If you’ve flown a drone, you know that battery life is a problem. Be extra careful when flying over water or your kid's birthday party, because you’ve got something like 20 minutes of flight time before the thing comes down. And you needn't have learned that lesson the hard way to get nervous about the idea of battery-powered aircraft with people inside.
Yet going electric could make commercial aviation—a significant source of humanity's greenhouse gas emissions—greener, as well as cheaper and quieter. It could open up routes to and from regional airports, a clean alternative to high speed inter-city trains. Those are the flights Zunum Aero hopes to make happen. The Kirkland, Washington-based startup is developing small electric planes that carry 10 to 50 passengers and could fly 700 miles between charging stops. Their trick is powering the plane's motors with electricity that comes from a jet fuel-burning generator as well as onboard batteries, like a Chevy Volt that's taken to the skies.
Today, Zunum is announcing that it has found the engine it needs to make that vision take off. The gas turbine is a modified version of the Ardiden 3Z engine made by Safran Helicopter Engines, here coupled to a generator that will deliver 500 kilowatts of electric power—enough for a couple of powerful motors. It's a crucial step, since today's batteries are far too big and heavy to make long-distance commercial flights even remotely possible.
Even fulfilling a basic FAA safety requirement—that you be able to fly for 45 minutes longer than it takes to reach your destination—would be a problem with burning some sort of fuel. “That would need a prohibitive amount of battery right now," says Zunum founder and CTO Matt Knapp. "Not to mention actually going somewhere.”
Zumum’s first aircraft, the ZA10, will be a sleek white machine with slender wings, two ducted fans mounted at the back, and room for up to a dozen passengers. But it’s starting with a more mundane looking flying test bed, a modified Rockwell Turbo Commander 840, a small plane with two, three-blade propellors and usually eight seats. Zunum will start by replacing the 840's left engine with its own electric motor, sticking a bunch of batteries in the fuselage, and testing at altitude next summer. By the end of 2019, Knapp expects to install the generator and test the hybrid system. Last, it will replace the propellors with ducted fans (a shrouded propeller that can develop more thrust), to test the entire powertrain. If all that goes well, the team will put all the elements into that new plane, of its own design.
Knapp says that with the hybrid system, its plane will need half the fuel that a comparable conventional plane burns. Unlike the plug-in hybrid Volt, where the engine cuts in when the batteries run out, Zunum will flit between the two depending on the flight profile. The generator spins up for power-hungry takeoff, or maybe if the pilot's fighting headwinds. For cruising, though, the batteries can do much of the work, before bringing the aircraft back to earth for a quiet, electric landing.
Zunum, which has financial backing from Boeing’s HorizonX venture arm, isn't not alone in trying to fill the skies with e-planes. Airbus is working with jet engine maker Rolls-Royce and Siemens on a hybrid-electric flight demonstrator called the E Fan X. Siemens showed it can make the tech work way back in 2011. Israel's Eviation showed off its "Alice Commuter" at the Paris Air Show last year, a fully electric, Tesla-style plane running off a 980-kWh battery pack—enough for 10 Teslas. NASA's X-57 is an all-electric affair, with 12 small motors and propellors lining the wings. NASA’s always wants the lessons it learns in the X-plane program to trickle down into commercial aviation. But with the taxiway already full of companies lining up to launch on electrons, that may not take too long at all.