Improved higher harmonic control analysis for HART-II rotor

A linear quadratic Gaussian controller for active vibratory loads reduction in helicopters is proposed based on a revisited higher harmonic control input. Conventional individual blade control input is redefined by using N-1/rev blade phase lead, N/rev collective, and N+1/rev blade phase lag signals by 1/rev frequencies modulation from the multi-blade coordinate transform. HART-II rotor is analyzed by the multi-body dynamic analysis combined with improved rotation formula on the geometrically exact beam equations equipped with the unsteady dynamic wake. A linear time-invariant representation for HART-II rotor is identified from the responses obtained by recursive Fourier series filter. A MATLAB/Simulink closed-loop control simulation is designed using the identified state-space realization. The N/rev vibratory loads are reduced by 50% while the steady trim function is valid, and the linear control results match well with the nonlinear responses. Furthermore, the multi-variable closed-loop stability estimated by the loop transfer functions using the disk margin analysis provide both gain and phase margins to the present control system.