Penguins are wobbly on land, but their extreme underwater agility involves the perfection of a twisting wing motion that is just now coming to be understood.
A new study found that by twisting their wings while pumping them under water to swim, the birds are able to vary the thrust of their flapping and increase control over their movements.
The motion is so useful researchers are testing it out on prototypes for new underwater spy vehicles.
"All this has become possible because of this penguin wing, which is using the same dynamic principles as fruit flies and other winged insects use in the air," said researcher Promode Bandyopadhyay of the Naval Undersea Warfare Center in Newport, R.I.
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To study the physics of penguins' swimming wing motions, Bandyopadhyay and his colleague David Beal, also of the Naval Undersea Warfare Center, built robotic models of penguin wings in the lab. While the wings twisted, the scientists measured the effect on lift, drag, thrust and other forces affecting a flying or swimming body.
They found that by slightly corkscrewing their flapping wings, penguins achieve a 20 percent increase in thrust, or push forward. This is because more surface area of the wing is being used to generate force.
"If you are not twisting, the inner part of the wing is not being used very well," Bandyopadhyay told LiveScience. "But when you twist the angle of attack, you're getting to use more of the wing. By twisting only slightly, you can vary the thrust by 20 percent with no loss of efficiency."
The twisting motion boosts the force significantly, but takes less energy than increasing the rate of flapping. It's also very useful for speed control — by altering the amount of twist, penguins have a good way to slow down or speed up without changing the pattern of their flapping.
The scientists think this type of motion could be built into wings on small underwater vehicles, such as military spy craft. To test the idea, Bandyopadhyay and Beal built two small vehicles with twisting wings that allow for good control over speed. The robotic craft, about 3 feet (1 meter) long, could potentially be used to detect an enemy approaching a larger underwater military target.
"Because its wings consume very little energy, this is going to swim in the ocean for months with very little energy consumption," Bandyopadhyay said. "If there is an enemy, this vehicle will be the first one to detect that, and swim up to the surface to report its finding."
The researchers will present their findings Nov. 23 at the annual meeting of the American Physical Society's Division of Fluid Dynamics.
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