help to hold the propeller solidly. 



Put a flat, good-sized bead on the free end of the wire, then 

 pass the end through the holes in the tin propeller bearing and 

 make a triangular loop on the wire just back of the bearing to 

 take the strands of rubber that make the motor. The bead 

 used helps to reduce friction. Make another small triangle of 

 wire and bend the free ends so that they can be bound securely 

 to the front of the rear skid strut about i inch from the backbone. 

 Pass the long strand of rubber that can be bought for this pur- 

 pose through this rear wire loop, then through the one on the 

 rear end of the propeller shaft, and so back and forth until about 

 ten strands are laid on. Tie the ends of the rubber together to 

 complete the last strand. 



To make the planes, cut two thin bamboo strips | inch wide 

 and 22 inches long and two 5 inches long, and bind their crossed 

 ends together so as to make a rectangular parallelogram of the 

 strips that will serve as the frame for the forward plane. In the 

 same way make the rear frame for the plane 10 by 4^ inches. 

 Cover the frames with strong but light paper, folding the paper 

 over the edge of the frame i inch and gluing it down. Fasten 

 the forward plane horizontally to the backbone, its long axis 

 at right angles to the latter, its front edge just back of the struts 

 that support the forward skids. Tack it lightly in place with 

 thread. The rear plane is fastened similarly with its hind edge 

 just in front of the brace that supports the rear strut. When the 

 planes are in place balance the machine on the forefinger placed 

 under the backbone near its center. If the planes do not lie 

 horizontally but tend to dip to one side or the other, their posi- 

 tion may need to be changed slightly. When they do balance 

 well, fasten them securely in place, daubing the bindings with 

 glue so that they will not slip. Guy threads may then be 

 run from the outer tips of the planes to the adjacent struts to 

 make them sufficiently rigid to stand the strains of flight 

 (Fig. 43). 



