Effect of Ground Proximity on the Regressive Lag Mode during Ground Resonance : An Experimental Study

This paper studies aerodynamic effects of ground on regressive lag mode damping during ground resonance. The experimental investigation is performed on a scaled helicopter model built to simulate the ground resonance scenario. The study involves both stationary as well as dynamic (oscillating) ground conditions. Experiments are conducted by measuring lead-lag damping at different rotor speeds (in the ground resonance regime) for different collective inputs. Results show that ground and its dynamics have a significant effect on regressive lead-lag mode damping during ground resonance. NOTATION e Hinge offset h Distance between rotor hub center and pitch/roll axis Ib Lead-lag moment of inertia for blade kG Thrust augmentation factor Mb Mass of the blade R Rotor radius Rcg Center of gravity of blade Ω Rotor anglular speed θ0 Collective input of blade pitch IGE In ground effect IMU Inertial Measurement Unit MPM Matrix Pencil Method OGE Out of ground effect RLM Regressive lead-lag mode damping during ground resonance.