Load Alleviation of Flexible Aircraft by Dynamic Control Allocation

Abstract

As wing designs aim for higher aerodynamic efficiency, the underlying aircraft structure becomes more flexible, requiring additional features to alleviate the loads encountered from gusts and maneuvers. While alleviating loads, it is desirable to minimize the deviations from the original flight trajectory. In this work, a dynamic control allocation method that exploits redundant control effectors for maneuver and gust load alleviation is proposed for flexible aircraft. The control architecture decouples the two objectives of load alleviation and rigid-body trajectory tracking by exploiting the null space between the input and the rigid-body output. A reduced-dimensional null space input is established, which affects the flexible output (but not the rigid-body output) when passed through a null space filter to generate incremental control signals. This null space input is determined by model predictive control to maintain the flexible output of the aircraft within specified values, thereby achieving load alleviation. Numerical simulations are used to illustrate the operation of this load alleviation system on nonlinear models. It is shown that the proposed load alleviation system can successfully avoid the violation of load bounds in the presence of both gust disturbances and maneuvers with minimal effect on the trajectory tracking performance.