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Saturday, March 1, 2008

Heli-Expo Show Day: Sikorsky Shows Off X2 Prototype

James T. McKenna

SIKORSKY AIRCRAFT FELT AN APPEARANCE BY its X2 technology demonstrator at Heli-Expo today was important enough to interrupt the novel aircraft’s development test program.

A small development team based at subsidiary Schweizer Aircraft (designated Sikorsky’s Hawk Works rapid-prototyping center of excellence) has been striving to get the coaxial main-rotor, fly-by-wire demonstrator in the air for the first time. Unveiled in early 2005, the X2 program originally targeted a first flight by the end of 2006. Financial issues (tied in part to a 2006 Teamsters strike at Sikorsky and the production delays that followed it) and technical ones pushed that back. Sikorsky officials now hope to fly the aircraft by the end of next month.

As important as their drive to do that, they felt, was the need to show the rotorcraft world their progress on the program. So Sikorsky’s exhibit at Booth 641 features the live test aircraft. Development tests are on hold so attendees can kick the tires, as it were. (No kicking is permitted, nor is any attempt to do chin-ups on the ultra rigid main-rotor blades, which Sikorsky officials said are also the flight test articles).

The visit to Houston will carve about a week out of the development and test schedule, which has been progressing deliberately. Sikorsky President Jeff Pino told Rotor & Wing his marching orders to the X2 team have been: "Fly when you’re ready."

Getting ready has taken longer than expected for a number of reasons, said Peter Grant, Sikorsky’s manager for advanced programs, during a visit with R&W at Sikorsky’s Stratford, Conn. headquarters.

A key reason is what Grant called the challenge of spatial integration. The X2’s fuselage is packed with components, systems, and plumbing, he said, to a degree unusual on even the most densely packed rotorcraft. That complicates the effort to design systems and resolve interference issues between them.

Another reason is that there is no power systems testbed or "iron bird" on which to shake down the components and plumbing of the X2’s design. Because X2 has from the start been a rapid prototyping effort, Sikorsky executives decided not to delay the development work by diverting time and effort to validate an "iron bird" as a platform representative of the live aircraft. Consequently, the learning about systems and component design must be done on the prototype.

The X2 program is divided into four elements of flight-envelope expansion, Grant said. They progress from "yard work," or initial hover and low-speed maneuvers done within the fence line of the Hawk Works prototyping center at Schweizer, to high-speed flight maneuvers.

At press time in early January, the X2 team was working on component and systems issues. Pino described them as minor problems with actuators and the aircraft’s combiner gearbox, which is designed to distribute power from the X2’s LHTEC T800-LHT-801 engine between the main rotors and the aft propulsor.

While the aircraft’s power system has been run to 85 percent or more, it had not yet been run with the main rotors mated to the aircraft (at press time). So, with the "yard work" yet to begin, it would appear that Sikorsky has a great deal of work standing between it and first flight of the X2.

Still, Grant and Pino said, the program has encountered no major problems and nothing to undercut confidence in the X2 concept. Sikorsky launched the program to demonstrate that a helicopter could be built to cruise at 250 kt without compromising its vertical-flight or hover capabilities. It is building on the XH-59A Advancing Blade Concept program run by the U.S. Army, Navy, Air Force and NASA in the 1970s.

Sikorsky will be presenting X2 updates each day at Booth 641.

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