Sikorsky X2 tops 250-knot goal

 - September 29, 2010, 6:36 AM

The Sikorsky X2 technology demonstrator last month unofficially set a new speed record for rotorcraft, as it reached 250 ktas at the company’s development flight center in West Palm Beach, Fla. The aircraft, which features contra-rotating coaxial main rotors and a pusher propeller, took off at 7 a.m. for its 17th flight, which lasted 1.1 hours. At the controls was chief test pilot Kevin Bredenbeck.

Achieving a speed of 250 knots has been the program’s main objective since its 2005 launch. The X2 reached the desired speed in level flight and 260 knots “in a very shallow dive,” said Sikorsky. From an aerodynamic standpoint, the aircraft performed “as predicted or even a bit better,” program officials told AIN.

The vibration level was said to be similar to that of the Black Hawk military
transport at its cruise speed of 140 knots. Pilot workload was “on target” thanks to the fly-by-wire control system. The rotor speed-reduction system, which prevents the blade tips from going supersonic above 200 knots, was still operated in manual mode.

Bredenbeck reported a high level of consistency between the simulator and the actual aircraft. This explains the small number of flights performed to meet the assigned speed, vibration and workload objectives. The correlation between the simulator and the aircraft was improved after each flight. In turn, the pilot could train for the next one.

Sikorsky will record external noise levels during two upcoming flights in which the X2 flies a prescribed course above an array of microphones on the ground.

Another two flights will be conducted with a center hub fairing, which should translate into an extra 15 knots. So far, the X2 has flown with only two elliptical hub fairings at the top and bottom of the hub. Without any fairings, hub drag accounts for approximately 40 percent of all parasite drag. When all the fairings are included, Sikorsky expects to see a 20-percent reduction in drag.

After the remaining four of five data-gathering flights, Sikorsky will decide how to apply X2 technology to future products.