The secrets of bee flight

The current decline in UK bee numbers remains something of a mystery. And it's not the first time these friendly insects have set scientists a conundrum.

The persistent rumour that bumblebee flight escapes scientific explanation has been traced back by some to an aerodynamics research group in Gottingen, Germany, in the 1930s.

‘Supposedly someone did a back of the envelope calculation, taking the weight of a bumblebee and its wing area into account, and worked out that if it only flies at a couple of metres per seconds, the wings wouldn’t produce enough lift to hold the bee up,’ explains Charlie Ellington, Professor of Animal Mechanics at Cambridge University.

The tale lives on, but science has long since caught up with the bumblebee. In the 1990s, Ellington’s research group studied bee flight and exposed the mechanism behind the insect’s physics-defying acrobatics.

As a bee takes flight, air swirls in a tight circle, a vortex, over the leading edge of the wing. ‘The vortex is a low pressure region above the wing, and it sucks the wing upwards,’ explains Ellington. This is what gives the bee the extra bit of lift it needs to buzz around from flower to flower.

‘It’s just like if you move a spoon through a cup of coffee: you’ll see the flow swirl around the sharp edge,’ continues Ellington. ‘If you move the spoon quickly, you’ll actually see a dimple at the centre of the vortex caused by the lower pressure.’

Learning from bees

Aside from proving cynics wrong, research into insect and bird flight has some practical applications when it comes to designing micro air vehicles (MAVs). These flying robots could be used for remote observation, providing anything from military intelligence to information on accident scenes for emergency services.

       MAVs as imagined by the US air force

At tiny scales, the aerodynamic mechanisms at play are very different to those which influence the flight of jumbo jets, and insects can provide a useful model for coping with this new set of rules.

For now however, the focus of Ellington’s research has shifted away from bees. ‘The trouble is that micro air vehicles are still too big to really fly like an insect. We’re working on them, but we take a humming bird as a model,’ he says. Hummingbirds have attracted attention as their wings provide great lift with very little drag. ‘We’re looking at the surface detail of the feathers to find out why this is, with a view to putting them on a micro helicopter,’ comments Ellington.

The natural world can be a great source of ideas but imitating nature, a field known as biomimicry,  is also about recognising the limitations of the animal world’s designs more than simply copying literally. ‘Biomimicry as a term is frowned on by most people who do it,’says Ellington, ‘we’re taking biological inspiration instead.’

If research into bee-inspired robots does one day  prove successful, should we worry about swarms of robotic killer bees? Not according to Ellington: ‘I don’t think there’s any chance they could carry enough payload to do anything dangerous!’

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To find out more about how you can help give the bee population in your area a boost, visit National Science and Engineering Week’s Save our Bees campaign.

Find related websites about aerodynamics with physics.org

Watch bee flight in slow motion in this video.

Embedded youtube video

4 Mar 2009

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