Sikorsky-Boeing’s SB-1 Defiant has fallen months behind its scheduled first flight in the US Army’s Joint Multi-Role Technology Demonstration (JMR-TD), even as Bell Helicopter’s V-280 Valor marches toward its first flight in September.

The army’s JMR-TD serves as the precursor to the service’s Future Vertical Lift competition, which will replace the UH-60 Black Hawk, AH-64 Apache and CH-47 Chinook. Sikorsky-Boeing is pushing its coaxial rotor-pusher propeller Defiant. The Valor offers a tiltrotor that resembles an improved V-22 Osprey.

The Defiant was expected to fly this fall, but Boeing has pushed first flight until early 2018. The company did not encounter a significant issue that caused the delay, says Boeing’s Defiant programme manager, Pat Donnelly.

“Things aren’t happening as quickly as we would like,” he says. “Again there have been no negative elements going on, we’re marching down the path, we have stayed lockstep with our customer and they fully understand where we are.”

Rather than pitch its first flight as delayed, Boeing is couching Defiant’s premier as a less risky effort. Boeing could still play catch up to its original timeline but isn’t counting on that right now, Donnelly says.

“We do recognize that our flight test program probably has a year duration,” he says. “Certainly as we start to fly the aircraft while we still have to expand the envelope and approve all of the flight characteristics of this vehicle. We will be doing it with more confidence than you would be if you didn’t do all of this risk reduction effort beforehand.”

Boeing is continuing to procure main fuselage bodies for the Defiant even as the programme is in the midst of wind tunnel testing. The testing doesn’t inform Defiant’s design so much as help Boeing understand the helicopter’s rotor interactions and other elements that are difficult to predict with current modeling, Donnelly says.

“Collectively with the army [we’re] looking at the computational fluid dynamic tools that exist today and how we refine them to better model the way our configuration operates,” he says. “It was really just to help we do more predictions on what more future vertical lifts may happen to look like.”

As Sikorsky pursues JMR-TD, it’s continuing work on its smaller coaxial S-97 Raider. The helicopter both matures technology from its X2 demonstrator and could serve one of FVL’s capabbility sets, particularly if the army finds a need for a light variant, says Sikorsky’s vice president, Dan Spoor. The helicopter flew at 150kt, without the rear prop engaged, and is preparing for a 220kt flight in the second quarter to prove an FVL capability, Spoor says.