Application of nonlinear global analysis and system identification to aircraft-pilot coupled oscillations

We present a general framework for the global analysis of nonlinear pilot-induced oscillations (PIOs). The approach involves computation of nonlinear phenomena such as Hopf bifurcation that lead to large changes in structural stability of the pilot-vehicle system (PVS). As an example, the X-15 PIO caused by rate-limiting is considered. The result shows a large jump in limit cycle amplitude indicating a significant change in PVS structural stability. We also present results on PIO detection using subspace identification. Numerical results with linear airframe and rate saturating actuators show that this approach is feasible.