Several metal washers should be strung on the axle between the upper edge of the shaft and the propeller. These may be punched from a sheet of metal. A section of this tube may also be inserted part way in the propeller, and washers introduced where they meet. The second tube will insure smooth action. The projecting tube will serve also to remove the propeller far enough from the frame to prevent its striking. By freely oiling these parts, the propeller may be made to turn very freely. [Illustration: An ingenious adjustment of ailerons] [Illustration: Tuning up the model for a flight.] In bending the axle into a hook for holding the rubber strands of the motor, care must be taken to keep the ends of the strands on a line with the axle. After turning the wire into a hook, bend back the shank to the proper angle. It will be seen that if the motor carries the axle about from side to side, the friction will be considerably increased. Over this hook, slip a piece of rubber tubing before attaching the strands of rubber, since the metal is likely to cut and wear the motor. It will be found a good plan to tie the strands together just below the hook to keep them from slipping off. And, by the way, do not keep your motor wound up any longer than you can help before a flight, since the strain on the rubber in this position is very great. As motors have increased in power and distance qualities, the process of winding up has become a serious problem. The simple method of turning the propeller by hand takes too long, and a slip with a powerful motor may give one an ugly cut. An ordinary machine drill will do the work much more quickly. Some drills are geared so that a single turn of the wheel will give you ten revolutions of the propeller. To arrange your motor for winding with a drill, run the axle through the propellers and turn in the form of a closed hook. A small hook should then be fixed to the end of the drill, which may be inserted in this loop. Some boys use a double hook on the propeller, detach the strands of rubber, wind them up, and then attach them to the propeller. A very simple and ingenious method of winding up has been adopted in the remarkable model constructed by Mr. Mungokee. The motor is anchored by running the wire holding the strands through the supporting stick of the base, and bending the end into a hook which, as the rubber pulls, is held securely in a second hole at the side. [Illustration: Showing Construction And Mounting Of Propeller And Axle.] To wind up, it is only necessary to draw out this hook, attach it to the winding drill and turn. When wound up, the pull of the motor will obviously hold the end of the hook firmly in the hole, making it impossible for it to turn. This does away with extra hooks and the trouble of hooking up the motor when once it has been wound.