Whiffling-inspired gapped wings alter trim and mitigate gusts

Abstract

Some species of birds are known to whiffle, or fly inverted, in order to rapidly lose altitude, move laterally, or respond to gusts and atmospheric disturbances. Recently, gaps inspired by the bio-mechanics of whiffling have been found to change the forces and moments of an uncrewed aerial vehicle (UAV) wing. These novel gapped wings have been studied in terms of rapid descent and roll control. However, their potential as gust alleviation devices and overall impact on aircraft dynamics remained unknown. Here, we analytically determined the trim state, free response, and gust response of aircraft with varying gapped wings. The gaps shifted the aerodynamic center of the wing forward but in general beneficially decreased the wing's overall contribution to the aircraft pitching moment. This effect resulted in a steeper glide angle and higher velocity at trim. The gaps also reduced the phugoid mode by decreasing its natural frequency and increasing damping. However, all of the aircraft could require a controller for the short period mode due to a higher natural frequency. Finally, we showed that the gapped wings improved the aircrafts' response to transverse and streamwise gusts by increasing damping and reducing the maximum amplitude of oscillations. Despite some practical design challenges associated with the gapped wings, they ultimately benefited the aircraft's dynamic response and effectively mitigated gusts. Thus, the gapped wings could be a suitable control surface for gust alleviation.