Vibratory Loads Reduction Testing of the NASA/Army/MIT Active Twist Rotor

Abstract

Recent studies have indicated that controlled strain-induced hlade twisting can he attained nsingpiezoelectric Active Fiber Composite technology, and that such advancement may provide a mechanism for reduced rotorcraft vibrations and increased rotor performance. To validate these findings experimentally, a cooperative effort between the NASA Langley Research Center, the Army Research Lahoratory, and the MIT Active Materials and Structures Lahoratory has been developed. As a result of this collaboration a four-bladed, aeroelastically scaled, active-twist model rotor has been designed and fabricated for testing in the heavy gas test medium of the NASA Langley 'lkansonic Dynamics Thnnel. Initial wind tunnel testing has been conducted to assess the impact of active hlade twist on both fixed-and rotating-system vihratory loads in forward flight. The active twist control was found to have a pronounced effect on all system loads and was shown to offer generally reductions in fixed-system loads of 60% to 95%, depending upon flight condition, with 1.

Helicopter performance improvement by variable rotor speed and variable blade twist

“…However, they demonstrated that induced-strain actuation of blade twist was a feasible concept for rotor vibration control. The NASA/ARMY/MIT active twist rotor tested in the NASA Langley Transonic Dynamics Tunnel demonstrated rotor vibratory loads reduction in the fixed frame [10,11]. The active twist rotor of Sikorsky Aircraft also demonstrated 1% to 2% rotor power reduction in wind tunnel tests [12].…”

Smart Actuation for Helicopter Rotorblades

“…Early experiments on active twist involved changing the twist of the helicopter blade at the root of the blade [2]. Later experiments used a distributed actuation actuation system to modify the blade twist [46,50,58,66]. In a similar manner to the active trailing edge, the placement and the number of actuators modify the amount of vibration that are reduced.…”

The use of smart structures in the realization of effective semi-active Control systems for vibration reduction

“…1) that has been investigated under the Technical Cooperation Program involving the United States, Canada and Australia, (Nitzsche et al, 2001). Other example following in the same category is the Active Twist Rotor (ATR) program that was developed by NASA and other partners in the United States to reduce vibration in helicopter blades (Wilbur et al, 2002;Shin, Cesnik and Hall, 2005). The trailing-edge flap is another example of direct-active concept under investigation for use in rotorcraft to suppress vibratory hub loads and noise.…”