The consistency of helicopter ‘ground resonance’ and the unstable lateral-torsional vibration in standard rotor systems

Ground resonance is a specific unstable vibration caused by the modal coupling between the blades and fuselage of a helicopter structural system. On the other hand, the unstable vibration in a standard rotor model can also be triggered by lateral-torsional coupling. This paper studies the consistency of instability mechanisms between the ground resonance and the lateral-torsional coupling vibration. Based on the two-dimensional equivalent model of helicopter system, the critical elements leading to the ground resonance are firstly studied by modal analysis. Comparison between the ground resonance and the lateral-torsional coupling vibration is then performed in two aspects: critical elements causing instability in dynamic matrices and modal shapes in the modal coupling ranges. Results demonstrate that the instability mechanism of the ground resonance is consistent with which of the lateral-torsional coupling vibration. The reason why similar instability does not occur in the general rotor system with elastic supports is also clarified.