The Rayleigh-Ritz approach is used to investigate the dynamic characteristics of flapwise bending, lead-lag bending and torsion of a composite rotor blade. The analysis is formulated for a composite rotor blade consisting of a single box-beam made of four laminates(top and bottom flanges, and two webs). Each laminate is composed of a number of laminae with arbitrary fiber orientation and stacking sequences. The consitutive relations of an orthotropic lamina are used and the strain-displacement relations, strain and kinetic energies of a composite rotor blade are rederived in this analysis. The stiffness and mass matrices for free vibration of a composite rotor blade is derived from the strain and kinetic energies using a variational principle. In this approach, each natural eigenfunction is used as comparison functions. Numerical results are obtained for only selected symmetric laminates. A systematic study has been made to identity the importance of the stiffness coupling terms on blade dynamic characteristics with changing fiber orientations, thickness ratio, and pretwist angle. The fiber orientations and thickness ratio make a considerable influence on the natural frequencies. But the pretwist angle influence small on the 1st natural frequency only when the rotational speed is large.
