μ Control of an Ill-Conditioned Aircraft
In this chapter the methods introduced in Chapter 5 will be applied in control of an Advanced Short Take-Off and Vertical Landing (ASTOVL) aircraft. The model applied for the vehicle is valid at low speeds in the transition zone from jet-borne to fully wing-borne flight. In this flight condition the aircraft is unstable in the longitudinal axis and there is very poor decoupling between pilot commands and aircraft response. Furthermore the aircraft is extremely ill-conditioned as the gain of the system decays to zero at steady-state for one particular input direction. The limits this assign on the closed loop system will be thoroughly investigated. The control objectives for the aircraft will be discussed and a performance specification will be derived with due attention to the special gain characteristics of the system. For robustness to dynamic uncertainty, a diagonal dynamic multiplicative perturbation models will be applied at both input and output. A classical control configuration will then be investigated. For a modern design approach the general NΔK framework becomes a very natural way of formulating the control problem. This furthermore possesses the advantage that the uncertainty specification may easily be augmented with a parametric uncertainty description as well. This has been investigated in [TCABG95]. Here we will however confine ourselves to considering dynamic uncertainty. A complex μ optimal controller will be designed for the aircraft using D-K iteration.
KeywordsClose Loop System Robust Stability Classical Controller Bide Plot Pitch Rate
Unable to display preview. Download preview PDF.