Leading edge vortex in a slow-flying passerine

Florian T. Muijres*, L.C. Johansson, Anders Hedenström

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

28 Citations (Scopus)

Abstract

Most hovering animals, such as insects and hummingbirds, enhance lift by producing leading edge vortices (LEVs) and by using both the downstroke and upstroke for lift production. By contrast, most hovering passerine birds primarily use the downstroke to generate lift. To compensate for the nearly inactive upstroke, weight support during the downstroke needs to be relatively higher in passerines when compared with, e.g. hummingbirds. Here we show, by capturing the airflow around the wing of a freely flying pied flycatcher, that passerines may use LEVs during the downstroke to increase lift. The LEV contributes up to 49 per cent to weight support, which is three times higher than in hummingbirds, suggesting that avian hoverers compensate for the nearly inactive upstroke by generating stronger LEVs. Contrary to other animals, the LEV strength in the flycatcher is lowest near the wing tip, instead of highest. This is correlated with a spanwise reduction of the wing's angle-of-attack, partly owing to upward bending of primary feathers. We suggest that this helps to delay bursting and shedding of the particularly strong LEV in passerines. This journal is

Original languageEnglish
Pages (from-to)554-557
JournalBiology Letters
Volume8
Issue number4
DOIs
Publication statusPublished - 2 Nov 2011
Externally publishedYes

Keywords

  • Aerodynamics
  • Aeroelastics
  • Bird flight
  • Leading edge vortex
  • Pied flycatcher
  • Wind tunnel

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