Testing of Folding Wingtip for Gust Load Alleviation of Flexible High-Aspect-Ratio Wing

Folding wingtips have begun to feature on recent aircraft designs, as a solution for compliance with existing airport gate width regulations while enabling high-aspect-ratio wings for lower induced drag and better overall fuel efficiency. Recent studies have suggested that by allowing folding of the wingtip during flight, additional gust load alleviation can be achieved. This paper describes the first experimental study of the folding wingtip concept, when applied to a highly flexible, high-aspect-ratio wing. Using a low-speed wind tunnel with a vertical gust generator, the experiment examined the load alleviation performance through a range of one-minus-cosine gust inputs and found up to 11% reduction in peak wing-root bending moment. In addition, a movable secondary aerodynamic surface was fitted to the folding wingtip, which demonstrated that such a device was able to control the orientation of the folding wingtip effectively in steady aerodynamic conditions, as well as achieving further reduction in peak wing-root bending moment during gust encounters through active control.