Those crazy folks at the Defense Advanced Research Projects Agency (DARPA) always come up with the coolest military tech concepts, but a lot of them don't get past the drawing board. Now one of their wildest ideas is getting the green light, and will be turned into working prototypes by two competing manufacturers.

How do you double the speed of a helicopter? Maybe it shouldn't be as obvious as just stapling a couple extra engines onto it, but it seems to have worked, as the Eurocopter X3 is now the fastest helicopter ever built.

Yesterday Eurocopter unveiled its new helicopter… and boy, is it fast. Created in part to compete with Sikorsky's speedy X2 concept, Eurocopter's X3 can fly comfortably at 220 knots, where most of today's helicopters max out around 130-140 knots.

Most toy helicopters use electric motors, but the concept of a full sized electric 'copter has long been scuttled by the heavy batteries it would require. In recent years, however, battery technology has progressed to the point where Sikorsky thinks this is now a workable idea, and they have retrofitted a 50 year old design with electric power to prove it.