Assessment of tip planform effects on the hover characteristics of helicopter rotors

Abstract

A distinguishing feature of helicopters compared to other flight vehicles is their reliance on the main rotor for all forces and moments needed to operate the vehicle. With the use of cyclic and collective pitch variations, pilots can readily vary and control the thrust, propulsive and side forces. Pilots can also control the vehicle attitude by tilting the rotor disk. Because helicopters spend a bulk of the operations in hover, rotors are first designed to ensure optimum hover performance, before other aspects of operations such as forward flight and maneuvers. The objective of this research is to capture and investigate the effects of blade tip planform influence on rotor aerodynamics in hover. This work is guided by a set of test data for several advanced planforms, with the S-76 rotor serving as the baseline. The present studies indicate that swept tapered rotors with an anhedral tip achieve the best performance in hover. Therefore, detailed analysis of how the anhedral tip shape improves the flow field is investigated in the research. It shows from the results that adding anhedral angles to the tip changes the tip vortex position and blade wise circulation, hence a more uniform induced velocity distribution is obtained.