MOTOR DESIGN AND MATERIAL. Crankshaft: The crankshaft is supported in five bearings of more than ample size. It is extremely difficult, if not impossible, to design a shaft which will be light enough for aeronautical purposes, and still be sufficiently rigid without a special support. The propeller end of the shaft is supported in two places eleven and three-eighth inches apart, at one end in a plain bearing two and seven-sixteenth inches long and at the other in a combined radial and thrust ball bearing of ample size. This construction is stronger than is the case where the propeller is mounted immediately behind the last main bearing proper or even in some cases carried at a distance of several inches from the bearing without support. Any lack of mechanical or thrust balance is multiplied and transmitted directly to the last crank throw, the tremendous racking and twisting strain thus occasioned causing ultimate failure. The crankshaft is made of imported Chrome-Nickel steel, properly heat treated. This steel, particularly after heat treatment, has an enormous tensile strength combined with a very high elastic limit and great resistance to fatigue and crystallisation. Connecting Rods: The connecting rods are machined from a solid Chrome-Nickel steel forging, heat treated. The body of the rod is tubular, which cross section gives a maximum strength with minimum weight. Rough forging weighs five pounds; finished weight one pound eight ounces. Piston: The piston is long enough to give sufficient bearing surface to sustain the side thrust from the connecting rod and at the same time weighs but two and one-half pounds. The domed head, with properly placed ribs, assures strength. The piston pin bearing is seven-eighth inches diameter by two and three-fourth inches long. Reversing common practice, the pin turns in the piston instead of the rod end, as considerable gain in bearing surface is thus made. Engineers will appreciate that with a combined piston and rod weight of four and one-half pounds, the strains from twenty-two hundred reversals of motion per minute at normal speed are very slight. It has three rings together with fourteen oil grooves aiding the rings in retaining compression and assisting the oiling. All pistons are rough turned and then thoroughly annealed before grinding, to insure against warping in service. The piston rings are of clean springy iron, ground all over. As a ring must be tight on the sides as well as where it comes in contact with the cylinder, there must not be a variation in width of over a quarter thousandth of an inch. Cylinder: The cylinder is symmetrical in design, insuring even expansion without distortion. Valve-in-the-head construction gives an efficient shape of combustion chamber; the compact charge fired in the centre giving quick, complete combustion, and the large valves give free ingress and egress for the gases.