Many mysteries of flight remain

By Clara Moskowitz

updated 1:44 p.m. ET March 4, 2008

As anyone with a fear of flying will tell you, flight is a mystery.

The fact that heavy planes full of people can stay aloft is incredible. Even experts admit there is a lot we don't know about flight, including why animals do it so much better than our best aircraft.

Some examples:
A Blackbird jet flying nearly 2,000 mph covers 32 of its own body lengths per second. But a common pigeon covers 75 of its body lengths a second. The roll rate of the aerobatic A-4 Skyhawk plane is about 720 degrees per second. The roll rate of a barn swallow is more than 5,000 degrees per second. Some military aircraft can withstand gravitational forces of 8-10 G (Earth's gravity is equal to 1 G). Many birds routinely experience G-forces greater than 10 G and up to 14 G.

When it comes to flexibility and efficiency in the air, birds, bats and insects easily outperform airplanes. Researchers hope studying animals more closely may reveal some of the secrets behind flight.

Imitating animals
Nearly all airborne animals use flapping wings to fly.

When humans first dreamed of flight, many people naturally thought to imitate birds and create flappable wings.

In the 13th century the philosopher and Franciscan friar Roger Bacon proposed the idea of a flapping-wing vehicle, and in the 15th century, Leonardo DaVinci sketched flying machines with flapping wings.

But early attempts to fly like animals fell flat. For a vehicle carrying the weight of a human, the flapping speed required to create the necessary lift and thrust was an insurmountable obstacle. It wasn't until people tried using stable wings, for which the aerodynamics are much less complicated, that they were really able to get off the ground.

The first human flights involved gliders and, famously, a gargantuan steam-powered airship in 1852.

In 1903, the Wright brothers famously made the first controlled, powered and sustained heavier-than-air human flight using a contraption with wings fixed in place. Since their success, most human-carrying aircraft have followed suit with fixed wings.

"Because the nature of flapping flight is so complex, it's difficult to copy," said Sergey Shkarayev, a professor of aerospace and mechanical engineering at the University of Arizona. "People realized it's much easier to deal with fixed wings, as birds do when they soar. But you still need a propeller. Birds do not have this very important invention, like a wheel or propeller. People came up with a combination of a propeller and fixed wings. That’s how the Wright brothers succeeded."

Mini planes
While our 747s serve us pretty well, there are limitations to fixed-wing flight.

"With flapping wings we expect that they will have some qualities fixed wings don’t have, like the ability to do sharp maneuvers like hummingbirds," Shkarayev said.

Flapping wings also allow fliers to hover in one position, fly at very slow speeds and respond more flexibly to changing environmental conditions such as wind turbulence, rain and snow. Such flexibility even enables birds and insects to fly with broken wings.

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