Sikorsky X2 to begin final flight-test phase

 - July 15, 2010, 4:23 AM

Sikorsky Aircraft announced the X2 project just over five years ago at the 2005 Paris Air Show. Now the one and only example of what the helicopter maker calls a “technology demonstrator” is poised to break the record as the world’s fastest rotorcraft as it works its way toward a target speed of 250 knots and further proof of concept.

A modified Westland Lynx holds the current speed record for a helicopter–just over 216 knots–which it set on Aug. 11, 1986. But this was, of course, a singular event. The current in-production AgustaWestland Lynx 300 has a maximum cruise speed of 132 knots. Sikorsky aims to prove that the experimental X2 design will be able maintain sustainable cruise speeds well in excess of 200 knots.

The X2 reached its highest speed to date–181 knots–on May 25, completing the third of four phases in its flight-test program. Steve Weiner, Sikorsky director of engineering services, told AIN that phase four will “show how fast the X2 really can go.” The X2 has logged just over 11 hours on 12 flights.

After each test flight, engineers spend a few weeks analyzing the extensive data collected during the flight, looking for anomalies in the operation and performance of the aircraft. Changes are then made to improve the fidelity of the software driving the X2 simulator, which is used for both engineering research and pilot training.

“Kevin Brendenbeck, our X2 chief test pilot, basically flies the next envelope-expansion flight in the simulator before we test it in the aircraft,” Weiner said. “It gives the pilots a very good idea about what to look for on the flight.” The changes to the simulator model after each flight are getting smaller and so far there have been no technical show stoppers, he said.

Sikorsky Aircraft, a subsidiary of United Technologies, expects to fly the X2 again this month, signifying the start of the fourth and final stage of its testing. Depending on how a test flight is going, the pilots increase the airspeed in increments of about 20 to 30 knots.

“The rotors are designed to avoid blade-stall throughout the envelope,” Weiner explained. “With the coaxial main rotors, we avoid using the retreating blades for lift. The limiting factors for forward speed are power and drag and so far measured drag in flight test is matching our predictions. We have not yet reached max power. The airplane may go even faster than 250.” At speeds higher than about 200 knots, the rotational speed of the main rotors must be reduced to avoid the blade tips reaching supersonic speed.

When asked when the X2 would reach 250 knots, Weiner gave a broad estimate of “sometime this year.” Indeed, the program has progressed deliberately from the start. When Sikorsky president Jeff Pino announced the X2 program at Paris in 2005, he predicted the X2 would fly by the end of 2006. At the Heli-Expo show in February 2008, where Sikorsky exhibited the X2 publicly for the first time, Pino said, “The aircraft will fly when it’s ready. Safety comes first.” The demonstrator eventually made its first flight on Aug. 27, 2008. Sikorsky has designated neither a fixed number of flights nor hours for the test program.

While the 250-knot milestone engenders understandable excitement, the more long-lasting benefits of the test program are in the continual collection of data for potential production concepts. The end of phase four will also mark
the end of the X2’s flight-test program, but Weiner said the aircraft may also be used for other research, including investigating aspects of eventual production aircraft.

Applications for the X2 design include search and rescue, special operations, armed scout, targeting and virtually any other mission where the capabilities of high speed, maneuverability, quick acceleration and deceleration and low-noise levels are valued. “We’ve been talking to various potential customers about a lot of potential applications,” Weiner said. The coaxial main rotor, which eliminates the power-robbing tail rotor on a conventional helicopter, actually provides the X2 design better hover efficiency than a conventional helicopter of equal weight, he said, particularly in hot and high conditions. “It’s basically a helicopter that goes fast,” he added.

It is much too early to speculate on the price of yet-to-be-determined production derivatives of the X2, but Weiner said, “The price of the aircraft as a whole may not be much different from a helicopter of comparable size.” For one thing, he said, the X2’s rigid rotor blades provide a potential cost advantage over flexible blades and an articulated rotor system, though he declined to explain why.

Fly-by-Wire
The major features of the X2 include fly-by-wire flight controls; twin counter-rotating, coaxial main rotors (each with four rigid blades); a fairing over the rotor hub to reduce drag (not yet tested in flight); active vibration control; and a rear six-blade pusher propeller (or propulsor or auxiliary prop–it’s called a lot of things, said Weiner) that now runs continually in the X2. A single LHTEC T-800 turboshaft engine powers the aircraft (this engine also powered the Boeing/Sikorsky RAH-66 Comanche, which the U.S. Army canceled in 2004). The X2’s main rotor system, engine and propulsor are integrated.

Weiner said production derivatives will have a clutch to allow disengagement of the pusher propeller. Indeed, the propulsor was not connected during the X2’s first flight in August 2008, when it hovered and reached speeds no greater than 20 knots. It took another year before the X2 flew with the propulsor engaged.

In developing X2 technology demonstrator, Sikorsky built on several decades of company research, specifically the XH-59A Advancing Blade Concept demonstrator, which showed high speed was possible with a coaxial helicopter and auxiliary propulsion; the Cypher unmanned aerial vehicle, which expanded company knowledge of the flight control laws in fly-by-wire aircraft with coaxial rotors; and the Comanche, which developed company expertise in composite rotors and advanced transmission design.

In 2008, Pino predicted that the X2 will be a “game-changer” in the rotorcraft sector. If Sikorsky achieves its expected breakthrough speed record with the technology demonstrator this prediction may well start to stack up.    

Poles Prep S-70i for Black Hawk Export Market

The Sikorsky S-70i military helicopter–a new export variant of the UH-60M Black Hawk–made its first flight on July 1. Assembled in Poland by PZL Mielec, the first S-70i (S/N 0001) has the distinction of being the first Black Hawk assembled in Europe and the first helicopter produced by the Polish manufacturer, a long-time builder of fixed-wing aircraft. The aircraft made its first flight on July 1, after arriving at Sikorsky’s Development Flight Center at West Palm Beach on
May 4. Final assembly was completed in Poland on March 15. United Technologies is the parent company of both Sikorsky and PZL Mielec, which UTC purchased in 2007.

The S-70i and the standard UH-60M Black Hawk are virtually identical aircraft, with the chief differences related to items that are not exportable from the U.S.–mainly some avionics and radios–according to Debra Zampano, S-70i program manager, international programs. This results in the empty weight of the baseline S-70i being about 1,000 pounds lighter than the basic UH-60M. With a lower empty weight and same max gross weight (22,000 pounds) as the UH-60M, the S-70i is expected to have somewhat better performance than the UH-60M with comparable payloads. This will be verified in flight test. Both models are powered by twin T700-GE701D turboshaft engines rated at 3,988 shp (combined) for takeoff. The 30-second, one-engine-inoperative (OEI) rating is 1,940 shp.

Interestingly, Sikorsky had originally decided that the baseline S-70i would have the UH-60L’s composite-titanium main rotor blades and the C-version electronic engine control. These would have given the S-70i a lower max cruise speed and less range, as well as lower hover, OEI and all-engines-operating (AEO) ceilings than the UH-60M, which has wide-chord, composite main rotor blades and the D-version engine control. These latter two features were to be optional upgrades on the S-70i. However, customers have been asking for performance comparable to the UH-60M, and Sikorsky is considering making these items standard. In fact, S/N 0001 does have the wide-chord main rotor blades and D-version engine controls.

The UH-60’s performance numbers include: max cruise speed, 151 knots; max range (no reserve); 276 nm; hover in ground effect, 10,520 feet; hover out of ground effect; 6,010 feet; OEI service ceiling, 6,500 feet; and AEO service ceiling, 15,180 feet.

Because the UH-60M and S-70i are so similar, only one aircraft is being used for the qualification flights. Zampano said about 100 flight-test hours will be flown to meet the requirements of Sikorsky’s internal Quality Assurance Board. The second S-70i, which is the first production aircraft and is now under assembly at PZL Mielec, will begin production flight testing later this year in Poland.

The Polish aircraft manufacturer, which leverages Sikorsky’s global supply chain, is already gearing up to a planned production rate of about 20 S-70is in 2012. While only two will be completed for delivery in 2010, three units will be “in the production flow” by the end of this year, Zampano said. Next year, 11 are expected to be completed. Production space has been already dedicated at PZL Mielec and the second wave of employee training has begun to support the increase in production rate. The company employs about 1,500 people.

Primary customer interest for the S-70i is coming from counties in the Middle East and Latin America. “We are currently in negotiations with several launch customers,” Zampano said.

According to Matt Rogers, product marketing manager-Sikorsky military systems, international customers are seeking low-cost solutions and “the kind of performance that the Black Hawk can deliver.” Missions include tactical combat operations, search and rescue, medical evacuation and disaster relief. The price of a baseline-configured S-70i is less than $13 million (at 2011 values), he said.

Competing designs include the Mil Mi-17 and Eurocopter EC532 helicopters and under-development AgustaWestland AW149.