The aeroelastic stability analysis of composite rotor blades is invesigated using a large deflection beam theory. The beam theory uses Euler angles to describe the arbitrary large displacements and rotations. The sectional elastic constants of a composite box beam include warping deformation in the out-of-plane direction. Two-dimensional quasi-steady strip theory and Loewy＇s aerodynamic theory with the lift deficiency function are used for unsteady aerodynamic computation. The finite element equations of motion of a rotating beam are obtained from Hamilton＇s principle.
The optimization studies have been carried out for rotor blades with composite box-beam spars. The objective function is to minimeze the weight of rotor blades subject to frequency, aeroelastic stability and failure constaint. The design variables include the number of plies and ply angles of the laminate. The p-k method is used to determine aeroelastic stability boundary. The Tsai-Hill＇s structural failure criteria are used in this analyses. The frequency variation range for the first lag. flap and torsion modes are restricted wihtin 3%. Through the optimization procedure, the weight reduction of composite rotor blade is 20% and the aerodlastic stability characteristics have been improved significantly.
