[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
One Number Describes Animal Flight...
Pterosaurs etc aren't mentioned BUT...
One number explains animal flight
Engineers and evolutionists take note: wings and tails beat to the same
One number describes the beating of animal wings and tails, researchers
have found. The simple rule of thumb for animal locomotion could help to
design miniature flying machines.
"We've described the geometry of the wingbeat," says Graham Taylor of the
University of Oxford, UK. Swimmers and fliers from insects to whales all
cruise at the speed that lets them slip along most easily, he and his
Wings and tails create eddies as they move. These need to be left behind,
because turbulent air or water is more difficult to travel through. So
limbs shed vortices at the bottom of their downstrokes. Flap too quickly,
and you have to fight this turbulence on the way up. Too slowly, and
A quantity called the Strouhal number measures how efficiently an animal
cruises. The number describes how much up-and-down movement a wing or tail
makes relative to a creature's forward speed. It is calculated as stroke
speed multiplied by size, divided by forward speed.
Flying and swimming is most efficient at Strouhal numbers of 0.2-0.4. The
cruising speeds of everything from bumble-bees to blue whales, via
mackerel, locusts, pigeons and bats, fall in this range, Taylor's team