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Can Electric Aircraft Take to the Skies?

Electric aircraft are breaking records and beginning to gain aviation industry interest
Green Flight Challenge



flickr/nasa hq photo

Dully whining electric motors may soon compete with roaring turbofans in the sky as battery-powered planes and helicopters take flight.

Aircraft are emerging as the new frontier in electric vehicles as new technology and market demand converge to drive development. More energy-dense batteries, lighter components and more efficient power electronics are making plug-in airplanes a realistic prospect. Talk of taxes on greenhouse gas emissions and more stringent noise regulations have sent engineers looking beyond pistons and turbines.

In addition, electric aircraft have begun to post impressive results. Chip Yates, an electric vehicle developer, set a manned electric air speed record of 202.6 mph two weeks ago. The 16-minute flight over the Mojave Desert bested the previous electric speed record of 175 mph.

Last year, Pipistrel USA won NASA's Green Flight Challenge with an electric airplane that flew 200 miles with a fuel-equivalent efficiency of 403.5 passenger miles per gallon, which is the fuel efficiency divided by the number of passengers. Pascal Chretien, an aviation consultant and a test pilot, built and flew the first manned electric helicopter last August.

Why has it taken so long for airplanes to boldly go where cars have been for years?

The aviation industry is conservative about new technologies, stemming from culture as well as regulations, according to Peter Harrop, chairman of IDTechEx, a market research and consultancy firm. IDTechEx published a major report last month on the state of electric aviation throughout the industry.

The report details developments in electrical technologies, from airships to unmanned aerial vehicles. Harrop said much of the progress is driven by high fuel prices and market competition, especially in civil aviation.

Boeing and Airbus take notice
Though only small companies and entrepreneurs are currently making fully electric airplanes, larger manufacturers such as Boeing Co. and Airbus are investigating how to electrify portions of aircraft operations as the push for bigger, faster and farther yields to cheaper, quieter and greener. "We're on the tipping point," Harrop said.

One example is the auxiliary power unit in commercial aircraft. The device, usually located in the tail, is a generator that provides electricity to the plane when it's on the ground and gives power to start the main engines. It usually runs off a small turbine, but airline manufacturers are developing battery and fuel cell auxiliary power units to reduce their emissions and curb fuel use on the ground.

Another target is electrifying how planes move on the ground. Most aircraft taxi using thrust from their engines. At low speeds, this is tremendously inefficient; jet engines on an airliner can use 5 megawatts of energy, but a comparable electric drive system would use 2 kilowatts while producing no pollution and minimal noise, according to Harrop.

Boeing and Airbus are experimenting with electric landing gear that allow aircraft to turn, taxi and reverse on their own power without a truck to push the plane back from the gate. These systems can also integrate regenerative braking so that the energy from slowing a landing aircraft could charge batteries.

Some niche aviation applications are also looking to trade hydrocarbons for electrons. Harrop noted electric aircraft could be useful as trainers for pilots because the aircraft are cheap to operate and trainers seldom venture far enough to test range limits.

Defense contractors are also pursuing electric drivetrains to make stealthier unmanned aerial vehicles that have a minimal heat signature. They could also be charged on the fly from photovoltaic panels.

A mechanically simpler helicopter?
Electrification can also provide safety advantages. Hybrid electric propulsion can help extend flying time in emergencies. Electric drivetrains are also less mechanically complicated because electric motors can directly drive propellers and rotors, leaving fewer things that can go wrong in flight.

This is especially important for helicopters, according to Chretien. He observed that most helicopter crashes result from pilot error, followed by mechanical failure. Though the mechanisms behind helicopter flight are complex, the mechanical underpinnings are old and haven't changed much since helicopters were first developed, despite the preponderance of modern electronic instruments.

"It didn't make sense to me that the most advanced platform would be running on medieval technologies," he said. "It's an issue when it comes to reliability."

That's not to say electrics are without their troubles. As a new technology, electric propulsion is not necessarily more dangerous, but the field is less mature than conventional flight. After breaking the speed record, Yates' plane was forced to make a dead-stick landing when a malfunctioning cell knocked out power to the motor.

Storing the electrons needed to power an airplane also carries its own unique risks, as poorly cooled high-technology batteries can catch fire or explode.

Rotary aircraft are particularly challenging because their flight characteristics depend so much on weight and relative power. Even Sikorsky Aircraft Corp., one of the world's largest helicopter manufacturers, struggled with developing an electric aircraft and scrapped plans to test a prototype last year, citing safety concerns.

Chretien's prototype electric helicopter is scarcely more than steel tubing and a chair. Powered by up to 600 amps from 128 pounds of lithium-ion polymer batteries, the contraption can fly using two pairs of counter-rotating coaxial blades for up to 12 minutes.

Though it is just a proof concept, he said the industry is due for another technological leap now that manufacturers are getting diminishing returns from developments in turbines and piston engines. "If we can succeed in helicopters, the fixed-wing market will be a breeze," he said.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500

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