Helicopter blade twist optimization in forward flight

Abstract

Improving the efficiency of the helicopter is one of the main objectives in helicopter design. Endurance, ceiling and maximum forward flight are strongly connected with the aerodynamic field around the main rotor and its power consumption, in particular the induced power used to generate the thrust needed to fly. It’s possible to minimize this power with the uniformization of the inflow along the blade for all the azimuthal positions. The main objective of this paper is to find for each flight condition the blade twist distribution that minimizes power. The model is based on Blade Element Momentum theory for hovering condition and Blade Element theory for forward flight. It is tested using the flight test data of the UH-60A. The idea is to divide the blade in sections and impose on them a linear or quadratic twist behaviour. The first concept use only a section with linear or quadratic twist distribution. The second concept uses two segments each with a linear twist distribution. In this study different inner segments were analysed corresponding to 40%, 50%, 60% and 70% of the blade length. Finally, the last concept takes in account the main rotor of the Sikorsky UH-60A Black Hawk. It considers three sections and two airfoils and the twist behaviours are linear in each segment.