Aircraft Efficiencies

The past seven years have witnessed remarkable developments in aircraft. They have marked the advent, for example, of autogyros, cantilever monoplanes, landing flaps, variable-pitch airscrews, and retracting undercarriages. Equally apparent to engineers will have been the perfection of powerful and compact engines weighing little more than 1 lb. per h.p., the adoption of skin stressing and ducted cooling, the shrinkage of wing area until nearly twice as much load is carried per square foot, and the elimination of exposed struts, wires, levers, and rivet heads. Speeds have advanced greatly with little sacrifice in flying weight per brake horse-power or in useful load. Thus there has occurred a very notable increase in the efficiency of aircraft, exercising a profound influence on aerial transport. Many methods of construction, which have been especially devised to meet stringent conditions as regards economy in weight, should also find application in other high-class engineering productions. Again, the new knowledge of fluid motion and matters associated with it, constituting the engineering science of aerodynamics, must eventually prove of service in hydraulics, heat transfer, ventilation, and kindred subjects.

In the paper some of the main considerations affecting the efficiency of aircraft are described. Exhaustive discussion would form too comprehensive a subject, and it has been decided to consider especially those factors in which fluid motion plays a prominent part. Where possible, however, the treatment takes into account structural and other efficiencies attainable in given circumstances. The point of view adopted is that of civil transport, where efficiency is most urgent. Discussion will turn essentially on speed and, in justification, it may be remarked at once that (a) speed is exceptionally important in the air since the drift of head winds must be subtracted in full, and (b) high speed is the prerogative of aircraft, being in the nature of things most economically and safely attained in their case.