Aircraft load alleviation during maneuvers using optimal control surface combinations

Abstract

Control laws in aeronautics are designed to ensure, above all, good handling qualities. However, during extreme maneuvers, which have to be taken into account for aircraft certification, a number of critical structural load limits cannot be guaranteed by this baseline controller. To avoid some modifications of the control law, a solution consists of judiciously exploiting the redundancy of the control surfaces. The aim of this paper is first to find an optimal strategy of the control surface use, which leaves the initial flight behavior unmodified but alleviates a structural load during a selected maneuver. Model predictive control theory solves this offline control allocation problem under actuator saturation constraints. In addition, an identification procedure is proposed to synthesize a new mixing unit that can reproduce this optimal strategy. This methodology is applied to a flexible transport aircraft to alleviate the bending moment at the external wing during a sudden and strong roll maneuver. Copyright © 2006 by ONERA.