Hybrid-Electric Airplanes Are Taking Off

Cambridge University hybrid airplane

It’s been nearly 20 years since the Toyota Prius hit U.S. roads with a hybrid gas and electric engine, creating mainstream acceptance of hybrid vehicles.

And now, similar power systems are making their way into single-seat sport aircraft, a market that’s still considered a cottage industry, but accelerating rapidly.

Battery size and costs are shrinking while efficiency is improving at about 5 percent annually, says Prof. Paul Robertson, whose engineering students at Cambridge University in England tested a hybrid-power single-seat plane in December 2014.

That craft—weighing less than 450 kilograms/1,000 pounds with 16 lithium-polymer batteries in its wings—recharges in-flight. The hybrid engine system uses an estimated 30 percent less fuel compared with a fuel engine alone.

“In the longer term we shall be running some more student projects looking at alternative fuels including higher bio-ethanol content and an electrically assisted taxi system (wheel motors) to reduce ground-level noise and shorten the takeoff run,” Robertson says.

Batteries remain too heavy to be an efficient standalone airplane engine, Robertson says. But the hybrid or parallel engine can reap the benefits of electric flight— quieter operation, less vibration and reduced emissions—while also cutting the use of fossil fuel.

One popular vision of electric aviation starts with the radio-controlled models most people associate with battery-power. In fact, options are expanding to include photovoltaic cells, fusion, and other engines that complement a gas motor, Robertson says. The real-life goal is finding a balance between power and economy, while capitalizing on greater reliability, thanks to fewer moving parts.

Skeptics argue, however, that weight, excess heat from battery discharge, and a need for back-up power in case of emergency will hinder adoption in planes. One high-profile example was the 2014 grounding of Boeing 787 Dreamliner jets because of damage from battery overheating.

Electric has made inroads in sport flying. In 2008, New Jersey inventor Randall Fishman developed an all-electric, motor-glider, the ElectraFlyer, with an 18-horsepower engine that can cruise at 70 miles-per-hour. Fishman created Electric Aircraft Corp. to build three different models that operate for up to 90 minutes before recharging—efficient for recreational flying but not competitive transportation when compared to the time or expense of driving door-to-door.

“We’re working on a hybrid design – if you want to go very far, very efficiently, hybrids have potential,” Fishman says. “You match the engine to the airframe and the drivetrain but you need power for takeoff and climb.”

One of Fishman’s designs has longer wings than conventional planes, allowing it to use wind thermals when aloft and can use its propeller spin to partially recharge batteries during flight.

Most electric planes are considered “ultra-light” or “sport” models that do not require U.S. Federal Aviation Administration approvals. Because small builders produce only a few planes at a time, Fishman says, the industry has seen scammers or failures whose start-ups promise new models, encourage investors or pre-orders, then neither build planes or return the money.

More than 60 percent of the U.S. flights in 2011 and most flights worldwide are “general aviation” or air taxi – personal and corporate aircraft. That market was hit hard by the rising price of gasoline in the 2000s recession, according to a 2012 report by the MIT International Center for Air Transportation.

Private pilots are cutting back flying time because of advancing age, rising costs and other interests among recreational flyers, the MIT survey found. The study reported that general aviation generated 496,000 jobs in the U.S. in 2009 and its total economic contribution in the is U.S. estimated at $76.5 billion.

Getting a piece of that market remains attractive to start-ups, academics and adventurers.

Terrafugia, based in Woburn, MA outside Boston, is developing a ‘flying car’ that is both driveable on U.S. streets and flown using extendable wings. A hybrid-power model appears on the company’s website as a goal within about 10 years.

Erik Lindbergh, grandson of the famed Jazz Age aviator, is also championing an electric future. His Powering Imagination project has teamed with Embry-Riddle Aeronautical University, promising an all-electric flight late in 2015. But his organization’s blog has been silent since August 2014 when he appeared at the annual Oshkosh Air Show in Wisconsin.

Embry-Riddle spokesman James Roddey says students at the Daytona Beach, FL school will work on an all-electric motor-glider using an airframe from Lockheed Martin’s famed “Skunk Works” research-and-development facility.

The large-scale commercial passenger plane makers are watching and collaborating with the tinkerers. Airbus Group has unveiled its E-Fan 2.0 battery-powered airplane, intended as a training model for flight schools by 2017.

Boeing Corp. supported Robertson’s Cambridge University project and other initiatives, including a research center in Madrid that has flown fuel cell and cryogenic fueled aircraft.

“Our mission is to keep our sights on finding innovative solutions and technologies that solve our industry’s toughest challenges and continually improve environmental performance,” said Marty Bradley, Boeing’s principal investigator, in a statement after the Cambridge University test flight.

Image courtesy of Cambridge University

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