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ZaphodHarkonnen
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Re: Northrop Grumman B-21 Raider Production And Delivery Thread

Wed Feb 05, 2020 1:09 am

texl1649 wrote:
Exactly, a mini B-2. Single truck MLG’s, this looks more akin to an FB-111 size delivery platform than a B-1, let alone a B-52. Presumably it is to be vastly more easily maintained than the B-2 parent design, or B-1’s shown in the background.


Oh, totally. Especially if they were able to make good reuse of the hardware and avionics built for the F-35. The biggest difference then becomes the basic airframe and other larger components.
 
DigitalSea
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Re: Northrop Grumman B-21 Raider Production And Delivery Thread

Wed Feb 05, 2020 5:27 pm

Maybe the USAF/USG did it right this time, field something not incredibly exotic that can utilize existing technology to achieve high production numbers without the high price tag.
 
744SPX
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Re: Northrop Grumman B-21 Raider Production And Delivery Thread

Wed Feb 05, 2020 6:08 pm

Sizing it around 2 F135's (if that is the final config) is a good call.
 
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Slug71
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Re: Northrop Grumman B-21 Raider Production And Delivery Thread

Thu Feb 06, 2020 1:32 am

texl1649 wrote:
Exactly, a mini B-2. Single truck MLG’s, this looks more akin to an FB-111 size delivery platform than a B-1, let alone a B-52. Presumably it is to be vastly more easily maintained than the B-2 parent design, or B-1’s shown in the background.


A larger frame is probably not needed in today's battlefield. I think the Bomber role has diminished over the years with advancements of missiles. Ships and Subs can now deliver a bulk of the payload.
 
MohawkWeekend
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Re: Northrop Grumman B-21 Raider Production And Delivery Thread

Thu Feb 06, 2020 1:55 am

Silly thought I guess but I read recently that the USN is working on fitting more air to surface weapons to the P-8. Might an even more adapted version of her be the bombtruck the Aussie's could use instead of a B-21. And the USAF could use her as a with a much cheaper replacement of the B-52? Imagine a rotary cruise missile launcher and a few extra wing pylons. Silly thought.
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    texl1649
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Thu Feb 06, 2020 2:36 am

    Slug71 wrote:
    texl1649 wrote:
    Exactly, a mini B-2. Single truck MLG’s, this looks more akin to an FB-111 size delivery platform than a B-1, let alone a B-52. Presumably it is to be vastly more easily maintained than the B-2 parent design, or B-1’s shown in the background.


    A larger frame is probably not needed in today's battlefield. I think the Bomber role has diminished over the years with advancements of missiles. Ships and Subs can now deliver a bulk of the payload.


    I agree it makes some sense. The FB-111 was, after all (in perhaps a bit of irony) a supplemental type developed due to USAF concerns about B-52’s wearing out (cracks/fatigue)...and was retired when the B-1B made it un-needed (again, the irony is palpable). A 120,000 lb MTOW and 35K lb ordinance payload is probably, if I am guessing right, in the range of what this aircraft could deliver based on the renderings (that’s what the FB-111A spec’d out at).

    I would also agree that it makes sense to size around something similar/based on two F135’s, and just pray it isn’t as obnoxiously underpowered as the T-30’s (not that this can go Mach 2 anyway). An F135, if modified without an afterburner and to fly subsonic, might be quite efficient, but I’d be curious if folks like Revelation here might opine as to modifications that might make that engine work better for this, and other possible future subsonic non-tactical operations. Using ‘standard’ fighter engines on long bomber missions isn’t really ideal; the B-2 has to refuel every 6 hours.
     
    DigitalSea
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Thu Feb 06, 2020 5:18 am

    texl1649 wrote:
    Using ‘standard’ fighter engines on long bomber missions isn’t really ideal; the B-2 has to refuel every 6 hours.


    No kidding? Wow.
     
    aumaverick
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Thu Feb 06, 2020 2:16 pm

    texl1649 wrote:
    Slug71 wrote:
    texl1649 wrote:
    Exactly, a mini B-2. Single truck MLG’s, this looks more akin to an FB-111 size delivery platform than a B-1, let alone a B-52. Presumably it is to be vastly more easily maintained than the B-2 parent design, or B-1’s shown in the background.


    A larger frame is probably not needed in today's battlefield. I think the Bomber role has diminished over the years with advancements of missiles. Ships and Subs can now deliver a bulk of the payload.


    I agree it makes some sense. The FB-111 was, after all (in perhaps a bit of irony) a supplemental type developed due to USAF concerns about B-52’s wearing out (cracks/fatigue)...and was retired when the B-1B made it un-needed (again, the irony is palpable). A 120,000 lb MTOW and 35K lb ordinance payload is probably, if I am guessing right, in the range of what this aircraft could deliver based on the renderings (that’s what the FB-111A spec’d out at).

    I would also agree that it makes sense to size around something similar/based on two F135’s, and just pray it isn’t as obnoxiously underpowered as the T-30’s (not that this can go Mach 2 anyway). An F135, if modified without an afterburner and to fly subsonic, might be quite efficient, but I’d be curious if folks like Revelation here might opine as to modifications that might make that engine work better for this, and other possible future subsonic non-tactical operations. Using ‘standard’ fighter engines on long bomber missions isn’t really ideal; the B-2 has to refuel every 6 hours.


    I think you hit the nail on the head. With the F-15E/F-35 payloads specked at 23,000 and 18,000 lbs respectively, and the B-2 at 40,000 lbs, there is a sweet spot gap. The B-21 can fill the payload gap of the F-35 and provide a contested environment penetration platform via stealth the F-15E lacks. The B-2 is overkill a lot of times, and was always meant to be a nuclear deterrent. The B-52 is overkill, and the B-1s are just plain worn out. Meanwhile, the F-15Es lack the legs or stealth for some missions, and the F-35 was never meant to be a medium sized bomber. This is where I hope the B-21 fills that sweet spot of capability.
    I'm just here so I won't get fined. - Marshawn Lynch
     
    LightningZ71
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Thu Feb 06, 2020 8:22 pm

    I would imagine that the only substantive changes that could be made to the F-135 for use in the B-21 would be the removal of the Afterburner section and the associated plumbing changes that go with that. It might not be too crazy to suggest that the could keep the majority of the HPT and LPT sections, as well as the "hot" section while using a larger fan with a larger bypass, keeping the more expensive portions of the engine the same, but making it more efficient in other areas where the cost is lower, but, I would suspect that that's too much of a change for them to keep development costs under control. I do suspect that, due to its smaller size, and generally more efficient engines, that it should get better range than the B-2 between required refills if it keeps the same fuel fraction.
     
    Ozair
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Thu Feb 06, 2020 9:17 pm

    LightningZ71 wrote:
    I would imagine that the only substantive changes that could be made to the F-135 for use in the B-21 would be the removal of the Afterburner section and the associated plumbing changes that go with that. It might not be too crazy to suggest that the could keep the majority of the HPT and LPT sections, as well as the "hot" section while using a larger fan with a larger bypass, keeping the more expensive portions of the engine the same, but making it more efficient in other areas where the cost is lower, but, I would suspect that that's too much of a change for them to keep development costs under control. I do suspect that, due to its smaller size, and generally more efficient engines, that it should get better range than the B-2 between required refills if it keeps the same fuel fraction.

    Given the B-21 has long range operations in the pacific theatre as its primary mission I expect it will surprise on the distances the jet will operate without refuelling. The advantage the B-21 has is that the F135 will continue to go through significant upgrade. P&W have already proposed the Growth Option One and Two packages which both bring increased thrust and reduced fuel burn.

    Depending on what happens with the AETP the B-21 could also be a candidate for conversion to that engine which would increase range again, potentially by as much as 25% beyond current projections. Noting as well the B-21 is considered an excellent candidate for DEW and therefore an efficient engine that can also rapidly recharge those weapons would be advantageous.
     
    744SPX
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Fri Feb 07, 2020 12:15 am

    Given that the B-21 is "2/3" size of B-2, putting a larger fan on the F-135 would probably be overkill as it already has enough thrust (unless they want a better thrust to weight ratio than the B-2) 2 F-135's dry is 56K lbs thrust and the 4 F-118's are 68k, so it would appear the B-21 will already have a superior thrust to weight ratio assuming it is 2/3 the weight...
     
    SuperiorPilotMe
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Fri Feb 07, 2020 1:09 am

    744SPX wrote:
    Given that the B-21 is "2/3" size of B-2, putting a larger fan on the F-135 would probably be overkill as it already has enough thrust (unless they want a better thrust to weight ratio than the B-2) 2 F-135's dry is 56K lbs thrust and the 4 F-118's are 68k, so it would appear the B-21 will already have a superior thrust to weight ratio assuming it is 2/3 the weight...


    LightningZ71’s post had me thinking. The F135 is not quite, but close enough to 2 engines in one as far as (afterburner) thrust is concerned. I wonder if you could use one for a strictly unmanned, “mini-me” version of the B-21.
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    Ozair
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Fri Feb 07, 2020 2:25 am

    SuperiorPilotMe wrote:
    LightningZ71’s post had me thinking. The F135 is not quite, but close enough to 2 engines in one as far as (afterburner) thrust is concerned. I wonder if you could use one for a strictly unmanned, “mini-me” version of the B-21.


    No reason they couldn’t and there are plenty of single engine UCAVs already, additionally the B-21 has been suggested all along as an optionally unmanned platform. The X-47b operated with an F100 off a carrier deck so you are in essence suggesting an upsize to that platform. Do you need the thrust of F135 though? Thrust would be dependent on what you perceive as the intent of the development, a loyal wingman to manned B-21s, additional unmanned assets to make up for not enough bombers, assume conventional weapons only? If you drop the payload to say 10k lbs in two bays (enough to take a 5k GBU-28 or similar sized weapon) and keep the same basic planform you should be able to maintain a decent range, would need to have pacific theater in mind, in a high stealth package.

    How about operating a fleet of “B-212s” associated with a mothership “KB-21” tanker and (USAF turn off now) use hose and drogue with the software developed for the X-47b and MQ-25?
     
    LightningZ71
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Fri Feb 07, 2020 1:18 pm

    In reference to using a larger fan section on the F-135 as it is installed in the B-21, I was suggesting it more as an efficiency measure and less as a thrust production issue. The F-135, for the B-21, is plenty powerful. However, it is optimized for its use in a multi-role supersonic fighter as it currently exists. Given that it is expected that the B-21 will be subsonic, it makes sense to use a higher bypass ratio for fuel efficiency gains. The caveat here is that it will be costly to have such a significant difference on the F-135 in the B-21 from a development, purchasing and maintenance perspective, and, it will consume more volume inside of the already restricted interior volume that the B-21 will have to work with.
     
    texl1649
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Fri Feb 07, 2020 5:57 pm

    It’s intriguing to consider and hopefully USAF has some of this in the ‘big picture’ development plans, Ozair. I do think the prospects of that stuff (remote refueling/drone versions) being part of the development programs though is pretty darn low. Procurement has been too costly/delayed on too many platforms for the USAF to actively encourage that, at this point.

    I do think hose/drogue refueling is the only thing that can make sense once a drone tanker is considered for actual development.

    Lightningz71 I agree it would be an issue it’s just that running two F135’s for 10-20 hour subsonic 30K foot missions seems a bit...inefficient. We don’t need this thing to compete with an A321NEO/779 in fuel efficiency by any means, per pound of cargo per mile, but it’s always good to see a rational amount of fuel burn (and operational cost when incorporating tankers) in real mission planning/training.
     
    RJMAZ
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Thu Feb 20, 2020 1:36 am

    texl1649 wrote:
    Lightningz71 I agree it would be an issue it’s just that running two F135’s for 10-20 hour subsonic 30K foot missions seems a bit...inefficient.

    I think it will use a pair of GE passport engines. Most likely uprated slightly from the standard 84kn to about 90kn. That would be extremely efficient.

    The B-2 has four 77kn for a total of 308kn. Two 90kn passport engines would have 59% of the thrust. So the aircraft weights would be about 60% of the current B-2.

    OEW: 46t
    MTOW: 102t
    Fuel capacity: 45t
    Internal bomb capacity: 11t

    This seems perfect and it would not surprise me if it can still go close to the B-2 range of 6900nm.

    The GE passport engines are the same weight and slightly shorter than the F-135. The fan diameter is only 6inch larger.

    The bypass ratio is 5.6 vs 0.57 that would result in a 20-30% range boost right there.
     
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    keesje
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Sun Mar 01, 2020 10:04 am

    The most likely adversaries would be the big phazatron, bars radars of Su-30 like interceptors and SAMs like S-400 because those are widely exported. Putin keeps refusing them to Iran.
    "Never mistake motion for action." Ernest Hemingway
     
    Ozair
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Tue Mar 10, 2020 2:52 am

    The USAF is close to selecting a first base for the B-21, both of the options being existing B-1 bases which makes sense given the B-21 will replace the B-1 initially before then replacing the B-2.

    Anyone have a preference? Ellsworth is less populated so perhaps a better location for an initial bed down but as a long term Training and Main Operating Base perhaps Dyess is a better location for familes and long term posting?

    Dyess or Ellsworth to Get First B-21s

    The Air Force will soon start studies assessing the environmental impact of basing the B-21 Raider at Dyess Air Force Base, Texas, and Ellsworth Air Force Base, S.D., the service announced on March 6. One of the two locations will be the first base to host the bomber.

    Typical environmental assessments consider the impact of operations, noise, and pollution from a weapon system on the local area’s population, agricultural enterprises, water quality, transportation, cultural resources, airspace, and wildlife.

    The two bases were chosen because they already operate B-1B bombers, which means basing the B-21s in either location will “minimize mission impact, maximize facility re-use, minimize cost, and reduce overhead, as well as leverage the strengths of each base to optimize the B-21 beddown strategy,” according to the Air Force announcement. Public hearings will be held in nearby locations through April.

    The announcement, published in the Federal Register, said the environmental impact analysis will support the choice of “Main Operating Base 1” for the B-21, which will include B-21 operational squadrons, a B-21 formal training unit, and a weapons generation facility. The announcement noted the B-21 will be capable of “penetrating and surviving into advanced air defense environments,” delivering both conventional and nuclear weapons. Future beddown locations will be chosen after MOB 1 is selected.

    ...

    https://www.airforcemag.com/dyess-or-el ... rst-b-21s/
     
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    LyleLanley
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Tue Mar 10, 2020 4:26 am

    Ozair wrote:
    Anyone have a preference


    Having been to both I’ll take neither if possible, but Ellsworth wins by a mile if it’s a “fish or steak” choice. With low levels out of the picture, even more so. Winters in South Dakota > year-round Texas, and families are generally happier up there, too.
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    DigitalSea
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Tue Mar 10, 2020 5:50 am

    Ozair wrote:
    The USAF is close to selecting a first base for the B-21, both of the options being existing B-1 bases which makes sense given the B-21 will replace the B-1 initially before then replacing the B-2.

    Anyone have a preference?


    Hickam, it's time.
     
    aumaverick
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Tue Mar 10, 2020 1:10 pm

    Ozair wrote:
    The USAF is close to selecting a first base for the B-21, both of the options being existing B-1 bases which makes sense given the B-21 will replace the B-1 initially before then replacing the B-2.

    Anyone have a preference? Ellsworth is less populated so perhaps a better location for an initial bed down but as a long term Training and Main Operating Base perhaps Dyess is a better location for familes and long term posting?

    Dyess or Ellsworth to Get First B-21s

    The Air Force will soon start studies assessing the environmental impact of basing the B-21 Raider at Dyess Air Force Base, Texas, and Ellsworth Air Force Base, S.D., the service announced on March 6. One of the two locations will be the first base to host the bomber.

    Typical environmental assessments consider the impact of operations, noise, and pollution from a weapon system on the local area’s population, agricultural enterprises, water quality, transportation, cultural resources, airspace, and wildlife.

    The two bases were chosen because they already operate B-1B bombers, which means basing the B-21s in either location will “minimize mission impact, maximize facility re-use, minimize cost, and reduce overhead, as well as leverage the strengths of each base to optimize the B-21 beddown strategy,” according to the Air Force announcement. Public hearings will be held in nearby locations through April.

    The announcement, published in the Federal Register, said the environmental impact analysis will support the choice of “Main Operating Base 1” for the B-21, which will include B-21 operational squadrons, a B-21 formal training unit, and a weapons generation facility. The announcement noted the B-21 will be capable of “penetrating and surviving into advanced air defense environments,” delivering both conventional and nuclear weapons. Future beddown locations will be chosen after MOB 1 is selected.

    ...

    https://www.airforcemag.com/dyess-or-el ... rst-b-21s/


    My guess is it'll be Ellsworth. The Bone is the only true flying tenant on base, it is more remote, and has increased bombing range access. It could very easily see a transition and consolidation of the B-1s to Dyess with the ramp up of the B-21 while the B-1s are phased out. Onboarding and basing of the Raider at Ellsworth first and coupled with a transition of a squadron of B-1s to Dyess, and then, initial onboarding of Raiders at Dyess coupled with a withdrawl of a B-1 squadron.
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    texl1649
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Tue Mar 10, 2020 3:34 pm

    Dyess would be my preference, just because I live in Texas. I also believe there are a lot more B-1’s there vs. Ellsworth today, but could be mistaken.
     
    aumaverick
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Tue Mar 10, 2020 5:48 pm

    texl1649 wrote:
    Dyess would be my preference, just because I live in Texas. I also believe there are a lot more B-1’s there vs. Ellsworth today, but could be mistaken.


    Dyess is home to the B-1 school house, which is another reason for it to remain focused on the Bone while Ellsworth spools up the Raiders first.
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    zululima
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Sat Apr 04, 2020 5:44 pm

    A few details about operating altitude and engines:

    http://aviationweek.com/defense-space/aircraft-propulsion/new-usaf-materials-hint-high-altitude-role-b-21

    “The B-21 is not expected to use low altitude training routes,” the Air Force poster says.

    The B-2 was originally conceived as a high-altitude bomber, but a last-minute requirements change during the development phase forced Northrop Grumman to redesign the bomber for a low-altitude mission. As a result, the trailing edge was transformed from a simple W-shape to the sawtooth design seen today. The B-2, like the preceding B-52 and B-1B fleets, need low-altitude training routes.

    The renderings of the B-21 released by the Air Force so far reveal a trailing edge that resembles the original, high-altitude design for the B-2. The Air Force has never confirmed operational details about the future stealth bomber.


    “The B-21 engine noise is expected to be quieter than the B-1B and about the same or quieter than the B-2,” the poster says.

    Previously, the only detail released by the Air Force about the B-21’s engines is that Pratt & Whitney is named as one of seven of Northrop’s suppliers. The poster data appears to confirm expectations that the B-21 would use a non-afterburning engine


    So, RJMAZ's suggestions of uprated GE Passport engines is wrong, as expected.

    I couldn't get any of the linked documents as the B21EIS website wasn't responding.
    I didn't get a 'Harumph' outta that guy!
     
    744SPX
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Sun Apr 05, 2020 4:07 am

    The noise levels, altitude requirement and manufacturer would certainly seem to suggest a non-afterburning F135 variant...

    This article has a lot of good info on the altitude requirement as relating to the B-2

    https://www.thedrive.com/the-war-zone/1 ... pabilities
     
    Ozair
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Sun Apr 05, 2020 9:21 am

    zululima wrote:

    So, RJMAZ's suggestions of uprated GE Passport engines is wrong, as expected.

    I couldn't get any of the linked documents as the B21EIS website wasn't responding.

    I don't think RJMAZ was suggesting that the B-21 would use the GE Passport engine, just comparing the option. We have known for quite a few years that P&W had been awarded the contract and was the engine provider for the B-21. I think the general consesus is it will be a F135 derivative but I can't remember if that has been confirmed yet.
     
    Ozair
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Thu Jul 02, 2020 10:48 pm

    Another sign that the B-21 appears to be moving both to schedule and likely has few development issues.

    House slides money into B-21 bomber procurement account

    An amendment to the House version of the fiscal 2021 defense policy bill would move some funding for the secretive B-21 bomber program from its research and development account to procurement, a sign that production activities could be picking up.

    The amendment transfers $20 million into “Long Range Strike Bomber advanced procurement” and would “allow the program to begin some procurement activities ahead of schedule,” according to the legislation.

    ...

    https://www.defensenews.com/air/2020/07 ... t-account/
     
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    phatalbert
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Sat Sep 26, 2020 3:08 am

    “ Because Whiteman is the only current location with a B-2 mission, we must remain operational until sufficient B-21 aircraft are at Ellsworth AFB. Whiteman does not have the space or existing facilities necessary to accommodate B-21 training and operational missions and B-2 missions simultaneously. That said, we're excited about the Air Force's decision to eventually house the B-21 Raider here! This means Team Whiteman will continue to support the nuclear triad, as the B-2 has done for the past 30 years! #B2flyingsince89” from Whiteman AFB Facebook post.
    **Isaac**
     
    texl1649
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Sat Sep 26, 2020 4:21 pm

    Great news, #128. I was hoping the USAF wouldn’t hold onto some sort of notion that the exorbitantly expensive to operate B-2 would be kept just for a niche capability enhancement vs. a large B-21 fleet.
     
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    kitplane01
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Fri Oct 09, 2020 12:18 am

    I understand the B-21 is going to use the F-135 engine. But if the goal is subsonic fuel efficiency, then the F-135 has a painfully low bypass ratio producing sub-optimal fuel efficiency, and the world is filled with civilian engines who's exact goal is subsonic fuel efficiency (and they cost must less).

    The only reason I can think of is that the F-135 has a much smaller inlet (because low bypass ratio) which helps with stealth.
     
    aumaverick
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Fri Oct 09, 2020 12:00 pm

    kitplane01 wrote:
    I understand the B-21 is going to use the F-135 engine. But if the goal is subsonic fuel efficiency, then the F-135 has a painfully low bypass ratio producing sub-optimal fuel efficiency, and the world is filled with civilian engines who's exact goal is subsonic fuel efficiency (and they cost must less).

    The only reason I can think of is that the F-135 has a much smaller inlet (because low bypass ratio) which helps with stealth.


    Kit, you've probably hit on one of the main considerations: stealth. However, just because the same engine is being used does not preclude it from being optimized for the aircraft. I would expect the F135 used on the F-35 to be modified to meet the design requirements of the larger aircraft the B-21 is expected to be compared to its smaller stealthy cousin. Additionally, while it may be noted to use the F135 engine, it may only be the main core, while other aspects are modified to create a complete sub variant of the engine.
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    744SPX
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Fri Oct 09, 2020 3:01 pm

    Well, the F-118 engines in the B-2 are basically F-110's with an improved and just slightly larger (~1 inch, if that) fan. The F-135 already has a higher bypass ratio than the F-110 so the low bypass ratio may not be an issue at all.
     
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Sat Oct 10, 2020 2:10 am

    Context: Why doesn't the B-21 use a civilian engine....

    744SPX wrote:
    Well, the F-118 engines in the B-2 are basically F-110's with an improved and just slightly larger (~1 inch, if that) fan. The F-135 already has a higher bypass ratio than the F-110 so the low bypass ratio may not be an issue at all.


    Bypass ratio of an F-135: 0.57:1
    Bypass ratio of a RR Pearl 700: 6.5:1

    It's a huge difference.

    The Pearl is optimized for the Gulfstream 700, 0.9 Mach at 50,000 ft. That's as fast and as high as a B-21 will fly.
    The F-135 is optimized for supersonic, which the B-21 will not do.

    And if you don't like the RR Pearl, pick a different one. To find a bypass ratio of 0.57:1 .. look in a history book. The Boeing 727 had a higher bypass ratio. Not the 737 but the one we don't use anymore.
     
    ZaphodHarkonnen
    Posts: 1082
    Joined: Sun Jan 04, 2015 10:20 am

    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Sat Oct 10, 2020 6:35 am

    I expect the core reason is that it's good enough and keeps development/maintenance costs down as it shares almost total commonality with the F-35 engines. It also means any future advancements for the engine with F-35 use can be dropped into the B-21. It may not be the 'perfect' engine. But good enough is good enough.
     
    RJMAZ
    Posts: 2284
    Joined: Sat Jul 09, 2016 2:54 am

    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Sat Oct 10, 2020 11:46 pm

    I found out the answer to this question a few months ago.

    The only reason is that a higher bypass engines moves a larger volume of air at a slower speed to produce the same thrust. So the already subtantional intake and exhaust ducting inside of the B-21 would have to be made larger for a higher bypass engine. The extra volume that this ducting takes up inside the fuselage could simply be used for extra fuel capacity combined with a more compact low bypass engine.

    In civilian aircraft where the engine is outside of the body there is little extra intake and exhaust weight with the larger diameter high bypass engines. It does not have to sacrifice fuel capacity like a stealth design.

    There would be a sweet spot where a higher bypass ratio would provide additional performance to the B-21 and the added interior volume taken up is minimal. At Mach 0.9 and 50,000ft the efficiency gains of high bypass engines also reduces. I expect between 1:1 and 2:1 ratio would be ideal.

    A modified F135 engine would do nicely.
     
    Ozair
    Posts: 5582
    Joined: Mon Jan 31, 2005 8:38 am

    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Sun Oct 11, 2020 11:33 am

    RJMAZ wrote:
    I found out the answer to this question a few months ago.

    The only reason is that a higher bypass engines moves a larger volume of air at a slower speed to produce the same thrust. So the already subtantional intake and exhaust ducting inside of the B-21 would have to be made larger for a higher bypass engine. The extra volume that this ducting takes up inside the fuselage could simply be used for extra fuel capacity combined with a more compact low bypass engine.

    In civilian aircraft where the engine is outside of the body there is little extra intake and exhaust weight with the larger diameter high bypass engines. It does not have to sacrifice fuel capacity like a stealth design.

    There would be a sweet spot where a higher bypass ratio would provide additional performance to the B-21 and the added interior volume taken up is minimal. At Mach 0.9 and 50,000ft the efficiency gains of high bypass engines also reduces. I expect between 1:1 and 2:1 ratio would be ideal.

    A modified F135 engine would do nicely.

    Noting as well an AETP F135 sized engine will be coming along. I would hope the B-21 intakes were designed to take advantage of that engine technology and thereby achieve the significant gains it will provide.
     
    texl1649
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    Joined: Thu Aug 02, 2007 5:38 am

    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Mon Jan 04, 2021 11:18 pm

    Relative to B-21 delivery goals/timeline for B-1B retirement needs;

    https://www.airforcemag.com/b-1s-can-ma ... g-the-way/

    The Air Force expects to have enough resources—money, spare parts, and maintainers—to keep the B-1B bomber flying safely at least until it can be replaced by the B-21, service officials said, now that Congress will let USAF retire 17 of the most problem-prone Lancers in the inventory. But the Air Force is well behind on a structural fatigue test meant to find life-limiting cracks and stress in B-1 airframes, meaning there could be some surprises ahead.

    Congress overrode President Donald J. Trump’s veto of the 2021 National Defense Authorization Act on Jan. 1, clearing the way for the Air Force to reduce the B-1 fleet from 62 aircraft to 45. The B-21 is expected to be delivered in sufficient numbers by 2031 to permit the rest of the B-1s to retire.

    Since September 2019, the Air Force has pushed to reduce the B-1 fleet in order to keep a smaller number of the bombers fully potent and ready for action. In recent years, lack of spare parts and a long list of structural and systematic gripes have driven the fleet’s mission capable numbers to as low as just six aircraft ready for combat.


    Some scary details including having to land a B-1 after the ejection seats failed.

    At the same time—around May 2018—a B-1’s ejection system failed during an inflight emergency. While the crew made a harrowing landing, the incident prompted yet another new wave of fleetwide B-1 inspections, Barnes said, further pressuring the maintainer force.

    “Since that time, we got the ejection system all fixed, and got that work off the field maintainers. We brought a lot of the repair work into the depot, …and then in 2019 … [we] stood up the dedicated repair line at Tinker …where we bring in aircraft for nothing but structural repairs. To my knowledge, it’s the only dedicated structural repair line in the Air Force,” Barnes said. Doing it that way allowed the Air Force to hire extra workers to do the surge repairs “and let the maintainers get back to their day-to-day job of launching aircraft and meeting mission needs.”

    Doing all that “significatly improved the availability of the fleet,” Barnes said. “It’s put the fleet in a very healthy position as we bring aircraft through depot, perform the structural repairs, and get a healthier aircraft back out to the field.” The fact that the aircraft are “healthier” also reduces the load of necessary inspections, allowing maintainers to focus on daily readiness.

    But some big repairs remain undone. A longeron replacement in the forward intermediate fuselage that will require substantial disassembly of the airplane will be an intensive process.

    “We are going to bring an aircraft into Boeing’s Palmdale, [Calif.], facility in April to perform a prototype of that repair,” Barnes said, “Where we will replace the forward intermediate fuselage, and we will repair the ‘shoulder’ longeron,” and this will be the prototype for a fleet-wide fix. The repair apparatus will be brought to the depot to be performed, “but that’s not going to happen until the ’23-’24 timeframe,” he said. “So, we’re still a few years away from where we have to be.”


    Getting the B-1’s retired/replaced by 2031 has to be a top priority.
     
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    LyleLanley
    Posts: 379
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    Re: Northrop Grumman B-21 Raider Production And Delivery Thread

    Tue Jan 05, 2021 2:33 am

    texl1649 wrote:
    Some scary details including having to land a B-1 after the ejection seats failed.


    Most definitely! Imagine getting to the end of the worst checklist imaginable for a flier, to the step that ends with 'EJECT ... D-RING PULL (ALL)' to then pause a few potatoes and say "uh oh".

    Very scary stuff!
    "I've sold monorails to Brockway, Ogdenville, and North Haverbrook, and, by gum, it put them on the map!"

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