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Unconventional lift-generating mechanisms in free-flying butterflies

Abstract

Flying insects generate forces that are too large to be accounted for by conventional steady-state aerodynamics1,2. To investigate these mechanisms of force generation, we trained red admiral butterflies, Vanessa atalanta, to fly freely to and from artificial flowers in a wind tunnel, and used high-resolution, smoke-wire flow visualizations to obtain qualitative, high-speed digital images of the air flow around their wings. The images show that free-flying butterflies use a variety of unconventional aerodynamic mechanisms to generate force: wake capture3, two different types of leading-edge vortex3,4,5,6,7, active and inactive upstrokes8, in addition to the use of rotational mechanisms3 and the Weis–Fogh ‘clap-and-fling’ mechanism9,10,11,12. Free-flying butterflies often used different aerodynamic mechanisms in successive strokes. There seems to be no one ‘key’ to insect flight, instead insects rely on a wide array of aerodynamic mechanisms to take off, manoeuvre, maintain steady flight, and for landing.

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Figure 1: Butterfly leading edge vortex structure.
Figure 2: Flow over the wings during the downstroke.
Figure 3: Wake capture.
Figure 4: Upstrokes with positive, neutral and negative (downwards) loadings produced during a single flight by a 434-mg male flying into a 1.5 m s-1 wind.

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Acknowledgements

We thank the Engineering and Physical Sciences Research Council instrument pool for use of their NAC500 high-speed video camera. R.B.S. was supported by a Biotechnology and Biological Sciences Research Council grant to A.L.R.T. A.L.R.T. was supported by a Royal Society University Research Fellowship.

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Srygley, R., Thomas, A. Unconventional lift-generating mechanisms in free-flying butterflies. Nature 420, 660–664 (2002). https://doi.org/10.1038/nature01223

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