The past six months have seen some remarkable advances in the budding world of electric flight, in a realm where until now internal-combustion engines have held firm: helicopters. Three separate demonstrations—of an electrically assisted helicopter and two tiny but fully electric choppers—suggest that the era of electric whirlybirds can't be far away.
The first development took place in early July 2011, when pilots at Eurocopter, the world's largest helicopter manufacturer, based in Marignane, France, test-flew a single-engine chopper that had been fitted with lithium-ion batteries and an auxiliary electric motor intended to help out in case of engine failure. Helicopter pilots deal with such emergencies using a technique called autorotation, which requires some deft manipulation of the helicopter's rotor when power first cuts out and again when the helicopter nears the ground. According to Jean-Michel Billig, executive vice-president for R&D at Eurocopter, the hybrid electric system his group designed provides the brief bursts of power needed at those two critical moments. "We're not talking about minutes here—we're talking about seconds," says Billig. With the new system, engine-off landings were "extraordinarily comfortable" from the pilot's perspective, he says.
Eurocopter is not the only helicopter manufacturer experimenting with electric power. Since 2008, Sikorsky Aircraft Corp. has been working to remove the normal piston engine from a small helicopter, a Sikorsky S-300C, and replace it with an electric motor, a demonstration project it calls Firefly. Sikorsky, based in Stratford, Conn., has been showing its modified S-300C at aircraft exhibitions but so far has not flown it.
So it came as a surprise to some when another group beat the venerable helicopter company into the air, in the year's second stunning development in electric flight. Solution F, a French company that builds race-car engines and associated equipment, underwrote the development of what in August became the first manned electric helicopter to take off and land on its own power. It was the result of an unlikely collaboration.
Pascal Chretien, an independent engineering consultant and commercial helicopter pilot, began working two years ago for Solution F, which was then starting to explore the helicopter-engine market. Chretien floated the idea of designing a hybrid-electric power plant, which he viewed as inherently safer than traditional designs for helicopters. That sparked discussions of building the world's first all-electric helicopter instead, a notion that captivated the imagination of this unlikely team. Chretien set about designing such a craft in mid-2010. "I pretty much did all the work as a volunteer," says Chretien. Solution F paid for everything else.
Chretien's design uses two counterrotating rotors, one on top of the other, spinning around the same axis, to avoid the need for a power-sapping tail rotor. Each of the main rotors is driven by a brushed DC motor, with a bank of lithium-ion batteries mounted under the pilot's seat. "The machine has buckets of power," says Chretien, although the maximum flight duration demonstrated so far is just 6 minutes.