Tolerance of aircraft longitudinal control to the loss of scheduling information : toward a performance oriented approach

Flight control laws are scheduled with respect to the flight point parameters. However systems failures can occur and induce a loss of these scheduling information. Today, it usually leads to switch to a lower level of automation that is more robust but less easy to handle (although aircraft is still safe). We would like to work on robust design methods to increase, as long as possible, the availability of functions that make flying task easy. This paper investigates the use of non-smooth optimization to solve a robust performance issue formulated as a minmax problem in a H∞ framework. Two algorithms have been benchmarked : HIFOO and HINFSTRUCT. From an application point of view, both algorithms provide real improvement of the robust performance; compared to the baseline controller designed using a worst case approach. Nevertheless HINFSTRUCT seems to be more reliable from a numerical point of view.