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Meeting	ACGS Committee Meeting 123 - Santa Fe, NM - March 2019
Agenda Location	7 SUBCOMMITTEE C – AVIONICS AND SYSTEM INTEGRATION 7.2 Flutter Suppression Phase II for a Flying-Wing Research Drone - Margins?
Title	Flutter Suppression Phase II for a Flying-Wing Research Drone - Margins?
Presenter	Dave Schmidt
Affiliation	DK Schmidt and Associates
Available Downloads*	presentation
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Abstract	David K. Schmidt, Schmidt and Associates Brian P Danowsky and Aditya Kotikalpudi, Systems Technology, Inc. Peter J. Seiler, University of Minnesota Julian Theis, Hamburg University of Technology Active control is being employed in a NASA-sponsored program to leverage structural flexibility in order to maximize aerodynamic efficiency of transport aircraft over their flight envelope, and in this context active flutter suppression (AFS) is a key high-risk enabling technology. Our research involves developing three candidate AFS control systems, and evaluating them in flight test using an unmanned flexible composite flying-wing drone as the test bed. The drone has a 10-foot wingspan with an aspect ratio of almost 10, weighs about 14 lb, and is modeled after the Lockheed-Martin BFF drone that preceded the X-56A. The test bed was designed, constructed, and ground and flight tested at the University of Minnesota UAV Laboratory. Three different teams are developing three different AFS controllers, one designed via a robust-H∞ formulation, one designed using output-feedback and a novel LQR formulation (STI’s MIDAAS), and a classical design based on the concept known as Identically Located Acceleration and Force (ILAF). Due to safety-of-flight considerations, the study has proceeded in two phases, with Phase I aimed at demonstrating damping augmentation of the flutter mode below the open-loop flutter speed. This phase was completed in late 2017, with all controllers successfully augmenting the damping of the target flutter mode below the open-loop flutter speed, and two controllers (MIDAAS and ILAF) actually expanding the flutter boundary. Phase II is underway, with the three controllers being designed to maximize the flutter speed, and flight testing is being planned for Spring 2019. But instead of maximizing the closed-loop flutter speed, the design objective is to maximize the airspeed at which the aircraft can meet a certain stability-robustness requirement, thus expanding the “service envelope” of the vehicle. We call this airspeed the “Robust Flutter Speed,” and preliminary results indicate that all three controllers can accomplish this goal. But at issue is the appropriate stability-robustness criteria to use. Sought is a criteria that is familiar and generally accepted by the flight-control community, and independent of the vehicle in question. The candidate currently being considered is selected to be consistent with the intent of SAE AS94900A, specifying SISO gain and phase margins on all loops broken at either the control inputs or the control outputs. Through discussion at this meeting, we hope to receive input from this community on the issue of the most appropriate robustness criteria to use in this study, and the topic of stability margins in AFS in general.