Northrop Grumman B-21 Raider (LRS-B)

Sundog said:
Yeah, I noted elsewhere that this is the biggest fail I've seen from an aerospace corporation in a long time for such an accomplishment. "Oh, it flew? Let's let everyone know it's a new bomber then..."
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This is Northrop's way of using a whole lot of words describing it without telling you anything that would actually inform you about anything classified or sensitive of nature about the said aircraft that has just made it's first flight. I'm still waiting for the chase plane footage to be released.
 
Sundog said:
Yeah, I noted elsewhere that this is the biggest fail I've seen from an aerospace corporation in a long time for such an accomplishment. "Oh, it flew? Let's let everyone know it's a new bomber then..."
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They have never really gotten ahead of the Air Force. Where's the Air Force announcement of first flight? With official photos?
 
bring_it_on said:
They have never really gotten ahead of the Air Force. Where's the Air Force announcement of first flight? With official photos?
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AF was not going to release official photos of taxi tests etc, so you go figure...
 
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Scott Kenny said:
Why wouldn't a B-21 be able to drop a GBU-57? I'll bet good money that center bay is at least the same volume as one of the B-2 bays, if not as long as the B-52's bay so it can carry ALCM-sized things internally. 28ft long and 6 ft wide.
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I do recall making a case that B-21's size may afford more airfields from which it may operate. Has anyone stated that the overall smaller size of the B-21 may have been a design factor specifically because of its RCS? I don't recall either way.
 
NeilChapman said:
I do recall making a case that B-21's size may afford more airfields from which it may operate. Has anyone stated that the overall smaller size of the B-21 may have been a design factor specifically because of its RCS? I don't recall either way.
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I haven't read anything concerning the choice of size of the B-21, but I suspect it was driven by the powerplant. Unlike most US aircraft programs, it appears B-21 did not use/require new engine development, instead using something relatively off the shelf (rumored to be PW9000/militarized PW1000 geared turbofan). I read somewhere that everything in the B-21 was TRL6 or better, which means the engine would have to be a pre developed item more or less. So I think the output of the chosen engine, combined somewhat with the desired range (noted as a very high priority requirement for the LRS-B program) determined the size and weight of the aircraft.
 
NeilChapman said:
I do recall making a case that B-21's size may afford more airfields from which it may operate. Has anyone stated that the overall smaller size of the B-21 may have been a design factor specifically because of its RCS? I don't recall either way.
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RCS is largely unrelated to size and larger is better in some respects (e.g. against low frequency radars).
 
NeilChapman said:
I do recall making a case that B-21's size may afford more airfields from which it may operate. Has anyone stated that the overall smaller size of the B-21 may have been a design factor specifically because of its RCS? I don't recall either way.
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Right now my theory is that NG switch from 4 engine into 2 engine config which reduce fuel and space requirements, which at the end drive the cost down.
 
Hanz2k said:
Right now my theory is that NG switch from 4 engine into 2 engine config which reduce fuel and space requirements, which at the end drive the cost down.
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If the engine is indeed something related to the PW1000 family, then it also has a much larger bypass and diameter than traditional fighter type engines like the F118 (and likely means the B-21 has rather huge fuel efficiency in comparison to the B-2). That probably drove the engine size/arrangement to be a twin rather than a 4, and the output of those two engines drove MTOW. My personal guess.
 
Josh_TN said:
I haven't read anything concerning the choice of size of the B-21, but I suspect it was driven by the powerplant. Unlike most US aircraft programs, it appears B-21 did not use/require new engine development, instead using something relatively off the shelf (rumored to be PW9000/militarized PW1000 geared turbofan). I read somewhere that everything in the B-21 was TRL6 or better, which means the engine would have to be a pre developed item more or less. So I think the output of the chosen engine, combined somewhat with the desired range (noted as a very high priority requirement for the LRS-B program) determined the size and weight of the aircraft.
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I'd read somewhere that the B-21 was using F135s without afterburners, though that would be horribly inefficient. A couple of high bypass turbofans would be so much better for the job.
 
Josh_TN said:
If the engine is indeed something related to the PW1000 family, then it also has a much larger bypass and diameter than traditional fighter type engines like the F118 (and likely means the B-21 has rather huge fuel efficiency in comparison to the B-2). That probably drove the engine size/arrangement to be a twin rather than a 4, and the output of those two engines drove MTOW. My personal guess.
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MTOW was drive by the mission requirements.
 
Scott Kenny said:
I'd read somewhere that the B-21 was using F135s without afterburners, though that would be horribly inefficient. A couple of high bypass turbofans would be so much better for the job.
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Eh, you might be surprised what efficiency looks like at high-altitudes with higher bypass ratios. I wouldn't be stunned if it has a bigger fan on a F135-core, but I would still be surprised (if it is in fact based on a F135).
 
_Del_ said:
Eh, you might be surprised what efficiency looks like at high-altitudes with higher bypass ratios. I wouldn't be stunned if it has a bigger fan on a F135-core, but I would still be surprised (if it is in fact based on a F135).
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Well, as @F119Doctor explained to me, the typical Supercruise engine means a relatively high mass flow core with a low(er) Overall Pressure Ratio than works well for subsonic cruise. Subsonic cruise wants a relatively small core with a high OPR, driving a larger fan.
 
Scott Kenny said:
Well, as @F119Doctor explained to me, the typical Supercruise engine means a relatively high mass flow core with a low(er) Overall Pressure Ratio than works well for subsonic cruise. Subsonic cruise wants a relatively small core with a high OPR, driving a larger fan.
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Generally sound, but like most things is always more complicated.

You can get x-amount of thrust by moving a lot of air relatively slowly, or smaller amounts of air more quickly. As speed approaches exhaust velocity, you will lose efficiency/thrust. That is one-reason why high-speed favours moving small amounts of air more quickly (low bpr or turbojet) over the generally more efficient propeller of high BPR. You also have drag comparisons for the large fans or propellers which increase with the square of speed which discourages large fans for supersonic speeds.

Best cruise altitude however is going to increase with lower bypass ratio.

Why do you imagine the subsonic B-2 and latest U-2 use a derated F110 core? Much bigger fans for those applications or the same diameter as the supersonic F-14/15/16? It's harder to get mass flow and pressure at higher altitudes.

In this (B-21) case, too, the bigger fans are generally less resilient to adverse flow in the duct. Might be why there were veiled comments about discussions and competing requirements from signature and propulsion/aero teams regarding the inlets.

My guess would be nothing in the large bypass ratio in this application (high-altitude, subsonic cruise with serpentine ducts). But I've been wrong before. Maybe PW will surprise me.
 
Sundog said:
MTOW was drive by the mission requirements.
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IMO, only if the engines were designed around the mission requirements. If the program required an off the shelf tech buy, what was on the shelf drove MTOW. That is very atypical for a U.S. aircraft program but IMO it is more likely than not in this case.
 
Josh_TN said:
IMO, only if the engines were designed around the mission requirements. If the program required an off the shelf tech buy, what was on the shelf drove MTOW. That is very atypical for a U.S. aircraft program but IMO it is more likely than not in this case.
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Given the very short development timeline, I strongly doubt that the engines are totally new.

They might be something weird like the F-110-232(?), with the CFM56-7 HP core and the F118 fan, but those are all individually qualified parts that only needed the combination proven.
 
_Del_ said:
Generally sound, but like most things is always more complicated.

You can get x-amount of thrust by moving a lot of air relatively slowly, or smaller amounts of air more quickly. As speed approaches exhaust velocity, you will lose efficiency/thrust. That is one-reason why high-speed favours moving small amounts of air more quickly (low bpr or turbojet) over the generally more efficient propeller of high BPR. You also have drag comparisons for the large fans or propellers which increase with the square of speed which discourages large fans for supersonic speeds.

Best cruise altitude however is going to increase with lower bypass ratio.

Why do you imagine the subsonic B-2 and latest U-2 use a derated F110 core? Much bigger fans for those applications or the same diameter as the supersonic F-14/15/16? It's harder to get mass flow and pressure at higher altitudes.

In this (B-21) case, too, the bigger fans are generally less resilient to adverse flow in the duct. Might be why there were veiled comments about discussions and competing requirements from signature and propulsion/aero teams regarding the inlets.

My guess would be nothing in the large bypass ratio in this application (high-altitude, subsonic cruise with serpentine ducts). But I've been wrong before. Maybe PW will surprise me.
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The Bill Sweetman article actually describes it as a PW9000 engine with a “medium bypass” of 4:1, which seems like an oddly specific guess for open source. Perhaps “high bypass” is an incorrect description, but I suspect it is something higher bypass than a stock unaugmented fighter engine.
 
Josh_TN said:
The Bill Sweetman article actually describes it as a PW9000 engine with a “medium bypass” of 4:1, which seems like an oddly specific guess for open source. Perhaps “high bypass” is an incorrect description, but I suspect it is something higher bypass than a stock unaugmented fighter engine.
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Few fighter engines even hit 1:1 bypass ratios... F414s are only 0.25:1, for example!
 
Josh_TN said:
The Bill Sweetman article actually describes it as a PW9000 engine with a “medium bypass” of 4:1, which seems like an oddly specific guess for open source.
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I say this with all respect to Sweetman, who I am sure has more credible people whispering in his ear than me (who has none), it would still surprise me.
Just eyeballing the engine area, the influx and what little we have seen of the efflux, makes me skeptical. The mission spent at high altitudes, more so.
4:1 based on a F135 core would make a massive fan/thrust. Rough math gives a 30" core. You're looking at a 10 foot diameter fan at 4:1. Something around a PW1000 core was also suggested once upon a time, but 4:1 there leaves the engines very, very compact and not, imo enough thrust.
 
_Del_ said:
I say this with all respect to Sweetman, who I am sure has more credible people whispering in his ear than me (who has none), it would still surprise me.
Just eyeballing the engine area, the influx and what little we have seen of the efflux, makes me skeptical. The mission spent at high altitudes, more so.
4:1 based on a F135 core would make a massive fan/thrust. Rough math gives a 30" core. You're looking at a 10 foot diameter fan at 4:1. Something around a PW1000 core was also suggested once upon a time, but 4:1 there leaves the engines very, very compact and not, imo enough thrust.
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As of 2010, there were reports that PW9000 was a gearless derivative of the PW1000G. Two sizes were mooted -- one at 15,000lbf and one at 30,000lbf. That second one was proposed as a fighter replacement engine saving 18% in fuel compared to existing F100 engines. That seems like a reasonably close fit to Sweetman's PW9000 (27k lbf) in the article. Probably not even 4:1 bypass but still way more efficient than the F118.
 
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Remember that the PW1000G already has a high speed low compressor rotor behind the fan and gearbox. I can envision that low compressor being replaced with something like the first two stages of the F135 fan to lower the fan pressure ratio, possibly a cropped 3rd third stage as a core flow supercharger to keep the OPR in the 40:1 range, with a bypass ratio around 2. This would keep most of the PW1000G architecture in place with the proven F135 front end structure, aero, and signature.

I don’t have any inside knowledge, just extrapolating from the 2010 AvWeek article on the proposed PW9000.
 
I think that the geared F-135 make more sense given the probable need for a cold flow for the effectors.

Personally, I see some in front of the outboard (split?) ailerons and on the trailing edge of the inboard elevons.

You are not gonna route hot exhausts along the wing for that on a stealth airframe.
 
Josh_TN said:
Would that make the central bomb bay significantly longer than the B-2's?
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It would not surprise me. B-21 is supposed to carry LRSO, which we don't know much about but seems likely to be ALCM-sized. If it was smaller, you would think the B-2 would also get it, but that isn't planned.
 
TomS said:
It would not surprise me. B-21 is supposed to carry LRSO, which we don't know much about but seems likely to be ALCM-sized. If it was smaller, you would think the B-2 would also get it, but that isn't planned.
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Is the B-2 bay too small for ALCM? I know it was never integrated, but I thought the B-2 used the same CSRL as the B-52.
 
No. B-2 has Boeing built lightweight (composite) AARLs (RLAs) designed specifically for ATB.
B-2 AARL length is 6,72 m so I hardly doubt that weapons bays are 7.5 m long (if we are talking of _weapons bays_, not about doors with chevrons).
My calculations using best factory drawings available give me something close to 7,0 m
 
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flateric said:
No. B-2 has Boeing built lightweight (composite) AARLs (RLAs) designed specifically for ATB.
B-2 AARL length is 6,72 m so I hardly doubt that weapons bays are 7.5 m long (if we are talking of _weapons bays_, not about doors with chevrons).
My calculations using best factory drawings available give me something close to 7,0 m
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Thanks. I didn’t realize every US bomber used a different rotary launcher.
 
Josh_TN said:
Thanks. I didn’t realize every US bomber used a different rotary launcher.
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I don't know if that's true.

I actually had a big brain fart above -- the B-52 and B-2 do in fact use the same CSRL. They may have unique versions but there must be enough in common (get it?) that contracts like this make sense.

Overhaul and Repair of B-2/B-52 Common Strategic Rotary Launcher (CSRL)

Federal Contract Opportunity for Overhaul and Repair of B-2/B-52 Common Strategic Rotary Launcher (CSRL). Posted Oct 2, 2013. Due Nov 18, 2013. AFLCMC Tinker AFB (DOD - USAF - AFMC - AFLCMC)
govtribe.com
 
paralay said:
weapons bay
B-2 7.5 m / 24.5 ft x 4.8 m / 16.0 ft
B-21 8.7 m / 28.5 ft x 2.44 m / 8.0 ft
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Sweep angle is 35, not 40. Distortion due to most spotters position play tricks. Hence while wingspan is 48 m, lenght is less, about 20-21 m.
 
TomS said:
I don't know if that's true.

I actually had a big brain fart above -- the B-52 and B-2 do in fact use the same CSRL. They may have unique versions but there must be enough in common (get it?) that contracts like this make sense.

Overhaul and Repair of B-2/B-52 Common Strategic Rotary Launcher (CSRL)

Federal Contract Opportunity for Overhaul and Repair of B-2/B-52 Common Strategic Rotary Launcher (CSRL). Posted Oct 2, 2013. Due Nov 18, 2013. AFLCMC Tinker AFB (DOD - USAF - AFMC - AFLCMC)
govtribe.com
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No, they are VERY not the same.
 
B-2 is using RLA. Not using/never used CSRL/CRL.
 

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