Higher Harmonic Control: Wind Tunnel Demonstration of Fully Effective Vibratory Hub Force Suppression
Abstract:Closed‐loop Higher Harmonic Control (HHC) has been demonstrated successfully on a dynamically scaled model of the three‐bladed CH‐47D Chinook rotor in the Boeing V/STOL Wind Tunnel. Vertical and in‐plane 3/rev hub forces were suppressed simultaneously, completely, and continuously as the model was “flown” throughout a wide test envelope which included trimmed flight up to 188 knots. This very effective multicomponent suppression was accomplished with a fixed‐gain feedback control law which is much simpler and faster than the adaptive control laws used recently by other investigators. The controller applied small amounts of oscillatory swashplate motion to Droduce multiharmonic blade pitch variations up to ±3.0 deg at very high speed. This control caused only small changes in rotor system loads and performance. A closed‐loop control response bandwidth of 1 Hz was demonstrated. Since this is the approximate bandwidth of maneuvers and gusts, the system can be expected to suppress vibration in unsteady flight conditions. These results were obtained in part by very precise swashplate control at the scaled 3/rev frequency, 69 Hz. The test was also successful in demonstrating swashplate actuators with hydraulic seals which showed little wear after 15 million high‐frequency cycles, about 25 percent of the desired service life for a full‐scale production design.
Document Type: Research Article
Affiliations: Boeing Helicopters, Philadelphia, Penn.
Publication date: January 1, 1989
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