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Because the Boneyard Buffs haven't had any avionics upgrades in over 30 years, so they wouldn't be able to carry anything PGM.  Also, the boneyard buffs had several unfortunate run-ins with a multi-ton guillotine and are junk.  Thanks stupid Carter and your weapons reduction treaties.

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Now you are arguing that one truck did not extend.  Followed by repair.

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Would they be able to use a current commercial engine or would it require a dedicated .MIL application engine?

If the B-52 is retrofitted with a 4-engine setup, the rudder will not be capable of maintaining control in asymmetric conditions. A 4-engine B-52 will require a new rudder. While an 8-engine retrofit would reduce the risk in this area, it would not eliminate the necessity for testing. The thrust range is the particular concern. The 17,000 pounds of thrust of the TF33 is already outside the limits of the rudder. The current B-52 is thrust limited and does not utilize full power. Many new engine programs have dreams of smaller runways, higher temperatures, and greater takeoff weights. These things will not be possible for the B-52. The new engine will most likely have to be de-rated to maintain a margin of safety or have a new rudder system designed. A new rudder would likely be cost prohibitive.

Performance Upgrades

Just as the DC-8 upgrade showed a decrease in payload and takeoff weight after upgrade, similar issues present when approaching a B-52 re-engine with the objective of increasing performance.

When Strategic Air Command installed the Electro-Optical Viewing System (EVS) on G and H-model B-52s it created a speed problem. Prior to the EVS modification, the aircraft was capable of 0.91 Mach. The EVS modification created issues with airflow over the nose and between the chin pods. Higher speeds create localized supersonic airflow and made the pitot-static system unreliable. As a result the B-52 was policy limited from its true top speed to a more reliable airspeed of 0.84 Mach. Therefore, new engines do not represent higher speeds for the B-52. Even if the EVS turrets are removed, it would only allow a return to the true aerodynamic limit of the airframe of 0.91 Mach. This speed is already achievable. Speeds greater than 0.91 Mach are unsafe because the B-52 has a well-defined Mach Tuck. Higher speeds would require a complete redesign of the entire aerodynamic surface. The B-52 is aerodynamically speed limited. In the area of speed, new engines accomplish nothing.

Many claim that new engines could increase the B-52’s payload, allowing it to carry more bombs. Also not true. The B-52 weapons carriage is volume limited, not weight limited. The only way to get more weapons is to create new racks to maximize the space available in the bomb bay and on the external carriage systems. New engines cannot give the B-52 more space to carry more bombs.

Others claim a new engine would make the B-52 more reliable. Again, not true. Hard as it may be to believe, the B-52 is one of the most reliable aircraft in the USAF inventory. Mission capable rates vary by year, but the B-52 has not fallen below 70% mission capable for decades, while the B-1B and B-2A have never been above 70%. 2016 Mission Capable Rates put the B-52 at 72%, B-1B at 46%, and the B-2A at 55%. Understand, the engines have nothing to do with the mission capable rates of any of these aircraft. The low rates for the B-1B and B-2A are not engine related, nor is the high rate for the B-52. The point is, the B-52 is already the most reliable bomber the USAF has in its inventory. The limiting factor for all the bombers is electrical and avionics related. There is a case to be made for increasing the reliability of all the bombers, but engines will not increase or decrease that reliability. If there is money to be spent on reliability, that money does not need to be spent on B-52 engines.

Still others make statements concerning the B-52’s lifespan and how new engines could let it fly far past 2050. These claims are also false. The limiting factor on the B-52 service life has always been, and remains, the upper wing surface. The B-52 upper wing surface was designed to give the aircraft a 35,000 hour service life.  The reason the H-model B-52 remains in service today is because it sat alert for decades and did not fly nearly as much as its predecessors. In terms of hours flown, the B-52 is middle-aged. However, that timeline will have an end state. The current projections of B-52s flying to 2040 are at current usage rates with current hours on its current wings. If the B-52 flies past 2050 in bulk, it will need to resurface the wings, new engine or not.

Granted, a new engine can and will increase range and endurance but these performance increases are a by-product of engine efficiency. A program dedicated to increasing these capabilities does not make sense. Some engineering studies have stipulated that better engines could increase the unrefueled range of the B-52 by as much as 45%,[19] however B-52 range is already the most impressive in the USAF fleet. The B-52 has many problems, however range and endurance are not among them. A program designed to fix non-existent problems does not need to exist.

For these reasons, a B-52 re-engine program should not strive to increase performance in any way. Performance may increase in some areas, but it should not be the objective of the program. Similarly, fuel savings should not be the objective either. The only objective for a B-52 re-engine that makes any sense is to reduce overall cost for the USAF.

Cost Savings

Because of these reasons, the goal of the B-52 re-engine program should be cost savings. The B-52 does not have a performance problem, nor does it have a fuel problem. The B-52 does have a cost problem, and that problem is entirely engine related. The TF33 engine, while easy to maintain by maintenance standards, is maintenance intensive. A modern engine would produce a drastic reduction in engine maintenance actions across the spectrum. But even that savings is not good enough. True cost savings exists only when the USAF divests itself of the TF33 engine fleet wide, not just for the B-52 fleet, but for the entire USAF fleet.

The TF33 has undergone an exponential increase in maintenance costs over the years, especially in depot. In FY99 it cost $286,000 to depot overhaul a TF33. Something that had to occur every 1500 hours. The studies done assumed cost to overhaul the engine would remain static with only inflation increases. By FY06 that cost had increased to $1.025M for each engine, much more than the studies had anticipated. By 2040, the projected end of the B-52 service, it could cost more than $7M to overhaul each TF33. While the B-52 program maintains 855 TF33 engines, the USAF as a whole cares for 2300 TF33 engines. True cost savings is in removing all of the TF33s. That means a re-engine program for the B-52, E-3, E-8, and OC/WC-135s and the facilities and programs to maintain those engines.[20] This is where true cost savings will be realized. The USAF must take a holistic re-engining approach towards the TF33 engine with the goal of removing it from the inventory.

Completely removing the TF33 from the inventory is the only way a re-engine program for the B-52 makes any sense.

Where the B-52 differs the most from all other re-engine programs, military or civilian, is when it comes to resale. The DC-8, 707, KC-135 and others all had residual value when their primary owners were finished with them. Re-sale recouped some of the sunk costs. The resale value of a B-52 is zero. Not because it has no value, but because it will never be sold. While it is in the US interest to equip allies and friends with military technology, that store does not sell everything. Air superiority, air transport, and air refueling have value to the coalition, and the US wants to equip its allies with these capabilities. However, global strike capabilities are an entirely different story. The ability to strike over intercontinental distances with significant mass is something the US holds dear and does not wish to export. Therefore, all of the cost involved in a B-52 re-engine and all of the savings must be realized with the primary owner.

The Way Forward

If the USAF decides to pursue a B-52 engine retrofit it should be done to maximize cost savings at the lowest possible technical risk. To reduce risk in the program, the following recommendations should be implemented:

The entire TF33 inventory should be divested. This requires engine retrofits for the B-52, E-3, E-8, OC/WC-135s. TF33 depot facilities and the programmatic infrastructure supporting such activities should be repurposed or divested. This will increase program and technical risk by including 4 other weapon systems, however, without the other weapon systems the program does not meet its primary goal of cost savings.

An 8-engine solution should be implemented. A 4-engine solution introduces unnecessary cost-prohibitive problems with asymmetric conditions and clearance volume under the wing. It also would require a ‘re-plumbing’ of fuel, hydraulic, pneumatic, and electrical systems.

A commercial, in-production engine should be selected. This engine will have to be modified for military use, but is still less risky than a completely new source-selected engine.

The engine should fit within the available volume of the existing engine nacelles. To design larger nacelles will have an adverse effect on the flight control systems.

The engine should be of comparable weight of the existing engine. Too heavy and the wing will suffer structural problems, too light and the wing will experience flutter. An engineering analysis will have to be done to optimize weight tolerance of a new engine.

Key Performance Parameters must not be based on performance increases. Any increase in performance will be a by-product of engine efficiency. This program must be viewed as a logistical program, not an operational one.

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"No Bid" is an acceptable answer.  Two things will not occur, the government will not be building engine plants, and money offered for production engines will not be, "price them as high as you want, we will not dictate your profit".

Engine manufacturers do not want or need to build boutique engines that are not profitable.

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I doubt you know about that cost, and if you do, you should consider that briefing you received, and the requirements.

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Why does the AF want to keep 8 little engines? Redundancy?

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61-007 was brought back from the boneyard to replace 60-047 not to long ago.

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And why can't they put it out to bid, with specs, to 2 or 3 engine manufacturers?  I want xxx engines based on a current design to fit into y. I'm not talking about giving them away, or designing engines from scratch.  We got to the moon from scratch in 10 years with slide rules and spacecraft with less computing power than an apple watch ,but nobody can figure out how to build 700-800 engines to fit in an existing airframe and make a profit?

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And zero reputable manufacturer will sign up to this.  Its not just engines, its all the ancillary equipment (stands, tools, spares, etc).  This small number of engines isn't worth the economy of scale to do.

Apollo was a national level effort, new B-52 engines aren't.  

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Isn't the Army looking at keeping Vietnam Era Hueys flying for 100 years?

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Thank you for the simple quick answer. Are the large single engines more fuel efficient and or require less man hours of maintenance? If so seems like that initial higher cost would be negated in the long term.

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Neither.
Modern engines designed and built with modern methods and materials intrinsically require less fuel to operate them and require less man hours to maintain them.

If it were feasible the best engine for the B-52 would be the CFM56-2A (includes thrust reversers).
The Navy's E-6B uses these engines, there were still engines on the wing that had never been demated until they cam upon their high time removal requirements.

Quoted:

Thank you for the simple quick answer. Are the large single engines more fuel efficient and or require less man hours of maintenance? If so seems like that initial higher cost would be negated in the long term.

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Man...can't we find some way to replace the old B-52s with something more modern but not 'holy Mother of God' expensive?

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Man...can't we find some way to replace the old B-52s with something more modern but not 'holy Mother of God' expensive?

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Why would you when the system is paid for and does the job well.
The Stratofortress has turned out to be the best return on investment the government has ever had.

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It costs less to keep flying than the B-1 or B-2. With new more fuel efficient engines that cost will go lower. The engines on it now have been out of production for decades. Parts have become difficult to find and are expensive. It wouldn't surprise me if some parts had to be custom made. I also read that those engines are supposed to be overhauled every 1500 hours. I would think that a modern engine could surpass this mark.

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It costs less to keep flying than the B-1 or B-2. With new more fuel efficient engines that cost will go lower. The engines on it now have been out of production for decades. Parts have become difficult to find and are expensive. It wouldn't surprise me if some parts had to be custom made. I also read that those engines are supposed to be overhauled every 1500 hours. I would think that a modern engine could surpass this mark.

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I think that's too big -thrust and physical size.

Remember one of the biggest issues is the rudder. We also can't certify a new engine install the same way they did on the 50s. Essentially your nacelle and pylon  can't be a negative pressure zone that is pulling in fresh air with oxygen. When you pull that handle the nacelle should no longer support a flame. Just because the old nacelle and pylon did it (I'm not sure if it did or didn't.) does not mean you can do it again.

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That assumes that we need a bunch of bombers. Do we?

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The Air Force says it wants to keep eight engines.

Here's a photo of two replaced by a single (used on the C-17, so in-service and in-production):

http://i27.tinypic.com/20jju5c.jpg

Concept images of four-engines:

https://i.kinja-img.com/gawker-media/image/upload/s--qRgu1S-F--/c_scale,f_auto,fl_progressive,q_80,w_800/fbxu5nazwzgjk7dzgifo.jpg
https://c1.staticflickr.com/1/448/19799476186_5e04e7e418_b.jpg

Old dog, new engines

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I believe so.
That logic could be applied across the whole military.
Do we need ten carriers? Do we need the amount of subs we have? Do we need all those ICBMs?

Thing about anything military related is you don't need it until you NEED it.

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There's miles of wiring and plumbing in those birds that would need to be removed / changed - a lot of which, I've been told, nobody is sure where it goes.

They're still wired for shit like the hound dog missile.

Evidently it would be cheaper to build a new airplane than remove all the obsolete stuff...at least that's the argument I've heard.

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Speculation is okay, probably healthy when trying to read between the lines from open sources.

We have had a few breaches here over the years that generated the '

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Would they be able to use a current commercial engine or would it require a dedicated mil application engine?

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Or just modify some 777s to drop bombs.

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To those who are saying that big-assed drones and cruise missiles will comoletely replace bomb trucks:

The cost per delivered ton of bombs via bomb truck is way, WAY lower.  In a long, drawn out war, that’s a big deal.

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Isn't the Army looking at keeping Vietnam Era Hueys flying for 100 years?

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To those who are saying that big-assed drones and cruise missiles will comoletely replace bomb trucks:

The cost per delivered ton of bombs via bomb truck is way, WAY lower.  In a long, drawn out war, that’s a big deal.

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Impossible without drawing a new fuselage from scratch unless the bomb bays are tiny.  The quick and dirty way is to think outside the box and copy the Heinkel method with vertical tubes poking through the lower moldline.  Drop SDB's and other tiny precision bombs.  Small impact on the fuselage structural integrity.