Robustness analysis of an integrated flight and propulsion control system using μ and the v-gap metric

This paper describes the application of two frequency domain analysis tools, the structured singular value μ and the v-gap metric, to the problem of evaluating the robustness properties of a multivariable integrated flight and propulsion control (IFPC) system for an experimental V/STOL aircraft configuration. Variations in aircraft parameters and dynamics over the V/STOL flight envelope are represented as linear fractional transformation (LFT) based parametric uncertainty descriptions, using a simple 'black-box' type modelling approach. Tight bounds on μ for the resulting high-order real parametric uncertainty model are computed by introducing small amounts of additional complex uncertainty, in order to analyse the stability robustness properties of the IFPC system. Stability and performance robustness of the IFPC system is also evaluated using the v-gap metric. Results generated by both analysis tools are seen to be consistent, and to agree well with evaluation results obtained for the IFPC system in piloted simulation.