First flight of the SB-1 Defiant compound helicopter prototype has been pushed to 2019, officials from program partners Boeing [BA] and Lockheed Martin [LMT] announced Dec. 12.
Sikorsky, which developed the underlying X2 technologies on which the Defiant is based, has long publicized 2018 as the year the Black Hawk-sized Defiant would first leave the ground.
The aircraft has been completely built, but will not fly until early 2019, Rich Koucheravy, Sikorsky’s director of business development for Future Vertical lift, told reporters during a Dec. 12 conference call.
“Defiant has been completely built,” Koucheravy said. “The aircraft will be, shortly, rolled out of the hangar.”
He did not give an exact date when the aircraft would emerge and official photos would be taken, but said it is “imminent.” It was only in the past two weeks that relatively minor engineering issues surfaced during ground runs of a mirror image of the aircraft bolted to the earth that the team was forced to inform the Army the aircraft would not fly by year end, Koucheravy and his Boeing counterpart said.
“As we develop this aircraft, we have a very deliberate process for getting to first flight,” he said. “We do have a couple of artifacts we continue to work on along with the Defiant build.”
Koucheravy is talking about the power train system test bed that has been running, with rotors, in West Pam Beach. The PSTB is identical to the prototype aircraft, but bolted to the ground for ground runs to shake out all the parts and pieces.
It was while running the PSTB that the engineering discoveries were found. The test bed was spun up to full power without rotor blades in October. In November, it was run with blades, fully mirroring the prototype that should fly early next year.
“That represented the first time that the Defiant configuration ran in concert,” Koucheravy said. “During the PSTB initial two-to-three runs, we did have some minor discovery. I won’t tell you the nature of the discovery. We expect these sorts of things to come up when you run a configuration stand for the first time.”
The Defiant team is working to make the fixes and get the test bed back into operation “shortly,” he said. It should be up and running within two weeks, he said. A three-week delay has translated directly into a three-week delay in first flight, barring no other discoveries, according to Randy Rotte, Boeing’s director of global sales and marketing for cargo helicopters and FVL.
Plans are now to run the PSTB for at least 15 hours, Rotte said. He characterized 2018 as an “exciting, challenging, productive, inventive … foundation-setting year for Defiant.”
He acknowledged the program started the year off with an engineering hurdle to overcome when the composite rotor blades production process proved a more difficult than anticipated nut to crack. Engineers also found that some of the transmission gears were not sufficiently hardened to perform as expected.
“We were kind of off-track when we first started the year, got back on track and have been really following closely our plan from back in April to today,” Rotte said. “When we were running the PTSB, we’re still on a path to first flight in 2018, and it was only after that, really, that some of that small things we have to go back and do work on pushed us beyond that.”
“For all intents and purposes, everything we know, those issues are behind us,” Rotte said of the rotor blade and gear-box issues that hampered the program earlier in the year. “They were both about manufacturing. They were not about design or configuration.”
The blades — Defiant has eight rigid composite rotors on a counter-rotating coaxial hub — and gear boxes now are “operating like champions,” he said.
As the PSTB has ran, the full-scale aircraft has some minor components and instrumentation that did not perform as indicated by scale models, Rotte said. A few “small pieces … required some repair,” he said. One recent discovery required 2-3 weeks to fix, he said, but would not give specifics.
“It’s literally been nothing about configuration, nothing about the different pieces,” Rotte said. “We should be back up and running with the PSTB in the next week or so and then we’re back on the path. It’s nothing that has required a redesign. … Basically some interactions that the models, perhaps, didn’t all capture.”
The Boeing-Sikorsky team is under no obligation for Defiant to lift off, but it owes the Army design and performance data under the engineering and manufacturing development contract it holds. Opponent Bell’s [TXT] V-280 Valor advanced tiltrotor is approaching the one-year anniversary of its first flight, which occurred Dec. 18, 2017.
Both teams regularly correspond with senior Army aviation leaders about their progress. The Army is conducting an ongoing analysis of alternatives in preparation for a decision sometime in fiscal 2021 whether to make FVL a program of record. Despite the most recent delay, Koucheravy said the Army will have all the data it needs in time for a 2021 decision.
“The purpose of deliberate testing is to slowly expand your do-not-exceed criteria on components,” Koucheravy said. “We are very confident in the basic design of this aircraft. We are very confident in our configuration and, frankly, we think it’s going to exceed expectations.”