Traditional helicopter blades have speed limitations brought on by their own inherently unstable shape. As the blade spins, its trailing edge causes drag that limits the lifting force of its leading edge, causing the helicopter to stall above a certain speed. A coaxial blade employs two sets of blades, each spinning a different direction, to counter this discrepancy.
A helicopter with coaxial blades can fly significantly faster than a traditional helicopter. According to Popular Mechanics, the experimental Sikorsky X2 can exceed 287 mph, whereas single-bladed helicopters cannot exceed 185 mph, with a theoretical maximum speed near 350 mph.
Inventors experimented with coaxial helicopter blades even before mankind achieved powered flight. The first coaxial rotors flew as toys in the 18th century, followed by steam-driven helicopter prototypes in the 19th century, according to the University of Maryland.
