Helicopters aren't known for their speed, which is why Sikorsky Aircraft is working on a chopper prototype with two sets of blades instead of one. The blades, which would spin in opposite directions, would create equal amounts of lift on both sides of the chopper.
In other words, by spinning in opposite directions, they'd balance out the loss of lift experienced by the retreating blade and let the chopper reach speeds of up to 334mph. There's no official test date for the chopper, but you must admit, design-wise the mock-up looks badass.
High-speed Helicopter Revolution [Popular Mechanics]