The wings of a honeybee generate lift by arcing back and flipping over on the return.
"The notion that engineers once 'proved' that bees can't fly has become an urban myth. So partly to restore the reputation of the profession, Michael Dickinson decided to investigate the forces at work during honeybee flight.
In 1996, Charlie Ellington at the University of Cambridge showed how vortices rolling along the leading edge of the wing were the vital source of lift for most insects. But this can't explain how a heavy insect with a short wing beat, such as a bee, generates enough lift to fly.
Dickinson and his colleagues at Caltech in Pasadena, California, filmed hovering bees at 6000 frames per second, and plotted the unusual pattern of wing beats. The wing sweeps back in a 90-degree arc, then flips over as it returns — 230 times a second. The team made a robot to scale to measure the forces involved.
It is the more exotic forces created as the wing changes direction that dominate, says Dickinson. Additional vortices are produced by the rotation of the wing. 'It's like a propeller, where the blade is rotating too,' he says. Also, the wing flaps back into its own wake, which leads to higher forces than flapping in still air. Lastly, there is 'added-mass force' which peaks at the end of each stroke and comes from the acceleration of the wing after it changes direction." (Phillips 2005:17)
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