Plane & Pilot
Tuesday, June 21, 2011

A New Era Dawns: Electric Flight


An update on airplanes in production, competition prizes and R&D


Aircraft giant Airbus has a stake in electric research with eGenius, (a CAFE race competitor). The two-seater aircraft was designed at the University of Stuttgart. The side-by-side eGenius has 60 kW (80 hp) of power, a max takeoff weight of 1,870 pounds, 250-mile range and 127-knot cruise. Fuel-cell power is also on the Airbus R&D agenda.

And how can you ignore the tiny, toy-like—but fully aerobatic—Cri-Cri from EADS Innovation Works, which takes a different approach to electrifying an existing airframe requiring minimal power to fly. Its four small brushless motors with counter-rotating props bring 1,000 fpm of climb and 30 minutes of air time. The fun project is purposed as a low-cost test bed for electric technologies.

So much more is going on: higher power-to-weight motors, electric-powered parachutes and trikes on the market, and companies like France's Electravia—with a line of existing and planned electric aircraft, including a two-seat Horten-style flying wing! Ah, those French.

Here's a snapshot of things to come. Someday, you'll find yourself reading a specifications box in an aircraft pilot report, and notice the following entry: FUEL BURN: N/A.

Energy Battle: David Vs. Goliath

It helps to understand the huge technical challenge electric flight still faces by comparing the energy densities of gasoline and batteries.

Lead-acid batteries like those in boats and cars, have been around for 150 years. They're cheap and relatively environmentally friendly to fabricate and recycle, compared to lithium-based (Li-Ion—lithium-ion, and LiPo—lithium-polymer) batteries.

Lead acids store around .6% the energy density of gasoline. Running the numbers tells us it takes 167 pounds of batteries to hold the same energy as a single pound of gas.

Lithium batteries as typically used in cameras, cell phones and radio control models store around four times as much energy as a lead-acid battery, but cost several times more per watt-hour. That still means an airplane needs to carry more than 40 pounds of batteries for the equivalent energy of a single pound of gas...that's less than one quart!

Looked at another way, that 25 gallons you fill up a typical LSA's wings with would require 6,000 pounds of lithium-technology batteries...and more than 10 tons of lead acids.

No wonder research into improving battery energy density is feverish around the world: Even a doubling of storage capacity would deliver multiple-hour flights. Many observers predict we'll have affordable, mass-produced battery technology with just that—two times the current capacity—by 2015.

Meanwhile, many R&D groups worldwide have already demonstrated increases up to four times in energy density for exotic research projects.

There's another factor: The best internal combustion engine converts only 25% to 30% of the energy potential of gasoline, whereas brushless electric motors operate at 80% and even higher efficiencies. Even so, we need more, and dramatic, breakthroughs in battery capacity to close the gap.

Demand creates industries: Will the move toward hybrid and electric cars and viable electric aircraft provide enough market incentive for long-range, fast, cargo-carrying electrics in our medium future? Nobody knows the answer yet...but many are bankrolling research in the expectation of a strong, "Yes!"


Resources
AERO's e-flight-expo
www.flight-expo.com

CAFE Green Flight Challenge
www.cafefoundation.org

Lange Antares 20E
www.lange-aviation.com

Lindbergh Electric Aircraft Prizes
http://lindberghprize.org
PC Aero
www.pc-aero.de

Randall Fishman's ElectraFlyers
www.electraflyer.com

Sikorsky Firefly
www.sikorsky.com

Taurus Electro G2 and G4
www.pipistrel.si

Yuneec International
www.yuneec.com





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