Nonlinear H_∞ control theory and implement in flight control

This paper investigates the implementation of nonlinear H_∞ control theory for F-16 flight control system. The nonlinear equations of motion with six degrees of freedom for F-16 are considered directly to design the nonlinear H_∞ flight controller by treating the longitudinal and lateral motions as a whole. The associated Hamilton-Jacobi partial differential inequality is solved analytically, resulting in a nonlinear H_∞ controller with simple proportional feedback structure. Real aerodynamic data and engine data of F-16 are employed to determine the angles of control surface deflection from the nonlinear H_∞ control command. Feasibility of tracking nonlinear H_∞ control command by using F-16 actuator system is discussed in detail, and the stability and robustness of nonlinear H_∞ flight control system implemented by F-16 actuators are confirmed over large flight envelope in a six degree-of-freedom flight simulator.