Sikosrky’s new electric helicopter, the Firefly, is actually a tried and true Hughes 269 airframe with an electric motor and lithium-ion batteries in place of the gasoline engine:
The 190-horsepower electric motor will draw power from three lithium-ion packs joined in parallel for a total of 135 amp-hours. Helicopters have never been known for their efficiency, and it looks like the Firefly is no exception. Sikorsky expects just 15 minutes of flight time from the craft, which at this point is merely a technology demonstrator.
This is clearly an early prototype with plenty of low-hanging fruit yet unplucked:
If they removed the drive shaft for the rear prop and used a separate motor there, along with eliminating extra main drive transmission parts, they could probably decrease weight and increase efficiency considerably. Perhaps they could even eliminate the swashplate linkages and use servos on the blades themselves, or servo-flaps.
(Hat tip à mon père.)