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Session: Flutter control
Session starts: Thursday 20 June, 16:00
Presentation starts: 16:00
Room: Room 1.4/1.5

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Bálint Patartics (HUN-REN SZTAKI)
Béla Takarics (HUN-REN SZTAKI)
Bálint Vanek (HUN-REN SZTAKI)
Ramesh Konatala (DLR)
Matthias Wüstenhagen (DLR)
Özge Süleözgen (DLR)
Manuel Pusch (Munich University of Applied Sciences)
Thiemo Kier (DLR)

Abstract:
Aeroelastic flutter is an adverse interaction between the structural dynamics and the aerodynamics of an aircraft, that manifests as undamped oscillations of the wings. It occurs at lower airspeeds for lightweight aircraft equipped with high aspect ratio wings, which would be desirable for fuel efficiency. To retain efficiency and ensure safe operations, active control solutions to mitigate this problem are widely explored in the literature. This paper presents two flutter suppression control design methods for the P-Flex flexible unmanned aerial vehicle developed within the FliPASED H2020 project. This aircraft has a wing bending-torsion dominated flutter mechanism that first appears at 56 m/s at roughly 8.65 Hz. Another flutter mode is present in the attainable fight domain at 69.9 m/s. The aeroelastic model of the P-Flex aircraft includes rigid body, structural, and unsteady aerodynamics which amounts to over 1000 states [1]. This model undergoes significant reduction to arrive to a control-oriented model applicable for control synthesis [2]. A custom-made actuator, called direct drive, is used to provide the sufficient bandwidth required by the high flutter frequency. Two control approaches are detailed in the paper. The first is an H∞ optimal solution that minimizes the sensitivity function of the closed-loop which in turn maximizes robust stability [3]. Structured H∞ synthesis is employed to obtain two controllers stabilizing the two flutter modes. Disk margin analysis verifies the achieved increase in the closed-loop flutter speed. The second approach finds two optimal blending vectors of the actuating signals and sensor measurements allowing for the isolated control of the unstable modes with minimal influence on the overall flight performance [4]. Both this and the H∞ method expand the safe flight envelope by 15% and are shown not to degrade the performance of the baseline controller which governs the rigid body motion of the aircraft. Also, the refinement of both control laws based on preliminary (below flutter speed) flight test results is presented. The final controllers are flight tested above flutter speed as elaborated in a different paper submitted to this conference [5]. References [1] Wuestenhagen M., et. al. “Aeroservoelastic modeling and analysis of a highly flexible flutter demonstrator”. In 2018 Atmospheric Flight Mechanics Conference, p. 3150. [2] Takarics, B., et. al. “Flight control oriented bottom-up nonlinear modeling of aeroelastic vehicles”. In 2018 IEEE Aerospace Conference, pp. 1-10. [3] Patartics, B., et. al. “Application of structured robust synthesis for flexible aircraft flutter suppression”. IEEE Transactions on Control Systems Technology, 30(1), pp. 311-325. 2021. [4] Luspay, T., et. al. “Flight control design for a highly flexible flutter demonstrator”. In AIAA Scitech 2019 Forum, p. 1817. [5] Bartasevicius J., et. al. “Lessons learnt from flight testing active flutter suppression technologies” Submitted to the 2024 IFASD.