Paul H. Mirick

Low-cost piezocomposite actuator for structural control applications

The design, manufacture, and testing of a low-cost, flexible, planar composite piezoceramic actuator device will be presented. The actuator uses interdigitated electrodes for poling and subsequent actuation of an internal layer of machined piezoceramic fibers. The fiber sheets are formed from monolithic piezoceramic wafers and conventional computer controlled wafer-dicing methods. The fabrication and use of fiber sheets allows precise handing and alignment of piezoceramic fibers during subsequent phases of actuator assembly. Test show that the actuator is capable of producing large, directional in-plane strains; on order of 2000 parts-per-million under a 4000 V peak-to-peak applied voltage cycle. Preliminary endurance testing indicates that the device is relatively durable, with no reductions in free-strain performance up to 90 million electrical cycles.

VIBRATORY LOADS REDUCTION TESTING OF THE NASA/ARMY/MIT ACTIVE TWIST ROTOR

Recent studies have indicated that controlled strain-induced blade twisting can be attained using piezoelectric active fiber composite technology, and that such advancement may provide a mechanism for reduced rotorcraft vibrations and increased rotor performance. In order to validate these findings experimentally, a cooperative effort between the NASA Langley Research Center, the Army Research Laboratory, and the MIT Active Materials and Structures Laboratory 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 Transonic Dynamics Tunnel. Initial wind tunnel testing has been conducted to assess the impact of active blade twist on both fixed- and rotating-system vibratory loads in forward flight. The active twist control was found to have a pronounced effect on all system loads and was shown to generally offer reductions in fixedsystem loads of 60% to 95%, depending upon flight condition, with 1.1o to 1.4o of dynamic blade twist observed. A summary of the systems developed and the vibratory loads reduction results obtained are presented in this paper.

Rotorcraft Aeroelastic Testing in the Langley Transonic Dynamics Tunnel

Wind-tunnel testing of a properly scaled aeroelastic model helicopter rotor is considered a necessary phase in the design and development of new rotor systems. For this reason, extensive testing of aeroelastically scaled model rotors is done in the Transonic Dynamics Tunnel (TDT) located at the Langley Research Center. A unique capability of this facility, which enables proper dynamic scaling, is the use of diflourodichloromethane, or Refrigerant-12 (R-12) as a test medium. The paper presents a description of the TDT and a discussion of the benefits of using R-12 as a test medium. A description of the system used to conduct model tests is provided and examples of recent rotor tests are cited to illustrate the types of aeroelastic model rotor tests conducted in the TDT.