Higher Harmonic Control with Pusher Propeller Active Vibration Control for Compound Lift-Offset Coaxial Rotorcraft

Abstract:
For compound lift-offset coaxial rotorcraft, main rotor higher harmonic control (HHC) combined with pusher propeller active vibration control (PAVC) was investigated as an alternative active vibration control (AVC) method to conventional fuselage force generators, which impose a severe weight penalty. A Rotorcraft Comprehensive Analysis System (RCAS) model of a modified Sikorsky XH-59A -- incorporating a NASTRAN elastic fuselage, a horizontal stabilizer, and the airframe wake velocity deficit acting on a pusher propeller — was coupled with the Viscous Vortex Particle Method (VVPM) to study moderate- and high-speed cruise conditions. A parametric study of the aircraft's shaft angle revealed total power variations up to 9% relative to the minimum, along with significant changes in vibration quantified by the intrusion index. Modeling aerodynamic interaction between the main rotor wake, pusher propeller, and horizontal stabilizer was shown to be important for vibration predictions, altering the cockpit intrusion index by up to 33%. Comparisons of closed-loop AVC methods, adding PAVC to HHC successfully reduced cockpit vibrations. However, control weighting is needed to better prioritize and exploit the authority of the large propulsor.

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