Northrop Grumman B-21 Raider (LRS-B)

[VTOLicious]

I think two F-135 don't have the capacity to push something like the B-21 not enough trust for a heavy bomber.

I think you need read some entry-level aerospace courses to discuss the subject.

That typo might be illuminating. I'm sure they could get enough thrust to power a bomber like this on two engines. But do they have enough trust? I'm not sure they'd be happy with the military equivalent of an ETOPS rating for a bomber carrying nuclear weapons over long distances.

TomS, that's exactly my thought.

 

[Airplane]

Why not three engines, with the 3rd being the centerline? 4 F-135s would be overkill for something smaller than a B-2 with a smaller payload. 2, as someone stated there is the trust issue. 3 would make sense.

 

[TomS]

Why not three engines, with the 3rd being the centerline? 4 F-135s would be overkill for something smaller than a B-2 with a smaller payload. 2, as someone stated there is the trust issue. 3 would make sense.

The layout of three is complicated, especially with two inlets. Four engines with two inlets is easy.

 

[VTOLicious]

I wonder if the quantity, location and dimension of the payload bays will be the same as on the B2...what are the options?

The length of the centerbody is dominated by the weapons bay length. Most probably the weapon bay(s) will have the same dimensions as on the B-2 (same armament options required?). I think two bays in tandem wouldn't work for a flying wing smaller than the B-2. Hence the B-21 would have either a single bay or two side by side.

X67, thx for posting those pics. http://www.secretprojects.co.uk/forum/index.php/topic,25915.msg274757.html#msg274757

Btw, wouldn't the B-21 be required to carry a MOP?

BR Michael

 

[quellish]

I wonder if the quantity, location and dimension of the payload bays will be the same as on the B2...what are the options?

Weapons bay volume is a primary driver for the size of the aircraft. It would not be surprising to find a very different weapon bay configuration on LRS-B.

Btw, wouldn't the B-21 be required to carry a MOP?

The MOP is an interim weapon providing an interim capability. By the time the B-21 is fielded a newer, smaller, more capable weapon will be available. It is unlikely that MOP was a requirement for LRS-B for this an other reasons.

 

[marauder2048]

Btw, wouldn't the B-21 be required to carry a MOP?

The Next Generation Penetrator will probably be an outgrowth of HVPW.

https://www.flightglobal.com/news/articles/us-air-force-considering-new-2000lb-rocket-propelle-412565

Surely they would build the bays around rotary launchers for LRSO.

 

[flateric]

Now it's being called Hard Target Munition (HTM) if memory serves me well and it didn't change name again.

 

[quellish]

The Next Generation Penetrator will probably be an outgrowth of HVPW.

It was the other way around. The High Velocity Penetrating Weapon was an outgrowth of the Next Generation Penetrator program. HVPM was validated and is considered technically mature enough to move to EMD. HSSW is another program that is part of the hardened target munitions portfolio.

MOP was a quick reaction, interim weapon design. It was designed to be incredibly inefficient, using a large amount of explosive to compensate for a less than ideal understanding of target coupling and effects. Only a handful of MOP were made, and even those are being modified due to some significant shortcomings.

 

[Ian33]

Reading 'abovetopsecret' on the web, there is a post by a person by the name of boomer135. This person is adamant that during their career they refuelled a manned demonstrator, size of a large fighter, two thirds a B2 wingspan that looked like a B2 bomber 'but with differences'.

The above was posted way back in 2014.

Just thought I'd share.

(Oh and yes, they are legitimate. Even has a great photo taken as they flew refuel over Groom lake.)

 

[marauder2048]

The Next Generation Penetrator will probably be an outgrowth of HVPW.

It was the other way around. The High Velocity Penetrating Weapon was an outgrowth of the Next Generation Penetrator program. HVPM was validated and is considered technically mature enough to move to EMD. HSSW is another program that is part of the hardened target munitions portfolio.

MOP was a quick reaction, interim weapon design. It was designed to be incredibly inefficient, using a large amount of explosive to compensate for a less than ideal understanding of target coupling and effects. Only a handful of MOP were made, and even those are being modified due to some significant shortcomings.

Thanks for the clarifications; the boosted penetrator effort is smeared across a couple of different programs.

 

[NeilChapman]

I wonder what they've learned about flight controls that has reverted the planform?

Since the B-2 was designed there have been many developments in flight controls - some of them in the last few years.
Tailless aircraft have been the focus of a lot of attention since the late 1980s. Removing the tail has benefits from a signature standpoint but removing that tail introduces yaw problems.

In the 90s there was a lot of work done on thrust vector control (including fluidic yaw vectoring). The state of the art in that area has advanced considerably since the B-2, which has a limited degree of thrust-based yaw control using differential engine thrust. That differential engine thrust is used on the B-2 to limit required control surface deflections - because those big control surfaces are not so good for the RF signature.

Also during the 90s DoD funded work to develop new kinds of control surfaces for both subsonic and supersonic aircraft. Some of that work is documented in "FATE" and "ICE" threads on the forum. The product of that work can be seen on the X-47A.

View: https://www.youtube.com/watch?v=Jt-Yp5WMW7s


More recently there has been work on "morphing" aircraft structures. This ranges from gapless control surfaces to changing the shape of the whole aircraft. Back in the 1980s the AFTI F-111 tested what we would now call a "morphing" wing. A morphing wing could offer many things to a flying wing aircraft. This could be dynamic twist to control yaw, "seamless" control surfaces, a changing airfoil, or an outer wing that changes shape and size for performance reasons.

View: https://www.youtube.com/watch?v=9ZpAHxMj5lU


And in the last few years NASA has experimented with altering the distribution of lift on a wing to control adverse yaw. The Prandtl-D test aircraft demonstrated a new way of implementing some old ideas using modern tools which could have significant advantages for an aircraft like the LRS-B.

View: https://www.youtube.com/watch?v=Hr0I6wBFGpY

It's just such a pleasure asking questions here. Thank you for your thoughtful reply.

I guess my thought would be that morphing structures would be pretty high risk for this particular bird. Perhaps the reduced size/weight/thrust ratios + the work you mentioned will assist in the low altitude maneuverability.

Has anyone seen how much smaller the payload is to be?

 

[NeilChapman]

Final production will be in Palmdale as it was for the B-2. One of the "rumored" major sub contractors is Spirit Aero Systems out of Wichita. Also, it's most likely a twin engined aircraft, as that would also greatly reduce cost. It's also smaller than the B-2.

A lot of the manufacturing will not be in CA, or at least isn't planned to be right now. This is one of the things affecting the EMD and unit costs. There is obviously a huge political dimension to where jobs and dollars will be going.

Well you tell them to come on down to North Carolina. We're quite proud of our military support. We have a great manufacturing base and would love to see some additional airplane production next to Honda Jet in Greensboro.

 

[NeilChapman]

So.

B-2 = 4 x F118 @ 17,300 lb st = 69,200lb st
Loaded Weight: 336,500 lb
Maximum Weight: 376,000 lb

B-21 = 2 x F135 @ 28,000lb st = 56,000lb st

Ratio of thrust : 0.8:1

Assuming same thrust/weight ratio, same basic performance:

Loaded Weight: 336,500 lb = 269,200lb
Maximum Weight: 376,000 lb = 300,800lb

The engine choice determines maximum speed, altitude and range. A low bypass ratio is better for top speed and high ceiling, a higher bypass ratio better for long range cruise.

F118 bypass ratio is I believe 0.87:1. F135 bypass ratio is 0.57:1. That could translate to potentially higher speed/altitude capability.

If the engine type is correct, these weight figures should be upper boundaries. If the emphasis for B-21 is high subsonic speed, it might have a higher thrust/weight ratio taking the maximum weights down from the above.

What are other candidate engines?

F414
F110-GE-129/132
F118
New design (e.g. Advent studies)

Thank you for the calculations. According to an unnamed source to defense news GE is not providing the engines. I have no way of knowing the reliability of "defense news" sources.

New Details Emerge On LRS-B Subcontractors

The GAO’s decision on an industry protest will determine which subcontractors develop building blocks of the next-generation bomber

www.defensenews.com

I just can't fathom a two engined bomber, the delivery mission is so critical. Is there some other reason that you would add so much extra power by including 4 engines in this platform? Where does the power for lasers come from? My understanding is that it's like cooling in your house. Too much is a problem. Seems like I read a good explanation of this elsewhere in the forum.

Is it likely that they would risk this program using a new engine (AETP)? I can see them wanting the extra cooling capacity for the hot section of the engine and the fuel that provides a heat sink for systems. Might a "block upgrade" to the existing F135 engine will get them these benefits as opposed to waiting for AETP to get finished? I read somewhere to expect marginal (10-20%) thrust increase as well as some reduction in fuel burn from updates to F135. Not sure where I read this but it wasn't too long ago. I guess I'm asking if it is a significant "risk" to get upgrades to current engines "approved" for use or is it a non-issue.

Thanks!

 

[AeroFranz]

Regarding reliability, something often overlooked is that if you have four engines, you are actually more likely to have at least one fail compared to two. Other point: if your engines are mounted in pairs, like on the B-1 and B-2, they are just as vulnerable as individually mounted engines. There's a high chance of one spewing a turbine and ripping into the neighbor. There is no amount of hardening that will stop a turbine blade spinning at tens of thousands of RPMs.
At this point i wouldn't wage on the B-21 (what a joke of a name... ) having two versus four engines, but it's not as one-sided as the previous posts make it out to be. Consider that two large engines are cheaper and more efficient than four smaller ones and associated systems (and we know cost was an important metric in the selection), which in turn leads to a smaller air vehicle.
On the negative side, larger diameter engines will require proportionally longer inlets and exhaust to hide the fan face and turbine sections, driving centerbody length. However a cranked kite is a nice way of divorcing span from centerbody length for a given leading edge sweep dictated by RCS considerations...

 

[quellish]

It's just such a pleasure asking questions here. Thank you for your thoughtful reply.

I guess my thought would be that morphing structures would be pretty high risk for this particular bird. Perhaps the reduced size/weight/thrust ratios + the work you mentioned will assist in the low altitude maneuverability.

Has anyone seen how much smaller the payload is to be?

Any of the things I listed *could* be technically mature enough to be used on the B-21. All but the Prandtl-D have been in development for a while, and there may be additional.... things.... that have been in development but are not public. Morphing structures for something as large as the B-21 would certainly be challenging. NG has done quite a bit of development on new types of control surfaces and thrust vectoring - I would be surprised if these were *not* used on the B-21.

It would be safe to assume the payload mass is in the neighborhood of 40,000 pounds.

 

[flateric]

Is "delivery mission" critical for triple seven?

 

[overscan (PaulMM)]

Is "delivery mission" critical for triple seven?

How many missions has the B-2 completed on 3 of its 4 engines that it couldn't have completed on 2? Presumably the USAF knows this.

How many engines did the FB-111 have?

I don't see any real technical reason for 4 engines. Modern civil engines can go hundreds of thousands of hours between failures. Reading a book on the B-29, and on that you were lucky if all 4 engines actually worked for the duration of the mission. Things have advanced since then.

 

[Sentinel36k]

Redacted.

 

[Flyaway]

quellish

Suppose one were to find certain technologies (convergent solution?) that would be applicable for two separate vehicles studied, perhaps an unmanned item and the LRS-B. Would it be possible the non LRS-B vehicle/study could act as risk reduction for the selected tech?

Sentinels

Maybe something in this as the RQ-180 is allegedly already in service and Sweetman seems to think the B-21 springs from the same well so to speak.

 

[Gridlock]

Only a handful of MOP were made, and even those are being modified due to some significant shortcomings.

Why do I get the feeling the main shortcoming was that they never worked at all?

 

[sferrin]

Only a handful of MOP were made, and even those are being modified due to some significant shortcomings.

Why do I get the feeling the main shortcoming was that they never worked at all?

Because you're suspicious of the "MIC"? It's not as though the US military had never designed and built a penetrating bomb before.

 

[NeilChapman]

Would NG be able to build their own weapons bay or would they contract this out?

 

[TomS]

They bay will be integral to the aircraft, so it's Northrop's for final assembly. Parts of it will undoubtedly be done by subs.

 

[Sentinel36k]

Not necessarily speaking of an rq-180 (if said platform exists) as the incubator of said tech.

Back to the B-21, “The B-21 has been designed from the beginning based on a set of requirements that allows the use of existing and mature technology” The use of both "existing" and "mature" makes one think.

Sentinel

 

[Flyaway]

This article indicates we will learn some more info next Monday.

A New Bomber Contest
—JOHN A. TIRPAK2/29/2016

​The Air Force will hold a service-wide contest to name the new B-21 bomber, Secretary Deborah Lee James announced at AWS16. James said she’s asking all members of the Air Force “family”—uniformed, civilians, and family members alike—to “learn more about the role this platform will play against the real threats that we will face” and submit appropriate nicknames, suggesting that she hopes the effort will lead to more advocacy for the system. James also said to “stay tuned” for more bomber details, which will be revealed to Congress Tuesday at a classified session with a Senate Armed Service Committee panel. James told reporters she and Chief of Staff Gen. Mark Welsh will deliver another “state of the Air Force” briefing March 7, at which she suggested more information about Northrop Grumman team members and other industrial aspects will be revealed. Congress has been given regular classified briefings on the B-21 since last spring, James said, adding that despite the disclosures made and to come, the system will remain highly secret.

 

[NeilChapman]

Is "delivery mission" critical for triple seven?

Well - no. If you're flying to Spain on a triple-seven can always land and fly another day. Whereas if you're the opening salvo's in an air superiority fight...

But I get all the points that were made. Two engines are fine.

 

[Sentinel36k]

A lot has happened with load control and FCS' since the B-2. With flexible high AR wings comes interesting loads on the wing. Even in GA there has been progress made.

Makes one wonder how RCS can be influenced by flex, and how one might measure a flexible aircraft's RCS in flight.

sentinel

 

[quellish]

A lot has happened with load control and FCS' since the B-2. With flexible high AR wings comes interesting loads on the wing. Even in GA there has been progress made.

Makes one wonder how RCS can be influenced by flex, and how one might measure a flexible aircraft's RCS in flight.

sentinel

Airframe flex can greatly influence RCS - which is one of many reasons that in flight RCS measurement is important. Assets like RAT-55 and the DYCOMS facility at Groom Lake are critical for both developing and maintaining VLO aircraft.

 

[CiTrus90]

Cross-posting from NASA N+3 Program Concepts thread here http://www.secretprojects.co.uk/forum/index.php/topic,10646.msg100315.html#msg100315

Northrop Grumman proposal for SELECT (Silent, Efficient, Low-Emissions Commercial Transport).

Maybe of interest

Regards.

 

[NeilChapman]

They bay will be integral to the aircraft, so it's Northrop's for final assembly. Parts of it will undoubtedly be done by subs.

I read they partnered with Boeing for B2 because of their history with bombers.

This left me wondering if that was relevant at this point since NG has done so many upgrades to B2, including the bomb bays. NG is also building the center fuselage for F35 which includes the aircrafts internal weapons bay. Would they have the comfort level to design and build the large single bay for B21?

Would this increase or reduce risk?

 

[Hobbes]

There is no amount of hardening that will stop a turbine blade spinning at tens of thousands of RPMs.

Incorrect. For civilian applications, a cowling that will contain a disintegrating turbine is a requirement. Can't see military applications settling for less.

 

[sferrin]

There is no amount of hardening that will stop a turbine blade spinning at tens of thousands of RPMs.

Incorrect. For civilian applications, a cowling that will contain a disintegrating turbine is a requirement. Can't see military applications settling for less.

Could swear I've seen a video where they did a catastrophic failure of a blisk and the casing contained it. (Then again I recall one coming apart in an F/A-18 and exiting the aircraft transversely so. . .)

 

[overscan (PaulMM)]

There is no amount of hardening that will stop a turbine blade spinning at tens of thousands of RPMs.

Incorrect. For civilian applications, a cowling that will contain a disintegrating turbine is a requirement. Can't see military applications settling for less.

Incorrect. The engine case (not cowling, that's aircraft structure) is generally intended to stop (low speed) fan blades. Not "a high speed turbine at tens of thousands of rpms".

 

[AeroFranz]

Which is why there is a cone of + or - 5 degrees ahead and behind the radial plane of the turbine where "thou shalt not put flight critical flight control systems". I'm paraphrasing, i don't know verbatim what FAR 25 says in that regard.
At any rate, didn't a Qantas A380 spew turbine blades in the last two years or so? i think this is the one i'm thinking of.

from Wikipedia:
"Qantas Flight 32 was a Qantas scheduled passenger flight which suffered an uncontained engine failure on 4 November 2010 and made an emergency landing at Singapore Changi Airport. The failure was the first of its kind for the Airbus A380, the world's largest passenger aircraft. It marked the first aviation occurrence involving an Airbus A380. On inspection it was found that a turbine disc in the aircraft's No. 2 Rolls-Royce Trent 900 engine (on the port side nearest the fuselage) had disintegrated. The aircraft had also suffered damage to the nacelle, wing, fuel system, landing gear, flight controls, the controls for engine No. 1 and an undetected fire in the left inner wing fuel tank that eventually self-extinguished.[1] The failure was determined to have been caused by the breaking of a stub oil pipe which had been manufactured improperly."

 

[Trident]

AFAIK a single loose turbine blade has to be contained, but with QF32 the disk burst, ejecting entire segments, which is not containable.

 

[VTOLicious]

I wonder if the quantity, location and dimension of the payload bays will be the same as on the B2...what are the options?

Weapons bay volume is a primary driver for the size of the aircraft. It would not be surprising to find a very different weapon bay configuration on LRS-B.

Hmm, don't you think the support of CSRL is a requirement?

Just thinking aloud...it could have one main bay at the centerline (B-2 bay volume, supporting CSLR) and 2 smaller lateral bays for additional armament and/or interchangeable sensors :

 

[Ian33]

Two main bays and two AAM bays to fit a pair of Meteor or said equivalent LRAAM either side gets my vote.

 

[quellish]

Hmm, don't you think the support of CSRL is a requirement?

I think the contractors may have been given the freedom to explore a range of solutions.

 

[marauder2048]

Hmm, don't you think the support of CSRL is a requirement?

I think the contractors may have been given the freedom to explore a range of solutions.

Does a rotary launcher help with volumetric efficiency? Or is the main motivation more flexible weapons selection and reliable weapons release i.e. no head-of-line blocking issues?

 

[Flyaway]

I wonder if the B-21 will have any air to air capability to defend itself.