In this paper an in-flight tracking control system minimizing vibratory loads at the frequencies 1/rev and 2/rev using steady deflections of active trailing-edge flaps is examined. The control system is based on the relaxed HHC algorithm and uses the Moore-Penrose pseudoinverse of a symmetrized transfer matrix to calculate the control commands for vibration reduction. The focus of the current investigation is on symmetrization effects of the transfer matrices used for controller design on the performance of the control system. In a theoretical pre-flight analysis bounds for the stationary solution of the state-space representation of the closed loop control system are derived on the basis of the Kalman decomposition controller in the frequency domain is calculated. This analysis shows the vibration reduction by the controller using the symmetrized transfer matrices to be close to the optimally achievable reduction. Subsequent, flight tests on a full-scale experimental helicopter in open and closed loop configuration not only verify the functionality of the in-flight tracking control system, but also validate the insignificance of the degradation in control performance due to transfer matrix symmetrization predicted by the theoretical analysis.
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