Determination of Stability and Control Derivatives Using Computational Fluid Dynamics and Automatic Differentiation

With the recent interest in novel control effectors there is a need to determine the stability and control derivatives of new aircraft configurations early in the design process. These derivatives are central to most control law design methods and would allow the determination of closed-loop control performance of the vehicle. Early determination of the static and dynamic behavior of an aircraft may permit significant improvement in configuration weight, cost, stealth, and performance through multidisciplinary design. The classical method of determining static stability and control derivatives—constructing and testing wind tunnel models—is expensive and requires a long lead time for the resultant data. Wind tunnel tests are also limited to the preselected control effectors of the model. To overcome these shortcomings, computational fluid * Graduate Student, NASA Langley Research Center, Multidisciplinary Optimization Branch, MS 159, Hampton, Virginia, Member AIAA † Research Scientist, Multidisciplinary Optimization Branch, MS 159, Senior Member AIAA ‡ Research Scientist, Dynamics and Control Branch, MS 132, Senior Member AIAA § Research Scientist, Dynamics and Control Branch, MS 132, Member AIAA Copyright  1999 by the American Institute of Aeronautics, Inc. No copyright is asserted in the United States under Title 17, U.S. Code. The Government has royalty-free license to exercise all rights under the copyright claimed herein for government purposes. All other rights reserved by the copyright owner. dynamics (CFD) solvers are augmented via automatic differentiation, to directly calculate the stability and control derivatives. The CFD forces and moments are differentiated with respect to angle of attack, angle of sideslip, and aircraft shape parameters to form these derivatives. A subset of static stability and control derivatives of a tailless aircraft concept have been computed by two differentiated inviscid CFD codes and verified for accuracy with central finite-difference approximations and favorable comparisons to a simulation database. Introduction Previous work attempted to determine stability derivatives from computational fluid dynamics (CFD) codes; for example, Finley used an Euler code to compute the forces and moments for a generic configuration from which a subset of the stability derivatives can be inferred by using finite-difference methods. Charlton employed a similar method on the Lockheed Martin Tactical Aircraft Systems—Innovative Control Effectors (LMTAS-ICE) configuration. No attempt was made to compute those derivatives analytically. The present work proposes to use one or more CFD solvers, augmented via automatic differentiation (AD), to directly calculate static stability and control derivatives of the LMTAS-ICE configuration. Using exact AD is ¶ The use of trademarks or names of manufacturers in this report is for accurate reporting and does not constitute an official endorsement, either expressed or implied, of such products or manufactures by the National Aeronautics and Space Administration