WASHINGTON — Despite a series of early production “hiccups” with the engines and wings, including an issue with air flow, the B-21 Raider bomber aircraft is largely on track, according to the chairman of the House Armed Services Seapower and Projection Forces Subcommittee.

Rep. Rob Wittman, R-Va., said he was largely pleased with the work prime contractor Northrop Grumman has been doing on the bomber program, praising in particular how the company has worked to integrate its subcontractors together to find solutions to early design problems. But he acknowledged there have been a few challenges that have popped up.

“This is an extraordinary, complex aircraft,” Wittman, who has oversight of the B-21, told reporters after a speech at the McAleese/Credit Suisse defense conference held in Washington on Tuesday. “The issue is not that you have these uncertainties. The issue is how you address them.”

Wittman’s comments are notable given the intense secrecy surrounding the B-21. The service plans to buy at least 100 Raiders at a price of about $550 million, in 2010 dollars, per copy. The engineering and manufacturing development phase is being carried out under a separate, cost-plus contract that is estimated to amount to about $21.4 billion.

Wittman highlighted several times the challenge of pushing air through the B-21’s engines. “This is a very, very different design as far as airflow, and there have been some design challenges there,” he said.

“Pratt and Whitney says one thing; if the exhaust, the ducting contractor says another thing and says, ‘There’s only so much air we can move through there,’ and Pratt & Whitney says, ‘No, we need a certain amount of air to go through the front of the engine,’ then the question is: How do you do that?” Wittman added.

“Do you split [the requirements] between the two? Does Pratt & Whitney say: ‘Well, we can change some of the cowling [the cover on the engine] on the surface face there to be able to do that,’ ” he wondered, noting this as something that could impact the B-21’s low-observable characteristics.

“It’s not just the engine, but it’s the ducting on the engine, too. I think all those things are elements that you would normally expect in an aircraft that’s new, that takes a concept from B-2, refines and uses it on this platform.”

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Richard Aboulafia, an analyst with the Teal Group, noted widespread speculation that the B-21 will be a twin-engine, rather than a quad-engine, plane. If that’s the case, early tests may have shown airflow issues that could require the Air Force and Northrop to make tough decisions on trade-offs because “turbines are hot and like large apertures ― two things that stealth hates.”

The B-2 uses four F118 engines, which produce about 17,000 pounds of thrust. Pratt & Whitney’s F135 engine, used in the F-35 Joint Strike Fighter and generally assumed to be the basis for the engines used in the B-21, can produce up to 43,000 pounds of thrust, which in turn requires greater air intake. Hence, the cowling for the B-21 engines may require trade-offs between the air coming in and the stealth characteristics.

For Aboulafia, this is ”one of the most complicated parts of designing a stealth plane because there are many variables, but two of the very biggest are stealth and range.”

“The turbine thing speaks to a possible need for compromise. It’s not a deal-killer, but could that impact range? Sure. Range or stealth: Which do you want to compromise on? Or find some permutation therein,” he said. “That’s the real black art of aircraft design ― the trade-offs.”

Other issues

More broadly, Northrop has been challenged to hire “enough engineers” to make sure the design stays on track, Wittman said, adding that the company is working to get an “Iron Bird” mock-up of the B-21 up and running — something that would serve as a physical test bed for some of the design and production elements.

The congressman also indicated there have been some “snags” with designing the wing for the B-21. It is believed Spirit AeroSystems is doing some of the work on the wing in their Wichita, Kansas, facility.

A spokesman for Northrop referred questions to the Air Force, while a spokesman for Pratt & Whitney declined to comment other than to say the company was “proud” of its work on the program.

“The Air Force remains confident in the B-21's progress and in delivering this new capability as planned in the mid-2020s,” Air Force spokeswoman Ann Stefanek said. “While we cannot speak to program specifics, the Air Force Rapid Capabilities Office is actively working with the contractor to ensure the program's success.”

Northrop's work on the B-21 remains largely shrouded in secrecy. (Northrop Grumman)

Other subcontractors for the Raider include BAE Systems, working out of Nashua, New Hampshire; GKN Aerospace in St. Louis, Missouri; Janicki Industries in Sedro-Woolley, Washington; Orbital ATK in Clearfield, Utah, and Dayton, Ohio; and Rockwell Collins in Cedar Rapids, Iowa.

Though perhaps minor issues, they are notable because part of Northrop’s plan to get the plane from contract to initial operational capability in about 10 years involves an admittedly fast-moving schedule, one the Air Force has raised concerns about. And part of that strategy for getting the bomber out on time involved a significant amount of subsystem work.

If those advanced components are having integration issues, even minor ones, it could force lag into an already tight program-production window, at a time when the Air Force is desperate to get the Raider fielded so it can begin retiring the B-1 and B-2 bomber fleets.

“Integration is a problem,” Aboulafia said. “You can save a lot of time with doing subsystems in advance, but integration is always going to complicate things here and there. It doesn’t make it a waste of time to do these designs in advance, but integrating, that’s another issue.”

Overall, Wittman praised Northrop for sticking to an “aggressive” schedule and said the company has been very smart about identifying potential issues early and then working to smooth them out before true production begins.