Dual-blade helicopter

Helicopter aren't known for their speed, which is why Sikorsky Aircraftis working on a chopper prototype with two sets of blades instead ofone. The blades, which would spin in opposite directions, would createequal amounts of lift on both sides of the chopper. In other words, by spinning in opposite directions, they'd balanceout the loss of lift experienced by the retreating blade and let thechopper reach speeds of up to 334mph.

Source: popularmechanics.comAdded: 25 May 2007