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MIT researchers create a model plane that lands on a wire

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July 21, 2010

A smoke visualization still of the actual vortex wake behind our glider during a free-flig...

A smoke visualization still of the actual vortex wake behind our glider during a free-flight high angle of attack landing (Image: Jason Dorfman MIT/CSAIL)

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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.

Stalling

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.

MIT's perching glider

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.

A smoke visualization still of the actual vortex wake behind our glider during a free-flig...

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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About the Author
Darren Quick Darren's love of technology started in primary school with a Nintendo Game & Watch Donkey Kong (still functioning) and a Commodore VIC 20 computer (not still functioning). In high school he upgraded to a 286 PC, and he's been following Moore's law ever since. This love of technology continued through a number of university courses and crappy jobs until 2008, when his interests found a home at Gizmag.   All articles by Darren Quick
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10 Comments

MIT Engineers and Scientists are the best Innovative people. Instead of wasting time, resources and energy on petty things like the above, why not they concentrate on pressing energy problems,health etc., Developing countries can immensely benefit by the innovative research by MIT people.

Dr.A.Jagadeesh Nellore(AP), India

Anumakonda Jagadeesh
22nd July, 2010 @ 07:15 am PDT

All this except the landing on a wire part has been done many times before called STOL. They would be far better off with a 1.25-1 wing aspect ratio like the Flying pancake that the Gov destroyed in the late 40's so no one would get the tech to make inexpensive aircraft carriers, putting their large, expensive jet landing ones being obsolete.

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.

jerryd
22nd July, 2010 @ 07:58 am PDT

I used to fly RC gliders many years ago and would 'catch' them, rather than risk a landing, with almost a replica of that maneuver. Very cool that they automated this.

William Volk
22nd July, 2010 @ 08:10 am PDT

I find it interesting that they have automated the process. That may work well for Drones and UAVs. In the Radio Controlled aircraft hobby we have a category of planes that can perform so-called 3D maneuvers. These are post stall maneuvers that rely on large control deflections, proper center of gravity, and powerful engines cabable of generating far more thrust than the weight of the aircraft. These aircraft can essentially touch down at zero airspeed. I'm still not sure I see the practical application here though. Even if an aircraft could be made to land on a wire like this, how does it takeoff? It would have to have massive amounts of thrust to lift off again. So what would the benefit be over a current gen VTOL aircraft? I guess lightweight drones or UAVs could use this technology, but I don't see passenger planes doing this anytime soon as the opening paragraph eludes to.

Jonathan Hatfield
22nd July, 2010 @ 08:23 am PDT

Another conspiracy theory needing non-circumstantial evidence.

ccguy
22nd July, 2010 @ 09:01 am PDT

Comme on!

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

Ariel Dahan
22nd July, 2010 @ 11:14 am PDT

Hatfield raised the question about takeoff. The wire becomes the basis for a slingshot launcher. The application is for "robotic" planes that can withstand high-g environments.

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).

Andrew M
22nd July, 2010 @ 10:18 pm PDT

Practical use,ask the Navy for one-everything from landing anything on a carrier to capturing UAV's on much smaller vessels.

May not be as important as curing deseases etc,but we live in a dangerous world.

Gra in OZ

gragraposker
23rd July, 2010 @ 03:38 pm PDT

This seems like nothing more than an exaggerated, precision landing flare that would work only for the lightest gliders. It would be useless for even a light UAV or any other kind of powered aircraft with mass exceeding a few kilograms.

Gadgeteer
25th July, 2010 @ 09:11 pm PDT

The Cobra dogfight manoeuvre entails massive power, while this landing on a string manoeuvre entails a precision, power-off, stall landing, quite different in every way! Not seen a MiG land in Cobra mode either, as it just isn't possible (would for one thing entail a very weird landing gear).

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!

Tord
26th January, 2012 @ 03:43 am PST
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