The wing, or patagium, produces lift, enabling the squirrels to glide. When I visited Stafford at the Glenn L. Martin Wind Tunnel at the University of Maryland in College Park, he drew a series of rhombuses to show me how squirrel wings look when spread out. It s the square shape that s of particular interest to him and Thorington. Our modern aircraft design tends to be long and narrow, so they wondered how the square wings worked. They were not as efficient as narrow designs in terms of drag.
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.