or beware squiffy aerodynamicists
they’re fat, they’re round, they can’t get off the ground…
The odd thing about this myth regarding bumblebees theoretically defying the laws of physics, is that the story is so widespread and has persisted for so long. The basic principles of bumblebee flight have been pretty well understood for many years. Somehow, though, the idea that bees ‘violate aerodynamic theory’ has become embedded in folklore.
The origins of this myth is unclear – one story tells of a dinner where a biologist asked an aerodynamics expert about insect flight. The aerodynamicist did a few calculations and found that, according to the accepted theory of the day, bumblebees didn’t generate enough lift to fly. The biologist promptly spread the story far and wide. Another version concerns a French entomologist, who applied the laws of air resistance to insects, and concluded that bumblebees clearly shouldn’t be able to get off the ground.
Returning to the first anecdote, the aerodynamicist, once he sobered up, realised that the problem was a faulty analogy between bees and conventional fixed-wing aircraft. Bees’ wings are small relative to their bodies. If an airplane were built the same way, it would never take off. But bees aren’t like airplanes, they’re like helicopters (a bit). Their wings work on the same principle as helicopter blades – to be precise ‘reverse-pitch semirotary helicopter blades’. A moving airfoil, whether it’s a helicopter blade or a bee wing, generates a lot more lift than a stationary one.
Another challenge with bees wasn’t figuring out the aerodynamics but the mechanics: specifically, how bees can move their wings so fast – roughly 200 beats per second, which is 10 or 20 times the firing rate of the nervous system. The trick apparently is that the bee’s wing muscles (thorax muscles, actually) don’t expand and contract so much as vibrate, like a rubber band. A nerve impulse comes along and twangs the muscle, much as you might pluck a guitar string, and it vibrates the wing up and down a few times until the next impulse comes along.
I also need to mention dynamic stall – which sounds like an oxymoron (and possibly handy to know about if you are at a dinner party with a squiffy aerodynamicist) – its the effect that occurs when the wings change their angle of attack – ie they don’t just flap up and down, they also do some interesting gyrations. The rapid change can cause a strong vortex to be shed from the leading edge (front) of the wing, and travel backwards over and above the wing. The vortex, containing high-velocity airflows, briefly increases the lift produced by the wing. As soon as it passes behind the trailing edge (back), however, the lift reduces dramatically, and the wing is in normal stall.
Bumblebee flight is being studied using lasers and special cameras. Much remains to be done to understand it fully, but the manoeuverability and efficiency of bumblebee flight tells us that we need to better understand it to improve our own methods of flying.
My observation is that they are blinking difficult to capture on film, especially in flight – constantly on the move, whizzing hither and thither – too much dynamic and not enough stall for my purposes.
‘there is an art, or rather a knack to flying. The knack lies in learning how to throw yourself at the ground and miss’
~ the late, great Adams Douglas Adams : Hitchhiker’s Guide to the Galaxy
sources : Cecil Adams and Wikipedia