The central member measures four feet two inches in length. The stick is one-half by one-fourth of an inch, with the forward part tapering gradually to one-fourth of an inch square. The base stick is eight inches in length, cut from a strip five-eighths by one-eighth of an inch. The diagonal pieces forming the triangle are cut from the same material, and meet at a point eight inches from the rear, thus affording a surface of twenty-four square inches. The wooden parts are glued and tied together, no nails or brads being used. The main plane is an exceedingly refined piece of workmanship. A glance shows that it is very speedy. The frame consists of steel wire one thirty-second of an inch in diameter. The plane measures sixteen and one-half inches in width and four and one-half inches in depth at the narrowest point at the center, and five and one-half inches in the widest part at the ends. It has four cross ribs of the same wire. The frame is covered, on the upper side, with oiled silk. The camber is slightly higher at the sides than the middle. The plan of fixing a rigid shaft for the propeller axle is very simple and effective. A piece of aluminum tubing is forced over the ends of the rear stick and glued firmly in position. A hole for the axle is then drilled through this tube, and the wooden stick which forms its core. The axle thus turns in what is really a metal shaft, and the friction is reduced to a minimum. A piece of tin tubing, a putty blower, for instance, will serve as well. In this particular machine, the propellers are cut from a board one-sixteenth of an inch thick and bent by steaming to the desired curve. The shafts of the propellers are formed of a very light steel wire, less than one thirty-second of an inch in diameter. This is passed through the hole in the rear stick and bent into a hook in the usual way. The motor anchorage consists of a wire passed through the central stick and bent back, and turned into two hooks. The rubber-strand motor consists of twenty strands of strip rubber one-eighth of an inch broad. A special preparation resembling cosmoline is used to lubricate the rubber, thus increasing the number of turns. The motor will take on one thousand turns without undue strain. CHAPTER X DESIGNING THE SKIDS Much more attention is paid to designing the skids for model aeroplanes in America than abroad. Since the American model usually rises from the ground under its own power, this detail of construction naturally has come to be of vital importance. By attacking the problems faced by the designers of large aeroplanes, our work is helpful in developing the science of aviation as a whole.