Investigation of Linear Higher Harmonic Control Algorithm for Rotorcraft Vibration Reduction

A linear quadratic Gaussian controller for active vibratory loads reduction in helicopters is proposed based on a revisited higher harmonic control input by active trailing-edge flaps. Conventional individual blade control input is redefined using N-1/rev inter-blade phase lead, N/rev collective, and N+1/rev inter-blade phase lag signals where 1/rev frequency modulation originate from the multi-blade coordinate transform. A Mach-scaled flap blade is designed and analyzed by the multi-body dynamics analysis DYMORE. A linear time-invariant representation is identified from N/rev envelopes of the input and output responses obtained by DYMORE analysis. A MATLAB/Simulink closed-loop control simulation is designed using the identified state-space realization. The N/rev vibratory loads are reduced up to 52% with flap deflections and the linear control results match well with the nonlinear responses obtained from DYMORE. Furthermore, the multi-variable closed-loop stability estimated by the loop transfer functions using disk margin analysis reveals sufficient gain and phase margins.