Butterflies point to micro machines

That is the confident prediction of scientists who have just studied the remarkable aerobatics of the butterfly.

" There is a lot of interest in this sort of thing from toy manufacturers "
Dr Adrian LR Thomas

The two Oxford researchers put red admirals in a specially designed wind tunnel and used high-speed cameras to analyse how the animals moved through the air.

The results of the experiments, they say, represent a major advance in our understanding of flight mechanics on the small scale, and will be invaluable to engineers trying to build "micro air vehicles".

"There is a lot of interest in this sort of thing from toy manufacturers and, of course, the military," Dr Adrian LR Thomas told BBC News Online. "We are now moving in the direction where we will soon be able to build 10-centimetre-wingspan aircraft, either radio controlled or autonomous.

"They would make an entertaining toy but if you put a camera on them then the [security agencies] could send them into small spaces such as caves to see what was going on."

Effortless switch

Dr Thomas has spent 12 years studying insect aerodynamics. The wind tunnel used in the butterfly experiments took three years to construct and fine tune.

With help of Dr Robert Srygley, red admirals (Vanessa atalanta) were trained to fly freely to and from artificial flowers in the tunnel. Wisps of smoke were blown over the insects' wings to see how they interacted with the air.

The visible turbulence was caught on an ultra-fast digital camera.

"The fluttering of butterflies is not a random, erratic wandering, but results from the mastery of a wide array of aerodynamic mechanisms," Srygley and Thomas report in the journal Nature.

They identified six different ways the butterflies flapped and rotated their wings to stay airborne. The insects moved effortlessly through the different mechanisms "much like a horse might switch between walking, trotting and galloping depending on what it wanted to do," Dr Thomas said.

Much to learn

The researchers found the insects could, at times, fly very efficiently, producing very little turbulence. On other occasions, the red admirals' wings deliberately created vortices to achieve extra lift.

"We saw conventional aircraft-style aerodynamics, two different kinds of leading-edge vortices, rotational mechanisms, wake-capture mechanisms and the so-called clap and fling."

It is known that insect wings produce 10 times the amount of lift achieved by aircraft wings (per unit of area).

Building tiny planes that were just scaled-down versions of the real thing would never get off the ground.

It is only by mimicking the insect world that micro air vehicles will get airborne efficiently. And while miniaturisation experiments are progressing fast, engineers confess they still have much to learn from the animal world.