Closed- Loop Control Test of the NASA/Army/MIT Active Twist Rotor for Vibration Reduction

摘要

Closed-loop vibration control tests were conducted on a twist-actuated model helicopter rotor in forward flight. The Active Twist Rotor (ATR) is a four-bladed, Mach-scaled, fully articulated rotor, with active blades. The active blades have embedded piezoelectric active fiber composite actuators that allow direct control of blade twist. The experiments were conducted at the NASA Langley Transonic Dynamics Tunnel. During the tests, the rotor system response characteristics were identified, using linear time-periodic (LTP) system identification techniques. Results indicated that the effects of periodicity on the system response are small, and hence time-invariant control techniques can be used. The control algorithm used is based on the modified T matrix approach, which results in a continuous-time control law. The control laws used were designed to reduce both 4P and 1P hub normal shears (the dominant vibration loads) simultaneously. Cyclic twist was used to control the 4P vibration, while collective twist was used to control the 1P vibration. It was found that a single control law could be used successfully throughout the test envelope (μ = 0.14 to μ = 0.333). At all advance ratios, the 1P and 4P vibrations were significantly reduced.