Sikorsky Aircraft has unveiled its much-anticipated “X2” technology demonstrator—a next-generation helicopter prototype designed to exceed speeds of more than 250 knots in level flight.
X2 will achieve this goal through the use of rigid, counterrotating rotor blades, coupled with a fly-by-wire control system that slows the blades as forward speed increases. This, according to Sikorsky, mitigates the speed-limiting retreating blade stall phenomenon.
“We want to break the paradigm of 160 knots,” said Sikorsky President Jeff Pino. “With fly-by-wire, we can keep the rotor blades apart and stop the flapping. The control rods run inside the shaft of the rotor blade.
“At 210 knots, the main rotor blades start slowing, at the 265-knot design speed, the retreating blades are 80 percent in reverse flow with 90 percent of the thrust going through the [aft-mounted] six-bladed propeller.”
Plans are to power the X2 with a Rolls-Royce 801 turboshaft producing 450 shaft horsepower, coupled to the same automatic vibration control system on the Sikorsky S92 medium-lift utility helicopter.
Since the demonstrator has no tail rotor, hover turns will be accomplished with aerodynamic surfaces. In the interest of drag reduction, the X2 will feature flush-riveting and retractable landing gear.
“I don’t know when it will fly, or when this will be a production aircraft,” Pino said. “I’ve instructed our engineers to fly it when it is ready to fly. What we do know is that this could be the future of our business.
“This is not an airplane that we’ve taught to hover; it’s a true helicopter that will exceed 250 knots. We are not going to let [Sikorsky Aircraft founder] Igor [Sikorsky] down.”