The battery pack consists of a stack of thin lithium-polymer cells that resemble foil-wrapped legal pads. “We always thought the batteries would come to us,” Buck says—meaning that they sized the airplane and motor for batteries that didn’t yet exist. “There are batteries out there that have five times the energy density of those we can buy today, but they’re only in the lab.” And the Sonex team wanted the electric airplane to be comparable in price to the aircraft now being built from the Waiex kits. “We’ve always believed in an airplane that would be available at a price the average pilot could afford,” says Buck, “so that the whole airplane, including the engine, would cost about the same as a new car, around $26,000.”
Batteries are, in the final analysis, the key to the whole project. Controllers are tricky but feasible; motors are delicate and expensive, but technically straightforward. It’s really on batteries—developing ones that are powerful, durable, and not prone to burst into flame if mistreated—that the future of electric airplanes hangs.
A gasoline powerplant, with its fuel, accounts for about a quarter of an airplane’s takeoff weight. An electric powerplant is somewhat heavier to begin with; it adds 75 pounds to the weight of the Waiex because the batteries alone weigh 200 pounds. The big disadvantage is that the energy available from all those batteries is equivalent to only a couple of gallons of gasoline. Observes Buck: “We pilots would consider that ‘unusable’ ”—the technical term for dregs in the bottom of the fuel tank that may not be available in all flight attitudes.
Buck aims at an airplane of conventional dimensions—with a little more wingspan than most, but able to be tucked comfortably into an ordinary hangar—and having climbing and cruising capability comparable to that of a gasoline-powered airplane in every respect except, perhaps, duration of flight. In other words, he and Monnett want to prove that an electric airplane can look and fly just like a gas-powered one.
Greg Cole sees things a little differently.
Cole, 46, is a freelance aeronautical engineer. His Oregon company, Windward Performance, produces a carbon-fiber sailplane called the SparrowHawk, which, at 155 pounds empty, weighs less than many of the pilots who fly it. Cole is a bit of a visionary. He is concerned not just about the price of gasoline, but also about aviation as a whole—the possibility that the cost and the complexity and stress of flying modern airplanes might drive people away from flying. He is not just an engineer; he is a reformer. Cole, like Monnett, is preparing to manufacture an electric two-seater. The wingspan of his design is a glider-like 51 feet—a rather cumbersome size for taxiing, parking, and hangarage at many general-aviation airports. The longer an airplane’s wingspan, though, the less power it needs to lift a given weight. Cole’s motor, similar in design to Buck’s but smaller, is rated at just 40 hp. If he can keep his airplane’s empty weight below 500 pounds or so—the SparrowHawk demonstrates his ability to engineer very light, yet strong structures—he will be able to climb at 660 feet a minute and cruise at 70 mph on the electrical equivalent of one gallon of gas per hour. “We need to get into lower-power airplanes,” he says. “We need to do smaller.” He brushes aside objections that his design will not mesh easily with existing infrastructure. Electric—smooth, quiet, non-polluting, and with motors that will never fail or wear out—is “a completely viable way to revolutionize aviation.”
The aviation he is talking about is recreational: “I’m not looking beyond two seats.” His airplane will cost $50 an hour to operate; $30 of that is a reserve for replacing the battery pack after 500 to 1,000 charging cycles. Because the airplane itself has very low drag and is highly efficient, the cost of the electric “fuel” is negligible. Cole’s ultimate vision of sustainability is right out of the Whole Earth Catalog: A couple of small wind-powered generators on the roof of a hangar would, with sufficient wind, provide power for one or two flights a week. In a pinch, he concedes, “You could always top off from [an electric socket in] the wall.”
Cole has made little effort to publicize his project; Monnett, on the other hand, announced his “E-Flight Initiative” in 2007 at the Experimental Aircraft Association’s annual Oshkosh fly-in and displayed a mockup of the new powerplant. But a 59-year-old retired jeweler and self-taught engineer from New Jersey, Randall Fishman, stole a march on both Monnett and Cole. In 2008 Fishman, whom his friends used to call Doctor Gizmo, flew his single-seat electric airplane in front of cheering crowds at Oshkosh. The airframe is a discontinued Moni motor glider (built from a kit designed, coincidentally, by John Monnett before he started Sonex), modified and refitted with an 18-hp electric motor. It can cruise at 70 mph, using just 6 hp to stay aloft. A 90-minute flight consumes 5.6 kilowatt-hours of electricity—about 70 cents’ worth, at present rates. It recharges from a wall outlet in six hours.
“I used to like to fly ultralights, but they were powered by Rotax snowmobile engines,” Fishman says. “They were so loud. And after you flew for a while and landed, your body would still be vibrating.” In his pursuit of quiet, vibration-free flight, Fishman has been honored by the EAA, which recognized his contribution to light aircraft design with the 2008 August Raspet Award. (John Monnett is a previous winner, as is Pete Buck, though not for their work in electric power.) And this year the Lindbergh Foundation awarded him a $10,580 grant.
Like the Wright brothers, Fishman started with a bicycle. He used to have to pedal uphill to get to his jewelry store, and he didn’t want to arrive sweaty. When he saw an ad for an electric bicycle motor, he thought: That would be nice. More than 20 years, hundreds of thousands of dollars, and several electric conveyances—a scooter, an ultralight Trike, and the
ElectraFlyer-C—later, Fishman is working on a two-place electric airplane he says will be ready to fly this fall. With motor experts, he has developed an electric propulsion kit including 100-hp motor, battery pack and battery management system, and throttle to control the speed at which the batteries discharge.