A structure load alleviation control system for a large aircraft

Abstract

By using active control technology (ACT) on a large flexible aircraft it is possible to effect some alleviation of dynamic loads to which the wing is subjected when the aircraft performs some commanded manœuvre or when it encounters unwanted atmospheric turbulence. The design of such a load alleviation control scheme by means of linear optimal control theory is described in this paper. Of particular concern are the effects upon the aircraft's structural behaviour of using impaired optimal feedback control caused either by the use in the design method of simpler mathematical models to describe the aircraft dynamics, or by the practical impossibility of obtaining for measurement the complete state vector of the aircraft, or by the failure of particular motion sensors. A simple algebraic method of accounting for the deficit in steady-state load values, which occurs as a result of having to use such reduced- order feedback control, is presented in addition to several results which illustrate the effectiveness of the load alleviation scheme when the aircraft encounters turbulence.