Optimization and comparison of alternative flight control system design methods using a common set of handling-qualities criteria

Abstract

Optimization and comparison of several alternative control system design methods against a common extensive set of dynamics response criteria is demonstrated using the Control Designer’s Unified Interface (CONDUIT). The alternative methods considered are Classical, LQR, Dynamic Inverse and H-infinity as applied to the design of lateral/directional control laws for a transport aircraft. From poor initial guesses for the design parameters of each alternative method, CONDUIT first achieved a feasible design space that satisfied the stability and handling qualities to the best (Level 1) criteria. Final controller tuning was accomplished to minimize the performance metrics of crossover frequency and actuator RMS, while maintaining the Level 1 design criteria. An important *Flight Control Technology Group Leader, Associate Fellow AIAA †Graduate Student ‡Research Scientist This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States finding of this research is that the alternative design methods optimized against a common set of design requirements yield controllers whose performance and stability robustness characteristics are quite similar to one another. A stronger discriminator than design method is the controller architecture (1 or 2 degree-offreedom), which plays an important role in determining the achievable design space. This research demonstrates the feasibility and emphasizes the need to analyze and optimize perspective control designs against a comprehensive set of design requirements. CONDUIT has proven to be an especially effective environment for this task. INTRODUCTION The design, integration, and flight test development of flight control systems factor significantly into the overall time and cost of aircraft development. By one estimate, over 25% of developmental flight testing hours for the UH-60 (BlackHawk) and RAH-66 (Comanche) helicopters were associated with flight control-related issues. With costs that reach $50K per flight test hour for a modern flight test facility, there remains a considerable premium on control law design