A semi-active Magneto-Rheological Fluid-Elastic (MRFE) device has been assembled and evaluated in control experiments to demonstrate its utility to compensate for measured changes as a helicopter lag damper. The baseline damper used in this study was a Fluidlastic~? FL-103 0-8 damper manufactured by Lord Corporation for the Bell 430 helicopter. This damper was disassembled and modified to include two internal magnetorheological control valves, and the existing hydraulic fluid was replaced with magnetorheological fluid. Hence, the resulting prototype damper is a retro-fit design that can easily be installed in a test rotor in future evaluations. The MRFE damper was subject to extensive performance characterization at displacement amplitudes ranging from 0.8 mm to 3.4 mm, temperatures ranging from 20°C to 55°C, and control currents up to 2.0 A. Using this database and a hydro-mechanical model of the damper, control systems were designed to track a reference damping profile, which is a function of amplitude only, in the presence of measured amplitude and temperature variations at the rotor lag/rev frequency (3.8 Hz). Both open-loop (interpolating look-up table) and closed-loop (proportional-integral and gain scheduling) techniques were employed in simulations and experiments. The results demonstrated that all of the control schemes were effective, though minimum tracking error was achieved with the closed-loop systems. Comparing the two closed-loop systems, the gain scheduling controller provided a faster response overall, but the improvement was marginal.
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