No snake truly flies, but three species of Southeast and South Asian snakes have evolved the capacity to glide up to 30m. In the process they are teaching us about fluid dynamics, with possibilities that their methods could be applied to future technology.
Gliding is a common skill for arboreal creatures, allowing them to get from one tree to another to escape predators or in search of food or mates. However, creatures like flying squirrels or frogs assist their travels with membranes stretched between limb or digits. In this snakes have something of a disadvantage.
The fact that they manage suggests they must have some tricks up their...well saying sleeve would be just insensitive now wouldn't it? Associate Professor Lorena Barba, who works in mechanical and aerospace engineering at George Washington University thought this was worth exploring.
A Nature paper in 2002 showed that flying snakes suck in their stomach so their underside is concave like a Frisbee.
Barba built a computer model of the way these snakes travel through the air and compared it with observed behavior of one species Chrysopelea paradisi. Her paper, Lift and Wakes of Flying Snakes, in Physics of Fluids, proves there is a place for poetry in science.
“The hope is that if you understand this aerodynamic mechanism, then you can find another application where it could be useful, some other design or device,” says Barba.
Most flying craft and creatures generate aerodynamic lift through the angle of attack in this case the angle between the slope the snake holds itself at and the direction it moves through the air. Up to a certain point a larger angle generates more lift, but if the angle becomes steep enough an object can stall and the lift drops drastically as air flowing over the upper surface detaches from that surface.
Flying snakes, brilliant aerodynamic engineers that they are, have done something different. Up to 30° the lift increases with angle. However, instead of stalling at this point it jumps sharply up to 35°, and then drops slowly.
“With simulation, you can really see the fine details of what is happening in the air as it moves around the object,” Barba says. “We decided it would be revealing to use this tool to find out, first of all, if we could observe the same feature of lift, and if so, if we would we be able to interrogate the flow by getting detailed quantities and visualizing it.”
Barba's team were able to replicate these results and found it's all in the curves. The snakes flatten themselves out to maximize lift, but also produce small vortices from the way they bend their bodies, which add an extra upward force that is crucial to their capacity to glide so far.
Barba's work only explains the rigid snake, but she hopes a more sophisticated model will explain why the snakes undulate as they travel. She speculates that the work could lead to better design of wind turbine blades.