Development and Evaluation of a Generic Active Helicopter Vibration Controller

A computerized generic active controller has been developed for alleviating helicopter vibration by closed-loop implementation of higher harmonic control (HHC). This controller provides the capability to readily define many different algorithms by selecting from three control approaches (deterministic, cautious, and dual), two linear system models (local and global), and several methods of limiting control. A non-linear aeroelastic analysis was used to evaluate alternative configurations as applied to a forward-flight simulation of the four-bladed H-34 rotor operating on the NASA Ames Rotor Test Apparatus (RTA), which represents the fuselage. Excellent controller performance is demonstrated for all three control approaches for steady flight conditions, having moderate to high values of forward velocity and rotor thrust. Reductions in RTA vibration from 75 to 95 percent are predicted with HHC pitch amplitudes of less than one degree. Good transient performance and vibration alleviation is also demonstrated for short duration maneuvers involving a sudden change in collective pitch. The existence of multiple HHC solutions to achieve low vibration indicates the potential for calculating solutions that also reduce the detrimental effects of HHC on blade stresses and rotor performance. The effect of controller tuning on system performance is also discussed.