Helicopter vibration reduction using robust control

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Helicopter vibration reduction using robust control

Mannchen, T.

This dissertation presents a control law for a BO 105 helicopter to reduce vibration and gust sensitivity using individual blade control. H_infinite control synthesis is used to develop a robust controller for different helicopter flight conditions. In simulation, hub load vibration can be cancelled in three outputs simultaneously, e.g. in all three hub forces. Reducing hub vibration, however, does not necessarily lead to reduced vibration in the cabin. Therefore, a finite-element model of the flexible fuselage is coupled with the aeromechanical rotor model. Then, a simultaneous vibration reduction is achieved at the pilot and co-pilot seats. To reduce gust sensitivity, lag damping must be enhanced, which requires the lag rate of the blades to be fed back. However, the control law is developed with the constraint of no sensors and, consequently, no measurements in the rotating blades. The use of a model-based control strategy enables lag damping to be enhanced by feeding back the observed lag rates, only requiring measurements of the hub loads. In order to consider the periodicity of the plant in the controller design, a time-periodic gain-scheduled controller is developed.