Northrop Grumman B-21 Raider (LRS-B)

Interesting that the two engine B-21 contrail appear significantly lighter / narrower than the F-16 chase plane. Since the contrail is formed from freezing water vapor from the burning fuel, does this mean the B-21 is burning less fuel than the F-16 at this flight condition? This assumes they are at the same altitude and contrail conditions, which can change rapidly.

It could also mean that the shape of the nozzle is flattening the exhaust stream, making the contrail thinner top to bottom turns less visible. but you would think this would result in a wider, if fainter, contrail
 
@F119Doctor : I think this is more related to the the lift. The jet expansion is fairly local at subsonic speed but the DelatP in the trailing wake freeze the moisture into contrail. Hence why a higher loaded wing would contrail more white than another one.
 
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F119Doctor said:
Interesting that the two engine B-21 contrail appear significantly lighter / narrower than the F-16 chase plane. Since the contrail is formed from freezing water vapor from the burning fuel, does this mean the B-21 is burning less fuel than the F-16 at this flight condition? This assumes they are at the same altitude and contrail conditions, which can change rapidly.

It could also mean that the shape of the nozzle is flattening the exhaust stream, making the contrail thinner top to bottom turns less visible. but you would think this would result in a wider, if fainter, contrail
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My initial guess would be nozzle shape.
 
NMaude said:
An educated guess however can be made.
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Someone from the B-21 test program was wearing a black jacket with three patches: a B-21 Combined Test Force emblem, a Northrop Grumman-issued B-21 Raider patch, and a patch for the Pratt & Whitney PW1500 geared turbofan (GTF) engine. Make of it what you will.
 
It would be very interesting if the B-21 has production PW1500G high bypass geared turbofan. Getting a 74” diameter inlet buried in the wing would be quite an accomplishment.

The max thrust of the PW1500G is 25k lbs. 2 x 25k = 50K for the B-21 vs 4 x 19k = 76k for the B-2 with the F118. The thrust lapse at cruise conditions would be greater for the PW1500G, although the SFC would be significantly better.
 
F119Doctor said:
Getting a 74” diameter inlet buried in the wing would be quite an accomplishment.
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Feeding high bypass engine with S-duct and it's unsteady separated flows needs some fcuking magic. Flying high with them at B-2 flight envelope ceiling or even higher needs even more magic.
So... No.
GTF core? Quite possible (was discussed here thousand times in context of PW9000).
 
I'm sure modern CFD helped a lot in defining and optimizing the inlet design. During B-2 flight test, the USAF was pleasantly surprise when we had no compressor stalls at max AOA and side-slip during max/min throttle bangs. We also did a lot of ground-based propulsion integration testing as early as possible during the program.
 
Hydroman said:
I'm sure modern CFD helped a lot in defining and optimizing the inlet design. During B-2 flight test, the USAF was pleasantly surprise when we had no compressor stalls at max AOA and side-slip during max/min throttle bangs. We also did a lot of ground-based propulsion integration testing as early as possible during the program.
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I know that P&W was doing a lot of work with NASA studying high bypass engines ingesting boundary layer air for aft mounted semi-submerged engines on transport aircraft. This was supposed to improve fuel consumption. It is possible that the B-21 has taken this research to a fully submerged high bypass engine.
 
Hydroman said:
I'm sure modern CFD helped a lot in defining and optimizing the inlet design. During B-2 flight test, the USAF was pleasantly surprise when we had no compressor stalls at max AOA and side-slip during max/min throttle bangs. We also did a lot of ground-based propulsion integration testing as early as possible during the program.
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It’s funny, there seems to be very little information out there on the development of the F118 engine itself.
 
F119Doctor said:
I know that P&W was doing a lot of work with NASA studying high bypass engines ingesting boundary layer air for aft mounted semi-submerged engines on transport aircraft. This was supposed to improve fuel consumption. It is possible that the B-21 has taken this research to a fully submerged high bypass engine.
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DOD_110570205.mp4_snapshot_00.14_[2024.09.18_23.08.56].jpg
 
NUSNA_Moebius said:
Potentially it could trade the large fan for two medium fan stages to make transonic speeds more feasible.
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I will not rehash all the previous discussions on the matter, but I think the consensus was that a medium bypass would be both much more easy to integrate for reasons of intake, exhaust, and maintenance but also more efficient in the 40-50,000 foot altitude band B-21 is expected to cruise at. A pure civilian turbofan will be larger diameter and harder to design around, and also it might be sub optimal at the relatively higher altitudes B-21 is expected to operate at.
 
I should’ve clarified my emphasis on dual fan stages as that was the real point of my post. I guess almost all medium bypass engines feature 2 fan stages after doing some research. Are any geared PW turbofans used on larger business jets that would be optimized for high cruise altitudes? A medium bypass F135 seems sensible trading 3 fan stages for 2 if the rest of the core is common to what’s in the F-35.
 
I do not know what engine B-21 uses, but I suspect it is highly efficient compared to the fighter type engines B-2 uses. I think Hydroman commented that at the time they were sufficiently worried about engine stall with a non linear intake that they were unwilling to attempt any more fuel efficient turbine given the technology at the time. I think it is safe to assume whatever the engine situation is in B-21, it is drastically more fuel efficient for its expected envelope.
 
I think it's safe to say that whatever patch those test pilots were wearing was entirely unrelated to LRS-B flight test ;)
 
_Del_ said:
There are pretty good reasons to avoid higher-bypass ratios regardless of the diameter when you're going to spend much time at higher altitudes.
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RQ-4 Global Hawk uses a RR F137 engine with a bypass ratio of 5:1… Not as large as current civilian turbofans, but does not seem to impact its high altitude performance.
 
And altitude. There’s good reason the high flying bizjets have bypass ratios in the single digits and the F137 is a 60k ft capable derivative of the AE 3007 found in the Citation X, itself possessing a 51k ft flight ceiling.
 
NUSNA_Moebius said:
And altitude. There’s good reason the high flying bizjets have bypass ratios in the single digits and the F137 is a 60k ft capable derivative of the AE 3007 found in the Citation X, itself possessing a 51k ft flight ceiling.
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Which probably makes a modified PW800 (Same core with PW1100G/1500G, smaller direct drive fan, originally designed for a 51kft bizjet) a possible option…? Although the current largest member of that family (PW815GA) only has a max thrust of 16klbs, PW offered a modified version for B-52 reengine that has a max thrust of 18klbs…
 
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JoshuaH said:
Which probably makes a modified PW800 (Same core with PW1100G, smaller direct drive fan, originally designed for a 51kft bizjet) a possible option…? Although the current largest member of that family (PW815GA) only has a max thrust of 16klbs, PW offered a modified version for B-52 reengine that has a max thrust of 18klbs…
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PW brochure for B-52 reengine attached
 

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www.twz.com

B-21 Raider Fleet Size Under Review

The Air Force's official plan has been to buy 100 B-21 Raiders, but that could now be set to change, according to Northrop Grumman.
www.twz.com www.twz.com
Kathy Warden, Northrop Grumman’s CEO, talked about the present state of the B-21 program and her company’s expectations for the future during a quarterly earnings call earlier today. The Air Force’s publicly stated plan has long been to buy at least 100 Raiders, but there have been discussions for years now about the possibility of the service acquiring significantly more of the bombers.
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“I think that’s exactly what the Air Force is looking at,” Warden said. “They are undertaking a force structure design review and the Secretary [of the Air Force Frank Kendall] has been open about looking at the various options they have for increasing their force size, and has talked specifically about NGAD, and we know that B-21 is in the mix, as well.”
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www.airandspaceforces.com

Northrop: Air Force Weighs More B-21s in Force Structure Study

Northrop Grumman officials said the Air Force is considering its long-term B-21 fleet size as part of a force structure review.
www.airandspaceforces.com www.airandspaceforces.com
 
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Forest Green said:
www.defensenews.com

Northrop expects next B-21 contract by year’s end

The Air Force is rethinking its approach to air dominance, which Northrop Grumman thinks could show whether more B-21s are in the cards.
www.defensenews.com www.defensenews.com
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The Air Force is likely to award Northrop Grumman a second low-rate initial production contract to build the B-21 Raider by the end of the year, company officials said Thursday.

Northrop expects volume on the B-21′s low-rate initial production to increase in the fourth quarter, which will help drive the company’s sales.
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Looks like it's game time for Northrop!

Good article, but curiously tries to put a bad image to the B-21 program by mentioning NG's loss on the program so far. Also declining to comment on the fact that the program is rapid and relatively cheap is mysterious
 

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