Home Adaptations Wings & Flight Physics of Flight

Physics of Flight

Trumpeter Swans (Courtesy NEBRASKAland Magazine/NGPC)

Some birds use their wings to glide through the air. They seem to drift along effortlessly.

To do this, the bird relies on simple physics. The bird's wing is not entirely flat – it's actually curved. As air moves over the top of the wing, the air has a longer distance to go than the air moving under the wing. But the same amount of air is moving both over and under the wing.

The result is that the air moving over the top of the wing produces less pressure on the wing than the air moving under the wing. This causes the wing to be pushed up from below and pulled up from above. The result: the bird is lifted into the air! By tilting its wings forward or backward, a bird can change its speed while gliding.

See how the physics of flight works

Swainson's Hawk (Courtesy NEBRASKAland Magazine/NGPC)

SOARING
Some birds, such as hawks and osprey, use warm air currents to soar through the air. As the sun's energy warms the earth's surface, warm air is created and rises.

This uplifting of warm air is known as a thermal.

Soaring birds use the lift (upward force that opposes the pull of gravity) from this warm air to soar. Sometimes people say these birds are "riding the thermal."

Because soaring birds don't have to flap their wings very often, soaring flight takes very little energy.

FLAPPING
Gliding and soaring are good ways to fly, but at some point, almost all birds use flapping.

Flapping is a complicated process: birds must work to create their own thrust or push to propel themselves through the air while working to minimize the drag their wings and body create.

Common Mergansers (Courtesy NEBRASKAland Magazine/NGPC)

To do this, birds change the angle of their wings as they flap. By twisting the front part of the wing downward, they can create a large amount of thrust, which pushes both downward and to the rear.

On the upstroke, many birds partially fold up their wings to minimize the drag. Then, on the down stroke, they open up their wings again. The part of the wings which is not folded up (the outer most area) is twisted to reduce air resistance and minimize drag.

Many birds use both flapping and gliding to fly. For example, a cardinal will flap several times, then glide for a short distance. It will repeat this pattern over and over as it flies.

A hummingbird is unique because it's able to hover in the air for long periods of time by flapping its wings. It was once thought they accomplish this unusual feat the same way hovering insects do. However, research shows that they use a wing stroke all their own.

Other birds support 100 percent of their weight with the down stroke during slow flight or short term hovering. Insects support half their weight with each stroke. But hummingbirds support 75 percent of their weight on the down stroke and 25 percent on the up stroke. They've adapted some insect flight characteristics but take advantage of being equipped with bird wings that flex, twist, and arch, unlike the rigid wings of insects.