Articles

Why a Butterfly Flutters By

by David Catchpoole

Have you ever thought that the butterfly, with its jerky fluttering flight, is a ‘primitive’ and inefficient flyer? After all, its wings don’t look even remotely aerodynamic, compared to the beautifully streamlined ‘aerofoil’ wings of birds and airplanes.

Indeed, just 10 years ago, conventional laws of aerodynamics could not explain how any of the insects could fly at all,1 let alone manoeuvre so masterfully at low speeds—hovering and flying backwards and sideways, in complete control.

In the last decade, however, researchers have uncovered a variety of ‘unconventional’ ways that these gossamer aeronauts use their wings to stay aloft.2 For example, one particular flapping movement creates a spiralling airflow (vortex) along the edges of the wings, generating some of the lift which ‘conventional steady-state aerodynamics’ could not account for.3

Now, after filming red admiral butterflies flying in a ‘wind tunnel’, researchers have been surprised by a whole range of complicated wing movements which generate more lift than simple flapping would do: ‘wake capture, two different types of leading-edge vortex, active and inactive upstrokes, in addition to the use of rotational mechanisms and the Weis-Fogh “clap-and-fling”? mechanism’.4 What is more, the red admirals often used completely different mechanisms on successive wing strokes!

So, rather than being ‘primitive’, we now understand that butterflies flutter because they choose each wing stroke from a customized armoury of twists, flaps, claps and flings. In the words of the researchers, ‘the fluttering of butterflies is not a random, erratic wandering, but results from the mastery of a wide array of aerodynamic mechanisms’.4 No wonder butterflies are so adept at taking off, manoeuvring, maintaining steady flight and landing.

Aeronautics engineers even desire to copy these mechanisms, e.g. for robotic spy ‘insects’,5 but there is still a long way to go before they can match the capabilities of insect flyers.6

For example, the software design in man-made aircraft requires many man-years of work and powerful computer chips for its implementation. In contrast, the flight control centre in the brain of a fly has been estimated at about 3,000 neurons, which ‘gives the insect less computational power than a toaster, yet insects are more agile than aircraft equipped with superfast digital electronics.’7 So how do insects exercise flight control over such a wide range of aerobatic abilities?8 One commentator observed, ‘If engineers ever understand that, there will be a revolution in aeronautics.’7

There is one engineer who understands. He is the One who originally put these flying marvels together in the first place—the Lord, the Maker of the heavens and the earth, and the sea, and all that is in them.

References
Brookes, M., On a wing and a vortex, New Scientist 156(2103):24–27, 1997.
Wieland, C., Why a fly can fly like a fly, TJ 12(3):260–261, 1998.
Insects—defying the laws of aerodynamics? Creation 20(2):31, 1998.
Srygley, R.B. and Thomas, A.L.R., Unconventional lift-generating mechanisms in free-flying butterflies, Nature 420(6916):660–664, 2002.
Butterflies point to micro machines, BBC News, <news.bbc.co.uk/2/hi/science/nature/2566091.stm>, 13 January 2003.
Sarfati, J., Can it bee? Creation 25(2):44–45, 2003.
Zbikowski, R., Red admiral agility, Nature 420(6916):615–618, 2002.
See also: Sarfati, J., Astonishing acrobatics—dragonflies, Creation 25(4):56, 2003.
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