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Wake structure and wingbeat kinematics of a house-martin Delichon urbica

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Author

Summary, in English

The wingbeat kinematics and wake structure of a trained house martin in free, steady flight in a wind tunnel have been studied over a range of flight speeds, and compared and contrasted with similar measurements for a thrush nightingale and a pair of robins. The house martin has a higher aspect ratio (more slender) wing, and is a more obviously agile and aerobatic flyer, catching insects on the wing. The wingbeat is notable for the presence at higher flight speeds of a characteristic pause in the upstroke. The essential characteristics of the wing motions can be reconstructed with a simple two-frequency model derived from Fourier analysis. At slow speeds, the distribution of wake vorticity is more simple than for the other previously measured birds, and the upstroke does not contribute to weight support. The upstroke becomes gradually more significant as the flight speed increases, and although the vortex wake shows a signature of the pause phase, the global circulation measurements are otherwise in good agreement with surprisingly simple aerodynamic models, and with predictions across the different species, implying quite similar aerodynamic performance of the wing sections. The local Reynolds numbers of the wing sections are sufficiently low that the well-known instabilities of attached laminar flows over lifting surfaces, which are known to occur at two to three times this value, may not develop.

Publishing year

2007

Language

English

Pages

659-668

Publication/Series

Journal of the Royal Society Interface

Volume

4

Issue

15

Document type

Journal article

Publisher

The Royal Society of Canada

Topic

  • Biological Sciences

Keywords

  • Delichon urbica
  • image velocimetry
  • digital particle
  • wind tunnel
  • vortex wakes
  • bird flight
  • aerodynamics

Status

Published

Research group

  • Animal Flight Lab

ISBN/ISSN/Other

  • ISSN: 1742-5662