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Science 29 February 2008:
Vol. 319. no. 5867, pp. 1250 - 1253
DOI: 10.1126/science.1153019
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Reports

Leading-Edge Vortex Improves Lift in Slow-Flying Bats

F. T. Muijres,1 L. C. Johansson,1 R. Barfield,1 M. Wolf,1 G. R. Spedding,2 A. Hedenström1*

Staying aloft when hovering and flying slowly is demanding. According to quasi–steady-state aerodynamic theory, slow-flying vertebrates should not be able to generate enough lift to remain aloft. Therefore, unsteady aerodynamic mechanisms to enhance lift production have been proposed. Using digital particle image velocimetry, we showed that a small nectar-feeding bat is able to increase lift by as much as 40% using attached leading-edge vortices (LEVs) during slow forward flight, resulting in a maximum lift coefficient of 4.8. The airflow passing over the LEV reattaches behind the LEV smoothly to the wing, despite the exceptionally large local angles of attack and wing camber. Our results show that the use of unsteady aerodynamic mechanisms in flapping flight is not limited to insects but is also used by larger and heavier animals.

1 Department of Theoretical Ecology, Lund University, SE-223 62 Lund, Sweden.
2 Department of Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, CA 90089–1191, USA.

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

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Aeroecology: probing and modeling the aerosphere.
T. H. Kunz, S. A. Gauthreaux Jr, N. I. Hristov, J. W. Horn, G. Jones, E. K. V. Kalko, R. P. Larkin, G. F. McCracken, S. M. Swartz, R. B. Srygley, et al. (2008)
Integr. Comp. Biol. 48, 1-11
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Science. ISSN 0036-8075 (print), 1095-9203 (online)