Helicopter Rotor In-Plane Stability Enhancement Using Trailing-Edge Flaps

The coalescence of a helicopter rotor lagging mode and its coupled rotor/airframe modes can lead to an instability phenomenon called air resonance. This paper investigates the use of piezoactuated trailing-edge flaps to actively enhance the damping of the rotor mode involved in this aeromechanical phenomenon. Numerical simulations as well as flight-test data for the hingeless EC145 helicopter with trailing-edge flaps were used for this purpose. Initially, a numerical model was validated against flight-test data in order to match accurately the phase and gain of the dynamic behavior of the helicopter system actuated by the trailing-edge flaps. The validated model was then used to design a model-based controller for rotor blade lead-lag damping enhancement. The performances of the closed-loop concept were then assessed in simulations and flown during flight tests for the first time for rotor stability enhancement. The presented results show a significant improvement in the transfer behavior of the system at...