Flight Control Design Based on Nonlinear Model with Uncertain Parameters

Abstract

A simplified but significantly nonlinear model is used for the short-period longitudinal flight control problem, with c* taken as the output. Uncertainty is included in the model by allowing for a large range in velocity and air density, without any provision for their measurement. The output c*(t) is to lie within specified bounds in response to a range of step commands. A recent exact design technique for uncertain nonlinear systems is used. In this technique, the nonlinear plant set is replaced by a linear time-invariant plant set, which is precisely equivalent to the nonlinear set with respect to the problem tolerances. The design execution then involves frequency response concepts and techniques. For a large problem class, the resulting design is guaranteed to solve the problem for the specific class of inputs posed. The design was simulated with excellent results. a *( C/y C* F(s) G(s) Iy J k Iti L(s) £ m mp nmp P(s) (P q = 6 r(t) R(s) s S T(s) 3 3,