An Experimental Investigation of the Effects of Aeroelastic Couplings on Aeromechanical Stability of a Hingeless Rotor Helicopter

A 1.62-m diameter rotor model was used to investigate aeromechanical stability, and the results were compared to theory. Configurations tested included 1 a nonmatched stiffness rotor as a baseline, 2 the baseline rotor with negative pitch-lag coupling, 3 the combination of negative pitch-lag and structural flap-lag coupling on the baseline rotor, 4 a matched stiffness rotor, and 5 a matched stiffness rotor with negative pitch-lag coupling. The measured lead-lag regressing mode damping of the five configurations agreed well with theory, but only the matched stiffness case with negative pitch-lag coupling was able to stabilize the air resonance mode. Comparison of theory and experiment for the damping of the body modes showed significant differences that may be related to rotor inflow dynamics.