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Science 11 May 2007:
Vol. 316. no. 5826, pp. 894 - 897
DOI: 10.1126/science.1142281
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Reports

Bat Flight Generates Complex Aerodynamic Tracks

A. Hedenström,1* L. C. Johansson,1 M. Wolf,1 R. von Busse,2 Y. Winter,2,3{dagger} G. R. Spedding4

The flapping flight of animals generates an aerodynamic footprint as a time-varying vortex wake in which the rate of momentum change represents the aerodynamic force. We showed that the wakes of a small bat species differ from those of birds in some important respects. In our bats, each wing generated its own vortex loop. Also, at moderate and high flight speeds, the circulation on the outer (hand) wing and the arm wing differed in sign during the upstroke, resulting in negative lift on the hand wing and positive lift on the arm wing. Our interpretations of the unsteady aerodynamic performance and function of membranous-winged, flapping flight should change modeling strategies for the study of equivalent natural and engineered flying devices.

1 Department of Theoretical Ecology, Lund University, SE-223 62 Lund, Sweden.
2 Department of Biology, University of Munich, Germany.
3 Max-Planck Institute for Ornithology, Seewiesen, Germany.
4 Department of Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, CA 90089–1191, USA.

{dagger} Present address: Department of Biology, Bielefeld University, D-335 01 Bielefeld, Germany.

* To whom correspondence should be addressed. E-mail: anders.hedenstrom{at}teorekol.lu.se

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Science. ISSN 0036-8075 (print), 1095-9203 (online)