Even though I’ve only ever seen bats flit across a night sky, there’s something distinctive about their flight pattern that makes them instantly recognizable, even in the dark. That’s because bats’ wings are unique in the animal kingdom, a kind of super-evolved model for flight that lets them change direction in milliseconds at incredible speeds—one wing has 25 joints and 34 degrees of freedom, and its skin can stretch 400% without tearing.
A group of scientists at Brown University are replicating the bat’s unique anatomy in the hopes of applying its fundamental mechanics to aerospace engineering. "Bats are different than all other flying animals," says study co-author Kenny Breuer, who worked with biologist Sharon Swartz on the study. "We’re focusing on understanding how bats fly, and understanding the essential elements of that from an engineering perspective."
But asking a bat to fly at a certain speed in a small enclosed space wasn’t in the cards. So the team set out to build a workable model that’d allow them to test things like flapping frequency, amplitude, and angle. Using a 3-D printer, they prototyped dozens of model wings made of silicone skin and plastic bones. Cables serve as tendons, and three small motors set the wing in motion. The final working model, which was published in the February issue of Bioinspiration & Biomimetics, included the following insight:
One experiment looked at the aerodynamic effects of wing folding. Bats and some birds fold their wings back during the upstroke. Previous research from Brown had found that folding helped the bats save energy, but how folding affected aerodynamic forces wasn’t clear. Testing with the robot wing shows that folding is all about lift. In a flapping animal, positive lift is generated by the downstroke, but some of that lift is undone by the subsequent upstroke, which generates negative lift. By running trials with and without wing folding, the robot showed that folding the wing on the upstroke dramatically decreases that negative lift, increasing net lift by 50 percent.
The study was funded in part by the Air Force, which should give you some idea about how this information will be used. DARPA and other government agencies are increasingly interested in small, unmanned aircraft—especially those that can turn and change course at the drop of a hat. "There’s a lot of interest in building what are called micro-air vehicles," notes graduate student Joseph Bahlman. "The theory, what we’re developing here can be used to improve the efficiency of aircraft in general." But batwing micro-drones won’t hit the market for some years. For now, the team will focus on testing materials for the "robatic" wing.
[H/t The Verge]