Graham Warwick
Sikorsky is emphasizing growth capability to stay ahead of evolving threats as it unveils its offering in the U.S. Army's Future Attack Reconnaissance Aircraft (FARA) competition, the Raider-X.
The coaxial rigid-rotor compound helicopter is a development of the S-97 Raider prototype now in flight testing.
The Raider-X is about 20% larger, with a 14,000-lb. gross weight compared with 11,000 lb. for the S-97, and a 39-ft. rotor diameter compared with 34 ft. for the Raider. The Army requires a rotor diameter of no more than 40 ft. so that FARA can fly between buildings in urban combat.
The Raider-X will exceed the FARA's threshold maximum speed of 180 kt. Sikorsky is not saying how fast it will fly, but notes the S-97 has reached 215 kt., and 207 kt. in level flight—exceeding the 205 kt. target in the Army's initial capability document, says Tim Malia, director of Future Vertical Lift - Light.
The Army subsequently reduced the threshold maximum speed to enable a wider competition for the FARA program. But Malia says the greater speed and payload capability of Sikorsky's X2 coaxial rigid-rotor compound configuration compared with a conventional helicopter provides growth capacity.
“We looked at a single main rotor helicopter for FARA, but it would be minimally compliant in the early 2020s. We need to be able to stay ahead of the threat into the 2030s and 2040s,” he says.
Bell is proposing a winged, single-main-rotor helicopter for FARA, while AVX Aircraft is offering a coaxial-rotor, ducted-fan compound. Boeing and Karem Aircraft have yet to unveil their concepts.
“Single main rotor will not be able to keep up. It's already tapped out meeting the minimal FARA requirements. It does not have the ability to grow capability over time,” Malia says. “We didn't want to pull out all the stops to be minimally compliant when we had X2 able to carry more payload and go faster.”
The Raider-X has four-blade rotors and a pusher propulsor. The coaxial rotors generate lift only on the advancing sides, eliminating retreating-blade stall and enabling higher speed. At high speed, 90% of the engine power goes to the propulsor, says Bill Fell, senior experimental test pilot. The propulsor is declutched at low speed to reduce noise.
The Raider-X closely resembles the S-97 prototype, with side-by-side seating. Compared with tandem seating, this improves crew coordination and situational awareness, Malia says. “And we can do it aerodynamically because of the robust performance inherent in X2. We are not trying to get out every last ounce of drag.”
Behind the cockpit is a large internal weapons bay. Internal carriage of missiles and unmanned aircraft—which the Army calls air-launched effects (ALE)—is a FARA requirement, but Malia says the cabin-like volume of Raider-X's bay provides growth space for future, larger systems. “The minimum threshold works now, but what if in 2030 there is a new ALE that can be decisive, but can't be carried?” he asks.
The Raider-X is powered by a single 3,000-shp-class General Electric T901 turboshaft—government-furnished equipment to all FARA bidders. “We do not have an additional engine to increase speed,” Malia says, referring to the supplemental power unit in Bell's 360 Invictus. This augments power from the single T901 to give the single-main-rotor, tandem-seat Invictus a 185-kt. maximum speed.
“We use the power available and have a solid design built around it,” he says. “The T901 provides speeds out of the chute in excess of requirements and, as it improves, we can take direct benefit. We have a growth path to additional speed and payload as the T901 power increases.”
Sikorsky is using the industry-funded S-97 prototype to reduce risk for its FARA bid, conducting flight testing to validate design models and optimize the Raider-X. This includes flying new rotor blades designed to reduce drag and vibration. “We are getting exactly the results the models said,” Malia says.
With two rotor systems and a propulsor, Sikorsky is paying close attention to the Raider-X's cost. “We have done a complete affordability analysis and design to cost. We are extremely confident we will come in under the cost goal,” he says.
Several divisions of parent company Lockheed Martin are part of Sikorsky's FARA team, Malia says, including Aeronautics, Missiles and Fire Control and Rotary and Mission Systems. Swift Engineering will build the airframe if Sikorsky wins one of two FARA competitive prototype contracts scheduled to be awarded in March 2020. The Army flyoff is planned for 2023, with the first unit to be equipped by 2028.
“There is a critical cap in vertical lift, in attack/reconnaissance, and that gap is really impactful to the Army in the 2020s, ‘30s, ‘40s, even ‘50s. So there is a need for a long-term solution,” Malia says. “The threat is projected to evolve rapidly, so we require significant capability growth on our side to stay ahead. Raider-X can provide an asymmetric advantage in the 2030s-50s.”
https://aviationweek.com/defense/sikorsky-unveils-raider-x-proposal-fara-armed-scout
