Helicopter Vibration Reduction in Forward Flight using Blade Integral Twist Control

Active integral twist control for vibration reduction of helicopter rotors during forward flight is investigated in this paper. The twist deformation is obtained us-ing anisotropic piezocomposite actuators embedded in the composite blade construction. An analytical frame-work has been developed to examine integrally-twisted helicopter blades and their aeroelastic behavior during forward flight condition. This is accomplished by modi-fying an existing multi-body dynamics code, DYMORE, with active material constitutive relations. An Active Twist Rotor (ATR) blade was designed in accordance with this framework. A four-bladed fully-articulated ATR system was built and tested to demonstrate the present concept in forward flight. In parallel, the im-pact of the integral twist actuation upon the fixed- and rotating-system loads during forward flight is estimated by the proposed analysis. While discrepancies are found in the amplitude of the loads under actuation, the pre-dicted trend of load variation with respect to its con-trol phase correlates well with the experiments. Using the analysis, system identification is performed to esti-mate the harmonic transfer functions of the ATR sys-tem based on linear time-periodic (LTP) approach. A vibration minimizing closed-loop controller can then be designed based on this system identification results