Stability margin analysis of multivariable aircraft control system under single loop perturbation

The multivariable aircraft control system probably becomes unstable caused by those perturbations occurred in all control loops simultaneously or only one of the loops. This paper presents a method to evaluate the stability margin of multivariable aircraft control system under single-loop perturbations by using the structured singular value. By introducing the diagonal multiplicative perturbation matrix at the system input node, system stability margin under single-loop perturbations can be calculated. The evaluation method can handle with three types of the single-loop perturbations, including complex perturbation, amplitude perturbation and phase angle perturbation. The method can evaluate more accurately the stability margin of the multivariable closed-loop system under single-loop perturbations. Simulations on a typical lateral-loop simulation model of a kind of aircraft and an F16 simulation model are given, and the results show the effectiveness.