Aerodynamic prediction of helicopter rotor in forward flight using blade element theory

Abstract

In this study, the helicopter blade in forward-flight condition was investigated. The blade element theory (BET) was used throughout this analysis to investigate the angle of attack variations at the blade cross sections, lift distribution along the blade and effects of increasing helicopter speed. Prouty's helicopter data was used to validate the analysis results. In this analysis, the helicopter blade was divided into 50 equally spaced elements and the azimuth ψ was set at 7.2° for each movement of the blade. The helicopter speed of 80 m/s was considered. The analysis revealed that the computation results were in good agreement with Prouty's diagram. Furthermore, it was also evident that in the case of a helicopter in forward-flight condition, the blade at retreating side was generally at low angle of attack and experienced low lift, in contrast to the blade at advancing side. The increment of the helicopter speed affected the lift distribution along the blade. The reverse flow area was widened two times from that given by the original Prouty's diagram. In addition, it was proven that each helicopter has its own speed limit called velocity never exceed (VNE). It was also shown that BET is important in conducting the analysis to modify the helicopter blade design for the aerodynamic characteristics' improvement as well as stability and general performance enhancement for the helicopter.