Aircraft parameter estimation - A tool for development of aerodynamic databases

With the evolution of high performance modem aircraft and spiraling develop mental and experimental costs, the importance of flight validated databases for flight control design applications and for flight simulators has incre ased significantly in the recent past. Ground-based and in-flight simulator s are increasingly used not only for pilot training but also for other appl ications such as flight planning, envelope expansion, design and analysis o f control laws, and handling qualities investigations. Most of these demand a high-fidelity aerodynamic database representing the flight vehicle. Syst em identification methodology, evolved over the past three decades, provide s a powerful and sophisticated tool to identify from flight data aerodynami c characteristics valid over the entire operational flight envelope. This p aper briefly presents aircraft parameter estimation methods for both stable and unstable aircraft, highlighting the developmental work at the DLR Inst itute of Flight Mechanics. Various aspects of database identification and i ts validation are presented. Practical aspects like the proper choice of in tegration and optimization methods as well as limitations of gradient appro ximation through finite-differences are brought out. Though the paper focus es on application of system identification methods to flight vehicles, its use in other applications, like the modelling of inelastic deformations of metallic materials, is also presented. It is shown that there are many simi lar problems and several challenges requiring additional concepts and algor ithms.