After short development, X2 makes first flight

 - October 7, 2008, 9:31 AM

Sikorsky’s futuristic X2 is up and flying, but it could be a decade before the technology is applied commercially, according to program manager Jim Kagdis.

Thirty-eight months after Sikorsky formally announced the X2, the “technology demonstrator” compound helicopter made its first flight on August 27 from a small taxiway at the Sikorsky-Schweizer rapid prototyping facility in Horseheads, N.Y. During the 30-minute flight, Sikorsky chief test pilot Kevin Bredenbeck conducted slow forward, aft and sideways flight; hover, and hover turn maneuvers using differential collective; pedal turns; and three landings. The company will conduct more low-speed flight tests at Horseheads before transferring the X2 to Sikorsky’s larger West Palm Beach, Fla. flight-test facility by year-end, where the company will test the aircraft at speeds from 40 knots to the 250- to 265-knot maximum speed.

Sikorsky is financing the fly-by-wire X2 with an eye to deploying its key components in future manned and unmanned military helicopters. 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 coaxial main rotors and the Aero Composites six-blade pusher propeller/propulsor mounted at the end of the tailboom. The propulsor was not engaged during the X2’s first flight.

The X2 combines components from the RH-66 Comanche and existing production Sikorskys, including the S-76, Black Hawk and CH-53, as well as other manufacturers’ aircraft. For example, the X2’s cyclic is from the Comanche, but its retractable main landing gear was modified from that of 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.

Bredenbeck reported that the X2 has a benign cabin environment, with little vibration, low noise signature and good exterior visibility. “One of my biggest issues was keeping my feet off the pedals” while making hover turns using the differential collective for directional control, he said, noting that “the control power was phenomenal.”

He added that hovering was achieved with 60 percent collective with “plenty of margin left and plenty of control response.” Takeoff weight was 5,200 pounds.
This first phase of the flight test program will be conducted at speeds up to 40 knots; phase two from 40 to 120 knots; phase three from 120 to 180 knots; and phase four from 180 to maximum speed. Plans call for the propulsor to be engaged at speeds beginning at 80 knots. Phases two through four will be conducted in West Palm Beach.

Sikorsky’s goal is to have the demonstrator attain maximum forward speed and break the helicopter speed record by the end of next year. The current record, 249 mph, was set in 1986 by a heavily modified Westland Lynx.

Steve Weiner, Sikorsky’s director of engineering sciences, said the X2’s development has been “sporty,” noting that it took Sikorsky fewer than 20 months from bareheaded engine runs to first flight. However, that schedule could have been even shorter had the company not opted to divert resources from the X2 program to meet commercial obligations for six months in 2006, according to Kagdis. Sikorsky also halted the test program earlier this year to campaign the X2 for static display at trade shows.

“We felt it was critical to introduce the X2 to customers,” said Kagdis. “So we took it out of the build and test phase to solicit input from customers.”

To a lesser extent, he added, the program was delayed by “traditional issues you have with any new aircraft program,” mostly with regard to instrument package installation. 

The X2 has a two-seat cockpit but will be flown only single-pilot during initial flight testing as the telemetry instrumentation will occupy the rear cockpit.

Commercial Applications
According to Kagdis, Sikorsky envisions a variety of commercial and military applications for X2 technology, including offshore support, EMS, SAR, escort/gunship and UAV. “If an S-76 can fly three missions a day to [an offshore oil] rig, the X2 could run four or five. And in EMS and commercial SAR, time is critical. So for those applications, the X2 has caught our commercial customers’ eyes.”

One military option for the X2 would be to serve as a scout/escort/gunship for the MV-22 Osprey tiltrotor, according to Kagdis, as conventional helicopters are too slow for the mission.

“By the middle of next year we will have a good amount of [flight-test] data in our library. We will be able to assess it and the completed market assessments and determine the best way to go forward. But it is fair to say that it will be eight to ten years” before X2 technology is available for commercial customers and “significantly after that for military customers,” Kagdis said.

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. Some of that experience came as a result of exposing Sikorsky’s corporate culture to that of its smaller and more nimble Schweizer subsidiary, acquired in 2004. 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.

Although the aircraft is already in flight test, Sikorsky still needs to fabricate a few parts for the X2, including the main rotor hub fairing and the landing gear doors.