Aeroelastic Stability Analysis of a Composite Bearingless Rotor Blade

The aeroelastic stability of flap bending, lead‐lag bending and torsion of a bearingless composite blade in hover is investigated. The analysis is formulated for a bearingless configuration consisting of a single flexbeam with a wrap‐around type torque tube and the pitch links located at the leading edge and trailing edge of the torque tube. For analysis, the outboard main blade and the torque tube are assumed to be made of metals (isotropic materials) and the flexbeam is assumed to be an I‐section made of three laminates, top and bottom flanges and web. Each laminate is composed of a number of laminae with arbitrary ply orientation. The constitutive relations of an orthotropic lamina are used and the strain‐displacement relations are modified for an open laminated section. Numerical results are calculated for selected bearingless blade configurations, categorized as symmetric and antisymmetric, based on the lay‐up of laminae in the flexbeam. A systematic study is made to identify the importance of the stiffness coupling terms on blades stability with changing fiber orientation and for different configurations.