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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.

The results from a study aimed at improving the aerodynamic characteristics of composite tiltrotor blades through the use of extension-twist elastic coupling are presented. A set of low-twist model-scale helicopter rotor blades was manufactured from existing molds, with a view towards demonstrating the passive blade twist control concept. Hover testing of the set of rotorblades was conducted with the primary goal of measuring the change in blade twist as a function of rotor speed. The blades were spun through the 0-800 rpm range, with a corresponding sweep of collective pitch at 100 rpm intervals to determine the effect on the blade elastic twist obtained.Data

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