Northrop Grumman B-21 Raider (LRS-B)

I'm more and more convinced that the B-21 has two weapons bays, probably about the same size as the B-2's with a rotary launcher in each. If you look at the bottom of the B-2 you can see it goes weapon bays in the middle, then two access doors for the engines on each side, then doors for the landing gear. From what I can tell the B-21's landing gear is only slightly closer together than the B-2's is, but with the B-21 likely only having two engines it will be able to dispense with two of the engine access doors. Meaning even if the space between the landing gear is somewhat narrower there's still plenty of room for two weapons bays to easily fit. It seems unlikely that with all the space available the B-21 would only have one weapons bay.

Here's a pic of the bottom of the B-2 that shows all the doors on the bottom. The B-21 will have the same sort of doors in the same spots, but with one fewer engine access door on each side.

attachment-steve-harvey-DoLPc45oEuo-unsplash.jpg
 
NCQ said:
I'm more and more convinced that the B-21 has two weapons bays, probably about the same size as the B-2's with a rotary launcher in each. If you look at the bottom of the B-2 you can see it goes weapon bays in the middle, then two access doors for the engines on each side, then doors for the landing gear. From what I can tell the B-21's landing gear is only slightly closer together than the B-2's is, but with the B-21 likely only having two engines it will be able to dispense with two of the engine access doors. Meaning even if the space between the landing gear is somewhat narrower there's still plenty of room for two weapons bays to easily fit. It seems unlikely that with all the space available the B-21 would only have one weapons bay.

Here's a pic of the bottom of the B-2 that shows all the doors on the bottom. The B-21 will have the same sort of doors in the same spots, but with one fewer engine access door on each side.

attachment-steve-harvey-DoLPc45oEuo-unsplash.jpg
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Which is why the exhaust streams will not be merged into one. It takes away from space for payload and fuel inside the structure.
 
steelpillow said:
The reverse is actually true. One of the great benefits of the all-wing design is span loading; put the weight where the lift is, don't put the lift metres from the weight.
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I would need serious convincing. You still need to keep the left side of the aircraft connected to the right side. The B-2, for example, still has a center-section "box" structurally.

Flight is going to generate many circumstances with asymetrical forces, and moving weight outboard of the cg makes the job of that box more difficult, not less.

(It's also a lot easier to put my engine thrust through the cg when they are mounted somewhere in the deep/tall center-section than in a wing that twists, bends, and tapers, but that's another discussion)
 
Obviously all conjecture at this stage but looking at the washout, I wonder if they wanted a platform that had more natural yaw stability than the B2? Very often the B2 is pictured flying [at low speeds] with both drag rudders open to improve yaw stability. This all points (IMO...) to high altitude operation. How high, though? My grandchildren might find out!
 
bring_it_on said:
While the payload is definitely TBD, I think the SecDef's comments on its efficiency and range should probably lay to rest any doubts on its ability to match or exceed the unrefueled range of the B-2 or B-1. If it has shorter legs, I seriously doubt he would have stuck his neck out and claimed an exact opposite in prepared remarks.

The range of the B-21, Austin said, is unmatched by any other bomber.

"It won't need to be based in-theater, it won't need logistical support to hold any target at risk," the secretary said.

www.defense.gov

World Gets First Look at B-21 Raider

As the first strategic bomber in more than three decades, the Air Force's B-21 will serve as the backbone of America's bomber force, Secretary of Defense Lloyd J. Austin III said.
www.defense.gov
Click to expand...
Click to expand...
But range only means something if we know what payload is associated with it. If the range gets cut in half, just to carry a useful payload, then how much value does it have?

I keep hearing, "well it doesn't need to carry as much as a B-2". Well, why not? Saying, "it wasn't a requirement" doesn't answer the question.


 
Some here at SPF may laugh at my naivety but would the DOD/USAF proceed to build a bomber with “dramatically” less payload than its other bombers?

If yes is this the reason we’ll see B-52s forever with talk of “bomb trucks” like B-17s loaded with JASSMs?
 
bobbymike said:
Some here at SPF may laugh at my naivety but would the DOD/USAF proceed to build a bomber with “dramatically” less payload than its other bombers?

If yes is this the reason we’ll see B-52s forever with talk of “bomb trucks” like B-17s loaded with JASSMs?
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giving transport aircraft offensive capability is meant more to give enemy war planners more headache. B-17 will be heavily used and strained for its primary mission during onset of war. I doubt any can be spared launching cruise missiles.
 
_Del_ said:
steelpillow said:
The reverse is actually true. One of the great benefits of the all-wing design is span loading; put the weight where the lift is, don't put the lift metres from the weight.
Click to expand...
I would need serious convincing.
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I would refer you to almost any and every text book on structural design, flying wings, etc. etc. It is a very fundamental fact. But please, don't take it from a retired engineer whose expertise does not convince you, go read those books for yourself.
 
sferrin said:
But range only means something if we know what payload is associated with it. If the range gets cut in half, just to carry a useful payload, then how much value does it have?
Click to expand...

Yes and I'm sure its range would be at a useful payload under a given mission scenario just like it is for every other bomber or aircraft before it. The B-2 can probably fly a lot farther if it was flying empty as well. They haven't said a whole lot but sticking one's neck out and saying that it will fly farther than the current bombers is pretty bold for it to be just a random remark written into a speech of the highest ranking DOD official.
sferrin said:
I keep hearing, "well it doesn't need to carry as much as a B-2". Well, why not? Saying, "it wasn't a requirement" doesn't answer the question.
Click to expand...

We don't know how much it carries. Apparently a few here have *confidently* figured out size, payload, range and even mission from the handful of pictures. We'll see if that stands the test of time when actual data is revealed over the coming months --> years. As to how much it will carry and it being determined by its actual payload requirement..then I agree.

Payload is one attribute..same for range, LO signature, mission systems and hitting a APUC of $550 million to field a fleet of at least 100 as is the program requirement. Every attribute there impacts the other so one can only assume that it was derived after some very careful analysis by SMEs and the bomber community.

So if the question was - "how much bomber can we afford for $550 MM APUC" then we seem to have an answer to it. Within those constrains, we will need some time to see which attributes, amongst signature, range, payload, mission-systems, etc were given more importance..
 
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bring_it_on said:
sferrin said:
But range only means something if we know what payload is associated with it. If the range gets cut in half, just to carry a useful payload, then how much value does it have?
Click to expand...

Yes and I'm sure its range would be at a useful payload under a given mission scenario just like it is for every other bomber or aircraft before it. The B-2 can probably fly a lot farther if it was flying empty as well. They haven't said a whole lot but sticking one's neck out and saying that it will fly farther than the current bombers is pretty bold for it to be just a random remark written into a speech of the highest ranking DOD official.
sferrin said:
I keep hearing, "well it doesn't need to carry as much as a B-2". Well, why not? Saying, "it wasn't a requirement" doesn't answer the question.
Click to expand...

We don't know how much it carries. Apparently a few here have *confidently* figured out size, payload, range and even mission from the handful of pictures. We'll see if that stands the test of time when actual data is revealed over the coming months --> years. As to how much it will carry and it being determined by its actual payload requirement..then I agree.

Payload is one attribute..same for range, LO signature, mission systems and hitting a APUC of $550 million to field a fleet of at least 100 as is the program requirement. Every attribute there impacts the other so one can only assume that it was derived after some very careful analysis by SMEs and the bomber community.

So if the question was - "how much bomber can we afford for $550 MM APUC" then we seem to have an answer to it. Within those constrains, we will need some time to see which attributes, amongst signature, range, payload, mission-systems, etc were given more importance..
Click to expand...
I'd suggest they modelled different ideas, from a new build B2, to a long range F22 or F35 cousin. This is what they have come up with. Whatever mission USAF wants (by definition this must be very flexible) this aircraft will be able to do. Range clearly set by american/allied bases, but presumably the aircraft only has to get to launch range for whatever its carrying.
 
Some appear to “want” the B-21 to have what they consider to be inadequate range/ payload performance so they can complain about it. This appears to be contributing to some making assumptions around how small the B-21 is that don’t appear to have any real (even limited) evidence behind them.

Right now we don’t know any of the significant design details of the B-21; it appears that those physicals present at the unveiling are making comments on how (surprisingly) close to the B-2 it is in size. If so this suggests preceding suggestions of a F-111H sized aircraft are probably just wrong but in fairness giving the limited evidence so far available this has not yet been definitively proved. However it appears some pre-judged what the B-21 would emerge as and had their grievances pre-arranged and ready to go.

This idea that the B-21 is a B-47 or theatre bomber analogue appears far fetched and directly at odds to what the US airforce is saying about the B-21. Even allowing for some potential spinning by the US airforce a fraud of that nature appears a step to far when they know they will face oversight and accountability on those points. And generally speaking who here on this forum really thinks the B-21 would have been planned as significantly shorter range than the B-2 or the other US bomber it will be replacing (the B-1B)?

The direct comparisons with the B-2 and the B-21 are interesting but can be pushed too far; there’s approx. 25 years between them in terms of technology and know-how. There’s been at least 2 generations of “stealth” aircraft in between them that has seen considerable developments and evolution in design and “under the skin” aspects. Plus more general aviation technology developments. It’s like comparing a Boeing 767 and 787 (while some appear convinced that the 767 just HAS to be better for some/any/ whatever reason).

It’s possible that the US Airforce have made a mistake with their underlying requirements for the B-21; they are not above reasonable scrutiny or criticism, they like all of us are fallible and make mistakes. When we know more about the B-21 those discussions can be had. But personally I’m guessing they (the US airforce) probably have a better idea of what they really want/ need/ can realistically afford than some website forum contributors with apparent axes to grind.
 
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sferrin said:
bring_it_on said:
While the payload is definitely TBD, I think the SecDef's comments on its efficiency and range should probably lay to rest any doubts on its ability to match or exceed the unrefueled range of the B-2 or B-1. If it has shorter legs, I seriously doubt he would have stuck his neck out and claimed an exact opposite in prepared remarks.

The range of the B-21, Austin said, is unmatched by any other bomber.

"It won't need to be based in-theater, it won't need logistical support to hold any target at risk," the secretary said.

www.defense.gov

World Gets First Look at B-21 Raider

As the first strategic bomber in more than three decades, the Air Force's B-21 will serve as the backbone of America's bomber force, Secretary of Defense Lloyd J. Austin III said.
www.defense.gov
Click to expand...
Click to expand...
But range only means something if we know what payload is associated with it. If the range gets cut in half, just to carry a useful payload, then how much value does it have?

I keep hearing, "well it doesn't need to carry as much as a B-2". Well, why not? Saying, "it wasn't a requirement" doesn't answer the question.
Click to expand...
But "it wasn't a requirement" IS the answer to why, if it turns out to be so. If the question is "Why wasn't it a requirement," I would assume USAF was made tough decisions in order to achieve a platform that could be produced at volume. But, frankly, we have no evidence of that massive of a payload cut yet.
 
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After what has been said by the officials unless they can back it up with with facts it is just misinformation. Otherwise we will keep guessing 'till the cows come home'.

Robert
 
bobbymike said:
Some here at SPF may laugh at my naivety but would the DOD/USAF proceed to build a bomber with “dramatically” less payload than its other bombers?

If yes is this the reason we’ll see B-52s forever with talk of “bomb trucks” like B-17s loaded with JASSMs?
Click to expand...
Absolutely. The USAF planned a subsonic, low altitude successor to the B-52 circa 1960. To make up for the intended low altitude flight profile, it had about the same MTOW as a late B-52 but a minuscule payload to allow for more fuel. So as early as 1960, the USAF had shifted away from the mode of thinking you suggest. The GWOT did bring about the use of heavy bombers as loitering CAS platforms, but that period is now dismissed as a historical aberration and a distraction from the joyous arrival of Cold War II.
 
There has been much speculation here about the qualities of the B-21. It is perhaps worth noting what some of the highly knowledgeable journalists who attended the unveiling have had to say in the many links provided:
  • Size is noticeably somewhat smaller than the B-2.
  • The fuselage is as capacious as the B-2.
  • It can carry existing nuclear or conventional weapons and has provision for future payloads.
  • It is designed for flexibility of operational role/scenario and for use in diverse allied environments.
  • Range is the greatest of any US strategic bomber yet. By this we mean range for a given payload.
One can dicker uselessly over its maximum payload, ultimate payload-range, suitability for role X, cockpit amenities, number of engines and so on. But of course much of that remains classified and the linked commentaries wisely avoid such speculations. Perhaps we have better things to do, too.
 
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Moose said:
But "it wasn't a requirement" IS the answer to why, if it turns out to be so. If the question is "Why wasn't it a requirement," I would assume USAF was made tough decisions in order to achieve a platform that could be produced at volume. But, frankly, we have no evidence of that massive of a payload cut yet.
Click to expand...
The very obvious reduction in size should be a clue. Some people are still denying that as well. It’s obvious that the B-21 is very much a cost driven compromise. The dollar has lost at least half its buying power since the end of B-2 production and given that the price tag of the B-21 is only a third as much without correcting for inflation, it’s clear that compromises were made. The fact that the B-21 has made it far enough to be effectively
uncancelable is something of a miracle to begin with.
 
TinWing said:
The very obvious reduction in size should be a clue. Some people are still denying that as well. It’s obvious that the B-21 is very much a cost driven compromise. The dollar has lost at least half its buying power since the end of B-2 production and given that the price tag of the B-21 is only a third as much without correcting for inflation, it’s clear that compromises were made. The fact that the B-21 has made it far enough to be effectively uncancelable is something of a miracle to begin with.
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On size reduction. This refers to the wing span and, probably, the overall wing area. Fuselage capacity is not thought to be reduced, which may or may not reference the payload bay. If a higher wing loading can be tolerated, this allows the same payload with a smaller wing. One benefit of this is a proportionate reduction in radar signature. More traditional ones include lower form drag and lighter weight. However stalling speed and hence things like takeoff and landing speeds, and maximum altitude, will suffer.
The significantly more advanced aerodynamic sophistication of the B-21 wing, as I mentioned earlier, may alleviate these disadvantages to a greater or lesser extent. Certainly, a smaller span should not be taken as strong evidence of reduced payload.

On cost. The B-21 is indeed driven by a requirement for lowered cost, especially maintenance costs. Hardly surprising, as the B-2 is something of a hangar queen and its stealth coatings are both expensive and short-lived. But there is no evidence that the new bomber's performance has been compromised to save money.
 
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quellish said:
steelpillow said:
One benefit of this is a proportionate reduction in radar signature.
Click to expand...
No.
Click to expand...
Radar signature is a function of the reflectivity and size of a given feature. The significant features tend to be surfaces, edges and holes. As these shrink, so too the signature shrinks in proportion. For example if an edge is reduced in length by 20% then the radiation it reflects is reduced by 20%. What part of that are you having trouble with?
 
Hanz2k said:
Well, my bet that biggest savings and at the end requirement for smaller airframe came from switching from 4 engine into 2 engine config.
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Probably the biggest contributor IMHO. But one can't rule out a smaller payload [to B-2] as well. There are some things we just won't know for a little while longer.
 
steelpillow said:
Radar signature is a function of the reflectivity
Click to expand...

Yes, mostly.

steelpillow said:
and size of a given feature.
Click to expand...

No.
Small feature can have a big return. Big feature can have a small return. RCS is not dependent on volume or physical size. The electrical size of something in relation to the frequency can affect the RCS. As a general rule though the size of an object does not have a direct affect on the RCS. Saying a given shape, made smaller, will produce a smaller RCS is not correct at all, and this has been known since the 1960s. It was this knowledge that allowed Boeing to create the SRAM (and other things) with a very small RCS even though it was "common knowledge" at the time that size and RCS were directly related (again, they are not).
 
bring_it_on said:
Hanz2k said:
Well, my bet that biggest savings and at the end requirement for smaller airframe came from switching from 4 engine into 2 engine config.
Click to expand...
Probably the biggest contributor IMHO. But one can't rule out a smaller payload [to B-2] as well. There are some things we just won't know for a little while longer.
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Weopon have became more compact: more energetic material (~100%), more precision, better engineering (flight vehicles design)... Hence a bigger bomb might not be required to get a greater boom.
 
quellish said:
steelpillow said:
Radar signature is a function of the reflectivity
Click to expand...

Yes, mostly.

steelpillow said:
and size of a given feature.
Click to expand...

No.
Small feature can have a big return. Big feature can have a small return. RCS is not dependent on volume or physical size. The electrical size of something in relation to the frequency can affect the RCS. As a general rule though the size of an object does not have a direct affect on the RCS. Saying a given shape, made smaller, will produce a smaller RCS is not correct at all, and this has been known since the 1960s. It was this knowledge that allowed Boeing to create the SRAM (and other things) with a very small RCS even though it was "common knowledge" at the time that size and RCS were directly related (again, they are not).
Click to expand...
Please don't offer me naive BS, I am a time-served EM engineer. I look forward to your citation for what "has been known since the 1960s".
 
steelpillow said:
The reverse is actually true. One of the great benefits of the all-wing design is span loading; put the weight where the lift is, don't put the lift metres from the weight.

Also, it is worth noting that the majority of thrust from a subsonic turbofan acts on the fan, compressor and combustion chamber. The exhaust only does much if you are using a very un-stealthy afterburner. Moving it inboard does help a bit, but even with a central nozzle the single surviving engine is still pushing hard on one side.
Click to expand...

Also, besides the span loading, the deep cross section throughout the center section should offer a lighter structure as the depth makes it easier to handle the bending moment.
 
NCQ said:
I'm more and more convinced that the B-21 has two weapons bays, probably about the same size as the B-2's with a rotary launcher in each. ... From what I can tell the B-21's landing gear is only slightly closer together than the B-2's is, but with the B-21 likely only having two engines it will be able to dispense with two of the engine access doors. Meaning even if the space between the landing gear is somewhat narrower there's still plenty of room for two weapons bays to easily fit. It seems unlikely that with all the space available the B-21 would only have one weapons bay.
Click to expand...
B21 may have 2 bays rather than 1 but the space available is narrower than un b2. By some 3.5 m. If one assumes two f135 for b21, compared to width taken by 4 f118, there is going to be another 1.2 to 1.3 m per engine. (Clearance between engines included) in other words, b21 will still have roughly one meter less space. Given that b2 evidently has the entire span between engine panels used for bomb bays, b21 will necessarily have that 1 meter less space for the width of its bays.
 
bring_it_on said:
While the payload is definitely TBD, I think the SecDef's comments on its efficiency and range should probably lay to rest any doubts on its ability to match or exceed the unrefueled range of the B-2 or B-1. If it has shorter legs, I seriously doubt he would have stuck his neck out and claimed an exact opposite in prepared remarks.

The range of the B-21, Austin said, is unmatched by any other bomber.

"It won't need to be based in-theater, it won't need logistical support to hold any target at risk," the secretary said.

www.defense.gov

World Gets First Look at B-21 Raider

As the first strategic bomber in more than three decades, the Air Force's B-21 will serve as the backbone of America's bomber force, Secretary of Defense Lloyd J. Austin III said.
www.defense.gov
Click to expand...
Click to expand...
I rewatched the part of the video, and the exact words Austin used to describe its range were:

"No other bomber can match its efficiency
It won't need to be based in theater,
it won't need logistical support to hold any target at risk"

The defense.gov site misquoted him by changing "efficiency" to "range". Hopefully the claim that the B-21 has a longer range than a re-engined B-52 doesn't start living as an urban legend. Either way, according to Northrop they have met or exceeded the requirements with the Raider, so the Air Force is getting what they asked for and think they need.
 
totoro said:
NCQ said:
I'm more and more convinced that the B-21 has two weapons bays, probably about the same size as the B-2's with a rotary launcher in each. ... From what I can tell the B-21's landing gear is only slightly closer together than the B-2's is, but with the B-21 likely only having two engines it will be able to dispense with two of the engine access doors. Meaning even if the space between the landing gear is somewhat narrower there's still plenty of room for two weapons bays to easily fit. It seems unlikely that with all the space available the B-21 would only have one weapons bay.
Click to expand...
B21 may have 2 bays rather than 1 but the space available is narrower than un b2. By some 3.5 m. If one assumes two f135 for b21, compared to width taken by 4 f118, there is going to be another 1.2 to 1.3 m per engine. (Clearance between engines included) in other words, b21 will still have roughly one meter less space. Given that b2 evidently has the entire span between engine panels used for bomb bays, b21 will necessarily have that 1 meter less space for the width of its bays.
Click to expand...
The space is narrower between the wheels on the B-21, yes, but it doesn't look anywhere near 3.5 meters narrower to me. Closer to 1 meter narrower at a maximum if I had to guess. Plenty of space for two B-2 sized bays assuming it indeed has two engines. But that's going off my best guess from the images available.
 
steelpillow said:
quellish said:
steelpillow said:
Radar signature is a function of the reflectivity
Click to expand...

Yes, mostly.

steelpillow said:
and size of a given feature.
Click to expand...

No.
Small feature can have a big return. Big feature can have a small return. RCS is not dependent on volume or physical size. The electrical size of something in relation to the frequency can affect the RCS. As a general rule though the size of an object does not have a direct affect on the RCS. Saying a given shape, made smaller, will produce a smaller RCS is not correct at all, and this has been known since the 1960s. It was this knowledge that allowed Boeing to create the SRAM (and other things) with a very small RCS even though it was "common knowledge" at the time that size and RCS were directly related (again, they are not).
Click to expand...
Please don't offer me naive BS, I am a time-served EM engineer. I look forward to your citation for what "has been known since the 1960s".
Click to expand...
https://www.secretprojects.co.uk/th...s-rq-170-sentinel-spy-drone.14143/post-139738
https://www.secretprojects.co.uk/th...s-rq-170-sentinel-spy-drone.14143/post-139849
 

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