ENGINE SHAPE AS AFFECTING AIRPLANE OPERATION 200025
The annual report covering transportation by the largest British air-transport company laid particular emphasis upon the greater value of the faster machines in its service. Granted that efficient loads can be carried, the expense, trouble and danger of the airplane are justified only when a load is carried at far greater speed than by any other means. A reasonable conclusion seems to be that we can judge the progress made in aviation largely by the increased speed attainable. It is interesting and possibly very valuable therefore to inquire into the relations of power and resistance as applied to small racing machines with aircraft engines that are available.
The engine builder is only too likely to think that he has reached the goal required by the aircraft builder if he can make the light-weight figure of the engine “dry,” in pounds per horsepower, low enough, but this attitude is not only erroneous but actually tends to the development for aircraft of engines that are very undesirable. Four specific and reasonable, although admittedly not absolutely correct assumptions, are made and, after analysis, they are stated to mean that engines are not penalized by placing them in different types of aircraft and that the consideration of the figures on a unit horsepower basis is justified. The radiator and wing drift are discussed, with accompanying tables of the sizes of various well-placed radiators and of the air-resistance characteristics of engines, and photographs of various types of engine. The subject of resistance coefficients is treated at some length and followed by an explanation of and comment upon a speed-resistance chart which is presented. The author states that resistance is more important than weight and urges builders to make the shape and disposition of their engines more suitable for airplanes, with low head resistance considered as a fundamental.