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You can when it’s standing still or at takeoff. But when it gets about 100 feet away, pfft! It’s gone.

The disappearance isn’t the result of some Star Trek-style cloaking device but something much simpler: This airplane is tiny — not much larger than splayed hand and with an engine about the size of a pinkie. It’s so small that a hundred feet in the air, it can’t be spotted, even by its chief designer, Gabriel Torres, a graduate student in aerospace engineering.

It probably comes as no great surprise that the disappearing act is part of the plane’s appeal.

Torres and his adviser, Thomas J. Mueller, Roth-Gibson Professor of Aerospace and Mechanical Engineering, are part of a group of engineers and students at universities and private companies trying to develop the world’s first micro aerial vehicles or MAVs. Instead of people and cargo, these toy-size planes would carry tiny video cameras and other sensors for a variety of potential applications.

In the near future, an infantry platoon leader may be able to pull a miniplane out of a backpack and send it off to scout out enemy positions on the other side of a hill or around the corner of a building. The images could be transmitted back to the screen of the soldier’s laptop computer.

An even smaller microplane with flapping wings might one day buzz down the hallway of a terrorist organization’s headquarters and attach itself to a wall or ceiling. Equipped not only with a video camera but a tiny microphone and possibly even sensors to sniff out drugs or weapons, such a vehicle would give new meaning to the expression "the office is bugged."

Not surprisingly the impetus for such devices comes from the military. Four years ago the Defense Department’s Defense Advanced Research Projects Agency allocated $35 million to spur development of a vehicle less than six inches at its widest point that could also fly up to six miles at as fast as 30 miles per hour. Ideally, the vehicle would also cost less than $1,000, making it a disposable item on the military scale of expenditures.

The Notre Dame model, developed by a team of six undergraduates that Torres led, can fly up to a mile at 30 miles per hour. It measures 10 inches at its widest point and is made of balsa wood with strips of carbon fiber reinforcing the tail and other edges. A shrink-wrap-type membrane covers its wide, truncated wings and fuselage.

The plane is powered by a tiny engine available off the shelf from Cox, a longtime producer of liquid-fueled radio-controlled cars and planes for hobbyists. The fuel "tank" is a plastic bottle that originally held a free sample of makeup. Cargo consists of a video camera about the size of a button off a winter coat and a transmitter the size of a match box. Fully loaded and fueled the plane weighs about three ounces.

The plane is launched by starting the engine and throwing it on the run like a dart. Once aloft, steering is performed by radio control of the wing flaps while the operator watches the feed from the on-board video camera. Remember, the vehicle is so small that you can’t steer it like a conventional radio-controlled plane, watching from the ground; it becomes invisible 100 feet away. Landings are undignified nose-over-tail tumbles over the turf, but because the plane is so light they usually don’t result in much damage, Torres says.

Earlier this year Notre Dame tested the plane against models developed at other universities in a competition at Arizona State University. Only one of the eight entries was able to accomplish the "mission," which was to fly four-tenths of a mile and transmit back a video image of the "target" — a three-foot-square of white cardboard lying on the ground with a large letter printed on it. Like the other entries, the Notre Dame plane fell victim to the thin air at the high-altitude location. There was too little oxygen for the engine to work efficiently and generate sufficient lift for prolonged flight.

If the military wants to make tiny spy planes, one might wonder why it doesn’t just instruct engineers to scale down the blueprints for a jet fighter or even those of a radio-controlled hobby plane. The reason is, it won’t work. The molecules that make up air present a vastly greater challenge for smaller, slower vehicles or animals than for 747s or eagles, which is why you never see mosquitoes soaring and gliding.

It’s been said that to a gnat, air "feels" like oil or honey feels to us. So when you’re tiny and trying to fly, the action is more like swimming. Even the tiny plane built by Torres and the undergrads — though it has a propeller and fixed wings — looks something like a bumblebee in flight, struggling forward with its nose up. (For more on the MAV project, visit the team’s website, www.nd.edu/~mav)

Researchers like Mueller are trying to understand how air flows over tiny wings so they can determine the most efficient shapes to use on micro aerial vehicles, be they fixed-wing or the flapping-wing type, which are called ornithopters.

Earlier this year Mueller hosted a conference at Notre Dame on fixed-, flapping- and rotary-wing vehicles. The meeting brought together 60 researchers from six countries, and not only aerospace engineers. There were biologists and zoologists. That’s because while little is known about the performance of wing shapes on airplanes that fly at low speeds, there’s a long history of research into how insects and small birds fly.

— Ed Cohen

Photo by Lou Sabo

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