Flying snakes are mysterious. How do they soar? Without wings or other helpful appendages, how do they glide from tree to tree?
A team of American scientists, including Lorena Barba of George Washington University and Jake Socha of Virginia Tech, has been studying the small flying snake – about a yard long with the girth of a human thumb — in the lowland tropical forests of Asia and Southeast Asia. They hope to be able to apply their knowledge to a new generation of airborne robotics.
This week they published a report, "Lifts and wakes of flying snakes", in the journal Physics of Fluids.
Flying snake: The movie
By observing snake flight in a wind tunnel, the researchers discovered that the reptile's shape actually helps generate a force of lift, and when the snake turns at a particular angle, it gets an added boost of lift.
The scientists then shifted to computer simulations. "Rather than fixed wings, animal fliers have flapping wings," Lorena explained in a statement. "In the case of gliders, their small scale means they're always in a flurry of whirling winds. By understanding how they can be graceful and efficient under these conditions, we can in turn use that knowledge to create small flying machines that are equally graceful."
Snakes on a plane
Like all snakes, the report points out, the flying snake in question has a tubular body with circular cross-sections. When it goes into glide mode – to move from one tree to the next – it shapeshifts its body to create a flatter profile. "During the glide, the snake undulates laterally," according to the report, "and the parts of the body that are perpendicular to the direction of motion act as lift-generating 'wings'"
Those little whirls of wind, or vortices, created by the air going around the special cross sectional shape of the snake's body, can give a flying snake an extra lift, Lorena said. "The shape of the snakes in flight — which is a flattened version of its shape at rest — gets help from little vortices around it."
There is these days scientific interest – especially in the fields of biomimetics and bioinspired design — in what natural movement can teach us about building robotic devices. As the report states: "Nature has evolved diverse solutions to animal locomotion in the forms of flapping flight, swimming, walking, slithering, jumping, and gliding."
Of the 30 or so independent animal lineages that have developed gliding flight through the ages, the study notes, the flying snake is the only animal known to glide without the help of any apparent flight apparatus.
Three species of snakes — in the genus Chrysopelea – are gliders. One, the paradise flying snake, is even able to swivel in mid-air.
So what lessons can we learn from this research? "Studying animal flyers is an exciting new frontier for engineering research, because they do many unexpected things to generate flight forces, be agile and navigate in the air," Lorena tells NPR. "We hope to learn the solutions that nature has found for flight at small scales—insects, birds and animal gliders are all quite small compared to airplanes."
The aerodynamics of airplanes, she says, "is well understood, and of course large aeronautical companies design very advanced flying machines. But you know the old urban myth about the bumblebee, and how aerodynamics knowledge would predict that it shouldn't be able to fly. It all boils down to the scale: because it is so small, it actually flies in the midst of many little gusts and whirls that it uses to defy gravity. The physics is very different from that of classical aerodynamics."
She adds, "we hope to be able to use that knowledge to guide the design of engineered devices that mimic nature in its solutions."
What is The Protojournalist? New-school storytelling, old-school reporting. @NPRtpj