Study of Singapore colugos reveal gliding secrets

High-tech backpack helps reveal lemur's flying secret
Roger Highfield, The Telegraph 6 Feb 08;

A high-tech backpack has enabled scientists to reveal the gliding secrets of a flying lemur, one of our more exotic cousins.

The feat could aid in the design of flexible winged aircraft, like hang-gliders or micro-air vehicles, according to the team that reports the work today.

They have used high technology to track Malayan colugos, which grow up to 16 inches and resemble large flying squirrels, in the rainforests of Singapore.

Colugos are also known as flying lemurs, but they don't really fly and they aren't lemurs. Although they are cousins to primates, including humans, they have wings of skin between their hands and feet that are the size of a large doormat when extended to allow them to glide.

Now Andrew Spence from the Royal Veterinary College, working with colleagues from the University of California, Berkeley, and the National University of Singapore, has documented the aeronautics of the Malayan colugo in the wild.

Using an accelerometer of the kind common in Nintendo's Wii, along with memory chips typical of an iPod, they created a backpack that could sense and record the creature's movements in three dimensions.

The study, published today in the journal Proceedings of the Royal Society B, has provided important information which improves our understanding of the behaviour of gliding animals, which will help aeronautical engineers.

"Despite being common throughout their natural range the Malayan colugo is quite poorly understood because it's hard to measure things about an animal that moves around at night, lives 30 metres up a tree, and can glide 100 metres away from you in an arbitrary direction in 10 seconds," says Spence, who did the work with postgraduate Greg Byrnes and Norman Lim.

"Our new sensing backpacks have given us an insight into the behaviour of these fascinating creatures."

The researchers were able to prove that the colugo can alter the aerodynamic forces acting upon it in flight, with the data that their tiny three-axis accelerometer chip recorded, in order to reduce the effect of landing forces, and thus limit risk of injury.

The creatures are able to glide at a steady speed and as they come in for landing they appear to be able to do a very precise manoeuvre that slows their speed and simultaneously orientates them correctly for spreading the impact of landing across all four limbs.

The researchers were able to demonstrate a drastic reduction in landing forces for glides longer than about two seconds, where colugos are able to use their wings in a parachute-like way. This reduction in impact forces over long gliding distances has been predicted from aerodynamic theory, but until now scientists have not been able to demonstrate it conclusively in the wild.

In the study, funded in part by the Singapore Zoological Gardens, the team caught the nocturnal adult colugos by hand whilst they were resting low on trees during the day. They shaved off a small patch of fur, stuck the backback to its exposed skin using a surgical glue and released the animals back in the wild.

Colugos, which can weigh up to 4.5llb, whose babies cling to their parents' bellies while they glide, were able to wear the sensors and glide uninhibited for several days before the adhesive fails and the backpack falls to the ground. The backpacks were then recovered using a radio receiver.

Natural flyers like birds, bats and insects outperform man-made aircraft in aerobatics and efficiency, reports a team of University of Michigan engineers who are designing flapping-wing planes with wingspans smaller than a deck of playing cards.

A Blackbird jet flying nearly 2,000 miles per hour covers 32 body lengths per second. But a common pigeon flying at 50 miles per hour covers 75, they point out. The roll rate of the aerobatic A-4 Skyhawk plane is about 720 degrees per second, while that of a barn swallow exceeds 5,000 degrees per second.

And while some military aircraft can withstand gravitational forces of 8-10 G, many birds routinely experience positive G-forces greater than 10 G and up to 14 G.

"Natural flyers obviously have some highly varied mechanical properties that we really have not incorporated in engineering," says Prof Wei Shyy. "Natural flyers have outstanding capabilities to remain airborne through wind gusts, rain, and snow."

Prof Shyy and his colleagues have several grants from the Air Force of more than $1 million annually to research small flapping wing aircraft. Such aircraft would fly slower than their fixed wing counterparts but would be able to hover and possibly perch in order to monitor the environment or a hostile area.