Several companies are building electric powered ultralight airplanes and motor gliders. And in July of 2010, Cessna announced it was developing an electrically-powered 172 as a proof-of-concept platform. However, the high power to weight requirement for hovering makes building an electrically-powered helicopter a difficult challenge. Even so, at the Experimental Aircraft Association (EAA) AirVenture exhibition Sikorsky Innovations, the technology development organization of Sikorsky Aircraft, introduced “Project Firefly,” an all-electric helicopter technology demonstrator.
In building the demonstrator, the Innovations team replaced the S-300C’s Lycoming 190-horsepower, 4-cylinder gasoline engine with an electric motor and two battery packs located on each side of the pilot producing about 370 volts. Integrated sensors provide real-time aircraft health information including temperature for left and right battery packs, flight time remaining and voltage on a panel mounted LCD monitor. The demonstrator features a 190-horsepower electric motor that weighs 180 lbs, and a battery system that weighs 1,100 lbs. Power output is the same as with the original piston engine, but because of the heavy weight of the lithium-ion batteries the empty weight is close to 2,050-pounds leaving just enough payload for a single pilot.
Nevertheless, Sikorsky expects the Firefly will have the same flight characteristics (including an 86-knot top speed) as the S-300C. Benefits include higher efficiency, less complexity and lower vibrations. With the current battery pack the expected flight time is 12 to15 minutes (the piston version goes 3.7 hrs on 32 gallons of fuel). According to Sikorsky, as battery technologies get better this will improve exponentially. First flight is anticipated in mid 2011.