Northrop Grumman B-21 Raider (LRS-B)

[NeilChapman]

So...

When is taxi testing to start?

 

[Fluff]

Just a hint - this is the B21 thread. We had a massive thread where 2 people argued forever over stealth. Please go there to have a massive argument over stealth. Thank you.

 

[overscan (PaulMM)]

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).

Quellish, but if we compare B2 with let say 50% sized B2 - the second should have smaller RCS. Is that correct?

Nope. The relationship between radar wavelength and size of physical features means a smaller B-2 could be more detectable to long wavelength radars for example.

 

[paralay]

,

 

[Hanz2k]

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).

Quellish, but if we compare B2 with let say 50% sized B2 - the second should have smaller RCS. Is that correct?

Nope. The relationship between radar wavelength and size of physical features means a smaller B-2 could be more detectable to long wavelength radars for example.

So basically it comes to the point, if some element of the airframe resonate with radar wavelength?
Can I read somewhere how certain wavelengths interact with airframe?

 

[steelpillow]

The discussion here on EM reflectivity, RCS etc is sadly ill-informed.

First of all, one needs to distinguish between gross or total characteristics across the frequency range on the one hand, as against frequency-dependent characteristics at a given frequency on the other. For example the total energy reflected is the sum of all the energies at each and every frequency reflected.
Other things being equal, a small object reflects less total energy than a large one. However if we focus on the frequency-dependent parameters, then the dominant frequencies shift with physical scale according to wavelength, in the well-known way, and in a constant-frequency environment all bets are off.

There are other ways here in which statements are being misinterpreted in the wrong context, but one example should be enough.

It is wise not to criticise a statement on a complex EM topic until you fully understand its context.

Anyway, I'm off to bed now. G'night all.

 

[LowObservable]

What are those, Adours?

 

[LowObservable]

Good grief, kids these days. Open sources. Read the history. Technological change since the late 1970s. CONOPS.

 

[overscan (PaulMM)]

Right - back to topic.

 

[sferrin]

I will be happy to eat crow if this thing can carry even one MOP.

 

[overscan (PaulMM)]

I don't think it will. It will have a replacement for MOP which is smaller but not necessarily less destructive. MOP was a quick development and not very optimised. There were statements in 2011/2012 timeframe about a smaller replacement for next-generation bombers.

 

[Rhinocrates]

That didn't take long.

View: https://www.youtube.com/watch?v=pIIjWfF9vvM

 

[Josh_TN]

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?

*IF* the engines are F135s, then I suspect that the bomber was sized around what a pair of them could power.

Well, my bet that biggest savings and at the end requirement for smaller airframe came from switching from 4 engine into 2 engine config.

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.

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.

If nothing else, all current bombers were designed with nuclear free fall weapons as the envisaged primary weapon, with long range external cruise missiles and role back type stand off weapons being not in existence or not the primary effector. The B-21 was I dare say designed with more of a conventional role in mind and I would think that in that mission the primary weapons would be small glide PGMs or else oversized penetrating bombs. The former gives a single platform much deeper magazines and allows for a much larger inventory of weapons (also it would leverage a high altitude envelope) and the latter is something that just can’t be delivered to a high threat area with stand off weapons or easily detected platforms. A lower payload split up among a larger number of aircraft was probably desirable.

Though as someone else posted, if the F135 is indeed the engine then the finished product’s size and capability was almost certainly derived from that, with the smaller size/payload (if that is the case) being the trade off for using an off the shelf current engine (and potentially tapping into its future engine upgrades).

 

[rooster]

They should have hired NBA basketball stars or midgets to throw off size analysis.

I think they did use people with various heights in the reveal. For a purpose.

 

[rooster]

I don't think it will. It will have a replacement for MOP which is smaller but not necessarily less destructive. MOP was a quick development and not very optimised. There were statements in 2011/2012 timeframe about a smaller replacement for next-generation bombers.

Does mop have earth penetration ability. Then its useless agaisnt say Iranian targets under mountains. I'm not sure why mop is even needed. Distributed smaller explosions are more destructive than 1 large one. Its not the 21 will be clearing forests for helicopter landing areas. They make for nice TV clips but....

 

[NCQ]

I don't think it will. It will have a replacement for MOP which is smaller but not necessarily less destructive. MOP was a quick development and not very optimised. There were statements in 2011/2012 timeframe about a smaller replacement for next-generation bombers.

Does mop have earth penetration ability. Then its useless agaisnt say Iranian targets under mountains. I'm not sure why mop is even needed. Distributed smaller explosions are more destructive than 1 large one. Its not the 21 will be clearing forests for helicopter landing areas. They make for nice TV clips but....

I think all we need to take out Iranian mountain targets are four Super Hornets with two GBU-24s each. They would operate in pairs of one E and one F...

Anyway, fairly in depth article from Air Force Magazine about the B-21 program and how we still know very little about the aircraft.

https://www.airandspaceforces.com/m...-21-bomber-remains-a-secret-following-reveal/

Also going to highlight this quote about the B-21's size from the reporter who was at the reveal:

Though the B-21 is supposed to be smaller than the B-2, its wingspan seemed nearly as wide, though with a possibly different angle of sweep than that of the B-2. The “fuselage” seemed to have a deeper keel than that of the B-2. No dimensions of the aircraft were offered.

 

[bring_it_on]

...

They should have hired NBA basketball stars or midgets to throw off size analysis.

I think they did use people with various heights in the reveal. For a purpose.

Not the reveal, but a day prior.

 

[Manuducati]

About the future first flight, and the Gulfstream used as a B-21 flying simulator...

B-21 Raider Test Pilots Talk About Its Upcoming First Flight

Working in simulators and testing systems on a surrogate Gulfstream jet, these test pilots are preparing to make the B-21's first flight.

www.thedrive.com

 

[Bhurki]

...

Width to height is near 8:1
If its 17 ft high ( just like B-2) then its about 140 ft wide at most.
For B-2, width to height is 10:1.

 

[Aeroweanie]

Northrop, U.S. Air Force Roll Out the B-21 Raider | Aviation Week Network

The B-21 Raider was displayed at the company’s secretive Plant 42 complex about 34 years after a similar ceremony for its predecessor the B-2.

aviationweek.com

The aerodynamics of this thing fascinate me; some comment is given in the article. The hundreds if not thousands of iterative computer designs have converged on several classic historical features that are generally ignored or forgotten by the mainstream.

The tailored airflow over the centre section echoes Reimar Horten's deep concern for the subtleties of the mitteneffekt (middle effect), which he never entirely resolved. He also wanted to improve the engine installation to a more conformal design.

Those intakes remind me somewhat of the NACA duct used for many small auxiliary intakes in the cold war era and trialled as an engine intake on the North American YF-93. No doubt the B-21 version is far more advanced, but the principle appears to be the same, and is I suspect the secret to decelerating the leading-edge flow at transonic speeds.

The wing outer sections have pronounced washout and, as far as I can tell, leading-edge droop. These features may be traced historically back through the majority of tailless swept wings, including the production Convair deltas, Avro Vulcan and Horten types, to the Dunne machines of the pioneer era and his 1909 patent. The first such design to fly, the D.5 biplane of 1910, received the first ever official certificate of performance for a stable aeroplane. Twenty or so years after that Ludwig Prandtl developed the theory of the bell-shaped lift distribution which offers the lightest structure and lowest drag for any given wing size, and for which these two features are necessary. Lippisch published a simplified calculation, which Horten adopted (though for some reason Lippisch seldom did). NASA only publicly caught up in this millennium, with Jonathan Bowers' PRANDTL-D flying wing project. Clearly, the key benefit for the digitally-controlled B-21 is not the inherent stability but Prandtl's minimal weight and drag. Once you sweep the wing, the stability comes with that package. Also of interest is that, right up to his rediscovery by Bowers, Prandtl was ignored by the mainstream and it was believed that these design features increased drag; this was voiced as a major criticism of the Dunne, and Northrop never incorporated them, not even in the B-2. Now, we see that they actually enhance the B-21's low drag characteristics.

The question I ask myself now is, did Northrop Grumman secretly take forward all these long-known but also long-obscure aerodynamic features, or did their computers arrive at something they knew nothing of beforehand? Either way, the B-21 looks like becoming a major vindication of all those maverick forebears.

Albion (Al) Bowers, not Jonathan Bowers. BTW, the first paper was "A Retrospective: Historical Flying Wing Examples" by Albion Bowers and David Lednicer.

 

[NeilChapman]

Questions...

1. Do we think that is the final color?

2. Anybody else find it interesting that the chiefs of both the Australian and U.K. Royal Air Forces were present?

3. NG states B-21 designed to fly "every day" as a "high cycle" aircraft. What would one consider as an acceptable number of expected lifetime flight cycles or flight hours for an airframe designed today?

Lastly...

When walking through the woods don't forget to look up.

Is it possible those are standard 2' drop ceiling tiles above this bomber? It looks like the lights are every 8 tiles apart. Looks bigger than 120' to me. And if I'm right, I'd appreciate the credit. ;-)

 

[Fluff]

Questions...

1. Do we think that is the final color?

2. Anybody else find it interesting that the chiefs of both the Australian and U.K. Royal Air Forces were present?

3. NG states B-21 designed to fly "every day" as a "high cycle" aircraft. What would one consider as an acceptable number of expected lifetime flight cycles or flight hours for an airframe designed today?

Lastly...

When walking through the woods don't forget to look up.

Is it possible those are standard 2' drop ceiling tiles above this bomber? It looks like the lights are every 8 tiles apart. Looks bigger than 120' to me. And if I'm right, I'd appreciate the credit. ;-)

View attachment 688452


View attachment 688452

U.K. or aus having some, leads to ‘strategic ambiguity’ for an enemy. Am I about to go to war with USA, or aus.

 

[aim9xray]

Nice drawing. However you need to make a fundamental decision to start with - four spike or six spike, mmkay?

 

[quellish]

You don't say...

Note that correlation is not necessarily causation though...

@flateric stated :

What for? It's a well known fact that Northrop has started an intense build-up at Site 4 after they have won LRS-B.

To which you replied:

Call me agnostic, but I'd still like to see concrete references for that "well known fact".

The photos of expansion at the Northrop Grumman Site 4 at Plant 42 readily show expansion between before the time of the LRS-B award and today/recently. That is reasonable evidence of the recent expansion.

If you are questioning whether a specific hangar is new or was built to support the LRS-B program, you can certainly try to prove or disprove that by looking at sources like the Air Force C1 construction budget requests for recent years, building permits for Los Angeles County / Palmdale, contacting Northrop Grumman public affairs, and many other ways. I leave that as an exercise for the reader.

 

[bring_it_on]

Is it possible those are standard 2' drop ceiling tiles above this bomber? It looks like the lights are every 8 tiles apart. Looks bigger than 120' to me. And if I'm right, I'd appreciate the credit. ;-)

They put colored tape on the floor to make measuring things easy

 

[LowObservable]

Quellish, but if we compare B2 with let say 50% sized B2 - the second should have smaller RCS. Is that correct?

RCS B-2 ~ 0.38 m2, B-21 ~ 0.156 m2
based on a comparison of the frontal view

PLEASE some of us are reading this with a mouthful of Tannat. Give us a

 

[rooster]

I don't think it will. It will have a replacement for MOP which is smaller but not necessarily less destructive. MOP was a quick development and not very optimised. There were statements in 2011/2012 timeframe about a smaller replacement for next-generation bombers.

Does mop have earth penetration ability. Then its useless agaisnt say Iranian targets under mountains. I'm not sure why mop is even needed. Distributed smaller explosions are more destructive than 1 large one. Its not the 21 will be clearing forests for helicopter landing areas. They make for nice TV clips but....

I think all we need to take out Iranian mountain targets are four Super Hornets with two GBU-24s each. They would operate in pairs of one E and one F...

Anyway, fairly in depth article from Air Force Magazine about the B-21 program and how we still know very little about the aircraft.

https://www.airandspaceforces.com/m...-21-bomber-remains-a-secret-following-reveal/

Also going to highlight this quote about the B-21's size from the reporter who was at the reveal:

Though the B-21 is supposed to be smaller than the B-2, its wingspan seemed nearly as wide, though with a possibly different angle of sweep than that of the B-2. The “fuselage” seemed to have a deeper keel than that of the B-2. No dimensions of the aircraft were offered.

I just don't think you understand

 

[aim9xray]

Quellish, but if we compare B2 with let say 50% sized B2 - the second should have smaller RCS. Is that correct?

RCS B-2 ~ 0.38 m2, B-21 ~ 0.156 m2
based on a comparison of the frontal view

PLEASE some of us are reading this with a mouthful of Tannat. Give us a View attachment 688453

Polar plot of LowObservables's Tannat spit take. Darn suspicious I'd say.

 

[Black Dog]

Questions...

2. Anybody else find it interesting that the chiefs of both the Australian and U.K. Royal Air Forces were present?

There has been some talk about the RAAF acquiring B-21s. Haven't heard much about it for the UK. With the most basic of calculations, an order of 24 aircraft would be approx ~24.5 bil in AUD, say another 6B for spare parts and other items/support. That's around 1/3rd of the projected cost for the Attack class submarines, so I don't think it's out of the question.

The main question is whether the technology transfer will be allowed. The F-22 obviously set a precedent, however this new AUKUS partnership is supposed to facilitate techonolgy sharing for this sort of thing. Realistically this tech would likely be preferred to be kept "in-house", however there are a couple of obvious benefits to allowing other (trusted) countries to purchase - more aircraft to keep production lines open longer and bring costs down, and having more of these aircraft in the air by way of allied hands.

I believe Japan and Australia were both interested in the F-22 in some capacity, and I think was some level of regret there about that not being allowed to happen. Had production lines open longer, it might've ended up providing the USAF an opportunity to purchase more F-22s at a later date had the production line not been shut down when it was. There was some talk about re-opening the production line a number of years ago, but obviously that was prohibitively expensive and everything got thrown into the F-35 basket until the NGAD arrives. The F-15EX order shows there weren't really enough F-22s ordered. I am digressing here, but it supports the idea that allowing foreign buyers can be beneficial.

 

[ZacYates]

Given Bill works for Northrop Grumman now, its not likely any time soon.

I wondered what had happened to Bill Sweetman. He had gone quiet lately. A Northrop sponsored book on the B-21 would be good though.

Somehow Bill's a friend of a friend on Facebook - for what it's worth he watched the whole thing at home like the rest of us!

 

[CiTrus90]

Just in passing and OT, but for the people still wondering if smaller/bigger size necessarily translates into smaller/bigger RCS, here's the ADM-20 Quail which was used as a decoy for B-52s in the 60s.

 

[overscan (PaulMM)]

I

Questions...

1. Do we think that is the final color?

2. Anybody else find it interesting that the chiefs of both the Australian and U.K. Royal Air Forces were present?

3. NG states B-21 designed to fly "every day" as a "high cycle" aircraft. What would one consider as an acceptable number of expected lifetime flight cycles or flight hours for an airframe designed today?

Lastly...

When walking through the woods don't forget to look up.

Is it possible those are standard 2' drop ceiling tiles above this bomber? It looks like the lights are every 8 tiles apart. Looks bigger than 120' to me. And if I'm right, I'd appreciate the credit. ;-)

View attachment 688452

If we go by the person to the right wingtip, he is approx. 75 pixels tall. Lets call him "Tim". I assume that he is standing below the front wingtip, which means he is in the right plane for maximum span, wingtip to wingtip.

The wingspan of the B-21 is 1947 pixels, which is 25.96 Tims.

If Tim is 5ft tall, then that makes the B-21 129 ft span. If Tim is 6ft, then its 155ft span.

My money's on 150ft+.

 

[Hydroman]

What I haven't been able to determine, is where are the egress panels? Does the flight crew sit more under those side windows? Are those the panels that get blown off for ejection? Because I don't see anything on the top between them for egress.

The egress panels are most probably those that can be seen in Overscan's close up picture. I've outlined the one on the right side of the craft:
View attachment 688379
I do not think those are for the ejection seats. I've made a quick drawing to get a (very) rough estimate of where the glazings are, and they clearly do not line up with where I'd expect the pilots to seat:
View attachment 688380
So, unless the seats slide to the sides during the ejection procedure, this is why I think those are emergency egress panels and (possibly) explosive ones. I think the crew is meant to enter and exit the B-21 in the same way as on the B-2, via a ladder on the bottom of the craft, but after the B-2's crashes in 2008 and 2021 it might have been noticed that in case the landing gear collapses while on the runway, the pilots only option to leave the aircraft would be to eject. Which is not great for the human body, unless necessary to avoid worse injuries or death.

I believe the ejection panels can't be seen in the available pictures due to a mix of the angles at which these have been taken, the lights used in the hangar and the kind of surface coating on the aircraft.

Edit: I also believe the side windows' shape and size are dictated by the structural requirements for these egress panels, rather than any laser/stealthiness theory.

B-21 evolved surface treatments, alien ship looking but I would expect this over many years of refinement. Even the B-2 has evolved treatments over the years since I was on the program up to 1996.

 

[Archibald]

Lets call him "Tim".

Monty Pythons and the holy grail intensifies... KABOOM !!!

 

[Flyaway]

Questions...

1. Do we think that is the final color?

2. Anybody else find it interesting that the chiefs of both the Australian and U.K. Royal Air Forces were present?

3. NG states B-21 designed to fly "every day" as a "high cycle" aircraft. What would one consider as an acceptable number of expected lifetime flight cycles or flight hours for an airframe designed today?

Lastly...

When walking through the woods don't forget to look up.

Is it possible those are standard 2' drop ceiling tiles above this bomber? It looks like the lights are every 8 tiles apart. Looks bigger than 120' to me. And if I'm right, I'd appreciate the credit. ;-)

View attachment 688452


View attachment 688452

U.K. or aus having some, leads to ‘strategic ambiguity’ for an enemy. Am I about to go to war with USA, or aus.

Both countries already operate unique US military technology. Weirdly I think the B-21 would be more exportable in limited circumstances than the NGAD technology wise. Unlike the B-2 it’s designed to be a multipurpose lower cost high cycle platform. I could imagine the B-21 slotting into the UK, Japan & Italian multi platform sixth generation combat aircraft. By the way Japan might be worth a sale after all they are in theatre so to speak.

 

[overscan (PaulMM)]

I

Questions...

1. Do we think that is the final color?

2. Anybody else find it interesting that the chiefs of both the Australian and U.K. Royal Air Forces were present?

3. NG states B-21 designed to fly "every day" as a "high cycle" aircraft. What would one consider as an acceptable number of expected lifetime flight cycles or flight hours for an airframe designed today?

Lastly...

When walking through the woods don't forget to look up.

Is it possible those are standard 2' drop ceiling tiles above this bomber? It looks like the lights are every 8 tiles apart. Looks bigger than 120' to me. And if I'm right, I'd appreciate the credit. ;-)

View attachment 688452

If we go by the person to the right wingtip, he is approx. 75 pixels tall. Lets call him "Tim". I assume that he is standing below the front wingtip, which means he is in the right plane for maximum span, wingtip to wingtip.

The wingspan of the B-21 is 1947 pixels, which is 25.96 Tims.

If Tim is 5ft tall, then that makes the B-21 129 ft span. If Tim is 6ft, then its 155ft span.

My money's on 150ft+.

Following up on this analysis.

The thrust from two F-135s is likely 56,000lb compared to 72,000lb for the B-2's 4 engines , which is roughly 75% of the thrust. I expect the weight of the B-21 to be roughly in the area of 75% the weight of the B-2.

Assuming density is the same, you would expect the B-21 to be 75% of the volume of the B-2.

Dimensions would be reduced by the third root of 0.75 which is 0.90.

So if B-21 was exactly the same shape as the B-2 but scaled to 75% weight, you would expect the wingspan to be 0.9 * 172 ft = 154.8ft.

A B-2 scaled to 130 ft would be 75% of the B-2 span, but the volume would be reduced to less than half (43%) of the B-2. This would seem to leave it too small, and overpowered.

Obviously tremendously oversimplified, as it isn't the exact same shape, but still interesting I think?

 

[steelpillow]

Albion (Al) Bowers, not Jonathan Bowers. BTW, the first paper was "A Retrospective: Historical Flying Wing Examples" by Albion Bowers and David Lednicer.

Thanks for the correction. Of course. Comes of knowing two Mr. Bowers in quite different fields of study.

 

[Fluff]

I

Questions...

1. Do we think that is the final color?

2. Anybody else find it interesting that the chiefs of both the Australian and U.K. Royal Air Forces were present?

3. NG states B-21 designed to fly "every day" as a "high cycle" aircraft. What would one consider as an acceptable number of expected lifetime flight cycles or flight hours for an airframe designed today?

Lastly...

When walking through the woods don't forget to look up.

Is it possible those are standard 2' drop ceiling tiles above this bomber? It looks like the lights are every 8 tiles apart. Looks bigger than 120' to me. And if I'm right, I'd appreciate the credit. ;-)

View attachment 688452

If we go by the person to the right wingtip, he is approx. 75 pixels tall. Lets call him "Tim". I assume that he is standing below the front wingtip, which means he is in the right plane for maximum span, wingtip to wingtip.

The wingspan of the B-21 is 1947 pixels, which is 25.96 Tims.

If Tim is 5ft tall, then that makes the B-21 129 ft span. If Tim is 6ft, then its 155ft span.

My money's on 150ft+.

Following up on this analysis.

The thrust from two F-135s is likely 56,000lb compared to 72,000lb for the B-2's 4 engines , which is roughly 75% of the thrust. I expect the weight of the B-21 to be roughly in the area of 75% the weight of the B-2.

Assuming density is the same, you would expect the B-21 to be 75% of the volume of the B-2.

Dimensions would be reduced by the third root of 0.75 which is 0.90.

So if B-21 was exactly the same shape as the B-2 but scaled to 75% weight, you would expect the wingspan to be 0.9 * 172 ft = 154.8ft.

A B-2 scaled to 130 ft would be 75% of the B-2 span, but the volume would be reduced to less than half (43%) of the B-2. This would seem to leave it too small, and overpowered.

Obviously tremendously oversimplified, as it isn't the exact same shape, but still interesting I think?

I was going the other way, B2 172 feet, each engine about 6 feet, so take 2 off, = 160 feet.

I'm sure USAF modelled many options before picking one.

I'd also suggest volume in the bomb bays, is more important than weight.

And If I was designing an aircraft for a 40 year life, for weapons as yet undesigned or even unthought of, I'd take the size in use now, and add a bit. You can always use that space for a fuel tank until its needed.

 

[VTOLicious]

I

Questions...

1. Do we think that is the final color?

2. Anybody else find it interesting that the chiefs of both the Australian and U.K. Royal Air Forces were present?

3. NG states B-21 designed to fly "every day" as a "high cycle" aircraft. What would one consider as an acceptable number of expected lifetime flight cycles or flight hours for an airframe designed today?

Lastly...

When walking through the woods don't forget to look up.

Is it possible those are standard 2' drop ceiling tiles above this bomber? It looks like the lights are every 8 tiles apart. Looks bigger than 120' to me. And if I'm right, I'd appreciate the credit. ;-)

View attachment 688452

If we go by the person to the right wingtip, he is approx. 75 pixels tall. Lets call him "Tim". I assume that he is standing below the front wingtip, which means he is in the right plane for maximum span, wingtip to wingtip.

The wingspan of the B-21 is 1947 pixels, which is 25.96 Tims.

If Tim is 5ft tall, then that makes the B-21 129 ft span. If Tim is 6ft, then its 155ft span.

My money's on 150ft+.

Following up on this analysis.

The thrust from two F-135s is likely 56,000lb compared to 72,000lb for the B-2's 4 engines , which is roughly 75% of the thrust. I expect the weight of the B-21 to be roughly in the area of 75% the weight of the B-2.

Someone already pointed out that a twin engine design needs to account for more excess thrust ( 1/2 vs 1/4 thrust loss in case of single engine failure).

 

[Mark Nankivil]

Just in passing and OT, but for the people still wondering if smaller/bigger size necessarily translates into smaller/bigger RCS, here's the ADM-20 Quail which was used as a decoy for B-52s in the 60s.

But the Quail was built specifically to mimic the radar reflection of a B-52 or similar - McDonnell went out of their way in the design to do that. Nothing with its shape that can be construed as an effort at stealth, it was essentially a flying radar reflector.

Enjoy the Day! Mark