The history of the Curtiss motor goes back to the early days at Hammondsport; it was the keynote of the development of the motorcycle, the airship, the aeroplane, and the hydro. From a crude single-cylinder engine used on an experimental bicycle, the motor has developed to an eight-cylinder engine giving over eighty horsepower, on which the reliability of the Curtiss aeroplane is dependent. Indeed, flight itself, in the history of the world, was delayed until the development of the gas engine made it possible to get a power that was applicable for this purpose, and one that was, at the same time, light enough.
To describe the motor intelligibly to one who has had no acquaintanceship whatever with gas engines would require many chapters, but to those who have ever examined automobile, marine, or other motors, the following technical data will give an idea of the distinctive feature of this aeroplane motor.
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.