title: Leading-edge vortex lifts swifts.
abstract: The current understanding of how birds fly must be revised, because birds use their hand-wings in an unconventional way to generate lift and drag. Physical models of a common swift wing in gliding posture with a 60 degrees sweep of the sharp hand-wing leading edge were tested in a water tunnel. Interactions with the flow were measured quantitatively with digital particle image velocimetry at Reynolds numbers realistic for the gliding flight of a swift between 3750 and 37,500. The results show that gliding swifts can generate stable leading-edge vortices at small (5 degrees to 10 degrees) angles of attack. We suggest that the flow around the arm-wings of most birds can remain conventionally attached, whereas the swept-back hand-wings generate lift with leading-edge vortices.
authors.affiliation: Department of Marine Biology (Experimental Marine Zoology Group), Groningen University, Post Office Box 14, 9750 AA, Haren, Netherlands. j.j.videler@biol.rug.nl
authors.forename: J J
authors.initials: JJ
authors.lastname: Videler
authors.forename: E J
authors.initials: EJ
authors.lastname: Stamhuis
authors.forename: G D E
authors.initials: GD
authors.lastname: Povel
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001717:Birds / Q000033:anatomy & histology / Q000502:physiology*; D005426:Flight, Animal; D008953:Models, Anatomic; D014921:Wings, Animal / Q000033:anatomy & histology / Q000502:physiology*