Globally stable nonlinear flight control system

The use of linear, constant feedback control in automatic flight control systems for aircraft inevitably gives rise to formidable design difficulties when attempting to satisfy the conflicting requirements for faithful tracking of a pilot´s manoeuvre commands and maintaining the aircraft´s trimmed attitude in the presence of atmospheric turbulence. Two nonlinear control policies, VICTOR and ZOC, are shown to provide superior performance and, when used simultaneously in the same flight control system, to assure global stability. Such stability obviates the need to provide adaptive control or gain-scheduling schemes to satisfy the flying quality requirements over the entire flight envelope of an aircraft. The potential performance of the nonlinear control is demonstrated by means of some results obtained from a digital simulation of a pitch-rate manoeuvre-demand system for a typical medium jet transport aircraft.