Induced shear actuation of helicopter rotor blade for active twist control

Induced shear based mechanism is used for attaining active twist in a soft-inplane hingeless rotor with a two-cell thin-walled airfoil section. The rotor properties dynamically represent a real rotor. A closed loop controller is developed to obtain the optimum voltage required to be given to the rotor blade for obtaining twist using strain rate feedback. Nonlinear relationship between piezoelectric shear coefficient and applied electric field is included in the controller design. Optimal placement of actuators lead to an overall vibration reduction of about 65%. Since thin-walled structures such as rotor blades are highly flexible and have strong aeroelastic effects, these effects on the loads and stability are thoroughly studied to evaluate the feasibility of the active twist rotor concept. No aeroelastic instabilities are found to occur due to active twist.