8 Stabilization of Unstable Aircraft Dynamics under Control Constraints M.G. Goman † and M.N. Demenkov * † De Montfort University, Faculty of Computing Sciences and Engineering, Leicester U.K. * Department of Computing Sciences and Control, Bauman Moscow State Technical University, Moscow, Russia Stabilization of the unstable dynamic linear system with control constraints is considered in terms of maximizing the size of the closed-loop system stability region. A controllability region for the open-loop system is a natural limit for the stability region of the closed-loop system with any designed controller. A relation between the controllability and stability regions is considered as a performance metric for controller assessment. The linear control laws maximizing the stability region for the constrained linear system are derived for two aircraft stabilization problems. 1 INTRODUCTION Stability augmentation of an aircraft’s dynamics by control system allows one not only to improve its handling quality characteristics, but also to expand the flight envelope and increase its performance characteristics. For example, an aircraft with aerodynamically unstable configuration stabilized by control system can provide higher lift-to-drag ratio or lower signature [1–3]. Critical flight regimes such as high-incidence departures or aeroelas- tic instabilities can be significantly relaxed or even eliminated by an active control approach [4]. The central problem in control law design for regimes with aircraft dynamic instabil- ity is in taking into account the realistic constraints for control effectors such as deflection limits and rate saturation. Unfortunately, in control design works the stabilization problem of unstable aircraft dynamics is usually considered as a linear one without the direct effect of nonlinear control constraints [5]. The control saturation can lead to significant degradation of dynamic characteristics or even to the loss of stability in the closed-loop system. The unstable constrained linear system has a bounded controllability region, where the stabilization problem can be solved. This fundamental fact is normally ignored or assumed insignificant. However, in many practical situations associated with a high level of instability and low control authority, the controllability region decreases significantly and classical linear control design methods lose their efficiency. © 2004 by CRC Press LLC