The effect of induced velocity variation on helicopter rotor damping in pitch or roll

Abstract

Tne present investigation is a continuation of a recent report by K. B. Amer on the aerodynamcc damping of a rotor with centrally arranged flapping hinges in a steady pitching or rolling motion. It considers the effect of variation in the induced velocity due to the changes in the distribution of the thrust around the rotor disc. The results are compared with the flight measurements given in Amer's report and the agreement 1s good. The rotor damping primarily depends on two quantities:- (a) the ratio of collective pitch to the thrust coefficient + solidity ratio (already found by Amer), and b) tip speed ratio x rotor angle of attack divided by collective pitch. With regard to the latter, the damping is increased if this expression is positive and decreased if it is negative. This means an increase in damping in autorotation and a loss in damping for helicopter flight, especially at higher tip speed ratios or in climbing flight.