The X3 is a hybrid aircraft that offers the speed of a turboprop-powered airplane and the full hover flight capabilities of a helicopter. It’s equipped with two Rolls-Royce Turbomeca RTM322 turboshaft engines, producing 2,309 hp each, powering a standard EC155 five-bladed main rotor system and two propellers on short-span fixed wings. The X3 first flew September 6th, 2010 and then in May of 2011 achieved a speed of 232 knots while using only 80 percent of prop shaft torque limit. The X3 is a proof of concept aircraft intended to demonstrate advanced technologies that could be used on high-speed helicopters in the next ten years.
The X3’s rotor speed is slowed down to reduce the Mach number of the advancing blade tip. To prevent retreating blade stall at high airspeeds the load on the rotor is reduced while the short span wings provide up to 40% lift instead. Also, the X3 does not have a tail rotor. So to counter the torque of the main rotor at low speed prop differential thrust is used. At high speed, remaining anti-torque function is realized by vertical fin flaps.
In May of 2012 the American Helicopter Society awarded Eurocopter’s X3 development team the Howard Hughes award for an outstanding improvement in fundamental helicopter technology brought to fruition during the preceding year.