EVALUATION OF AN ASYMPTOTIC METHOD FOR HELICOPTER ROTOR AIRLOADS

There are many approximate methods available for estimating the airloads on helicopter rotors. These methods vary widely in their degree of approximation, accuracy and detail of solution. One such method has been proposed by Van Holten, using an acceleration potential formulation combined with a matched asymptotic expansion technique to calculate the unsteady, three-dimensional airloads on a helicopter rotor blade in forward flight. The study presented here was undertaken to examine the validity and computational feasibility of this method, and evaluate it by comparison with experiment and other available methods. It is found that, within the restrictions of incompressible, potential flow and the assumption of small disturbances, the method does lead to a valid description of rotor flow conditions except under conditions favoring non-linear and interaction effects.