Will Toyota`s Prius system go airborne in Zunum? Curt Lewis

Zunum's Hybrid Jet Could Finally Make Electric Flight a Reality

Say what you will about the electric Chevrolet Volt, but GM's engineers created a clever solution to the problem of battery range and recharge time: Give the car its own generator. When the battery winds down to nothing, a small gasoline engine generates the electricity to keep moving. The arrangement extends the car's range and saves gasoline.

Aviation startup Zunum thinks General Motors' approach might be just the thing to bring electric propulsion to commercial aircraft. The company, based in Kirkland, Washington, is developing the flying equivalent of a Chevy Volt that uses a pair of ducted fans for propulsion. As the battery runs low, a jet fuel-burning turbine fires up to keep the juice flowing.

As crazy as it sounds, the aviation industry finds itself fascinated by electric airplanes, which require less fuel and make less noise than conventional aircraft. So far, though, the technology remains hobbled by the limitations of battery technology. The most successful electric airplanes thus far are, like Solar Impulse, wildly impractical or, like the Airbus E-Fan, limited by their range and speed. That two-seater musters just 60 minutes of flight at 137 mph from its 350-pound battery.

Zunum CEO Ashish Kumar says the hybrid approach could reduce noise by 75 percent and cut airline fuel costs by 40 to 80 percent, and he hopes to get a short-haul commercial plane with a seating capacity of 10 to 50 passengers into service within a decade. He figures the first planes will carry a battery pack good for 175 miles, with the generator extending the aircraft's range to 700 miles. But he sees that range climbing relatively quickly as battery technology improves.

"Power density is growing every year," he says. Each time customers swap an aging battery for a new one, they'll see a bump. "For a single airplane flying for 20 years, it'll grow to 40 percent, 60 percent and eventually may not need the generator at all."

Zunum is working with the University of Illinois to develop the battery technology, with funding from the venture capital arms at Boeing and JetBlue Technology Ventures, two companies exploring alternatives to jet fuel. Airbus, too, is exploring similar technology-called a serial hybrid-after deciding that batteries alone are impractical for large aircraft. But not everyone is optimistic.

"The energy density for batteries isn't high enough to even get a couple of people off the ground, let alone 30 or 40," says aviation analyst Richard Aboulafia. And if the hybridization scheme isn't as efficient as engineers hope, it could require just as much fuel as a conventional jet engine or turboprop-in a much newer, less proven, system. That means it might be wiser to focus on making conventional jet engines and the aircraft that use them more efficient through improved aerodynamics, composite materials, and the like.

"Aircraft efficiency improves by one percent every year, as it has every year for the last 60, since the dawn of the jet age," Aboulafia says. "It will be very hard to suddenly generate double-digit improvements."

What's more, Aboulafia says there is no market for the small commercial aircraft Zunum is proposing. Regional jets typically carry 60 to 160 passengers and carry passengers from smaller markets to major hubs like Chicago, Dallas, and Atlanta.

Kumar's answer? Remake the system. Small aircraft with low operating costs could allow airlines to fly shorter routes to the thousands of small airports commercial airlines usually ignore. Some 97 percent of air traffic passes through just 2 percent of the country's 5,000 airports, he says. Flying fewer passengers shorter distances to smaller airports could increase efficiency and reduce travel times. It might even reduce high congestion by encouraging people to fly instead drive.

Boeing, at least, likes that idea. "Our interest in Zunum Aero is fundamentally about making sure we're engaged with promising emerging technologies and business models that could potentially change the marketplace-in this case the smaller regional aircraft transportation system," says Steve Norlund, head of Boeing's HorizonX VC arm.

So if electric cars never quite offer the range for that annual trip to grandma's house, maybe it's time to consider flying instead.