Aeromechanical stability analysis and control of smart composite rotor blades

The use of segmented constrained layer damping treatment and closed loop control is investigated for improved rotor aeromechanical stability. The rotor blade load-carrying member is modeled using a composite box beam with arbitrary wall thickness. The ACLs are bonded to the upper and lower surfaces of the box beam to provide active and passive damping in the aeromechanical stability analysis. A finite element model based on a hybrid displacement theory is used to accurately capture the transverse shear effects in the composite primary structure, the viscoelastic and the piezoelectric layers within the ACL. The Pitt-Peters dynamic inflow model is used in the air resonance analysis under hover conditions. Rigid body pitch and roll degrees of freedom and fundamental flap and lead-lag modes are considered in this analysis. A transformation matrix is introduced to transform the time-variant system to a time-invariant system. A LQG controller is designed for the transformed system based on the available measurement output. The control performance is compared with the results of the open loop and the passive control systems. Numerical results indicate that the proposed control system with surface bonded ACL damping treatment significantly increases rotor lead-lag regressive modal damping in the coupled rotor-body system.