The aeroelastic response and stability of isotropic and composite rotor blades are investigated using a large deflection-type beam theory in hovering and forward flight. The finite element equations of motion for beams undergoing arbitrary large displacements and rotations, but small strains, are obtained from Hamilton's principle. The sectional elastic constants of a composite box beam including warping deformations are determined from the refined cross-sectional finite element method. Static and dynamic behavior of composite box beams is compared with the previously published experimental and theoretical results for verification. A two-dimensional, quasi-steady strip theory with the Drees linear inflow model is applied for the aerodynamic calculation. The nonlinear, periodic blade response is obtained by integrating the full finite element equation in time through a coupled vehicle trim procedure in the forward flight condition. After an equilibrium position is obtained, the aeroelastic stability analysis is performed for the linearized stability equations with respect to this equilibrium position.
In the hovering case, numerical results of stability analysis are verified and the effects of the structural couplings on the stability are systematically investigated for six ply configurations of the composite box beams. In the forward flight condition, the results of a full finite element analysis using the large deflection-type beam theory are compared with those of a previously published modal analysis using the moderate deflection-type beam theory and it is found that the nonlinear kinematic effects play an important role in the hingeless rotor aeroelastic analysis.
