WASHINGTON — Bell initially unveiled a ducted tail rotor design for its 360 Invictus but has now opted to switch to an open tail rotor on the aircraft, which is part of a prototyping competition to supply the U.S. Army with a Future Attack Reconnaissance Aircraft.
The company decided “months ago” to use a design based on its familiar 525 helicopter open tail rotor, Jayme Gonzalez, Bell’s program manager for the Invictus, told Defense News in an August 4 interview.
The Invictus, when it was first revealed in October 2019, featured a design based on 525 technology, but with several key differences, including 40-foot rotor blades, which the Army has said it would like to have. The aircraft also has a four-blade configured single main rotor, while the 525 has five blades.
The 525 Relentless is a commercial helicopter that is larger than the Invictus design and, according to Bell, has hit speeds over 200 knots in tests.
“We thought based on our analysis that [the tail rotor] would meet the handling qualities and the hover-out-of-ground effects requirements of the original solicitation,” Gonzalez said. But “as we built a scale model and did testing on it, we decided for the Increment 1 aircraft, in order to deliver the best mission with the performance, that we anticipate in a solicitation, that the Army will ask for, that we would modify to leverage a proven 525-based open tail rotor design for which we have a lot of flight hours substantiating.”
While Bell could have operated “perfectly well” with the ducted tail rotor, Gonzalez said, “we decided for consistency of the airframe that we would go ahead and change the [competitive prototype] tail rotor design as well.”
Considering the need to ensure plenty of aircraft weight can be devoted to weapons and mission systems, “with our overall weight management approach, it makes the open tail rotor attractive such that this is the path that we’re going to go down,” she added.
“It’s a better fit for the requirements package, it’s a better fit for the holistic weight approaches that we have for the aircraft, and allows us to make weight and performance trades to meet the Army mission,” she said.
The Army is interested in the balance between weight and speed and is considering capability parameters such as reaching 180 knots and weighing less than 14,000 lbs. The service plans to use a 3,000 horsepower engine. The Army will use the Improved Turbine Engine Program (ITEP) engine being designed to replace the engines in UH-60 Black Hawk utility and AH-64 Apache attack helicopters.
The Invictus will have a supplemental power unit for extra speed and power.
“The balance of speed required by the mission and the weight of the aircraft is a pretty sensitive ticker,” Gonzalez said.
The 525-based open tail rotor is also very mature from both a technology and manufacturability standpoint because of the development work on the 525 aircraft, she noted.
Bell is now over halfway through its aircraft assembly process for the competitive prototype it is building for the FARA program.
Lockheed Martin’s Sikorsky is also competing with its Raider X aircraft, which uses a coaxial helicopter design based on its X2 technology also used in its Defiant X entry to the Army’s other next-generation aircraft competition — the Future Long Range Assault Aircraft (FLRAA).
Bell is competing head-to-head with Sikorsky to build FLRAA with a tiltrotor aircraft — the V-280 Valor.
The company is also conducting activities in its system integration laboratory and its drive system test laboratory as it builds the 360.
“The aircraft, the airframe assembly is quite mature at this point and we are proceeding with installing systems,” Gonzalez said, “and we’ll proceed through the usual type of audits and proof loads and aircraft functional tests in the coming few quarters.”
Later this year, Bell will be “flying the lab” with all of the aircraft’s actuators and load systems active, Gonzalez said.
This will allow Bell to do failure injection testing to prove out its fly-by-wire control system and the rest of the avionics and electrical system integration, she added.
Drive-train test lab activity will wrap up in the next few months. By the end of the year, the aircraft will reach the point of final assembly.
“We’re coordinating really closely with the Army [program manager] for FARA on the requirements iteration,” Gonzalez said. “We have really close coordination with the Army’s system readiness directorate, that is to say we meet very frequently and they also participate in all our ongoing status reviews. We have a really strong relationship and that’s helped us with collaboration on requirements and for them to understand our status today.”
The service’s goal is to get both competitive prototypes to a first flight in the first quarter of fiscal 2023.
The Army Requirements Oversight Council earlier this year approved an Abbreviated Capabilities Development Document (A-CDD) that greenlights guidelines for the two companies to design and build their aircraft.
The service validated its final design and risk review for the competing FARA designs at the end of last year.