LONDON — The SB-1 Defiant Joint Multi-Role demonstrator aircraft’s delay for first flight can be attributed to challenges in manufacturing its complex rotor blades for the helicopter’s coaxial design, the U.S. Army’s JMR program manager told Defense News at DSEI, a defense conference in London, on Monday.

“The challenge has been the manufacturing of the blades, which is an interesting challenge,” Dan Bailey said. “Some people would think that’s not technology but actually it is.”

The Sikorsky-Boeing team building the demonstrator for the U.S. Army announced it would not fly in 2017 as planned due unspecified problems.

Defiant is one of two demonstrators that will fly as part of the JMR program demonstration that will help define and build requirements for the Army’s Future Vertical Lift program of record expected to launch in roughly the 2019 timeframe. Bell Helicopter is building the second demonstrator – a tiltrotor design called the V-280 Valor. That aircraft will fly in roughly 20 to 30 days, according to Bailey.

One of the efforts underway by the Sikorsky and Boeing team for the JMR program is to design a future program that would make the aircraft more affordable. One way of doing that is to move from having people build the rotor blades to having machines that can handle the complex task.

To achieve the proper aerodynamics for a rotor blade, it “requires some very laborious-type manufacturing,” Bailey said. “They are done in a manner that is multi-sheets of composite material and they have to be laid up in certain patterns, certain directions, for strength properties and they do that pretty much today with people.”

The team instead decided to build the rotor blades with a process that uses a machine that lays up the material as it goes, Bailey said.

“The challenge with that is you have to have a tool that allows you to lay up that material,” he added, which is “a long, tube-like configuration and that machine lays up the composite material around it,” to create a rotor blade spar, the main structural part of the blade, Bailey explained.

The tool has to be “a fairly long piece of tool, it can’t have any sag, it has to be very dimensionally specific and structured and that has been a challenge,” Bailey said.

The team started with one type of material to build the tool and then switched to a different material. This alteration ultimately caused the delay.

“The good news about that is we have completely removed that risk,” Bailey said, because it is going to be the same process the team would use to build rotor blades in a program of record.

The team has built two spars using the new tool and the problem seems to be resolved, Bailey said.

Defiant is still on track to fly in the spring or early summer timeframe, Bailey said, but added that the time associated with building all the rotor blades for the demonstrator is about 10 months behind.