Abstract: Helicopters should be expressed by space model in which the rotor blades have flag and lap degrees of freedom and the landing gears composed of shock absorbers and wheel tyres provide characteristics varied with frequencies. The paper derives augmented differential equations of motion for the system mentioned above for the first time. Computation methods are also given to determine the dynamic stability. The computation examples prove the reasonableness and effectiveness of the mechanical model and the computational methods presented in the paper.

Key words: helicopter, ground resonance, stability