Supplementary Notes on Drzewiecki's Theory of Airscrews

Abstract

In the previous contribution and in the reply to the discussion justice was not done to several points.It was made clear that a circulation of air was established round the airscrew at standstill, creating a certain velocity before the airscrew disc in such a way as to modify fundamentally the thrust on the blades. But it was not explicitly stated that at full speed (of the aeroplane) this component of velocity was ignored altogether and each blade was assumed to be attacking “ still ” air.This does not mean that the air was still until the blade actually drew level with it, for, if the analogy with lifting surfaces holds, we know that at a distance of twice the chord width in front of the blade the air is appreciably disturbed, and this disturbance may be by no means negligible even at four or five times the chord's width in front of the instantaneous position of the blade.