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Pushing the Boundaries

Robert J. Collier was an aviator and sportsman who, in 1910, commissioned a trophy to encourage the American aviation community to strive for excellence in aeronautical development. On March 15, 2011, the Sikorsky Aircraft Corp. X2 Technology demonstrator team was awarded the 2010 Robert J. Collier Trophy – and the team is poised once again to push the speed boundaries with the soon-to-be-developed S-97 Raider.

On March 15, 2011, the Sikorsky Aircraft Corp. X2 Technology demonstrator team was awarded the 2010 Robert J. Collier Trophy. It won a number of other top awards last year as well. (Photo courtesy of Sikorsky)

To put the achievement into perspective, it’s a pretty special award indeed – previous winners have included Orville Wright and Chuck Yeager. “I know our speeds pale in comparison with Yeager breaking the sound barrier at 748 mph,” said X2 chief test pilot Kevin L. Bredenbeck. “But we did this with a helicopter, and it is nearly double the lift-to-drag ratio of any rotorcraft and double the top speed of most conventional helicopters. And we had power remaining to go faster.”

Sikorsky president/CEO Jeffrey Pino is a strong proponent of developing high-speed, highly agile military aircraft such as the S-97 Raider. (Photo courtesy of Sikorsky)

Bredenbeck flew the X2 Technology demonstrator on Sept.15, 2010, at a speed of 250 knots in level flight at the Sikorsky Development Flight Center in West Palm Beach, Fla. The demonstrator also reached 260 knots in a very shallow (two to three degrees) dive during the flight. “It didn’t sink in,” he said, “until David Walsh, director of test for the X2 program, said, ‘Come home, we did it.’ ” Asked how he felt at the time, Bredenbeck said, “So surreal. One minute you kiss your wife goodbye and you’re letting the dog out to go outside and then the next, you’re at altitude, setting a record.”

High-speed vertical flight has been attempted before, notably by Canadair in the 1960s and by Bell/Agusta with the BA609. But these firms used “tilt rotors” – complex hybrid aircraft with rotors and not true helicopters. The X2 differs in that it is still a helicopter that can go fast, auto rotate and hover.

According to Steve Estill, Sikorsky’s vice-president for worldwide sales, it can match the speed of Bell/Agusta 609 tilt rotor with far less complexity. The X2 demonstrator is powered by a 1,452 shp, FADEC-equipped T800 turboshaft engine that was previously installed in one of the Sikorsky Comanche helicopter prototypes. It drives both the rotor and the pusher propeller through two gearboxes. This makes X2 technology well suited to missions such as search and rescue, military or flying fast to oil rigs, which would call for development of a light to intermediate X2 twin of the same size as the 12-passenger S-76 or 19-passenger S-92.

The Sikorsky X2 demonstrator reached a top speed of 260 knots in a very shallow (two-to-three-degree) dive during its record-breaking flight. (Photo courtesy of Sikorsky)

In 2005, Sikorsky committed resources to the X2 Technology program, and the demonstrator first flew on Aug. 27, 2008. It immediately caused a sensation, with Time magazine calling it one of the top 50 inventions of 2009. The single-engined fly-by-wire aircraft features coaxial rotors and a pusher propeller that Sikorsky believes will revolutionize the helicopter world with its speed.

Current helicopter speeds are limited by rotor aerodynamics but, in contrast, the X2’s coaxial rotor system is optimized for all regimes of flight by a fly-by-wire control system that slows the rotors at high forward speeds to prevent their tips going supersonic, while maximizing lift and minimizing drag by adjusting the pitch of the rigid, carbon-fibre blades. The counter-rotating rotors provide equal lift on each side of the aircraft and, unlike a traditional helicopter, are relieved of having to provide all the forward propulsion by a large pusher propeller at the rear of the fuselage. The rigidity of the blades allows the rotors to be closely spaced at only two feet apart, further reducing drag.
The accolades for both man and machine speak volumes about the program.  In April 2011, Professional Pilot magazine named the X2 demonstrator “Innovation of the Year.”

In recognition of an outstanding improvement in fundamental helicopter technology, the X2 was chosen by the American Helicopter Society as the winner of the 2011 Hughes Award. Bredenbeck was also honoured when the Society of Experimental Test Pilots recognized his accomplishments with the Iven C. Kincheloe Award for the year’s outstanding professional accomplishment in flight testing (previous recipients were Alan Shepard and Neil Armstrong). At the Dubai Air Show in November 2011, Flightglobal magazine named Bredenbeck “Aviator of the Year.”

“The team and I are still in shock from what was accomplished,” said the chief test pilot,” and that we have the potential to continue pushing out faster. So how did it feel? Honoured and privileged to have been on the pointy end of technology and been a part of this team, representing Sikorsky Aircraft, its heritage and legacy. I may be the one sitting inside that cockpit, the pointed end of technology, but I was never by myself. The entire X2 team was right beside me.”

For reconnaissance missions, the X2 Raider helicopter will have space aft of the two-pilot cockpit for armament and auxiliary fuel. In an assault configuration, the cabin affords space to accommodate up to six troops. (Photo courtesy of Sikorsky)

S-97 Raider: Outperforming the Conventional
While the X2 completed its final flight on July 14 last year after accumulating 22 hours over 23 test flights, it’s officially not the end of Sikorsky’s foray into high-speed flight. With the end of development, the X2 will be followed by its first application, the S-97 Raider high-speed scout and attack helicopter – and the U.S. Army is keenly interested.

The U.S. Army’s competition for the next-generation Armed Aerial Scout (AAS) is heating up among all rotary manufacturers. To meet the requirements, Bell Helicopter plans to re-engine a Kiowa with a Honeywell HTS900-2 engine and EADS North America and Lockheed Martin are converting an EC145 single-rotor helicopter into the AS645 Armed Scout. Sikorsky has entered an X2 aircraft design called the S-97 Raider helicopter to the competition.

“What can the S-97 offer that the others can’t? ” Steve Engebretson, Sikorsky’s AAS Scout director, was asked. “We have demonstrated a next-generation rotorcraft,” he replied, “that will outperform conventional helicopters in every aspect: high altitude, hover efficiency, manoeuvrability, and speed, as well as other performance parameters. By building the two Raider prototype aircraft, we will provide the U.S. government a head start on an affordable platform that can
be fielded in time to meet their needs for a new armed reconnaissance aircraft.”

Sikorsky officials put the timeline of the S-97 Raider’s development at 10-12 years. (Photo courtesy of Sikorsky)

Like the X2, the Raider prototypes will feature twin coaxial counter-rotating main rotors and a pusher propeller. In addition to flying at nearly twice the speed of a conventional helicopter, the aircraft will incorporate other key performance parameters critical to combat operations – increased manoeuvrability, greater endurance, and the ability to operate at high altitudes. For reconnaissance missions, the X2 Raider helicopter will have space aft of the two-pilot cockpit for armament and auxiliary fuel. In an assault configuration, the cabin affords space to accommodate up to six troops.

This is not the company’s first time in such a competition. In Feb. 2004, the U.S. Army cancelled the Sikorsky/Boeing RAH-66 Comanche which was to be the next reconnaissance and attack platform and expanded procurement of its existing aircraft, like the Black Hawk helicopter.

But the military also began a new effort to replace the Kiowa Warrior in the armed reconnaissance mission and cancelling the Comanche program set the stage for the current AAS competition. From a technology perspective, Sikorsky took advantage of lessons learned on fly-by-wire, composites and rigid rotors that were developed for Comanche.

Engebretson was also asked if there had been any representation to the Canadian Forces concerning the S-97. And while Sikorsky’s focus thus far had been on the U.S. military alone, he replied they are anticipating international interest in the near future. With the timeline for production of the Raider at “about 10 to 12 years,” according to Sikorsky officials, there is hope a Canadian Raider could very well be screaming across the skies.