Abstract: An analytical model of helicopter rotor/airframe coupled system with fuselage state feedback is presented, and the effects of feedback coefficients on the helicopter ground resonance stability are investigated. By Floquet theory and transition matrix technology, the modal frequency and damping values are resoluted and verified by numerical simulations for nonlinear model. Analytical results show that the regressive lag modal damping levels can be increased efficiently with fuselage roll state feedback introduced. However, the excessive roll amplitude feedback coefficients may result in significant decrements of helicopter dynamic stability while the regressive flap mode becomes dominant and unstable. The phenomenon arises physically from rotor flapping and fuselage mutual excitations in phase.

Key words: helicopter, ground resonance, state feedback, dynamic stability control, numerical simulation