Tuesday, December 7, 2010

Falling with Style

Its been a little while since I've posted anything. I suppose that's what the "semi-frequent" part of my blog description really means. So for the next couple of posts not only am I going to post them in rapid succession but they will also be slightly older stories. But, I figure, cool science is always cool science and so will allow myself to get away with it.

This story caught my eye because (1) I attended a talk by this researcher when I was in grad school and (2) it is about flying snakes.

You didn't know there were flying snakes? Well, then you are in for a treat, my friend, a real treat. Flying snakes or flying tree snakes belong to the genus Chrysopelea (family Colubridae) which can be found in Southeast Asia, India and southern China. Despite its name the snake doesn't actually fly. When they launch themselves off a tree they flatten their bodies and undulate to glide to their destination. Basically its body becomes like a big wing ideal for gliding.

The Paradise Tree Snake (Chrysopelea paradisi) is the most commonly studied of this genus. This snake is brightly colored, with a black body covered from head to tail with a yellow spotting pattern that at times can look stripped and has 5 yellow (sometimes orange) bars that span its width. It is native to the tropical forests of southern Thailand, Peninsular Malaysia, the Philippines, Singapore, and Indonesia. The vegetation in these forests can be quite diverse, including tropical broadleafed species and evergreens with little to no understory. Its diet consists of arboreal reptiles and amphibians (lizards, frogs, etc.) as well as small birds and even bats. Add together habitat and hunting and you can probably start see why this snake needs to fly.

A Virginia Tech researcher, John Socha, studies the kinematics of these snakes. He published a short article in Nature in 2002 (and a similar one in The Journal of Experimental Biology in 2005) where he looked at the full three-dimensional gliding trajectory of these snakes. First, in an open field, he built a 10 meter high tower/platform with a horizontal branch extending from the top. Then he carried his snakes to the top of the platform and videotaped and photographed them jumping off the branch and gliding to the ground. Besides the flying snake (which is obviously so very cool) my favorite part is the undergrad let's-call-them-lackeys running to get the escaping snake once it reaches the ground.

Anyway, he found that the snake prepares for take-off by hanging the front part of its body off the branch looped into a J-shape. When the snake jumps it accelerates up and way from the branch, straightening its body and flattening it by stretching out its ribs. The body width of the snake actually doubles and the stretching of the ribs curves the belly into a concave shape. Because the snake is falling it will gain speed and as it does that it will pitch its body downwards and curve into an S-shape. Then the snake starts undulating from side-to-side, starting at the front and moving down the body. This creates lift and allows it to go a further horizontal distance rather than falling straight down to the ground. C. paradisi is very adept at aerial manoeuvring, being able to turn without banking. It can even out-glide other gliders like flying squirrels (Petaurista petaurista) and flying frogs (Rhacophorus nigropalmatus).

Recently there have been some articles in various major news outlets about Socha's new research presented at the American Physical Society Division of Fluid Dynamics meeting in Long Beach, California and a paper accepted for publication in the journal Bioinspiration & Biomimetics. He explains in further detail the gliding motion of these snakes, having developed a mathematical model that explains how they travel such long distances. Basically it takes the gliding description above and explains it mathematically as well as explaining the gliding techniques of other species (mammals, frogs, lizards, etc.). The U.S. Pentagon and the Defense Advanced Research Projects Agency (DARPA) has had a big interest and funded a lot of this research, although they have yet to explain their big interest in the work.

Here is Socha's kinematics paper:
Socha, J.J. (2002) Kinematics: Gliding flight in the paradise tree snake. Nature: 418 (6898), 603–604. (DOI:10.1038/418603a)

This is Socha's flying snake page. It includes some great images and videos of his experiments as well as a fantastic links page to find out more about these snakes. I highly recommend checking it out!

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