The Prediction of Helicopter Rotor Hover Performance using a Prescribed Wake Analysis

Abstract

A method of calculating the performance of a helicopter rotor in the hover is presented. The method combines the downwash velocity distribution induced by a contracting spiral vortex wake with strip element-momentum theory. The shape of the wake takes a prescribed geometry developed from an extensive series of model tests made in the USA. The predicted thrust and power is in good agreement with measurements made on model and full scale rotors provided that the aerofoil data is sufficiently well defined. The calculated load distribution along the blade is also compared with measurements made on Wessex helicopters. The load distribution is shown to be very sensitive to a light wind but theory compares well with experiment when this effect is eliminated. The hover performance predicted using only the wake induced velocity distribution is also discussed. The rotor performance is shown to be too sensitive to the geometry of the wake for the method to be used as a design tool with confidence, and the mathematical representation of the wake needs improving. * Replaces RAE Technical Report 74078 - ARC 35652.