Wind Tunnel Study of Preview H2 and H∞ Control for Gust Load Alleviation for Flexible Aircraft

This paper describes simulation and wind tunnel test results of preview gust load alleviation (GLA) controllers based on H2 and H∞approaches. Aeroservoelastic model and gust generation system capabilities at the University of Washington's 3ft by 3ft low-speed wind tunnel allow low-cost testing and, hence, the completion of multiple GLA wind tunnel tests effectively and practically. The test article is a flexible half wing-body-tail model with active control surfaces, including two ailerons and an elevator. The work reported here demonstrates the feasibility of preview-information-based-control, allowing the control system to respond in advance of incoming gusts that would be, in flight, provided by light detection and ranging devices (LIDAR). In the wind tunnel, such advance warning is provided by measurements of the motion of gust generation vanes that send gusts into the test section. Discrete output feedback is augmented with various preview lengths of information. The experimental results show that gust load is reduced, compared to feedback only, as a function of preview length and is halved with full-gust preview information compared to open-loop control. Test results presented here validate simulation results and add insight. The paper is one of the earliest, if not the first, to report test results for a preview H∞ gust alleviation controller.