Helicopter Rotor Lag Damping Augmentation Based on a Radial Absorber and Coriolis Coupling

A radial vibration absorber is proposed to augment rotor lag damping. Modeled as a discrete mass restrained by a damped spring and moving along the spanwise direction within the rotor blade, it introduces damping into the lag mode of the blade through strong Coriolis couplings. A two degree-of-freedom model is developed and used to examine the effectiveness of the radial absorber in transferring damping to the rotor lag mode. Results indicate that it is possible to introduce a significant amount of damping in the lag mode with a relatively small absorber mass. The corresponding amplitudes of 1/rev periodic motions are not excessively large. Additionally, a classical six degree-of-freedom aeromechanical stability analysis is augmented with two absorber cyclic degrees of freedom in the nonrotating frame to examine the effect of the radial absorber on aeromechanical stability characteristics. These results indicate that ground resonance instability is eliminated for the range of absorber parameters considered, and in most cases, the stability margins are significant.