Part I: A second approximation to the induced drag of a helicopter rotor in forward flight. Part II: The instantaneous induced velocity at the blade of a finite-bladed rotor in forward flight

Abstract

In Part I, a method is derived for determining the induced drag of a helicopter rotor in forward flight from the distribution of circulation in the wake. Charts of the correction factor to be applied to the ordinary momentum value of induced drag are presented for ranges of flight parameters currently in use. In Part II, the expression for the instantaneous induced velocity at a blade is developed by application of the Biot and Savart Law to a helical wake surface on which the circulation distribution varies both with radius and with azimuth in a manner corresponding to the actual lift distribution on the blade.