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Electric Icarus: NASA Designs a One-Man Stealth Plane

Could the Puffin, an electric-powered flying suit, change the way we use the sky in war and peace?



NASA Langley/Analytical Mechanics Associates

A super-quiet, hover-capable aircraft design, NASA's experimental one-man Puffin could show just how much electric propulsion can transform our ideas of flight. It looks like nothing less than a flying suit or a jet pack with a cockpit.

On the ground, the Puffin is designed to stand on its tail, which splits into four legs to help serve as landing gear. As a pilot prepares to take off, flaps on the wings would tilt to deflect air from the 2.3-meter-wide propeller rotors upward, keeping the plane on the ground until it was ready to fly and preventing errant gusts from tipping it over. The Puffin would rise, hover and then lean over to fly horizontally, with the pilot lying prone as if in a glider. When landing, the extending spring legs would support the 3.7-meter-long, 4.1-meter-wingspan craft, which is designed with carbon-fiber composites to weigh in at 135 kilograms, not including 45 kilograms of rechargeable lithium phosphate batteries.

In principle, the Puffin can cruise at 240 kilometers per hour and dash at more than 480 kph. It has no flight ceiling—it is not air-breathing like gas engines are, and thus is not limited by thin air—so it could go up to about 9,150 meters before its energy runs low enough to drive it to descend. With current state-of-the-art batteries, it has a range of just 80 kilometers if cruising, "but many researchers are proposing a tripling of current battery energy densities in the next five to seven years, so we could see a range of 240 to 320 kilometers by 2017," says researcher Mark Moore, an aerospace engineer at NASA's Langley Research Center in Hampton, Va. He and his colleagues will officially unveil the Puffin design on January 20 at an American Helicopter Society meeting in San Francisco.

Moore and his colleagues at NASA, the Massachusetts Institute of Technology, the Georgia Institute of Technology, the National Institute of Aerospace, and M-DOT Aerospace named their craft the Puffin because "if you've ever seen a puffin on the ground, it looks very awkward, with wings too small to fly, and that's exactly what our vehicle looks like," he explains. "But it's also apparently called the most environmentally friendly bird, because it hides its poop, and we're environmentally friendly because we have essentially no emissions. Also, puffins tend to live in solitude, only ever coming together on land to mate, and ours is a one-person vehicle."

This design relies on electric motors. These remain efficient regardless of their size, whereas internal combustion engines become less efficient the smaller they are. As such, electric aircraft can use small motors while generating impressive propulsion—the Puffin can lift a person with just 60 horsepower.

At up to 95 percent efficiency, electric motors are far more efficient than internal combustion engines, which only rate some 18 to 23 percent. This means electric aircraft are much quieter than regular planes—at some 150 meters, it is as loud as 50 decibels, or roughly the volume of a conversation, making it roughly 10 times quieter than current low-noise helicopters.

This super-quiet quality makes the Puffin potentially ideal for covert military insertions of special operations units and other troops—indeed, it was originally aimed to launch from submarines; unmanned versions could also help transport supplies. Quieter aircraft  also mean that airports for civil applications such as personal travel and fast courier services could be located much closer to population centers and perhaps even residences without bothering others, significantly cutting down commute times. Inventors all over the world are still striving to develop personal air vehicles, the equivalent of a plane in every garage—for instance, Samson Motorworks is trying to develop a land/air-capable motorcycle.

In addition, since electric motors are so efficient, they also generate far less heat. This not only gives them a lower thermal signature for military stealth, but means they don't need anywhere near the same amount of cooling air flowing over them that internal combustion engines do, thereby reducing aerodynamic drag that can slow them down.

Because electric motors have fewer moving parts, they are perhaps 10 or even 20 times more reliable than piston engines. In addition, the Puffin's design allows pieces of either of its two electric motors to fail without any reduction in power to the prop rotors. The plane could also take a hard, forceful landing if necessary, as the landing gear supports the brunt of the load instead of the pilot, unlike some other one-man flying craft.

"The Puffin is an exciting idea.... It converges and demonstrates many technologies at once," said Brien Seeley, president of the Comparative Aircraft Flight Efficiency (CAFE) Foundation, a Santa Rosa, Calif.–based independent flight test agency that hosts the annual Electric Aircraft Symposium. "In my opinion, a mass-marketable version will need conventional seating, cup holders and a short runway for glide-in, view-ahead landings—but opening up people's imagination is the first essential step."

By March, the researchers plan on finishing a one third–size, hover-capable Puffin demonstrator, and in the three months following that they will begin investigating how well it transitions from cruise to hover flight. They are already looking past the Puffin, however. The next-generation of this design might incorporate more than just two pairs of prop rotors, so that if one was struck by, say, a bird or gunfire, the aircraft could survive on redundant systems. "We could make it so there's no single point of failure—that's the cool next step," Moore says.

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