Nonlinear Dynamics of Aircraft Controller Characteristics Outside the Standard Flight Envelope

Abstract

In this paper, the influence of the flight control system over the offnominal behavior of a remotely operated air vehicle is evaluated. Of particular interest is the departure/upset characteristics of the closed-loop system near and beyond stall. The study vehicle is the NASA Generic Transport Model, and both fixed-gain and gain-scheduled versions of a linear quadratic regulator controller with proportional and integral components are evaluated. Bifurcation analysis is used to characterize spiral and spin behavior of the aircraft in closed-loop form and yields an understanding of the underlying vehicle dynamics outside the standard flight envelope. The use of a “gain parameter” to scale the controller gains provides information on the sensitivity of stability to gain variation, along with tracking how the controller modifies the open-loop steady states. Hence, this provides a means of assessing the effectiveness of the controller and evaluating the upset tendencies of the aircraft.