MIT researchers create a model plane that lands on a wire
Airplane landings can be less than graceful. The aircraft slowly maneuvers into an approach pattern, begins a long descent, and then slams on the brakes as soon as it touches down, which barely seems to barely bring it to a rest a mile later. Birds, however, can switch from barreling forward at full speed to lightly touching down on a target as narrow as a telephone wire. MIT researchers have now given a foam glider this same ability using a new control system that could have important implications for robotic planes, greatly improving their maneuverability and potentially allowing them to recharge their batteries simply by alighting on power lines.
Birds can land so precisely because they take advantage of a complicated physical phenomenon called "stall." Even when a commercial airplane is changing altitude or banking, its wings are never more than a few degrees away from level. Within that narrow range of angles, the airflow over the plane's wings is smooth and regular, like the flow of water around a small, smooth stone in a creek bed.A bird approaching its perch, however, will tilt its wings back at a much sharper angle. The airflow over the wings becomes turbulent, and large vortices — whirlwinds — form behind the wings. The effects of the vortices are hard to predict: If a plane tilts its wings back too far, it can fall out of the sky. Hence the name "stall."
The smooth airflow over the wings of a normally operating plane is well-understood mathematically; as a consequence, engineers are highly confident that a commercial airliner will respond to the pilot's commands as intended. But stall is a much more complicated phenomenon: Even the best descriptions of it are time-consuming to compute.
Reap the whirlwind
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.
From spy planes to Tinkerbell
For some time, the U.S. Air Force has been interested in the possibility of unmanned aerial vehicles that could land in confined spaces and has been funding and monitoring research in the area. "What Russ and Rick and their team is doing is unique," says Gregory Reich of the Air Force Research Laboratory. "I don't think anyone else is addressing the flight control problem in nearly as much detail." Reich points out, however, that in their experiments, Cory and Tedrake used data from wall-mounted cameras to gauge the glider's position, and the control algorithms ran on a computer on the ground, which transmitted instructions to the glider. "The computational power that you may have on board a vehicle of this size is really, really limited," Reich says. Even though the MIT researchers' course correction algorithms are simple, they may not be simple enough.
Tedrake believes, however, that computer processors powerful enough to handle his and Cory's control algorithms are only a few years off. In the meantime, his lab has already begun to address the problem of moving the glider's location sensors onboard, and although Cory will be moving to California to take a job researching advanced robotics techniques for Disney, he hopes to continue collaborating with Tedrake. "I visited the air force, and I visited Disney, and they actually have a lot in common," Cory says. "The air force wants an airplane that can land on a power line, and Disney wants a flying Tinker Bell that can land on a lantern. But the technology's similar."
Video of MIT's perching glider landing on a wire can be viewed below.
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Dr.A.Jagadeesh Nellore(AP), India
The landing on a wire part is just computer control to hit it. Better to just stall onto a deck or land for more space than a helicopter needs.
What you show us on the video is nothing else than the Cobra dogfight manoeuvre that Mig22 did 10 years ago.
Ok, it\'s automated.
But it is still an aerodynamical brake by changing the incidence of the plane.
Not something I\'d to close to the ground unless I have high thrust power to recover...
Yet, it is the same idea as parking its car full speed braking and slidding. Or finishing a ski contest : You arrive full speed, and brake by changing direction and slide to stop.
Exactly the same way as \"space cowboy\" landed the shutlle, while arriving too fast. Just imagine a passenger airplane doing this... :-D
If coupled with the new (and yet to be commercially developed) Colossal-Carbon-Tube fibers, fairly large UAVs could be landed on, and launched from, the back of a truck (which road velocity could be added to the launch speed).
The fighter version of the Flying Pancake would not be able to make short landings, as it weighed a lot, while the low-powered Flying Flapjack indeed could do very short landings, due to its low weight, and huge wing area. Still a pity that the former never was test-flown, even once! I bet it would land like a DH Mosquito, needing high speed, and lots of room! Take-offs, with all that power would be a much swifter affair!