FOLLOWING a brief outline of the development of aircraft propellers and a statement of the most important fundamentals of propeller design, the authors discuss the problem of propellers for use on geared-down engines, this being the installation of reduction gearing between the crankshaft of the engine and the propeller hub when the increase of airplane-performance characteristics more than offsets the added complication of the installation. The advantages and the disadvantages of using reduction gearing are considered.
Concerning the installation of reduction gears, the authors state that the decision whether to use gears or not must result from a compromise between the gains and the losses involved and the amount of net gain depends largely upon the particular engine and airplane combination and its designed performance. It is said also that gearing is a design refinement and that, very often, a similar gain in performance can be obtained by using more care in attaining cleanness of the general design-characteristics of a given airplane. The authors believe that the trend in large multi-engine transport-airplanes will be decidedly favorable to the use of gearing.