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article imageAerospace Engineers Observe Birds, Bats, Insects

By Bob Ewing     Feb 5, 2008 in Science
Natural flyers like birds, bats and insects outperform man-made aircraft in aerobatics and efficiency. University of Michigan engineers are studying these animals as a step toward designing flapping-wing planes with wingspans smaller than a deck of cards.
University of Michigan engineers are learning about the birds and bats, why, because birds, bats and insects can outperform human-made aircraft in aerobatics and efficiency.
This period of observation is a step toward designing flapping-wing planes with wingspans smaller than a deck of playing cards.
Some comparisons from the press release:
A Blackbird jet flying 2,000 miles per hour covers 32 body lengths per second.
A common pigeon flying at 50 miles per hour covers 75.
The roll rate of the aerobatic A-4 Skyhawk plane is about 720 degrees per second.
The roll rate of a barn swallow exceeds 5,000 degrees per second.
Select military aircraft can withstand gravitational forces of 8-10 G.
Many birds routinely experience positive G-forces greater than 10 G and up to 14 G.
“Natural flyers obviously have some highly varied mechanical properties that we really have not incorporated in engineering,” said Wei Shyy, chair of the Aerospace Engineering department and an author of the new book “The Aerodynamics of Low Reynolds Number Flyers.”
“They’re not only lighter, but also have much more adaptive structures as well as capabilities of integrating aerodynamics with wing and body shapes, which change all the time,” Shyy said.
“Natural flyers have outstanding capabilities to remain airborne through wind gusts, rain, and snow.” Shyy photographs birds to help him understand their aerodynamics.
The pressure that is generated during flight causes the flapping wings to deform and; in turn, the deformed wing tells the air that the wing shape is different than it appears in still air. If appropriately handled, this phenomenon can delay stall, enhance stability and increase thrust.
Flapping flight is inherently unsteady and that is why it works so well. Birds, bats and insects fly in a messy environment full of gusts traveling at speeds similar to their own. Yet they can react almost instantaneously and adapt with their flexible wings.
The Air Force has given the researchers several grants that total more than $1 million a year to research small flapping wing aircraft.
The reasons for investing this money: these aircraft would fly slower than their fixed wing counterparts, and more importantly, they would be able to hover and possibly perch in order to monitor the environment or a hostile area.
The team’s current focus is on the aerodynamics of flexible wings related to micro air vehicles with wingspans between 1 and 3 inches.
“These days, if you want to design a flapping wing vehicle, you could build one with trial and error, but in a controlled environment with no wind gusts,” Shyy said. “We are trying to figure out how to design a vehicle that can perform a mission in an uncertain environment. When the wind blows, how do they stay on course?”
A dragonfly has remarkable resilience to wind, considering how light it is. The professor chalks that up to its wing structure and flight control. But the details are still questions.
“We’re really just at the beginning of this,” Shyy said.
Shyy is the Clarence L. "Kelly" Johnson Collegiate Professor of Aerospace Engineering. Other authors of the book, “Aerodynamics of Low Reynolds Number Flyers” are: U-M research scientists Yongsheng Lian, Jian Tang and Dragos Viieru, and Hao Liu, professor of Biomechanical Engineering at Chiba University in Japan.
Other collaborators on this research include professors Luis Bernal, Carlos Cesnik and Peretz Friedmann of the University of Michigan; Hao Liu of Chiba University in Japan; Peter Ifju, Rick Lind and Larry Ukeiley of University of Florida, and Sean Humbert of University of Maryland.
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