Dynamic Stability of Hingeless Rotor Blade in Hover Using Padé Approximations

Abstract

The dynamic stability of a hingeless rotor blade in hover is investigated using a finite-state, time-domain representation of the aerodynamic loads. The linearized equations of motion are obtained by perturbing the motion variables about nonlinear equilibrium deflections. The flutter analysis is performed in the time domain using three different approximations based on Loewy’s deficiency function. The most accurate approximation is obtained using a general nonlinear least-square optimization for the deficiency response function. This problem is subjected to zero and infinite frequency limits and nonnegative poles constraints. Numerical results for both divergence and flutter boundaries are depicted for a hingeless rotor blade configuration and compared to previous work. Two different scenarios for the flutter boundary are observed, depending on the range of lead–lag frequency, collective pitch, and the type of the approximations used.