Northrop Grumman B-21 Raider (LRS-B)

[bobbymike]

I don't think higher sweep necessarily means higher cruise speed requirement.
Airliners cruise around M0.8, just below drag rise, with very limited sweep- way less than the B-2. Having even more sweep would theoretically allow you to have really thick airfoils and still stay below drag rise, but i don't see it. The reason airliners try to unsweep the wing is because it gives better L/D.
Because of the way transsonic drag rises, you get diminishing returns for trying to fly faster. The B-21 needs a lot of range and cruise efficiency is at a premium. No, if NG incorporated more sweep, it's because of signature, IMHO.

Indeed, just look at the F-117.

Yep. If someone had flashed this around in 1984 and said it was a TAV. . .

It has probably been discussed on other threads but if you wanted the ideal stealth/speed trade-off in a heavy bomber what would it look like?

 

[sferrin]

I don't think higher sweep necessarily means higher cruise speed requirement.
Airliners cruise around M0.8, just below drag rise, with very limited sweep- way less than the B-2. Having even more sweep would theoretically allow you to have really thick airfoils and still stay below drag rise, but i don't see it. The reason airliners try to unsweep the wing is because it gives better L/D.
Because of the way transsonic drag rises, you get diminishing returns for trying to fly faster. The B-21 needs a lot of range and cruise efficiency is at a premium. No, if NG incorporated more sweep, it's because of signature, IMHO.

Indeed, just look at the F-117.

Yep. If someone had flashed this around in 1984 and said it was a TAV. . .

It has probably been discussed on other threads but if you wanted the ideal stealth/speed trade-off in a heavy bomber what would it look like?

Maybe like one of these? Who knows?

 

[NeilChapman]

I don't think higher sweep necessarily means higher cruise speed requirement.
Airliners cruise around M0.8, just below drag rise, with very limited sweep- way less than the B-2. Having even more sweep would theoretically allow you to have really thick airfoils and still stay below drag rise, but i don't see it. The reason airliners try to unsweep the wing is because it gives better L/D.
Because of the way transsonic drag rises, you get diminishing returns for trying to fly faster. The B-21 needs a lot of range and cruise efficiency is at a premium. No, if NG incorporated more sweep, it's because of signature, IMHO.

Indeed, just look at the F-117.

Yep. If someone had flashed this around in 1984 and said it was a TAV. . .

It has probably been discussed on other threads but if you wanted the ideal stealth/speed trade-off in a heavy bomber what would it look like?

Maybe like one of these? Who knows?

Would the horizontal stabilizers be necessary for some reason or are do just happen to be in these pictures?

 

[AeroFranz]

I don't think higher sweep necessarily means higher cruise speed requirement.
Airliners cruise around M0.8, just below drag rise, with very limited sweep- way less than the B-2. Having even more sweep would theoretically allow you to have really thick airfoils and still stay below drag rise, but i don't see it. The reason airliners try to unsweep the wing is because it gives better L/D.
Because of the way transsonic drag rises, you get diminishing returns for trying to fly faster. The B-21 needs a lot of range and cruise efficiency is at a premium. No, if NG incorporated more sweep, it's because of signature, IMHO.

It depends if you think it's the same kind of thing as a B-2 & I am not convinced it is. The B-21 maybe more like a heavy attack aircraft rather than just pure global bomber and therefore things like air to air capability and high dash speed may come into play for its design.

The picture below is what i'm talking about. Long range aircraft fly at the knee in the curve, the drag divergence Mach. If you want to fly faster, you get a disproportionate increase in drag, in turn you need more thrust, more fuel, bigger engine, bigger airframe. Hard to quantify precisely, but you could for example require flying just 10% faster and as a result your airplane takeoff gross weight goes up 30%. You must REALLY want that capability to justify the cost.

 

[overscan (PaulMM)]

The NASA/Northrop Environmentally Responsible Aviation (ERA) N+2 Advanced Vehicle Study shows that 35 degrees sweep always gives lower fuel burn than higher sweep. That study settled on 40 degrees as the least amount of sweep compatible with required stability margins, not because it was superior to 35 degrees in any specific performance metric.

 

[overscan (PaulMM)]

I don't think higher sweep necessarily means higher cruise speed requirement.
Airliners cruise around M0.8, just below drag rise, with very limited sweep- way less than the B-2. Having even more sweep would theoretically allow you to have really thick airfoils and still stay below drag rise, but i don't see it. The reason airliners try to unsweep the wing is because it gives better L/D.
Because of the way transsonic drag rises, you get diminishing returns for trying to fly faster. The B-21 needs a lot of range and cruise efficiency is at a premium. No, if NG incorporated more sweep, it's because of signature, IMHO.

It depends if you think it's the same kind of thing as a B-2 & I am not convinced it is. The B-21 maybe more like a heavy attack aircraft rather than just pure global bomber and therefore things like air to air capability and high dash speed may come into play for its design.

The picture below is what i'm talking about. Long range aircraft fly at the knee in the curve, the drag divergence Mach. If you want to fly faster, you get a disproportionate increase in drag, in turn you need more thrust, more fuel, bigger engine, bigger airframe. Hard to quantify precisely, but you could for example require flying just 10% faster and as a result your airplane takeoff gross weight goes up 30%. You must REALLY want that capability to justify the cost.

Indeed, if you are going to fly above Mach 0.9, the next sweet spot is Mach 1.4-1.6. I wouldn't absolutely rule out a supercruise B-21 on technical grounds (Northrop made the YF-23 after all) but it would need a higher wing sweep and cut into range and increase cost and risk significantly.

 

[dark sidius]

At this time nobody realy don't know what it will look like, the B-21 will be surely different than the drawing first picture, this picture represent the start of the program not the final Northrop plane. Second time we read an article about the speed .

 

[flateric]

why so stupid?

 

[marauder2048]

Indeed, if you are going to fly above Mach 0.9, the next sweet spot is Mach 1.4-1.6. I wouldn't absolutely rule out a supercruise B-21 on technical grounds (Northrop made the YF-23 after all) but it would need a higher wing sweep and cut into range and increase cost and risk significantly.

But a supersonic dash capability irrespective of efficiency may be essential to survival as the depressed trajectory SLBM threat will only tend to increase during LRS-B's lifetime.

 

[sferrin]

But a supersonic dash capability irrespective of efficiency may be essential to survival as the depressed trajectory SLBM threat will only tend to increase during LRS-B's lifetime.

Doubt supercruise ability would effect that scenario enough to matter. If you're on the ground both are just as dead and even for a supercruising bomber it's going to take several minutes to get up to speed. In a drag race from the runway how much further away would a supercruising bomber been when the missile hits six minutes from launch? Likely both are still on the ground unless they sit at the ready like they did in the 60s.

 

[TomS]

But a supersonic dash capability irrespective of efficiency may be essential to survival as the depressed trajectory SLBM threat will only tend to increase during LRS-B's lifetime.

We're not even standing ready alerts with the bomber force these days -- if you're worried about bolt from the blue attacks, that's what the SSBN force is for.

 

[marauder2048]

But a supersonic dash capability irrespective of efficiency may be essential to survival as the depressed trajectory SLBM threat will only tend to increase during LRS-B's lifetime.

Doubt supercruise ability would effect that scenario enough to matter. If you're on the ground both are just as dead and even for a supercruising bomber it's going to take several minutes to get up to speed. In a drag race from the runway how much further away would a supercruising bomber been when the missile hits six minutes from launch? Likely both are still on the ground unless they sit at the ready like they did in the 60s.

I'm struggling to find the study but I seem to recall that B-1b's supersonic dash capability was thought to improve its (on alert) survival rate by double digits against a depressed trajectory SLBM threat.
Of course, improving the hardness of the bomber a couple of psi provides for similar improvements in survivability once airborne over a faster, less hardened bomber.

Given LRS-B's liftetime and the projected reduction in the on-station SSBN force, putting a portion of the bomber force on alert during a crisis is not inconceivable.

 

[AeroFranz]

Giving the bomber a supersonic capability, regardless of whether it makes sense or not, is a sure way of increasing size and cost. Disproportionately. Remember, this is supposed to (theoretically) cost $550M/copy.

 

[NeilChapman]

Giving the bomber a supersonic capability, regardless of whether it makes sense or not, is a sure way of increasing size and cost. Disproportionately. Remember, this is supposed to (theoretically) cost $550M/copy.

What is expensive on B-21? That $510M in 2010 dollars for B-21 doesn't include EMD and testing.

I get that on B-2 everything was new. GAO estimated costs for F-22 was ~$400M per copy in 2012 (including EMD and testing) and that's a supercruise jet with some significant new development, no? I expect each F-22 was basically hand built as well. Techmat for B-21 is high so we assume many components in use on B2 and F35.

Is it the Nuc/Bio protection, skin, size? What components are making this bomber cost ~$400M more than F35?

 

[quellish]

Is it the Nuc/Bio protection, skin, size? What components are making this bomber cost ~$400M more than F35?

It's larger and has much more aggressive signature requirements.

 

[overscan (PaulMM)]

It will weigh more than 3 F-35s and the cost ($550 million) is only double the cost of a Dreamliner. Doesn't seem unreasonable.

 

[DrRansom]

Between hypersonic gliders and cruise missiles, the number of first strike weapons is increasing fast. Some of those won't need a SSBN to be launched either.

That could influence usaf thinking about supersonic dash.

 

[sferrin]

Between hypersonic gliders and cruise missiles, the number of first strike weapons is increasing fast. Some of those won't need a SSBN to be launched either.

That could influence usaf thinking about supersonic dash.

There are no hypersonic gliders. And the only nuclear-armed cruise missile in the US inventory is subsonic and 30 years old.

 

[NeilChapman]

Is it the Nuc/Bio protection, skin, size? What components are making this bomber cost ~$400M more than F35?

It's larger and has much more aggressive signature requirements.

I'm trying to isolate component costs to work through the $400M.

PaulMM - I'm not suggesting it's unreasonable. We're anticipating that it doesn't have the speed performance of an F-35. It will will probably weigh 4x an F35. There will probably be two less engines. That's probably a $20-$25M savings.

But won't have 4x the F35 avionics, comms, B-2 EWS etc.

How has RAM as implemented on B-2 and later F22 changed in the last 20 years? Will this be as expensive as built on B-2?

 

[DrRansom]

Between hypersonic gliders and cruise missiles, the number of first strike weapons is increasing fast. Some of those won't need a SSBN to be launched either.

That could influence usaf thinking about supersonic dash.

There are no hypersonic gliders. And the only nuclear-armed cruise missile in the US inventory is subsonic and 30 years old.

I meant looking forward, China is developing a nuclear hypersonic glider and I would expect Russia to follow suite.

If Russia / China have hypersonic weapons, and they will, the bomber force faces more low warning threats.

 

[Flyaway]

The B-21 maybe more like a heavy attack aircraft rather than just pure global bomber and therefore things like air to air capability and high dash speed may come into play for its design.

BS

Too lazy to do a proper response then.

 

[marauder2048]

Is it the Nuc/Bio protection, skin, size? What components are making this bomber cost ~$400M more than F35?

It's larger and has much more aggressive signature requirements.

Does a flying wing offer structural advantages w.r.t nuclear hardening e.g. blast overpressure over a more conventional design? The B-2 had to operate in a threat environment with nuclear-tipped SAMs.

 

[overscan (PaulMM)]

The B-21 maybe more like a heavy attack aircraft rather than just pure global bomber and therefore things like air to air capability and high dash speed may come into play for its design.

BS

Too lazy to do a proper response then.

Try asking a sensible question?

Everything known about the design purpose says its a bomber, not a heavy attack aircraft. Its drivers will be stealth, range, cost, stealth, payload, and stealth. Air-to-air capability, nope. High dash speed - too costly in time , money and risk.

 

[overscan (PaulMM)]

Is it the Nuc/Bio protection, skin, size? What components are making this bomber cost ~$400M more than F35?

It's larger and has much more aggressive signature requirements.

Does a flying wing offer structural advantages w.r.t nuclear hardening e.g. blast overpressure over a more conventional design? The B-2 had to operate in a threat environment with nuclear-tipped SAMs.

I'm pretty sure there were enough complications in the B-2 design without a requirement to structurarally survive nearby nuclear blasts. EMP hardening, sure, but nuclear blast-resistant structure/shape, no.

 

[dark sidius]

With what you say about it it will become a big target for S-400, if it have just the stealth capacity for survive.

 

[overscan (PaulMM)]

With what you say about it it will become a big target for S-400, if it have just the stealth capacity for survive.

You know the S-400 system capabilities? You know the B-21 radar cross section and ECM capabilities? You think the USAF know *less* about either than you do?

I don't think so.

 

[dark sidius]

Are you so confident that in a decade the stealth will be the biggest advantage in air superiority ? Don't you think the ennemy are working hard to defeat the stealth ? I think more that the survivability will be an addition of a lot of capacity , speed , stealth , directed energy, hypersonic missile ; air/air capacity winning is not cheap.

 

[overscan (PaulMM)]

It really doesn't matter if *I* am confident about it, as I don't make decisions for the US Air Force any more than you do. Please outline your qualifications to know better.

 

[flateric]

Too lazy to do a proper response then.

"High dash speed" for a flying wing with LE sweepback angle of 40? You gonna push Mach 3 from her? LOLd

 

[AeroFranz]

Maybe we could start by using the proper terminology. There are significant barriers to making a flying wing supersonic (actually it's pretty much impossible for stability and control purposes primarily, and other reasons after that). I can only guess some posts were actually referring to supersonic tailless deltas. Very different thing. Otherwise, no, a flying wing doesn't have the surfaces in the right places to cope with the aerodynamic shift.

 

[BarrelNut]

With what you say about it it will become a big target for S-400, if it have just the stealth capacity for survive.

That doesn't make much sense, considering that the stealth features are the main features needed in avoiding and suppressing S-400 type systems.

 

[Sundog]

With what you say about it it will become a big target for S-400, if it have just the stealth capacity for survive.

That doesn't make much sense, considering that the stealth features are the main features needed in avoiding and suppressing S-400 type systems.

Yeah, I think many Mach 3 aircraft look cool as well, but that doesn't make it the right platform for the mission. You'll find what many aviation fanboys don't understand is the mission defines the aircraft, not the other way around. I'm not knocking them for that, I was the same way until I became an Aero Engineer. It's obvious the NGB mission was based on a supersonic profile, but that also proved too costly, as noted by AeroFranz earlier. To reduce cost, they came up with a subsonic mission profile for the LRSB and found it met cost goals. The B-21 is the result of all of their (Both LM/Boeing and Northrop) design studies to best meet that mission profile.

 

[dark sidius]

With a subsonic speed you still fly hours and hours and hours to go on the theater and to destroy the mobile launcher it's not an advantage, the time you will be here it will be gone. And to escape a danger zone a dash speed is an assurance to survive the fighters.

 

[Airplane]

Are you so confident that in a decade the stealth will be the biggest advantage in air superiority ? Don't you think the ennemy are working hard to defeat the stealth ? I think more that the survivability will be an addition of a lot of capacity , speed , stealth , directed energy, hypersonic missile ; air/air capacity winning is not cheap.

The DoD is confident. Where are all the high speed and LO platforms? SR72 is in the works. Hypersonic weapons are in development. Doesn't make sense to me either to put all your billion dollar eggs into subsonic LO platforms (or like the -35 short supersonic dash). But with active stealth (black boxes modes and codes) the DoD has bet the farm and all it's cows and chickens on it.

 

[AeroFranz]

With a subsonic speed you still fly hours and hours and hours to go on the theater and to destroy the mobile launcher it's not an advantage, the time you will be here it will be gone. And to escape a danger zone a dash speed is an assurance to survive the fighters.

So who's paying for all that?

"And to escape a danger zone a dash speed is an assurance to survive the fighters."
Hmmm...there is no such thing as "assurance" in mission modeling, only probability.

 

[overscan (PaulMM)]

Maybe we could start by using the proper terminology. There are significant barriers to making a flying wing supersonic (actually it's pretty much impossible for stability and control purposes primarily, and other reasons after that). I can only guess some posts were actually referring to supersonic tailless deltas. Very different thing. Otherwise, no, a flying wing doesn't have the surfaces in the right places to cope with the aerodynamic shift.

Its certainly conceivable that the drawing released is at a deceptive angle like the first F-117A photo and the actual design is higher sweep than it appears, say 45 or 50 degrees. Whether that makes supersonic flight possible, I don't know. Stability and control issues resulting might be fixable with advanced control technology.

I don't think its likely, for the reasons listed above.

 

[flateric]

It's obvious the NGB mission was based on a supersonic profile

Par me? "Obvious"?

 

[bobbymike]

It's obvious the NGB mission was based on a supersonic profile

Par me? "Obvious"?

I am sure it was posted somewhere here a comparison of medium and long range VLO subsonic, LO with M2 dash and the relative costs per delivered munition, etc. A very long range, 40k minimum payload was the best solution and could actually, when you considered less tanking, fewer overseas bases needed, could hit more targets over a 30 day operation than a smaller M2+ regional bomber. IIRC the very fast large LO bomber would have been so expensive it would lose out cause you only had a couple dozen if that.

 

[NeilChapman]

Is it the Nuc/Bio protection, skin, size? What components are making this bomber cost ~$400M more than F35?

It's larger and has much more aggressive signature requirements.

Does a flying wing offer structural advantages w.r.t nuclear hardening e.g. blast overpressure over a more conventional design? The B-2 had to operate in a threat environment with nuclear-tipped SAMs.

I'm pretty sure there were enough complications in the B-2 design without a requirement to structurarally survive nearby nuclear blasts. EMP hardening, sure, but nuclear blast-resistant structure/shape, no.

I understand the B-2 has several nuclear hardening capabilities including at minimum

- protection against pre-detonation dust
- gamma-neutron radiation - passive thermal protection panels
- thermal wave - windscreen with a quick-reacting photochromic to redirect thermal waves
- EMP protection - detect nuclear flash and reboot all systems

Would these be considered protections to structurally survive nearby nuclear blasts?

I expect all these will be on B-21. My earlier question was regarding if these types of solutions are updated as often as electronics. e.g Are there faster cheaper better ways to accomplish these solutions today then back in 1990?

 

[NeilChapman]

Maybe we could start by using the proper terminology. There are significant barriers to making a flying wing supersonic (actually it's pretty much impossible for stability and control purposes primarily, and other reasons after that). I can only guess some posts were actually referring to supersonic tailless deltas. Very different thing. Otherwise, no, a flying wing doesn't have the surfaces in the right places to cope with the aerodynamic shift.

Thank you - Your details about the capabilities of a flying wing are what I hoping to learn from my original question.

My sense it that with B-21 it's being designed to mitigate as many risks to the mission as possible.

- Understanding that family of systems likely required to penetrate future A2/AD environments - B2 designed for solo but requires package
- B-2 doesn't have the LO signature that was originally expected - maybe in large part due to the low altitude requirement?
- B-2 RAM maintenance (until very recently) has been very time consuming
- B-2 RAM protections are expensive and limit forward deployment options
- B-2 original DMS promise not realized - never allowed quick deployment and en-route mission re-planning based on new threats.
- Rain issues with B-2 - Can't have rain issues if you need to operate in a tropical environment.
- High MCR - B-2 much better than 2013 ~45% - Changes to RAM maintenance. Be nice to be at executive or drone fleet rates >90%

Have to think that family of systems includes allowing the B-21 to "sniff-out" threats - much improved EWS - among other things. Is there a document that describes the family of systems discussed?

Hopefully family of systems includes F/A-XX as well.