Use of feedback control to address flight safety issues

This thesis addresses three control problems related to flight safety. The first problem relates to the scope of improvement in performance of conventional flight control laws. In particular, aircraft longitudinal axis control based on the Total Energy Control System (TECS) is studied. The research draws attention to a potentially sluggish and undesirable aircraft response when the engine dynamics is slow (typically the case). The proposed design method uses a theoretically well-developed modern design method based on Hinfinity optimization to improve the aircraft dynamic behavior in spite of slow engine characteristics. At the same time, the proposed design method achieves other desirable performance goals such as insensitivity to sensor noise and wind gust rejection: all addressed in one unified framework.; The second problem is based on a system level analysis of control structure hierarchy for aircraft flight control. The objective of the analysis problem is to translate outer-loop stability and performance specifications into a comprehensive inner-loop metric. The prime motivation is to make the flight control design process more systematic and the system-integration reliable and independent of design methodology. The analysis problem is posed within the robust control analysis framework. Structured singular value techniques and free controller parameterization ideas are used to impose a hierarchical structure for flight control architecture.; The third problem involves development and demonstration of a new reconfiguration strategy in the flight control architecture that has the potential of improving flight safety while keeping cost and complexity low. This research proposes a fault tolerant feature based on active robust reconfiguration. The fault tolerant control problem is formulated in the Linear Parameter Varying (LPV) design framework. A prime advantage of this approach is that the synthesis results in a single nonlinear controller (as opposed to a bank of "robust" controllers) with guaranteed robustness. Another important feature of this design platform is the ability to incorporate varied levels of flight performance without sacrificing stability. This implies that the closed-loop can be designed for a suitably degraded performance level as a consequence of component failures along with guarantees on the safety of aircraft operation.