How Squirrels Fly

Fascinated by the graceful gliding of these mammals with "wings," scientists take a close look.

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Squirrels also have a little flap on their patagium, a sort of winglet. The scientists noticed that the winglets curl upward, like the tips on many aircraft wings. One theory is that the slant reduces drag around the end of the wing. Another is that it acts to stabilize or control the glide. Or again, as in commercial planes, it may both increase flight efficiency and help control and stabilize the glide. This theory is quite likely, since the winglet is so far from the center of gravity that it has an exaggerated effect.

In 1999 Stafford spent about two months in Japan doing research with Takeo Kawamichi, a professor who has studied the Japanese giant flying squirrel for decades. Observing the squirrels in the wild, the scientists stayed up night after night making videos and measuring the animals’ speed and flight distances. Once, Stafford saw a giant squirrel at 2 a.m., or rather he saw the creature’s eyes glowing in the dark. Suddenly the eyes disappeared. "Did he just close his eyes, or did he move? They’re so quick and quiet you can’t tell."

 Coasting low and slow, the Japanese giant flying squirrel was recorded gliding for nearly 160 feet. There have been some reports of 500-foot glides, "but that was on a downhill slope," Stafford said.

Flying squirrels vary anatomically, he explained. "All have a small membrane between the neck and forelimbs, and this seems related to how they glide. Larger ones have a membrane between the hind legs. The smaller animals don’t have this, but they do have featherlike tails. What is the function of that?"

These questions brought Stafford and Thorington to the wind tunnel and into collaboration with its director, Jewel Barlow, and research manager, Robert Ranzenbach. I got a tour of this remarkable device with Barlow. We entered a vast room with tilting walls. With no parallel sides or right angles, the facility makes for odd optical illusions. On one side, tucked at the end of a 40-foot-long pollywog-shaped structure, is the fan itself, which is 19 feet in diameter and has a 2,000-horsepower electric motor. It spins seven propeller blades modified from a B-29 bomber and can generate winds up to 230 miles per hour. Opposite the fan in a section of an enclosed tunnel circuit is the test area with an observation window.

To test wind impact, the powerful fan blasts a stream of air on objects such as aircraft, boats, cars, "anything that the wind blows on or anything that moves through water or air," Barlow told me. At this particular wind tunnel, a lot of the experiments are conducted to evaluate how various design concepts affect the aerodynamics of new cars. Using three-eighths scale models that are about six feet long, automobile manufacturers try to find out what the level of drag is for a particular design, or the degree of wind noise or debris distribution, even windshield wiper efficiency on a gusty day.

"We also conduct experiments on wind flow around buildings," Barlow added. "We measure pressure distribution on models, which helps the structural engineers design windows and glass walls."

Not long ago on TV, I saw a weatherman standing in a test chamber, chained to the steel floor, while he volubly described what it is like to stand in a hurricane. At 100 miles per hour his cheeks rippled, his ears flapped and he stopped talking.

Stafford has built life-size model squirrels of clay, fiberglass and steel rods, reproducing the exact wing shape and several levels of camber, or wing curvature.

"We’re now testing steady mid-flight patterns. We don’t have the data yet to study turns. The wing needs to be totally stable for this kind of testing, which is why we build the models out of steel."


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