X2 could make first flight by month’s end

 - November 26, 2007, 9:02 AM

Sikorsky’s X2 technology dem-onstrator could fly by year-end, according to Peter Grant, Sikorsky’s director of advanced programs. The X2 is a coaxial rigid-rotor compound helicopter designed to achieve forward speeds up to 250 knots, and at that clip it would become the world’s fastest helicopter. The current helicopter speed record of 217 knots (set by a Westland Lynx) has stood for more than 20 years.

Grant said the X2 is undergoing a second round of ground tests at Sikorsky’s Schweizer subsidiary in Elmira, N.Y. “All major subsystems are installed,” said Grant. The ground testing, which was expected to be completed by the end of last month, involved rotors-off and rotors-on tests.

Sikorsky announced the X2
in 2005. Designed by a small, combined team from Sikorsky and Schweizer, the helicopter is an example of the company’s newly developed “rapid prototyping capability,” said Jim Kagdis, Sikorsky’s manager of business development and strategic planning.

Sikorsky conducted its first round of X2 ground tests more than a year ago and has spent the last year working on the helicopter’s fly-by-wire system, bench testing major subsystems, finishing final assemblies and writing the flight-test plan. The work was “basically the completion of the remainder of the building, testing and analysis,” said Grant. “We’re just working through the checklist and test procedures.”

A Military Lineage
The current max takeoff weight of the X2 is estimated to be 6,500 pounds, and the machine combines components from existing Sikorskys, including the S-76, Black Hawk and CH-53, as well as other manufacturers’ aircraft. For example, the X2’s retractable main landing gear was modified from a fixed-wing piston-engine Cessna. All of the components were scrutinized for their ability to enhance the X2’s mission of fast forward speed and low vibration, according to Grant.

Power for the X2 comes from a single LHTEC (Light Helicopter Turbine Engine Company, a Rolls-Royce and Honeywell partnership) T800 turboshaft engine rated at up to 1,680 shp. The T800 drives the twin four-blade Eagle Aviation contra-rotating main rotors and the Aero Composites six-blade pusher propeller, or auxiliary propulsion system, mounted at the end of the tail boom.

Sikorsky had previously flown the LHTEC engine on the RH-66 Comanche scout and attack helicopter prototype developed for the Army. That program was canceled in 2004 after expenditures of $6.9 billion and 20 years of development. LHTEC has developed a successful civilian variant of the T800, the CTS800. (Ironically, the same modified Westland Lynx that set the world speed record in 1986 served as a test bed for the CTS800.)

Sikorsky’s positive experience with integrating the T800 into the Comanche led it to select the engine for the X2, Grant said. “The engine has a good power-to-weight ratio and we’ve gotten excellent support for it,” Grant said.

The X2 has a two-seat cockpit but ill be flown only single-pilot during initial flight testing as the telemetry instrumentation will occupy the rear cockpit. After initial flight testing and some flight envelope expansion at Schweizer, Grant expects that further X2 flying will be moved to Sikorsky’s West Palm Beach, Fla. test site.

Grant emphasized that the X2 is a demonstrator for a “suite of technologies” that might have applications for future-design civilian and military rotorcraft, but it was unlikely that the twin coaxial main rotor system could be applied to smaller aircraft with smaller rotors due to its rigidity and resultant weight. “You’re probably not going to see these applications in the 3,000-pound weight class,” he said. “This [6,500 pounds] is around the size we would want to be the book end for the low end of the weight class. It is a lot easier to go big.”

As important as the application of X2 technologies to future rotorcraft is, the project’s immediate value to Sikorsky has been to enable the company–long wed to lengthy, military-style development programs–to acquire rapid prototyping capability, Grant said. Some of that came as a result of exposing Sikorsky’s corporate culture to that of its smaller and more nimble Schweizer subsidiary, acquired in 2004. Known since the 1930s for its gliders, Schweizer entered the helicopter market in 1986, when it bought the rights to the piston-powered Hughes 269 and 300. It later designed and produced a turbine-powered variant, the Model 333.

Schweizer has worked on a variety of rapid development programs for specialized aircraft, including the SA2-37B covert surveillance fixed-wing aircraft and the VUAV RQ-8B Fire Scout, developed with Northrop Grumman for the Navy.

“The methodology and design tools that have been advanced as a result of this effort [the X2] and the expertise gained by our engineers working on this effort are applicable to all of our programs,” said Grant. “We can now do a better job more quickly designing certain aircraft elements and leveraging those lessons learned,” he said.

“We turned the valve down on the [X2] program a little bit at the end of last year” while the company resolved several development issues, he added. But now, with the X2’s first flight looming, “we’re seeing the light at the end of the tunnel and we are pumped up.”