Gust Load Alleviation System for BWB (Blended Wing Body) Flexible Aircraft

Abstract: A new BWB concept aircraft was developed to meet the ACARE 2020 vision, NACRE-FW1. A patented feedforward controller was designed earlier at EADS Innovation Works to alleviate the gust loading, the controller was robust over various gust lengths and mass cases. The feedforward controller performed extremely well in reducing wing root moments for gusts longer than 60.9 meter, but the controller deteriorated the original aircraft performance by giving rise to the wing root moments for gust lengths shorter than 60.9 meter. This caused significant damage to the aircraft and affected the sizing issues of the wing root joints. This paper focuses on designing an additional robust control loop which would work together with patented Feedforward controller to improve the performance at shorter gust lengths. Emphasis was given on the reduction of wing root moments keeping the overall stability of the aircraft to an acceptable level. The paper originally contributes towards realising the use of an extra control loop to make the feedforward controller insensitive at short gust lengths, and further improving performance at longer gust lengths. For the control design, the non linear actuators model of the BWB aircraft was linearised with $2nd$ order approximation. New GLAS controller was designed to work together with feedforward controller using different design techniques namely, nominal SISO and modern Linear Quadratic Regulator and Hinfinity controller. The result shows that the nominal SISO controller significantly improves the GLAS's performance in terms of reduction of wing root moments compared to LQ and Hinfinity controller, which provides structural benefits.