MOST helicopters cannot fly faster than around 270kph (168mph). That is partly because of increasing vibration, but mainly because the spinning rotor blades provide both lift and propulsion. As the aircraft accelerates, the airspeed of a blade (and thus the amount of lift it provides) increases when that blade is moving forwards and decreases when it is moving backwards. Eventually, the imbalance becomes unsustainable. But faster helicopters would be useful, particularly for rescue missions and military operations, so engineers are constantly looking for ways to make them.

In a recent test flight in France the experimental Eurocopter x³ (pronounced “x cubed” and pictured above) managed 430kph. The x³ has a five-bladed main rotor and a pair of propellers on two short wings. This means it can hover like a helicopter, but when flying forwards can reduce the speed of the main rotor and let the wings provide part of the lift. Its propellers give the extra oomph. This puts it on the tail of Sikorsky’s experimental X2, which has set an unofficial world record for a helicopter by flying at just over 460kph. The X2 uses a pusher propeller mounted at the rear and has a pair of contra-rotating main rotors, one positioned above the other. That arrangement produces an equal amount of lift on each side.

Sikorsky, an American company, believes the X2 is capable of flying at over 500kph and is building a version called the S-97 Raider to be tested by America’s armed forces. A new transatlantic race, it seems, is on.