Flying snakes!

Lorena Barba and Jake Socha are respected research professors, but they’re just like the rest of us when it comes to the eews and ahhs of seeing flying snakes.

“Everybody gets a kick out of just watching them wiggle around” while in flight. “It’s pretty impressive, isn’t it?” said Barba, an associate professor of mechanical and aerospace engineering in the George Washington University School of Engineering and Applied Science.

“I meet people all the time who’ve never heard of these things,” said Socha, an assistant professor at Virginia Tech specializing in organismal biomechanics who got his undergraduate degree at Duke University in 1994. His interest in flying snakes goes back to shortly after his time at Duke, where he was influenced by renowned biomechanics expert Steven Vogel.

Barba recently led groundbreaking research on the aerodynamics of flying snakes, which are native to South and Southeast Asia. Her team built a computer model that used graphic processing units and applied computational fluid dynamics – which uses numerical methods and algorithms to solve and analyze problems involving fluid flows.

It’s the first work to study the lift of a flying snake’s cross-section computationally. A full understanding of the mechanics of the snakes’ flight could lead to answers for other small-scale flight projects, including the ideal air flow for a small wind turbine.

“Aerodynamics are very particular to size, shape and speed,” said Socha, a collaborator with Barba who has filmed flying snakes after launching them from cranes in their natural habitats. So flying snakes are “really most applicable to things that are small and not going very fast … small things that fly, like little micro air vehicles. Actually, you could make little robotic fliers based on the cross-section of the shape of the snake or the configuration of its body – and then potentially, you could get performance similar to what the snakes do.”

Elusive subjects

You can’t see flying snakes anywhere in this country. Even in their native habitat, it’s not easy to find them.

“It’s very hard to do these observations,” Barba said. “First of all, you have to find them in deep rain forests, and they’re not exactly numerous or very eager to deal with you. Videos are quite hard to get … and it costs a huge amount of money to send a team to Southeast Asia and get video. It’s a big production.”

“You need to find a big enough space to contain them,” Socha said, “and you have to start them from a height because they don’t glide up, only down.”

Although scientists refer to these animals as flying snakes, the flight process is more like short spurts of gliding. It’s not like a bird that can flap its wings and stay airborne for hours at a time.

These thin snakes – ranging from 2 feet to 4 feet long – jump from trees to the ground or to another tree by flattening their bodies into a concave C shape, falling to their landing spot. Some are known to glide 100 feet in the air.

Three species in the genus Chrysopelea are known to glide; one, Chrysopelea paradisi, has been seen twisting back and forth to make mid-air turns.

“It’s much quicker to jump and glide a fair distance than to slither down a tree, slither on the ground or slither up a branch, obviously,” Barba said. “It’s a locomotion advantage.”

Just why the snakes glide is a mystery.

“The number of observations of animals gliding in the wild is not particularly high,” Socha said. “We don’t have a good database of ‘Animal 1 jumped from Spot X and landed on Spot Y, and the reason that they did so.’ …

“I can infer, though, that it’s probably not chasing prey in the air because that would not be too effective. And from records, it seems they’re not gliding too often. If you look at something like a flying lizard, they seem to glide quite a lot.”

The air lift puzzle

Barba and Socha agree that the key to their research is understanding all of the aspects of how air swirls around these snakes.

“That is what we must focus on, because it’s shaped unlike anything that we are used to seeing as a flying creature,” Barba said. “This is what’s most mysterious.

“It doesn’t look like it should fly. So for that reason, we’re very curious to understand how it’s possible that this strange shape could be so efficient in getting the right forces from the air to fly so well. Flying snakes are even better gliders than flying squirrels. It really is quite phenomenal.”

Said Socha, whose team has built physical models with tubing, testing them in a wind tunnel: “One of our major questions is, how exactly is it able to glide? What are the physical phenomena that underlie its aerodynamic force production? To figure that out, you’re going to need to know what the air is doing around the animal and how the animal changes the air flow patterns. Figuring that out is not a simple task.”

Barba said two-dimensional cross-sections show how the snakes can generate a lot of lift. Three-dimensional cross-sections will probably show even more.

“In the future, we want to look at the 3-D geometry, focusing on the side-to-side undulations. When it’s flying or gliding, (the snake is) in a flat S shape, and that S shape is constantly reshaping. If you look at the head, it’s wiggling the head side to side quite quickly. As it moves its head side to side, that undulation travels back through its body.”

They hope a 3-D model can shed light on issues such as spacing’s role in aerodynamics.

“It’s essentially like, if you have two wings and you reposition those wings continuously, you will get different aerodynamics,” Socha said.

“If I have two wings and, instead of having them side by side like on an airplane, I put them in series one in front of another and change the up and down spacing, the back and forth spacing, you get different aerodynamics. That’s one of the things we’re trying to figure out.”