Performance and robustness metrics for adaptive flight control - Available approaches

A major obstacle for the certification of adaptive flight controllers is the lack of wellaccepted metrics that guarantee deterministic stability, robustness and performance characteristics when the adaptation is active. Since traditional robustness and performance metrics like phase and gain margin or damping coefficients are not applicable to adaptive controllers, new metrics that assess the robustness as well as the performance, especially of the transient dynamics, are required. For these metrics non-conservative and physically meaningful bounds have to be known. During the recent years numerous new metrics and techniques for the controller assessment have been proposed to address this gap. This paper seeks to provide an overview of these available approaches, which may be classified as analytical or simulation-based. In addition to reviewing available robustness and performance metrics with respect to their ability to reflect the behavior of adaptive controllers, the advantages and disadvantages of these classes will be considered.