Meeting Abstract

70.1  Thursday, Jan. 6  Aerodynamic effects of splayed primary feathers KLAASSEN VAN OORSCHOT, B*; TOBALSKE, B.W.; Univ. of Montana; Univ. of Montana brett.kvo@umontana.edu

Many birds that soar over land have emarginated primary feathers that may act like the winglets found on many modern planes. During flight, when producing lift, these feathers flex upwards and separate vertically. Evidence from prior research using fabricated wing models suggests that these feathers help to minimize the aerodynamic cost of wing-tip vortices that are created during flight. When air flows around a wing, high-pressure flow from under the wing curls up around the edges at the wing-tip, creating vortices that push the tip of the wing down. In recent years, many airplanes have been designed with vertical winglets to minimize tip losses due to these vortices. Following established wing theory for airplanes, we hypothesize that splayed primaries, like vertical winglets, reduce drag by spreading the tip vortex vertically and, thus, minimizing contact between the tip vortex and the main section of a horizontally-oriented wing. Particle image velocimetry (PIV) allows us to test this hypothesis by measuring the flow characteristics surrounding the wing-tip at resolutions which were previously impossible. We utilized PIV to test whether splayed primaries produce small, discrete vortex cores that develop independently of adjacent primaries or if tip vortices roll up as a single, large core. Furthermore, we compared lift-to-drag ratios with wings fixed in both emarginated and swept configurations through a range of attack angles and speeds. Our results indicate that wings with emarginated primary feathers produce more small vortices and better lift-to-drag ratios than wings without emargination. Here, I discuss these results as well as the ecological and evolutionary significance of our findings for over-land soaring birds.