Sikorsky defined the modern helicopter when the VS-300, with single main and tail rotors, made its first flight in 1939. Now the manufacturer wants to redefine rotorcraft with a configuration that offers higher speed, maneuverability and hover performance, but retains the helicopter’s defining low-speed agility while enabling unique flight characteristics.
Rolled out at Sikorsky’s development test center in West Palm Beach, Florida, on Oct. 2, the S-97 Raider is the second example of the new configuration and a third is on the way. First was the X2 technology demonstrator, which exceeded 260 kt. in 2010. The third, the Sikorsky/Boeing SB.1 Defiant, is to fly in 2017 under the U.S. Army’s Joint Multi-Role (JMR) technology demonstration.
While potentially a product in its own right, the Raider constitutes a crucial step in proving that Sikorsky’s rigid coaxial-rotor compound helicopter configuration can be scaled from the 6,000-lb.-gross-weight X2 to a 30,000-lb.-class Future Vertical Lift Medium utility rotorcraft that could replace thousands of Sikorsky UH-60 Black Hawks beginning around 2035.
The industry-funded Raider program also provides an opportunity for Sikorsky to hone the rapid-prototyping processes pioneered on the company-funded X2 and now being applied to the JMR demonstrator, the cost of which is being shared by industry and the Army.
“The philosophy behind the X2 technology demonstrator is carried over: a rapid prototyping culture with a small team brokering the best in industry and innovating at the system level to create an innovative assemblage of things we know and understand that has really good traceability [to production],” says Mark Miller, vice president of research and engineering.
Sikorsky emphasizes the X2 was developed not by invention, but intelligent integration of available technologies. The company first flew the rigid coaxial-rotor compound configuration in the 1970s with the XH-59A experimental helicopter. This was fast, exceeding 260 kt., but noisy, shaky, thirsty, complex and hard to fly, requiring two pilots to manage four engines.
The X2 demonstrator applied advances in fly-by-wire flight control, rotor-hub drag reduction, integrated auxiliary propulsion, active vibration control and lightweight, stiff composite blades and structures, to overcome the drawbacks and unlock the benefits of the configuration. The result was a single-pilot, single-engine aircraft with similar vibration levels to a Black Hawk while flying twice as fast.
The X2 was a $50 million internally funded effort that took 43 months to first flight and achieved the 250-kt. level-flight speed goal in 17 test flights. From launch of the Raider in July 2010 to a first flight in December will be 49 months, and the two-prototype program is expected to cost Sikorsky and its suppliers around $200 million. The first aircraft will be used for envelope expansion and the second for customer demonstrations.
Powered by a single 2,600-shp-class General Electric YT706, the 11,500-lb.-gross-weight Raider has 34-ft.-dia. hingeless rotors each with four blades. Coaxial rotors eliminate the need for an anti-torque tailrotor. Instead, the engine also drives a 7-ft.-dia. variable-pitch propeller on the tail that provides thrust for high speed, but can be disengaged via a clutch at low speed or in hover to increase safety and reduce noise.
The Raider is designed to exceed 220 kt. in cruise, but the propulsor will also enable new modes of flight, including level-attitude acceleration and deceleration and nose-pointing for weapons employment. The Raider test program is expected to explore the utility of these new characteristics.
Key to Raider’s rapid development has been a virtual design environment in which “we build before we build, and fly before we fly,” says Miller. “We have a full system-integration laboratory, with every piece of hardware and software—sensors, generators, hydraulics—in the lab so we can shake it all out before we fly,” explains Chris Van Buiten, vice president of technology and innovation. “We started to fly on the ground a year ago, so we could find problems well in advance.”
High-fidelity modeling and simulation tools play a key role. “Our purpose here is moving risk to the left, taking time up front to eliminate or minimize discoveries that would disrupt the program,” notes Miller. “We have had basically zero discovery in assembly.” Thanks to kinematic modeling, for example, the retractable main landing gear was installed in days, not weeks, and worked first time, he adds.
“Rapid prototyping does not mean cutting things out,” says Miller. “When you push fundamental discovery into flight test, you risk the aircraft being down for months. The X2 expanded the envelope very efficiently, in 17 flights. Flying is expensive and we want to be pushing the envelope, not learning how the aircraft works,” he says. “Sure, we will have discoveries in ground test and flight test, but we won’t stumble on something we stumbled on a year ago,” adds Van Buiten.
The company also relies heavily on its 53 supplier partners. “They provide 90% of the aircraft and Sikorsky does the integration and interface control documentation. This has allowed us to go fast with a high-quality culture,” explains Van Buiten. “We have suppliers from large to small, all with different degrees of go-fast, and they are delivering parts in a time-frame they are not used to. It is exciting to watch.”
“The industry is on the road to doing business with highly sourced, high-technology content,” asserts Miller. “While we have a very extensive sup-plier network, we have strong system-level modeling tools and interface controls—the virtual design environment needs those,” he says, noting the Raider suppliers all simultaneously work with the same design model, with no latency.
The first Raider is ready to go into ground test, says Van Buiten. “All the parts are in flow for the second aircraft, and the fuselage is done. We will have a bit of time in flight on No. 1 before we assemble No. 2 so we can incorporate any changes.” A four-phase flight-test program is planned for No. 1, beginning with hover and low-speed testing, then expansion of the speed and maneuver envelope, and “pulling Gs at speed and unconventional low-speed maneuvers” with the propulsor.
“We will pick up where the X2 left off,” says Miller. “We’ve been doing a lot of operational analysis and putting together vignettes to show how the unique flight characteristics of the aircraft can be used to fundamentally do things differently.” Helicopter, fixed-wing and tiltrotor pilots have all flown the Raider simulator and provided feedback incorporated into the vignettes. “We plan to do some very unique demonstrations to show what it can do.”
The industry-funded Raider prototypes are representative of the aircraft Sikorsky has offered to meet the U.S. Army’s Armed Aerial Scout (AAS) requirement, which is now in limbo because of budget pressures. “It is not a production aircraft, but is much more productized,” says Miller. The prototypes are not built to military specifications, but Sikorsky is maintaining traceability to a parallel, fully productionized and military-qualified, objective aircraft design.
“Anywhere there is a difference [between the designs] we have traceability to a detailed analysis of what that item will cost [in production],” explains Miller. “We fully understand the production aircraft. There are no leaps of faith.” This process is behind Sikorsky’s confidence in its highly public declaration last year that a production Raider would have a $15 million flyaway cost—25% more than an off-the-shelf helicopter—based on building 428 aircraft to replace the Army’s Bell OH-58D Kiowa Warriors.
Although AAS is on hold, Sikorsky is discussing with potential customers what they want to see demonstrated. “We have the opportunity to do some unique missionization of Aircraft 2, and bring in other technologies in collaboration with industry and customers,” says Miller. “We are sitting down with potential customers discussing how the aircraft might be uniquely configured.”
As Sikorsky prepares to fly the Raider, it already is feeding lessons learned to the JMR program with Boeing. “It is not complete transference, but we will get a running start on JMR,” notes Miller. The virtual design environment is “robust and transferable, and we took great pains to document the rapid prototyping process so we can continue to do programs very fast,” adds Doug Shidler, director of the JMR technology demonstrator program. “What we were able to do on Raider we are seeing on JMR.”