Direct pressure measurements using electronic differential pressure transducers along bird wings provide insight into the aerodynamics of these dynamically varying aerofoils. Acceleration-compensated pressures were measured at five sites distributed proximally to distally from the tertials to the primaries along the wings of Canada geese. During take-off flight, ventral-to-dorsal pressure is maintained at the proximal wing section throughout the wingstroke cycle, whereas pressure sense is reversed at the primaries during upstroke. The distal sites experience double pressure peaks during the downstroke. These observations suggest that tertials provide weight-support throughout the wingbeat, that the wingtip provides thrust during upstroke and that the kinetic energy of the rapidly flapping wings may be dissipated via retarding aerodynamic forces (resulting in aerodynamic work) at the end of downstroke.
Usherwood, James RHedrick, Tyson LBiewener, Andrew AengComparative StudyResearch Support, U.S. Gov't, Non-P.H.S.England2003/10/14 05:00J Exp Biol. 2003 Nov;206(Pt 22):4051-6.