Abstract: This paper presents a rigid-elastic coupled flight dynamic modeling method for a Heavy Lift Helicopter (HLH), considering the inherent characteristics of heavy weight and slow rotational speed. The method bridges flight dynamics and coupled rotor-fuselage aeroelastic dynamics, expanding the interested range of frequency to 5 Hz with an additional consideration of the elastic fuselage and blades. Based on the impedance matching method, explicit coupled dynamic equations were derived to simulate the helicopter aeroelastic characteristics in real flight. Finally, this model was used to calculate and analyze the flight and air resonance characteristics for an example HLH in hover. The results show that rotor-fuselage coupling causes the progressive lag mode and fuselage bending mode to approach each other and then separate after arriving at the same point with the increase of the rotational speed, which might result in high frequency transient vibration. The regressive lag mode is unstable without sufficient lag damping; however, with the increase of equivalent lag damping, the second order periodic lag mode will be coupled with the fuselage bending mode. The blade elastic modes are coupled with the fuselage bending mode and the collective flap mode without obvious instability.

Key words: helicopter flight dynamics, rotor-fuselage coupling, air resonance, impedance matching method, heavy lift helicopters, rigid-elastic coupling