Bio-aerial Locomotion 2011

Though they are called “flying squirrels”, they actually don’t fly but glide. There are 43 known species of flying squirrels in the world. For example, the Northern Flying Squirrel which has a total length from 23 to 35.6 cm weighs from 100 to 167 g at adulthood. Observations taken have shown that it can glide a distance up to 30.8 m. On the other hand, the Giant flying squirrel has a body length from 30.5 to 58.5 cm, a tail length from 34.5 to 63.5 cm and weighs from 1000 to 2500 g. As for the Giant squirrel, it can perform a glide of up to 450 m. I have taken those two completely opposite examples of flying squirrels to show that even the smallest or the largest species  can glide. But then the most important and crucial question is: ” How do they glide?”

Flying squirrels, just like the Draco lizards, have wing-like folds of skin called patagium which stretch from the forearms to the hind legs. According to research done by scientists, the patagium produces lift which allows the squirrel to glide.

In addition, squirrels have little flaps called winglets at the tip of their patagium which are similar to the winglets on the wings of an airplane. Normally, for an airplane, the winglets prevent the formation of vortices at the tips of the wings. Two problems that wing tip vortices create are an increase in drag forces on the aircraft and a possibility of flipping any airplane which encounters them. As such, by comparing those two winglets, scientists assume that a squirrel used its winglets to reduce drag and to stabilize and to control the glide.

Last but not least, flying squirrels also have a tail which acts as a steering organ, enabling them to change their course of flight in mid-air. However, all the above information about the functions of the “flying” organs are only theoretical  assumptions and no one has yet unraveled the true mechanism by which squirrels glide.

Here is a video of a simple plane named the “squirrel” which has been designed based on the anatomy of the flying squirrel. Note that the plane has square wings and winglets pointing upwards.

References

• Flying Squirrel Species Of The World
• Northern Flying Squirrel
• Giant Flying Squirrel- Walker’s Mammals of the World Volume 1 page 1292 By Ronald M. Nowak
• How squirrels fly by Michael Kernan- Smithsonian magazine, February 2001
• How things work: Winglets by George Larson – Air and Space magazine, September 01, 2001