Physics-Based Trim Optimization of an Articulated Slowed-Rotor Compound Helicopter in High-Speed Flight

Abstract

The present study focuses on the optimal trim states of a compound helicopter with an articulated main rotor, at a high-speed of 225 kt. In addition to conventional helicopter trim variables, variation in main rotor revolutions per minute, auxiliary thrust, stabilator pitch and aileron deflection are considered. Simulations are based on a compound derivative of a modified UH-60A helicopter with a 20,110 lb gross weight operating at standard sea level conditions. The results show that to achieve a reduced power requirement the stabilator should be used to bring the aircraft to a nearly nose-level pitch attitude, resulting in a significantly high wing lift share (approaching 70% in this study). Using the ailerons to introduce a roll right moment allows the rotor to operate at a higher lift-offset and generate its share of the lift with greater aerodynamic efficiency on the advancing side. In addition to the use of stabilator and ailerons, reduction in main rotor revolutions per minute is favored for low power, and the combination of these control surface and revolutions per minute settings reduces the rotor drag thereby requiring lower auxiliary thrust from the propulsor. The paper provides detailed discussions on the physical mechanisms producing changes to the trim state and the associated power benefits realized.