ν-Gap Analysis of Stability Margin Criteria

Summary

In this chapter, we present an approach to the HIRM+ stability margin clearance task which makes use of the tools introduced in Chapter 4; namely, the ν-gap metric and the generalised stability margin. For the single-loop criteria our results are largely in agreement with the baseline method. Indeed, the single-loop analysis may be regarded as an exercise in calibrating the generalised stability margin against the standard Nichols exclusion regions. However, the generalised stability margin also applies directly to a multi-loop analysis (and is just as easily calculated in that case). For this (non-standard) multi-loop criterion we find many extra violations occurring well inside the flight envelope. These violations are not an artifact of any conservatism in the analysis since, at these flight points, we can demonstrate relatively small gain/phase offsets which, when applied simultaneously at each input and output, lead to instability.