Abstract: Helicopter rotor blade dissimilarities such as blade to balde aerodynamic, stiffness, mass and damping unbalanced are most likely to ccour in operations. To study the effects of blade dissimilarities to helicopter self-excitations, analytical model of rotor/fuselage coupled stability is presented which is appropriate to helicopter ground resonance, hovering or trimmed flight air resonance. Equivalent hinged stiffness rotor blade and dynamic inflow model are taken into account. Dynamic equations of each blade and fuselage motions are derived, respectively, at rotating and fixed frame coordinates. The model is then employed in study of the effects of a damper failure on ground resonance stability. Numerical simulations are conducted to demonstrate the blade flap, lag, fuselage roll and pitch responses. The regressive lag modal damping is resolved with Floquet transform matrix technology and verified by time-domain analysis. It shows that the characteristics of each blade lead-lag behavior is very dissimilar arising from a damper failure, and the regressive lag modal damping has above 60% decrement.

Key words: helicopter dynamics, ground resonance, numerical simulation, damper failure