Modeling the Benchmark Active Control Technology Wind- Tunnel Model for Application to Flutter Suppression

This paper describes the formulation of a model of the dynamic behavior of the Benchmark Active Controls Technology (BACT) wind-tunnel model for application to design and analysis of flutter suppression controllers. The model is formed by combining the equations of motion for the BACT wind-tunnel model with actuator models and a model of wind-tunnel turbulence. The primary focus of this paper is the development of the equations of motion from first principles using Lagrange’s equations and the principle of virtual work. A numerical form of the model is generated using values for parameters obtained from both experiment and analysis. A unique aspect of the BACT wind-tunnel model is that it has upperand lower-surface spoilers for active control. Comparisons with experimental frequency responses and other data show excellent agreement and suggest that simple coefficient-based aerodynamics are sufficient to accurately characterize the aeroelastic response of the BACT wind-tunnel model. The equations of motion developed herein have been used to assist the design and analysis of a number of flutter suppression controllers that have been successfully implemented. 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 and demonstrate flutter suppression using spoilers. Accomplishing these objectives required the design and implementation of active flutter suppression. The multiple control surfaces and sensors * Aerospace Research Engineer, Senior Member AIAA. Copyright © 1996 by the American Institute of Aeronautics and Astronautics, Inc. No copyright i s asserted in the United States under Title 17, U.S. Code. The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Governmental purposes. All other rights are reserved by the copyright owner. on the BACT enabled the investigation of multivariable flutter suppression. And the availability of truly multivariable control laws provides an opportunity to evaluate the effectiveness of a controller performance evaluation (CPE) tool[3] used to assess openand closed-loop stability and controller robustness when applied to multivariable systems. An underlying requirement of all these objectives is the availability of a mathematical model of the BACT dynamics. A mathematical model is the basis for nearly all control design methods, therefore an appropriate model is essential. The importance of having a good model of the dynamic behavior cannot be overstated and the model must be developed with a mind toward the needs of control law design. In addition, appropriate models are required to accurately assess system performance and robustness. Extensive analysis and simulation are usually required before controller implementation to assure that safety is not compromised. This is especially true in the area of aeroservoelastic testing in which failure can result in destruction of the windtunnel model and damage to the wind-tunnel. Mathematical models for control law synthesis must characterize the salient dynamic properties of the system. One of the most important properties to accurately model is the frequency response in the vicinity of the key dynamics over the anticipated range of operating conditions. In the case of flutter suppression, the key dynamics occur near the flutter frequency and the operating conditions correspond to a wide range of dynamic pressures and Mach numbers representing both stable and unstable conditions. Also important are the key parametric variations associated with the system and the uncertainties associated with the assumptions and limitations of the analysis tools and other data used to build the model. The development of the model of the dynamic behavior of the BACT presented herein was motivated by several factors. A primary motivation was based on the fact that the tool normally used at NASA Langley to model aeroelastic systems, ISAC[4], is unable to model spoilers. Since the demonstration of flutter suppression using spoilers was a key objective of the BACT project an alternative modeling approach was needed. Another motivation for the particular modeling approach taken here was the desire to assess the impact of model uncertainty and parametric https://ntrs.nasa.gov/search.jsp?R=20040110943 2017-09-13T22:29:32+00:00Z