Abstract: It is more difficult to investigate the helicopter dynamic stability in forward flight than in hover. Air resonance dynamic stability in forward flight is examined. The structure modeling, aerodynamic modeling and equations of motion of rotor and body are derived. The eigenvalues, eigenvectors and mutual excitation of different degrees of freedom of representative instances are calculated and analyzed. The equations with periodic coefficients are solved. The effect of parameters on air resonance dynamic stability is investigated. The influence of air resonance dynamic stability is investigated through the analysis of mutual excitation of different degrees of freedom.

Key words: helicopter, forward flight, air resonance, degrees of freedom