I asked Robert Spaulding, former commander of the Air Force’s 509th Operations Group – the nation’s only B-2 Stealth Bomber unit – what the few existing photos of the B-21 tell us.
Spaulding is a retired Air Force brigadier general who’s now a senior fellow at Hudson Institute where his work focuses on US-China relations, economic and national security, and the Asia-Pacific military balance.
Northrop Grumman
NOC
Even when combined with artist concepts previously released by Northrop Grumman, it’s a small selection. But a trained eye such as Spaulding’s can still discern some hints from what we can see.
For a start, the B-21’s design is clearly evolutionary. It’s another flying wing – if the photos and illustrations shown thus far are truly representative. Would the Air Force, as some have suggested, have any incentive to cloak the actual design or alter images of it to throw open-source intelligence collection off?
“That wouldn’t be consistent with my experience,” Spaulding says. “They’re going to be flying this around [when flight testing begins] so it would hard to just not show it.”
However, he does concede that the images thus far released do not show the back portions of the aircraft, areas where stealth, infra-red signature and other design features are sensitive.
A three-quarter image shown from what appears to be the same photo session as recently released photos of the aircraft outside Northrop’s Plant 42 in Palmdale does offer some additional clues as to B-21 features however.
From this angle and from several head-on angles, it’s obvious that the engine intakes on either side of the cockpit hump are far more integrated into the bomber’s upper blended fuselage skin. Their lower profile contrasts strongly with the B-2’s similarly located engine inlets.
“What that tells me,” Spaulding says, “is that they’ve figured out how to deal with the airflow disruption that the B-2 suffers from. We don’t know how they did that, but it would be interesting to understand.”
The B-2’s engine nacelles appear to rise higher above the blended fuselage to capture airflow from the bomber’s leading edge, likely to enable operation at minor nose-up pitch angles where airflow might otherwise be blanked.
Figuring out how to minimize airflow disruption from the B-21’s leading edge appears to be a real advance Spaulding says, allowing for the radar return-generating inlets to be well concealed from adversary ground radars or even airborne radars operating below the B-21’s projected high altitude flight path.
“The engines are also buried in these airplanes to reduce the ability of radars to look down at the top of the aircraft and get a return from [a turbofan] blade.”
The design might suggest that the Raider will have a more straight-and-level flying attitude in operation but Spaulding reckons such limitation would not make sense. “Perhaps they’ve used software in the digital engine controller to be able to run at high [angle of attack] with very small intakes.”
This would certainly jive with the engine-run testing the aircraft is currently undergoing though all modern aircraft are put through propulsion systems testing on the ground before taking flight. It may suggest that there’s more to the B-21’s powerplants than is immediately obvious.
Flying the B-2 or B-21 with stealth in mind relies in part on keeping the aircraft profile stable. Piloting the bombers using differential thrust from the twin engines to yaw them to change heading or get around a corner rather than banking into turns as with a conventional aircraft could help maintain a stealth profile, making it harder for radar and other detection systems (including optical) to pick them up.
“I think that would be something you certainly could do,” Spaulding acknowledged without elaborating further. The technique could be of greater value given the B-21’s thinner head-on profile.
One of the other most apparent differences in the two generations of stealth bombers is the shape of the cockpit windows. The view out of the B-2’s cockpit would seem to be a good deal better than that of the B-21 given the relatively large roughly rectangular shapes of its cockpit glass.
The B-21 has more minimal, less geometrically shaped cockpit glass set what looks to be further away from the nose of the aircraft. What that means is hard to say, Spaulding observes while adding that, “The overall shape of any stealth aircraft is 80 percent of its solution to the [detection] problem. The rest is materials and how you operate it.”
Maximizing visibility for the crew cannot interfere with the shape or materials elements he says, suggesting that these may have dictated the odd window shapes. They may have been more optimized for stealth and less for visibility Spaulding says with the B-21’s reported optionally-manned capability.
Computers don’t need to see the way pilots do and the flush-mounted air data sensors visible along the B-21’s lower and upper fuselage testify to the degree of fly-by-wire automation the bomber will rely on operating with live aircrew or as an autonomous ghost ship.
“If they’ve reduced visibility beyond where you’d normally feel comfortable with this kind of aircraft, then they’re comfortable with the [reality] that this thing flies itself. If it can land by itself, it gives you even more comfort.”
Whether the B-21 will fly fully unmanned missions remains a debatable question given operational flexibility and ethical concerns and the sheer rarity of the small fleet planned. Nonetheless, assumed autonomous operation impacted its design.
This may have extended to size. The pictures don’t give a strong impression of its relative scale Spaulding agrees. “The sense that I get looking at it is that it is a smaller airplane.”
That would imply a smaller payload he says, noting that its weapons loadout could be different and less general purpose than that of the B-2. A single bomb-bay rather than the two bomb bays of the B-2 may be the result, one that would be in keeping with the single truck main landing gear of the Raider as opposed to the Spirit’s double truck design.
The B-21 appears to bulge more below the wing than the B-2, giving it a thicker double-chin look than its predecessor. The shape may be size driven. If the Raider’s scale is significantly smaller than the Spirit, the bulge may be needed simply to enclose the weapons payload Spaulding observes.
However, it is likely linked to stealth as well, possibly to the rear of the aircraft.
“One of the main things the B-2 gave up was some of its stealth character. The Air Force made the decision late in the [development] program to make it capable of flying at low-level. That required a re-design of the back end of the aircraft.”
A curving or compound under-fuselage shape that flows aft into the as yet unseen trailing edge of the Raider could be harder for radars to paint than the flatter bottom seen on the B-2.
What existing B-21 photos don’t reveal are the materials and coatings that add to its low observability.
“The maintainability of the B-2’s skin has improved dramatically in terms of downtime required [to maintain/refresh it]. The lessons would have been incorporated into this [B-21] vehicle. I think it will be much easier to maintain and to keep in a ready status than the B-2 initially was.”
The B-21 may in fact indicate a return to stealth that has been out of fashion lately as advanced radars have theoretically eaten into the ability of the F-35 and other tactical aircraft to remain hard to detect. Its apparent optimization for high altitude mission profiles suggests this Spaulding opines.
“Yeah, there are a lot of [stealth detection] advances but there’s a test environment where you’re using a radar to find the aircraft and then there’s an operational environment where you’re trying to find that aircraft while that aircraft is trying to kill you. The introduction of stealth has made the ground game quite difficult if you’re trying to defend against attack. The B-21 just complicates that problem.”
While it will eventually be visible “in the wild”, Spaulding says the most revealing views of the B-21 have not yet been shown. At the annual Air Force Association conference earlier this month Air Force Chief of Staff General CQ Brown, affirmed that the first flight of the Raider could take place before the year’s out.
Maybe then we will be able to see all the B-21’s external secrets but if the photos are limited, don’t be surprised.
Read the full article here