Meeting Abstract

104.5  Tuesday, Jan. 7 09:00  The aerodynamic effects of morphing wings during flapping and gliding flight KLAASSEN VAN OORSCHOT, B*; MISTICK, E; TOBALSKE, B; Univ. of Montana; Harvard Univ.; Univ. of Montana brett.kvo@umontana.edu

Dynamic changes in wing shape are characteristic of bird flight, and it is generally hypothesized that these changes in morphology allow birds to modulate aerodynamic force production across a range of flight styles, including flapping take-off and gliding flight. While birds are commonly seen morphing their wings, the underlying aerodynamic effects influencing a bird’s choice to modify wing shape remains unclear. Here, we measure aerodynamic forces of extended and swept wings in raptors across three orders (Falconiformes, Accipitriformes, and Strigiformes), ranging in body mass from 56 g to 763 g. We dried wings from the same individual in extended and swept configurations and then simulated gliding flight using a wind tunnel and flapping take-off flight using a propeller model. Our results show that extended wings produce greater absolute forces in both gliding and flapping flight, a result that is concomitant with increased surface area. However, once surface area was normalized, swept wings produced more lift and less drag than their extended counterparts during gliding flight when attack angles were greater than ~20 degrees. Conversely, during flapping flight, the extended wings still outperformed the swept wings across all angles of attack. In gliding flight, extended wings marginally outperformed swept wings at angles less than ~20 degrees. Our results suggest the presence of leading-edge vortices (LEVs) on the swept wings during gliding flight. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-0809127 and DGE-1313190 and the Herchel Smith-Harvard Undergraduate Science Research Program.