Aerospace Technical Center (CTA)

12228-900 São José dos Campos, São Paulo, Brazil

This paper deals with the helicopter ground resonance phenomenon, more specifically, with a simplified two-bladed hingeless rotor model analysis, which takes into account the lead-lag degree-of-freedom of a rigid blade and the longitudinal and lateral degrees-of-freedom of the rotor support. The analysis neglects both the blade out-of-the-plane motion and aerodynamics effects. The stability analysis of the dynamics system takes the state-variable approach and utilizes the Floquet theory for solving the differential equations in the nonrotating reference system. Results show modal frequency and damping diagrams as function of rotor rotational speed for hingeless rotor configurations including no damping on both support and blades, including damping on both blades, and including an inoperative blade damper. Similar results are shown for an articulated rotor configuration including an anisotropic support. Modal damping diagrams for both rotating and nonrotating frame analyses are presented for hingeless rotor configurations including damping on both blades and including an inoperative blade damper. Results also include effects of inertial coupling variation in the rotating frame. Eigenvector analysis enlightens the inherent connection of divergence and resonance instabilities with in-phase components of displacements and corresponding time rates for all configurations studied.