Combining robotic modelling with slow-motion videos of airborne honeybees may have helped researchers explain the curious aerodynamics of bee flight.
Aeronautical engineers had previously 鈥減roven鈥� that bees cannot fly. So Michael Dickinson, an insect flight expert and colleagues at Caltech in Pasadena, California, US, decided to investigate the forces actually at work during honeybee flight.
In 1996, Charlie Ellington at Cambridge University, UK, showed how vortices rolling along the leading edge of many insects鈥� wings were a vital source of lift.
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Most flying insects beat their wings in large strokes 鈥� typically flapping in arcs of 145掳 to 165掳 at a frequency determined by body size 鈥� to generate aerodynamic forces sufficient for flight. But this cannot explain how a heavy insect with a short wing beat, such as a bee, generates enough lift to fly.
Exotic forces
Dickinson and his colleagues filmed hovering bees at 6000 frames per second, and plotted the unusual pattern of wing beats. The wing sweeps back in a 90藲 arc, then flips over as it returns 鈥� an incredible 230 times a second. The team made a robot to scale to measure the forces involved. See a video of a bee in a flap, here (5MB, .avi format).
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. 鈥淚t鈥檚 like a propeller, where the blade is rotating too,鈥� he says. Also, the wing flaps back into its own wake, which leads to higher forces than flapping in still air. Lastly, there is another peculiar force known as 鈥渁dded-mass force鈥� which peaks at the ends of each stroke and is related to acceleration as the wings鈥� direction changes.
The work may help engineers design rotating propellers or more stable and manoeuvrable aircraft. But 鈥渋t proves bees can fly, thank God鈥�, adds Dickinson.
Journal reference: Proceedings of the National Academy of Sciences ()
