This paper presents a successful treatment of the helicopter vibration reduction problem at high advance ratios, taking into account the effects of dynamic stall. The ONERA model is used to describe the loads during stall, in conjunction with a rational function approximation for unsteady loads for attached flow. This study represents the first successful implementation of vibration reduction in presence of dynamic stall, using single and dual trailing edge flap confogurations. A physical explanation for the vibration reduction process is also provided. Saturation limits on the control deflections are imposed, which limit flap deflections to a practical range. Effective vibration reduction is achieved even when imposing practical saturation limits on the controller. Finally, the robustness of the vibration reduction process in the presence of a freeplay type of nonlinearity is also demonstrated.
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