Robust Multivariable Flutter Suppression for the Benchmark Active Control Technology (BACT) Wind-Tunnel Model

The Benchmark Active Controls Technology (BACT) project is part of NASA Langley Research Center’s Benchmark Models Program for studying transonic aeroelastic phenomena. In January of 1996 the BACT wind-tunnel model was used to successfully demonstrate the application of robust multivariable control design methods (H∞ and μ-synthesis) to flutter suppression. This paper addresses the design and experimental evaluation of robust multivariable flutter suppression control laws with particular attention paid to the degree to which stability and performance robustness was achieved. Introduction Active control of aeroelastic phenomena, especially in the transonic speed regime, is a key technology for future aircraft design.[1] The Benchmark Active Controls Technology (BACT) project is part of NASA Langley Research Center’s Benchmark Models Program[1,2] for studying transonic aeroelastic phenomena. The BACT wind-tunnel model was developed to collect high quality unsteady aerodynamic data (pressures and loads) near transonic flutter conditions. Accomplishing this objective required the design and implementation of active flutter suppression. Two spoilertype control effectors were utilized to investigate the potential for using spoilers to suppress wing flutter. In addition, multiple control surfaces and sensors enabled the investigation of multivariable flutter suppression. An added benefit of multivariable control laws was to provide an opportunity to evaluate the effectiveness of an on-line controller performance evaluation (CPE) tool[3] to assess openand closed-loop stability robustness of multivariable systems. The control law designs were performed in two stages. The first stage involved the design and test of single-input/single-output (SISO) controllers to demonstrate and assess the potential for using spoilers to suppress wing flutter. Since similar designs have been successful in the past,[4] this approach also served to reduce the risk of implementing active flutter suppression and thereby increase the probability of achieving the program objectives. The SISO control results also provided a benchmark for evaluating the benefits of multi-input/multi-output (MIMO) control. The second stage involved the design and test of MIMO controllers to demonstrate the potential for enhanced performance and robustness afforded by the robust multivariable design methods. The design strategy involved using a single fixed control law to suppress flutter over the anticipated range of wind-tunnel operating conditions (rather than using a scheduled control law, for example). This served to simplfy the controller implementation and data analysis, and is representative of how flutter suppression could be effectively implemented on an actual aircraft. This same strategy was applied to both the SISO and MIMO control law designs. Before the design and analysis of the control laws is discussed a short description of the windtunnel model and the mathematical model used for the control design is presented. The design objectives are then discussed followed by discussions of the SISO and MIMO design efforts. Finally, analysis and wind-tunnel test results will be presented. https://ntrs.nasa.gov/search.jsp?R=20040110354 2017-08-28T02:33:47+00:00Z