The aeroelastic response and stability are investigated for isolated composite hingeless rotor blades in the hovering flight condition, using both a large deflection-type beam theory and a three-dimensional aerodynamics. The finite element equation of motion for a rotating beam is obtained from Hamilton's principle. The formulation of three-dimensional composite box beam formulation consists of two-dimensional cross-sectional and one-dimensional global beam analysis. No kinematical restrictions are imposed on the magnitude of displacements and rotations in the strain-displacement relation, and the effective 6 X 6 sectional stiffness for the composite beam including warping deformation is determined from the refined cross-sectional finite element method. A three-dimensional aerodynamic model, based on the unsteady vortex lattice method with a prescribed wake geometry, predicts the unsteady airload of multi-bladed rotors and the effect of the interblade unsteady wake dynamics beneath the rotor blades on the aeroelastic response. It is found that the effects of three-dimensional aerodynamic tip-relief and unsteady wake dynamics, not predicted in the two-dimensional aerodynamics, play an important role in the composite hingeless rotor aeroelastic analysis in hover. Finally, parametric studies are performed systematically to investigate the effects of composite structural coupling, linear pretwist and precone on the blade's aeroelastic stability, especially for the lightly damped lead-lag modes of six configurations of the composite box beam.
