Note 3 — The Beginnings

Nothing has been found that would indicate how much consideration they had given to forms of power for propulsion other than the choice they had apparently made quite early—the internal-combustion, four-stroke-cycle piston engine. Undoubtedly, steam was dismissed without being given much, if any, thought. On the face of it, the system was quite impractical for the size and kind of machine they planned; but it had been chosen by Maxim for his experiments,[3] and some thirty-five or forty years later a serious effort to produce an aviation engine utilizing steam was initiated by Lockheed. On the other hand internal-combustion two-stroke-cycle piston engines had been built and used successfully in a limited way. And since, at that time, it was probably not recognized that the maximum quantity of heat it is possible to dissipate imposed an inherent limitation on the power output of the internal-combustion engine, the two-stroke-cycle may have appeared to offer a higher output from a given engine size than the four-stroke-cycle could produce. Certainly, it would have seemed to promise much less torque variation for the same output, something that was of great importance to the Wrights. Against this, the poor scavenging efficiency of the two-stroke operation, and most probably its concurrent poor fuel economy, were always evident; and, moreover, at that time the majority of operating engines were four-stroke-cycle. Whatever their reasoning, they selected for their first powered flight the exact form of prime mover that continued to power the airplane until the advent of the aircraft gas turbine more than forty years later.