Integrated actuation system for individual control of helicopter rotor blades

Integrated actuation system for individual control ofhelicopter rotor bladesDariusz Bushko, Ralph Fenn, Mike Gerver, John Berry, Frank PhilipsSatCon Technology CorporationCambridge, Massachusetts 02142Donald J. MerkleyU.S. Aiiny AATDFort Eustis, VirginiaABSTRACTThe unique configuration ofthe rotorcraft generates problems unknown to fixed wing aircraft. These problems includehigh vibration and noise levels. This paper presents the development and test results of a Terfenol-D based actuator designedto operate in an individual blade control system in order to reduce vibration and noise and increase performance on ArmyUH-60A helicopter. The full -scale, magnetostrictive, Terfenol-D based actuator was tested on a specially designed testbedthat simulated operational conditions of a helicopter blade in the laboratory. Tests of actuator performance (stroke, forcemoment, bandwidth, fatigue life under operational loading) were performed.Keywords: smart structures, magnetostrictive actuators, vibration control, helicopters, actuators1. ROTORCRAVF VIBRATION ATTENUATIONHelicopters have unique problems resulting from the continuously changing aerodynamic conditions as blade is travelingthrough various angles around its axis of rotation. Depending on the particular helicopter's mode of operation (hover, forwardflight, etc.) the rotor blade is subjected to the combination of typically highly turbulent air streams induced by motion of theentire helicopter and its rotor blades. At given moment each section of the blade in span direction may actually be exposed todramatically different aerodynamic conditions. Consequently, vibration, noise and considerable degradation of rotorcraftperformance are observed. In fact, aerodynamic interactions taking place in the vicinity of the helicopter rotor are typically aprinciple source of helicopter noise. Vibration induced problems include pilot and passenger fatigue, increased maintenance,payload damage, additional structural weight to carry fatigue loading, and undesired noise signature. Vibration reductionsystem ofthe helicopter rotor blade is the goal ofthe presented work.The primaiy objective here is to design a practical vibration reduction system for the Army UH-60A helicopter. Since thepresented technology is well scaleable towards larger systems the choice ofthis particular aircraft is specially suitable due to itssizable blade profile and relatively low revolution rate of the rotor. The adopted approach is to attack the problem at its roots,namely, rotor blades. The idea is to control aerodynamic response ofthe rotor by inducing a pre-defined pitch angle variation ofvarious sections of the rotor blades in order to dampen momentary blade vibrations. Obviously this additional control functionfor the blade pitch angle tuust be virtually negligible to primary flight control functions (cyclic and collective pitch anglecontrols).