Many mysteries of flight remain

Shkarayev designs flapping-wing miniature aircraft called micro air vehicles. His fliers have wingspans of 5 to 8 inches and can be remotely controlled.

These machines are highly sought after by the military, and could also have scientific and commercial uses.

"There is a lot of interest in miniaturized technology," said Wei Shyy, chair of the Aerospace Engineering department at the University of Michigan, who also designs small flapping-wing vehicles. "For example, you can send one of these fliers for surveillance in Afghanistan or Iraq. They could send them to fly out to monitor the situation, take videos and see what's really going on in the field. Or you can send these into a nuclear disaster area when you don’t want to send humans."

To better engineer his aircraft, Shyy photographs birds and designs computational models to try to understand their aerodynamics.

Wing physics
When birds and insects fly, their wings change shape constantly to accommodate environmental conditions. But the physics of these changing wings is complicated.

"How much flexibility is really desirable? If you have too much flexibility you can be sloppy, maybe worse than having no flexibility," he said. "That is a big question."

Peter Ifju is a professor of mechanical and aerospace engineering at the University of Florida who collaborates with Wei Shyy.

"I think we've still got a long way to go to figure out some of the bigger questions," he said. "Physically, what are they doing to the air to produce such efficient lift? There are all kinds of flow physics we just don't understand. We can see what they're doing, but we don’t understand how that interacts with the air."

On a basic level, he said, birds are swimming through the air as people do through water. When we swim we push water away from us to create thrust forward and up, while trying to cause as little drag as possible.

"Birds have a similar philosophy," he said.

Animals will always have some advantages over machines, such as the ability to use their nervous systems to sense subtleties about the environment around them and alter their flight accordingly.

"We are not trying to just copy nature," Shyy said. "Some things nature does, we simply cannot make. We are trying to take a fundamental understanding of nature, then apply engineering knowhow."

Ornithopter enthusiasts
Natural flight is not just popular for its military applications. A community of enthusiasts has sprung up around ornithopters — another term for flapping-wing vehicles.

"The reason why a lot of people have pursued this idea over the years is not for any practical application, but more to prove that it can be done," said Nathan Chronister, who founded the Ornithopter Zone Web site, a hub for flapping-wing hobbyists. "The idea kind of took hold several hundred years ago before the airplane was invented. It was logical. People watched birds flying and thought maybe we could do that too. It ended up being more technically challenging than the airplane. But there are still those who want to show that we can fly the way birds do, also."

Chronister studies the history of ornithopters and designs his own vehicles ranging in wingspan from 6 inches to 5 feet. He is involved in the Ornithopter Society, which publishes a quarterly newsletter with updates about ornithopter design.

"People who are interested in ornithopters usually are people who enjoy working on technical challenges," he said. "It comes out of an admiration for bird flight, and enjoying the challenge of trying to imitate that."

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