September 18, 2009 12:51:14 pm
Scientists studying the flexible wings of insects have discovered what makes them so efficient compared to the rigid wings of a man-made aircraft.
Researchers at Oxford University and the University of New South Wales used high-speed video cameras to capture how locust wings change shape in flight,then reconstructed these shape changes in 3D using computer modelling,and finally ran simulations to discover how the wings enable the tiny insects to make inter-continental flights.
A report of the research has been published in this week’s Science journal.
“Until very recently it wasn’t possible to accurately model the wings of insects in flight,partly because they flap so fast and partly because their shape is very complicated,” said an author of the paper,Dr Graham Taylor of Oxford University’s Department of Zoology.
“But with faster cameras and advanced 3D simulation technology,we can now see that the reason locust wings are so efficient is that the wing’s complex,changing shape ensures that air always flows smoothly over its surface,never becoming detached as it would with a flat wing.
By channelling the airflow in this way,insect wings produce about 50 per cent more lift than similar rigid wings.”
Another author of the paper,Professor Adrian Thomas,said,”We always thought that insects,with their complicated wing structures full of twists,curves and ridges,must know something about aerodynamics that engineers do not,now we know what that is.”
“It really is throwing down the gauntlet to engineers looking to build micro air-vehicles,telling them that if they want these tiny flapping aircraft to be efficient as well as powerful flyers then they will need to have wings that change shape just like an insect’s.”
After the scientists finished capturing images in multiple,high-speed digital video cameras,they used 3D models in computer simulation to predict the aerodynamic flow generated by the flapping wings.
The team then re-ran the simulation with two simplified wing designs. In the first design,they removed the wrinkles and curves but left the twist,while in the second design they replaced the wings with rigid flat plates.
The results were clear — the simplified models produced plenty of lift,but were much less efficient,requiring much more power for flight,the reason being that the complex deforming shape of the real wings allowed air to flow smoothly over their surface. When they put the flat plates,the flow separated away from the surface,resulting in high but costly lift.
The consequences were dramatic — the fully deforming wings generated one and a half times the lift of the flat plate wings for the same amount of power.
“The ‘bumblebee paradox’,claiming that insects defy the laws of aerodynamics,is dead,” Thomas said.