Abstract: With the method of first order approximation,the characteristics of limit cycle of ground resonance system of helicopter with nonlinear damping have been analyzed.The relevent formulae have been derived,and corresponding cornputer program has been developed.Some model of helicopter being taken as an example,the influences of the states and the vibrntion modal param-eters of the fuselage system on the characteristics of limit cycle of ground resonance system have been investigated,the performance of nonlinear blade damping in the depression of ground reso-nance has been analvzed,and the relation between the rotating speed of rotor and the energy transference of rotor system to fuselage system has been shown.

Key words: ground resonance-helicopters, nonlinear damping, limit cycle