Design of Nonlinear Flight Controller for Fighter Aircraft

Abstract

A nonlinear flight controller is developed using dynamic inversion principles. The nonlinearities in the equations of motion arising from inertia coupling and the gravity vector are compensated by dynamic inversion. Control and state decoupling is demonstrated for conventional aileron, elevator and rudder control surfaces using a static control allocation matrix and choice of stability axis rates for feedback respectively. We demonstrate that the right hand sides of the equations of motion can be approximated by using flight path variables and traditional feedback signals like normal and lateral accelerations. Further, except for the inertia compensation and gravity compensation terms which contain sine and cosine functions, the remainder of the controller can be designed in the linear domain. The simulation results are presented for a case where a nonlinear high performance fighter aircraft is undergoing a high angle of attack stability axis roll maneuver. This maneuver exercises the aircraft over a very wide dynamic range in a short time and demonstrates the capabilities of the nonlinear controller.