| The flutter stability of flap bending, lead-lag bending, and torsion of helicopter rotor blades in hover is investigated using a finite element formulation based on Hamilton's principle. Quasisteady strip theory is used to evaluate the aerodynamic leads. The nonlinear equations of motion are solved for steady-state blade deflections through an iterative procedure. The equations of motion are linearized assuming 5ade motion to be a small perturbation about the steady deflected shape. First, the formulation is applied to single-load-path blades, for example, articulated and hingeless blades. Numerical results show very good agreement with existing results obtained using a modal approach. The second part of the application concerns multiple-load-path blades, namely bearingless blades. The flexure of a bearingless blade consists of multiple beams (flexbeams and torque tube) leading to redundancy. The formulation is modified so that the multibeams of the flexure could be modelled individually. Numerical results are presented for several analytical models of the bearingless blade. Results are also obtained using an equivalent beam approach (the common approach) wherein a bearingless blade is modelled as a single beam with equivalent properties. The comparison between the two sets of results shows that the equivalent beam modelling is inaccurate. |
