Gust Load Alleviation on a Large Transport Airplane

Abstract

This study develops an active control technology to reduce the incremental dynamic loads of a large four-engine transport airplane flying through a gust field. The mathematical model of the proposed gust-alleviation system features composite structural motions (for example, rigid-body motions, elastic vibrations, and deflections of control surfaces) and unsteady aerodynamic forces induced by the structural motions and the gusts. A clear outline of the procedure is first provided to determine the aeroservoelastic equation of the system. Then, an adaptive feedforward controller that uses the preview information of the gust sensed by an onboard alpha probe is designed to operate the ailerons symmetrically to alleviate the wing-root bending moment induced by the gust. The rigid-body motions due to travelling gusts are also compensated for using symmetrical deflections of the elevators. To solve the problems of weight drift and weight bias that are commonly encountered in adaptive control, the circular leaky least mean-squared algorithm is applied to update the weights of the adaptive controller. The simulation results show that a large transport airplane equipped with the proposed gust-alleviation system experiences a significantly lower wing-root bending moment in both stationary and nonstationary gusty environments.