CONTROL OF INTEGRAL TWIST-ACTUATED HELICOPTER BLADES FOR VIBRATION REDUCTION

Closed-loop active twist control of helicopter rotor blades with integral actuation is investigated in this paper. The focus is reducing hub vibration induced in forward flight. As part of this effort, a four-bladed fully-articulated Active Twist Rotor (ATR) system has been designed and tested successfully in wind tunnel in open-loop actuation. The integral twist deformation of the blades is obtained using active fiber composite actuators embedded in the composite blade construction. An analytical framework is developed to examine integrally twisted helicopter blades and their aeroelastic behavior during different flight conditions. This aeroelastic model stems from a three-dimensional electroelastic beam formulation with geometrical-exactness, and is coupled with finite-state dynamic inflow aerodynamics. Open-loop control test results from the wind-tunnel experiment are used to validate the established aeroelastic model. A system identification methodology that assumes a linear periodic system is adopted to estimate the harmonic transfer function of the ATR system. A vibration-minimizing controller is designed based on this result, which implements a classical disturbance rejection algorithm with some modifications. Using the established analytical framework, the closed-loop controller is numerically simulated and the hub vibratory load reduction capability is demonstrated.