Analytical Method of Ground Resonance for Helicopters with Ski Landing Gears

An analytical method of ground resonance dynamic stability countering the helicopters with ski landing gears is provided. Firstly, according to the characteristic of ski landing gears having large deformation acted by helicopter weight and rotor thrust, the stiffness and the deformation of landing gear are calculated using finite element method step by step. Through comparison of Coulomb friction coefficient, the friction forces on ski applied by ground and relative motion between ski and ground can be determined. Secondly, considered the function of dampers mounted between landing gears and the airframe, the finite element method for computing elastic stiffness of landing gear is extended to be adapted to complex stiffness calculation. Finally, the analysis of the ground resonance dynamic stability of helicopters with ski landing gears is preformed by using blade vibration modal method and considering different rotor hub configurations. Analytical method is verified by examples. Results of engineering examples show that the method has a clear physical conception and is convenient for use. It can be adapted to analyze the ground resonance of helicopters with ski landing gears and different rotor hub configurations.