23rd Congress of International Council of the Aeronautical Sciences, 8-13 September, 2002, Toronto, Canada
Paper ICAS 2002-5.7.4

CONTROL LAW SYNTHESIS FOR AIRCRAFT AUTOPILOT WITH NONLINEAR ELEMENTS

R. Szabolcsi
Miklos Zrinyi National Defense University, Hungary

Keywords: nonlinear systems, describing function, additive uncertainty, optimal control

During control law synthesis for aircraft autopilot there is applied the linear or linearized model of the aircraft.Taylor series method is used for linearization of the aircraft model.The aircraft mathematical model mainly determined for the rigid-body case.In this particular case the high frequency oscillations of the fuselage elastic motion are omitted. There are some types of nonlinear effects,which can be experienced during modeling of elements of automatic flight control systems.These nonlinearities are dead-zone,saturation,relay characteristics or theirs combination etc,which dynamics should be considered during controller synthesis. In this paper aircraft dynamics will be considered with its elastic motion of the fuselage.The elastic motion dynamics is added to the rigid aircraft model as the additive type uncertainty.The nonlinear element to be considered during controller synthesis will be dead-zone plus saturation, which represents typical nonlinear transfer characteristics of the two degree-of-freedom electromechanical gyroscopes. Considering fuselage elastic motion and nonlinearity the control law for the aircraft autopilot will be synthesized.The pitch angle control system will be used for control law synthesis and test of the designed system.

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