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MIT Glider Lands On a Perch Like A Bird
MIT researchers have developed a foam glider that can land on a perch like a parakeet. To match this commonplace avian feat, they had to master the stall, a maneuver that requires the plane to tilt its wings back at a very sharp angle, creating a turbulent air flow that brings the plane to a near halt in mid-air. See the video below for some great slow-motion footage of the MIT glider in flight.
(MIT glider lands on perch)
To design their control system, MIT Associate Professor Russ Tedrake, a member of the Computer Science and Artificial Intelligence Laboratory, and Rick Cory, a PhD student in Tedrake's lab who defended his dissertation this spring, first developed their own mathematical model of a glider in stall. For a range of launch conditions, they used the model to calculate sequences of instructions intended to guide the glider to its perch. "It gets this nominal trajectory," Cory explains. "It says, 'If this is a perfect model, this is how it should fly.'" But, he adds, "because the model is not perfect, if you play out that same solution, it completely misses."So Cory and Tedrake also developed a set of error-correction controls that could nudge the glider back onto its trajectory when location sensors determined that it had deviated from it. By using innovative techniques developed at MIT's Laboratory for Information and Decision Systems, they were able to precisely calculate the degree of deviation that the controls could compensate for. The addition of the error-correction controls makes a trajectory look like a tube snaking through space: The center of the tube is the trajectory calculated using Cory and Tedrake's model; the radius of the tube describes the tolerance of the error-correction controls.
The control system ends up being, effectively, a bunch of tubes pressed together like a fistful of straws. If the glider goes so far off course that it leaves one tube, it will still find itself in another. Once the glider is launched, it just keeps checking its position and executing the command that corresponds to the tube in which it finds itself. The design of the system earned Cory Boeing’s 2010 Engineering Student of the Year Award.
The measure of air resistance against a body in flight is known as the "drag coefficient." A cruising plane tries to minimize its drag coefficient, but when it's trying to slow down, it tilts its wings back in order to increase drag. Ordinarily, it can't tilt back too far, for fear of stall. But because Cory and Tedrake's control system takes advantage of stall, the glider, when it's landing, has a drag coefficient that's four to five times that of other aerial vehicles.
I'm always impressed by research that brings the dreams of science fiction authors to life. For example, consider the biomimetic tracer-bird from Roger Zelazny's excellent 1980 novel Changeling, illustrated by Esteban Maroto. This device could easily land on a high perch to perform its surveillance duties.
"He saw the blue-bellied, gray-backed thing upon the sill overhead. It was turned as if watching them. A portion of its front end caught the sunlight and cast it down toward them... The tracer-bird followed their every step, hung upon their words..."
(From Changeling by Roger Zelazny)
See what Stanford engineers are doing on the other side of the country in Perching Project Drones Wait For You . Read more details about the perching glider at the MIT press release.
Scroll down for more stories in the same category. (Story submitted 10/11/2010)
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