replacing engines on the buff

[Marko Dash]

would it be more practical to replace the 8 engines on the B-52 with four GE90-115B's, or to build a new heavy bomber from the ground up?

[The Duchess of Zeon]

would it be more practical to replace the 8 engines on the B-52 with four GE90-115B's, or to build a new heavy bomber from the ground up?

There's been plans to replace the engines repeatedly but they've never gone anywhere.

I sometimes wonder if Boeing isn't going to roll out a B-3 proposal at sometime in the near future which will consist of them taking the plans for the B-52H, replacing the engines with four new ones, and making it out of composites. God knows it would probably beat all possible competition hands-down...

[Beowulf]

Considering the next bomber is almost certainly going to be a big, slow bombtruck, such a proposal would probably work rather well.

[Frank Hipper]

would it be more practical to replace the 8 engines on the B-52 with four GE90-115B's, or to build a new heavy bomber from the ground up?

There's been plans to replace the engines repeatedly but they've never gone anywhere.

I sometimes wonder if Boeing isn't going to roll out a B-3 proposal at sometime in the near future which will consist of them taking the plans for the B-52H, replacing the engines with four new ones, and making it out of composites. God knows it would probably beat all possible competition hands-down...

Designing a composite-built B-52 would be about as difficult as reverse-engineering one from scratch; keeping the basic concept of a straightforward large bomber, but designing from the ground up would most likely be the simpler option.

[The Duchess of Zeon]

would it be more practical to replace the 8 engines on the B-52 with four GE90-115B's, or to build a new heavy bomber from the ground up?

There's been plans to replace the engines repeatedly but they've never gone anywhere.

I sometimes wonder if Boeing isn't going to roll out a B-3 proposal at sometime in the near future which will consist of them taking the plans for the B-52H, replacing the engines with four new ones, and making it out of composites. God knows it would probably beat all possible competition hands-down...

Designing a composite-built B-52 would be about as difficult as reverse-engineering one from scratch; keeping the basic concept of a straightforward large bomber, but designing from the ground up would most likely be the simpler option.

It was more a reference to Boeing's 747 line, the Plane Which Just Keeps On Evolving.

[Einhander Sn0m4n]

It was more a reference to Boeing's 747 line, the Plane Which Just Keeps On Evolving.

Now there's a hilarious idea: a 747 used as a bomber! Hell, we've already figured out how to put a spinal-mount Big Honking Raygun on the damn thing!

[CC]

It was more a reference to Boeing's 747 line, the Plane Which Just Keeps On Evolving.

Now there's a hilarious idea: a 747 used as a bomber! Hell, we've already figured out how to put a spinal-mount Big Honking Raygun on the damn thing!

Not that hilarious. They've had paper studies of converting the 747 probably since before it was even rolled out. I believe Carter wanted to bring in an air launched cruise missile carrying 747 after cancelling the B-1A. Secret Projects has some discussion on them. Of the more peculiar conversions are dedicated ALCM carriers, an amphibious 747, and an ICBM launching 747.
Thread #1
Thread #2
Lots of ALCM carrier stuff

[Howedar]

would it be more practical to replace the 8 engines on the B-52 with four GE90-115B's, or to build a new heavy bomber from the ground up?

God in heaven, what the hell would you need that kind of thrust for? Try being less of a google warrior and being a little more in possession of a clue. A B-52 could fly on two GE90's of any mark. Probably one, if you could duct tape it to the top. Specifying the -115B, or whatever else, just makes you look like a tool.

[Stark]

Holy shit - is the GE90 ~120,000 pounds whereas the current TF33's are ~18,000 each?

I guess the 777 needs a hell of a powerplant. What's the difference between commercial and military jet engines?

[Howedar]

The trailing term of the GE-90 refers to the nominal maximum thrust. The GE90-115B is good for on the order of 115,000lbs of thrust.

[raptor3x]

Holy shit - is the GE90 ~120,000 pounds whereas the current TF33's are ~18,000 each?

I guess the 777 needs a hell of a powerplant. What's the difference between commercial and military jet engines?

Commercial engines tend to require maximum fuel efficiency and lower cost, thus they use higher bypass ratios and lower turbine inlet temperatures. Military engines, on the other hand, are usually all about maximum specific thrust and thus they have much higher compressor ratios and lower bypass ratios in the compressor and use exotic materials and cooling setups in the first turbine stage so that the turbine inlet temperature can be cranked up.

[Stuart]

There's been plans to replace the engines repeatedly but they've never gone anywhere.

They've always been shot down on they grounds that they offer insufficient advanatges in comparison with their cost. Also, having eight engines dow give some advantages, lose one and there are still seven left. I don't think we'll see a re-engining program anytime soon although current plans are that the B-52 fleet will outlast the B-2 and probably the B-1. The worry is the wing main spar. That's a single forging and the machinery required to make it was scrapped years ago. If that spar starts to develop cracks, there's not much we can do about it.

I sometimes wonder if Boeing isn't going to roll out a B-3 proposal at sometime in the near future which will consist of them taking the plans for the B-52H, replacing the engines with four new ones, and making it out of composites. God knows it would probably beat all possible competition hands-down...

The problem there Your Grace, is that the bomb bay on the B-52 is optimized for nuclear weapons. It isn't actually that big and its load of conventional bombs is comparatively restricted. The last of the specially-modified "Big Belly" B-52s went years and years ago, I'm pretty sure Davis Montham turned them all into saucepans way back.

So, if we were going to produce a new heavy bomber (and a lot of work is going on into that right now), we've got to think pretty hard about what we want it to do. That's always the first question and usually the hardest one to answer. If we want it for nuclear strike, we're looking at a hypersonic manned atmosphere-skimmer (like the fictional B-106 Aurora). However, if we're looking at a conventional bomb truck things change.

To list some probable requirements (not in priority order).

Very heavy bombload (circa 84,000 pounds)
Very long endurance (to provide time to get to a target area and then loiter over that area)
High operational ceiling (to get it above anti-aircraft fire),
Elaborate command and control facilities (to interface with ground troops)
Precision guided munitions capability (for precision air support)
Good crew facilities (to keep the aircraft operational and on station for long periods).

Put together, that isn't like anything we have right now. One possibility might be to take the C-17 and give it a new fuselage (the temptation for the USAF being that it would have B-17s again).

On the 747 issue, there have been a lot of proposals for bomber versions of the Boeing 747. Most of them were politically inspired and had little foundation in real possibilities (for example, one idea, to roll a Minuteman out of the back of a 747 and fire it was an engineering impossibility.) The problem with the 747 is that its wing is in the wrong place; a bomber should really have a high wing so its bomb bay is as large and as uninterrupted as possible.

[CC]

Aside from the resulting center of gravity issues from dropping a 70-80,000 pound missile (which can probably be dealt with), what makes it an engineering impossibility? A C-5 managed to air launch a Minuteman I in 1974 after all.

[Stuart]

Aside from the resulting center of gravity issues from dropping a 70-80,000 pound missile (which can probably be dealt with), what makes it an engineering impossibility? A C-5 managed to air launch a Minuteman I in 1974 after all.

It was impossible to fit the missile and the command control system in the same aircraft. In effect, the idea combined all the worst aspects of ballistic missiles and bombers without the advantages of either. The C-5/Minuteman launch was very much public relations.

[CC]

Why would you need an onboard C&C system any more complicated than already existed on the Buff or currently exist on our nuclear capable aircraft? In essence, it's just a (very much) larger SRAM or Skybolt and I'm not aware of any special C&C requirements for them. If you put a PAL on the missile that locks out missile ignition (along with warhead detonation) without the proper code, then that should be enough. Of course I may simply be missing something important, and I'd welcome any corrections.

[CC]

Addendum:
The first image on the first thread I linked (this image if the link will work) is for a six engined version that would have carried the missiles in wingpods. Certainly that would have possessed enough room in the remainder of the aircraft for the C&C. While I'm no expert on aircraft, the other, more conventional "shove out the back", plane in that image seems to have the high wing you said is necessary for a bomber.

[Howedar]

On the 747 issue, there have been a lot of proposals for bomber versions of the Boeing 747. Most of them were politically inspired and had little foundation in real possibilities (for example, one idea, to roll a Minuteman out of the back of a 747 and fire it was an engineering impossibility.) The problem with the 747 is that its wing is in the wrong place; a bomber should really have a high wing so its bomb bay is as large and as uninterrupted as possible.

I don't know if I agree with that fully. There are a couple of considerations that make a low/mid wing more desirable. I assume loading of ordinance is made a lot easier by increased ground clearance, and I know that the aerodynamics of a low-wing jet transport/bomber are better than those of a high-wing. It's not a clear-cut issue in my professional opinion.

[Howedar]

Shit. That was a Stuart quote, in case anyone gets confused. Shame on me for not previewing.

[Starglider]

I don't know if I agree with that fully. There are a couple of considerations that make a low/mid wing more desirable.

The B-1 and Tu-160 do demonstrate that a low-wing layout is quite practical (and to some extent, desirable) on a high capacity heavy bomber. I assume the B-70 is classified as mid-wing?

[Howedar]

No, they do not demonstrate that in any way, shape or form. They happen to have low wings. That doesn't demonstrate anything other than the fact that someone within the engineering organizations felt that the low wing was the best choice in that specific case.

The B-70, strictly speaking, has a high wing configuration. It's not really a relevant comment on the design though. Airplanes are not designed or characterized by this apparent notion of "pick one element each from bins A, B, C, D and E". Not all typical characterization methods are relevant in all cases.