Variable structure robust flight control system for the F-14

In this paper, a flight control law for a simplified F-14 aircraft model is designed based on variable structure control (VSC) theory. For m-input, q-output linear uncertain systems (q < m), a VSC law is derived. For the derivation of the control law, a choice of a sliding surface is made so that the zero dynamics of the system are stable. The linear lateral and longitudinal dynamics of the F-14 are decoupled. This allows design of lateral and longitudinal flight controllers separately. An application of variable structure system (VSS) theory to control of lateral dynamics is presented. A control law is derived for the control of roll angle, lateral velocity, and yaw rate. The chosen sliding surface for the controller design is a linear function of the tracking error, its derivative, and the integral of the tracking error. Simulation results are presented to show that in the closed-loop system, precise bank angle trajectory tracking and regulation of lateral velocity and yaw rate can be accomplished in spite of aerodynamic parameter uncertainty.