Sikorsky and Boeing have finalised the design of the team’s offering for the US Army’s joint multi-role technology demonstrator (JMR-TD), called the SB-1 Defiant.

The configuration is a militarised and scaled up version of Sikorsky’s X2, the rigid rotor coaxial compound helicopter that demonstrated a 250kt (460km/h) speed in level flight in 2010.

“In addition to speed, the low-speed manoeuvrablity is also quite significant, as well as the high-hot performance,” says Doug Shidler, Sikorsky’s JMR programme manager, meaning the aircraft can hover 6,000ft above sea level on a 35˚C (95˚F) day.

The SB-1’s pusher propeller will allow it to move forward and back at a level attitude or pitch 20˚ nose up or down without moving forward or back, which is impossible with current rotorcraft. The aircraft will be able to cruise at more than 250kt, outpacing the army’s 230kt speed requirement.

The coaxial rotors create very little downwash compared with a traditional helicopter, Shidler says. It is also maritime capable with folding rotor blades.

Pat Donnelly, Boeing’s JMR programme manager said the aircraft is designed to carry 12 fully equipped troops, plus crew of four. To do that, the cabin is about 50% larger than the Sikorsky UH-60 Black Hawk, he says.

Because it is using off-the-shelf Honeywell T55 turboshaft engines, the Defiant demonstrator will fall short of the army’s fuel efficiency and range desires, Donnelly says.

The production model of the aircraft is designed with engines that meet the army’s 229nm (424km) range requirement based on fuel efficiencies expected from the future affordable turbine engine (FATE), Shidler says.

Two participants will compete for a contract to build a future vertical lift (FVL) aircraft, the overriding long-term effort to replace the army’s entire inventory of rotorcraft beginning with utility platforms like the UH-60 around 2030.

X2 technologies, including rigid coaxial rotors and fly-by-wire flight controls, already have been parlayed into the Sikorsky S-97 Raider, the Defiant’s smaller brother.

While the X2 weighed about 2,720kg (6,000lb), the Raider weighs about 5,000kg. A functional prototype of the Raider was unveiled in early October and is scheduled for first flight by the end of the year.

Weighing in at over 13,600kg, the Defiant is much larger in comparison. A ground test rig for the engine, rotors and transmission is scheduled to fire up in 2016 with first flight scheduled for the end of fiscal year 2017 at Sikorsky’s West Palm Beach, Florida facility.

“We wanted to demonstrate the scalability of this configuration and architecture,” Shidler says. “As the army develops their future vertical lift requirements, we now have a tool set that can scale along with their requirements.”