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American Association for the Advancement of Science

A model to explain how animals fly

A fruit bat (Cynopterus brachyotis) flying in a wind tunnel.
[Image courtesy of Jose Iriarte-Diaz]

We humans are often jealous of animals that can fly. But in reality, the ability to travel through the air for great distances requires very special skills, and a human in the air would be just about as clumsy as a fish out of water.

A female ruby-throated hummingbird, Archilochus colubris.
[Image courtesy of Edwin Yoo]

In order to control themselves, flying creatures need to use specialized movements, or maneuvers, to get from one place to another. For a long time, researchers have wondered exactly how they do it. Now, researcher Tyson Hedrick and colleagues have created a model of flight for small creatures (like insects) and large ones (like birds) to better explain how it's done.

So how do these animals, blessed with the gift of flight, actually maneuver through the air? Hedrick and his team specifically studied low-speed, mid-air turns in a variety of winged animals, and found that their in-flight maneuvers are only accomplished with something they called "flapping counter-torque." Basically, this means that when a flying animal turns in the air, its wing-flapping speed increases during the down-stroke on one side, and during the up-stroke on the other side. This kind of imbalance allows the animals to turn slowly through the air.

The researchers documented this information and worked it into a model for four species of insects, two bird species, and a bat. Then, they compared their model to actual video footage of animals flying.

They discovered that flying animals that are similar in shape also have the same mid-air turning dynamics, as far as wing-flapping goes, no matter how big they are. So, for example, a fruit fly and a hummingbird both require the same number of wing flaps to finish a turn.

A hawkmoth (Manduca sexta) feeding on a flower.
[Image Science/AAAS]

Perhaps one day, this research will help us humans create better flying machines in the future since we will never get off the ground ourselves.


This research appears in the 10 April 2009 issue of Science.