Military, Products

Sikorsky Assembles X-2 Demonstrator @ "Hawk Works"

By James T. McKenna | July 1, 2006

Attack, Observation/Patrol

Relying on its new Schweizer Aircraft center for rapid prototyping, the manufacturer plans to start to ground tests of the high-speed, coaxial aircraft this month.

Sikorsky Aircraft is completing installation of subsystems in its coaxial X-2 technology demonstrator aircraft at its Schweizer Aircraft "Hawk Works" in preparation for the start of a full ground-test program this month and a first flight by the end of the year.

"We are absolutely and definitively on track to fly this demonstrator in 2006," said Sikorsky’s new president, Jeff Pino. "All major systems’ detail design is complete. The first round of rotor testing is complete. Main shafts and transmissions are in fabrication and we’ll ground test the aircraft" this month.

He said the company already has overcome key technical challenges in developing a fully fly-by-wire demonstrator aircraft that can cruise above 250 kt. while preserving all the vertical flight characteristics of a traditional helicopter.

Pino showcased the X-2 aircraft in his presentation at the American Helicopter Society International’s annual Forum May 9 in Phoenix, offering attendees the first views of the assembly of the actual demonstrator aircraft, some of which are shown here.

Pino’s predecessor, Steve Finger, stunned the AHS Forum in 2005 by unveiling the X-2 program to retain "the hover efficiency of a helicopter while creating a new helicopter spectrum in speed," as Pino put it. Skeptics then and since challenged Sikorsky’s aspirations, saying the company could not overcome fundamental problems–specifically, the lift-drag properties of the advancing-blade configuration and the hub drag of a coaxial rotor–that make a high-speed coaxial helicopter unfeasible.

"Our team has conquered, at least analytically, both of these challenges," Pino told the AHS gathering.

Sikorsky’s small team of X-2 engineers has come up with a new rotor blade design that "achieves an L-over-D significantly better than demonstrated back in the 1980s, when we flew" the NASA/U.S. Defense Dept. XH-59A Advancing Blade Concept aircraft. Team members in Stratford, Conn. and Schweizer’s facility near Elmira, N.Y. did this "by creatively merging essentially three airfoils into one new blade," Pino said. "The technology that we imparted was the transition."

Regarding hub drag, Pino said, that "working with our sister division at the United Technology Research Center, and using empirically derived [computational fluid dynamics] results, we know the drag is low enough."

He said Sikorsky and Schweizer have developed a packaging and fairing solution "that reduces coaxial rotor hub drag to where it compares favorably with single-main-rotor helicopters–about 25 percent of the total drag."

Sikorsky at AHS displayed the actual auxiliary propulsion system propeller that would provide much of the aircraft’s thrust in high-speed flight.

"The state-of-the-art auxiliary propulsor is bred from a successful line of propellers built for racing aircraft, transmitting power from our single LHTEC engine efficiently and smoothly," Pino said. The LHTEC engine was developed for the canceled U.S. Army RAH-66 Comanche on which Sikorsky partnered with Boeing.

The aircraft will use a triply redundant fly-by-wire system, with no mechanical backup, to distribute power demands between the main rotors and that propulsor and to manage aircraft stability. Schweizer first flew a 333 as a surrogate fly-by-wire test aircraft last November.

The photos here show two angles of the X-2 demonstrator’s joined nose, main fuselage and tail cone (opposite and below left ) at Schweizer’s facility, including one with the LHTEC engine installed, and the aircraft’s tail cone (below). Assembly has progressed considerably since these photos were taken.

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