A Sikorsky-Boeing team has selected a slightly modified Honeywell T55 engine to power the SB-1 Defiant, a high-speed, medium-lift rotorcraft demonstrator scheduled to fly in 2017.
The 4,000shp-class T55, which already powers the Boeing CH-47 Chinook, was selected as an off-the-shelf option for the demonstrator, says Pat Donnelly, Boeing’s director for the future vertical lift (FVL) programme.
The T55 rotor already has a variable-speed capabilitiy, but it will be expanded for the SB-1 Defiant, Donnelly says. The low-end of the speed range will be extended to about 85%, he says, adding that a turbofan variant of the T55 already operates at that speed.
“All we’re doing is altering the governor to operate at the lower ends,” Donnelly says. “That is something that’s not a technically-challenging requirement.”
The joint venture submitted its risk assessment on the SB-1 Defiant to the army last week after completing the preliminary design. A final design is scheduled to be ready by early next year.
Sikorsky-Boeing are among four bidders developing demonstrators under the army’s joint multi-role technology demonstration programme, which aims to prove the feasilbility of a high-speed rotorcraft to replace thousands of conventional helicopters.
A Bell Helicopter-Lockheed Martin team is developing a third-generation tiltrotor called the V-280 Valor. Karem Aircraft, founded by the designer of the original Predator unmanned air vehicle (UAV), is developing an optimum speed tiltrotor. AVX Corp, a start-up founded by former Bell engineers, is proposing a design powered by a coaxial rotor for lift and two ducted fans for forward thrust.
The army plans to select at least two of the bidders to build and fly demonstrator aircraft in 2017.
The SB-1 design builds on Sikorsky’s work developing a high-speed propulsion system using a coaxial, rigid rotor system with a rear-mounted propulsor for thrust.
Sikorsky has demonstrated the system in-flight with the X2 project, which achieved speeds over 260kt in level flight before the aircraft was retired. Sikorsky also is developing the S-97 Raider with the same propulsion system. The S-97 is be demonstrated to the army next year as a lightweight, high-speed alternative for special operations and armed scout missions.
But the biggest prize in the rotorcraft market is the potential FVL programme.
If the Sikorsky-Boeing team is selected for the possible FVL contract, the operational aircraft will be powered by a more advanced propulsion system under development by the US Army called the future affordable turbine engine (FATE), Donnelly says.
The army could still decide to upgrade its fleets of Boeing AH-64 Apaches and Sikorsky UH-60 Black Hawks. But if the army chooses to recapitalize the fleets with an all-new design, the FVL-Medium is the favoured approach.