ALLEVIATION OF DYNAMIC STALL INDUCED VIBRATIONS USING ACTIVELY CONTROLLED FLAPS

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. Single and dual actively controlled flaps are used to reduce vibrations. Successful vibration reduction is demonstrated over the entire range of advance ratios considered (0.3 ≤ μ ≤ 0.45). This study represents the first successful implementation of vibration reduction in presence of dynamic stall, and physical explanation for the vibration reduction process is also provided. A methodology for accounting for the increased drag and power penalty associated with flap deflection is also described. Finally, saturation limits on the control deflections are imposed, which keep flap deflections in a practical range. Effective vibration reduction is achieved even when imposing practical saturation limits on the controller.