Boeing B-52J / B-52 Re-Engining

Kiltonge said:
241 pages summarised: does it have New START fins Y/N.
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New START fin? well they could always reintroduce the original tall tail-fin, I never liked the new fin introduced on the B-52G. It, to me, looked like someone had got a giant pair of hedge-clippers and snipped off the tip of the tail-fin.
 
NMaude said:
New START fin? well they could always reintroduce the original tall tail-fin, I never liked the new fin introduced on the B-52G. It, to me, looked like someone had got a giant pair of hedge-clippers and snipped off the tip of the tail-fin.
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The tall tail actually was less safe than the shorter one (in a reversal of normal experience).
It was easier to damage in sudden maneuvering or rough air, and the extra area didn't contribute anything to yaw prevention, directional stability, etc.
 
Ha! Always heard it referred to as Barksport. Never visited; almost got there and then turned right to go to the Base in the middle of "L". Spent a year there one month dodging pine trucks. Got to see one or two unique catastrophic TF34 failures there.
 
aim9xray said:
Ha! Always heard it referred to as Barksport. Never visited; almost got there and then turned right to go to the Base in the middle of "L". Spent a year there one month dodging pine trucks.
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Ah, yeah, loggers be crazy, yo.


aim9xray said:
Got to see one or two unique catastrophic TF34 failures there.
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Ingested a few turkey vultures?
 
Oh no, far more interesting. Misaligned oil jet caught fire (internal engine fire). LPT shaft (long tom) was 3/4 melted through (circumference) when it failed (in tension load). With nothing to take thrust loads, the shaft and LPT shifted aft until the last stage mechanically interfaced the stators.

RUD and excitement ensued.

With no fan flow, the mixture is super rich, and the HPT overtemps and it then slags itself creating GE turbine gravel. Not to be outdone, the C sump oil return line is severed and that uncontained oil flow then catches fire. Now you have an internal and external engine fire. The pilot pulls the fire handle and stopcocks the throttle and and the engine shuts down, seizing to a stop and the fires go out.

The incident aircraft and wingman IFE'd to Eglin uneventfully. But on postflight, the pilot reportedly climbed up on the horizontal stab for a looksee. He reached over, grabbed the engine [core flow] exhaust nozzle, swung it through a 20 degree arc and called down to the ground "that's not normal, is it?"
 
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aim9xray said:
Oh no, far more interesting. Misaligned oil jet caught fire (internal engine fire). LPT shaft (long tom) was 3/4 melted through (circumference) when it failed (in tension load). With nothing to take thrust loads, the shaft and LPT shifted aft until the last stage mechanically interfaced the stators.

RUD and excitement ensued.

With no fan flow, the mixture is super rich, and the HPT overtemps and it then slags itself creating GE turbine gravel. Not to be outdone, the C sump oil return line is severed and that uncontained oil flow then catches fire. Now you have an internal and external engine fire. The pilot pulls the fire handle and stopcocks the throttle and and the engine shuts down, seizing to a stop and the fires go out.

The incident aircraft and wingman IFE'd to Eglin uneventfully. But on postflight, the pilot reportedly climbed up on the horizontal stab for a looksee. He reached over, grabbed the engine [core flow] exhaust nozzle, swung it through a 20 degree arc and called down to the ground "that's not normal, is it?"
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That's definitely interesting, in the Chinese sense of the phrase... Yikes!

Glad pilot and wing were okay after that...
 
aim9xray said:
Oh no, far more interesting. Misaligned oil jet caught fire (internal engine fire). LPT shaft (long tom) was 3/4 melted through (circumference) when it failed (in tension load). With nothing to take thrust loads, the shaft and LPT shifted aft until the last stage mechanically interfaced the stators.

RUD and excitement ensued.

With no fan flow, the mixture is super rich, and the HPT overtemps and it then slags itself creating GE turbine gravel. Not to be outdone, the C sump oil return line is severed and that uncontained oil flow then catches fire. Now you have an internal and external engine fire. The pilot pulls the fire handle and stopcocks the throttle and and the engine shuts down, seizing to a stop and the fires go out.

The incident aircraft and wingman IFE'd to Eglin uneventfully. But on postflight, the pilot reportedly climbed up on the horizontal stab for a looksee. He reached over, grabbed the engine [core flow] exhaust nozzle, swung it through a 20 degree arc and called down to the ground "that's not normal, is it?"
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You might be interested to know that having the thrust loads on the LPT causing it to move axially to mechanically interfere with the static parts during a shaft failure is a design requirement. Otherwise, the unloaded turbine will accelerate and over speed to the point of rotor rupture and uncontained pieces of the turbine disk flying out at very high speed ! It has happened in the past.

FYI - while you might think it is intuitive that the turbine is loaded aft, that is not always the case. The air pressure loads on the front and rear faces of the turbine disks can exceed those of the turbine blades. There is a lot of design work on managing the secondary airflow for cooling, bearing compartment sealing, and thrust load management.
 
F119Doctor said:
You might be interested to know that having the thrust loads on the LPT causing it to move axially to mechanically interfere with the static parts during a shaft failure is a design requirement. Otherwise, the unloaded turbine will accelerate and over speed to the point of rotor rupture and uncontained pieces of the turbine disk flying out at very high speed ! It has happened in the past.
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I did not know that; thank you. Explains the ball bearings up front and the roller bearing support in back. That would also allow for the axial thermal expansion/contraction of the LPT & HPT shafts.

In fact, that is indeed what happened, an uncontained LPT failure although I don't think the disk burst. The engine case was cut circumferentially. Back in the engine shop, it took only the removal of two sheet metal screws in the stub pylon and the rear of the engine was rolled away from the front.
 
aim9xray said:
I did not know that; thank you. Explains the ball bearings up front and the roller bearing support in back. That would also allow for the axial thermal expansion/contraction of the LPT & HPT shafts.

In fact, that is indeed what happened, an uncontained LPT failure although I don't think the disk burst. The engine case was cut circumferentially. Back in the engine shop, it took only the removal of two sheet metal screws in the stub pylon and the rear of the engine was rolled away from the front.
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You are correct that most jet engines have one ball bearing per rotor for axial positioning, usually toward the middle, with one or more roller bearings to accommodate thermal growth of the rotor towards each end. There are exceptions..
 
That makes sense Forest Green moving to a two bomber force for the USAF, after all the B-1B was only ment to be an interim bomber in the first place hence the main reason why only 100 were ever produced back in the 1980s then to be replaced by the B-2 or at least that was the initial plan.
 
Not normally a Podcast person, but this was a fun listen!

Mike hosts Col. Joseph Little, callsign “Little Joe,” to discuss how the US Air Force is modernizing the legendary B-52 BUFF to keep it flying into the 2050s—100 years after its first flight. Col Little is a B-52 Weapons Systems Officer, a US Air Force weapons school graduate, a former test squadron commander, and currently serving as the Detachment 5 Commander of the Air Force Operational Test and Evaluation Center (AFOTEC), where he oversees the B-52J program.
The B-52J modernization program is a $48 billion transformation designed to extend the bomber's life into the 2060s. It includes new engines, advanced cockpits, upgraded radar, and more, making it the most significant overhaul in the aircraft's history.
This episode covers not just the tech but also tactics, weapons, historical milestones, and untold war stories. Whether you're a fan of military aviation or interested in strategic operations, this insider’s look at the B-52 is a must-listen!
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bobbymike said:
So how’s total thrust and range compared to the old ones?
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TF33-P-3: max power 17,000 lbf (5 min limit), military power 16,500 lbf (30 min limit), max continuous power 14,500 lbf; sfc .78 lb fuel/lb thrust/hour

F130 (modified BR725): max power 17,000 lbf; sfc .657 lb fuel/lb thrust/hour

In addition to burning less fuel, the F130 has fewer parts, is more durable (longer times between planned maintenance and fewer unplanned maintenance actions), and is much easier to work on.
 
BlackBat242 said:
TF33-P-3: max power 17,000 lbf (5 min limit), military power 16,500 lbf (30 min limit), max continuous power 14,500 lbf; sfc .78 lb fuel/lb thrust/hour

F130 (modified BR725): max power 17,000 lbf; sfc .657 lb fuel/lb thrust/hour

In addition to burning less fuel, the F130 has fewer parts, is more durable (longer times between planned maintenance and fewer unplanned maintenance actions), and is much easier to work on.
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My memory is a little fuzzy, but those SFC numbers appear to be at cruise conditions, probably 40K, 0.85M. Takeoff SFC numbers should be closer to 0.55 for TF33, 0.4 for the F130. But the cruise numbers are more applicable for range comparisons.
 
BlackBat242 said:
TF33-P-3: max power 17,000 lbf (5 min limit), military power 16,500 lbf (30 min limit), max continuous power 14,500 lbf; sfc .78 lb fuel/lb thrust/hour

F130 (modified BR725): max power 17,000 lbf; sfc .657 lb fuel/lb thrust/hour

In addition to burning less fuel, the F130 has fewer parts, is more durable (longer times between planned maintenance and fewer unplanned maintenance actions), and is much easier to work on.
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and sadly, no more big clouds of dark smoke :(
 
I can remember seeing the B-52H performing at RAF Luechars airshow many years ago and wondering about all the smoke that came from the engines, that was a characteristic part of early B-52s with the TF-33 engines and it left an impression on me and one that has not left after all those years.
 
I had always wondered about what the cause was about the excess smoke from the B-52 TF-33 engines, now I know that it was partially combusted JP-8. At least the new engines won't have that problem they will burn 100% of the fuel leaving no smoke trail at the back.
 
Early jet engine combustors tended to run with a rich fuel / air ratio in the front end combustor before being diluted with additional cooling air towards the rear before reaching the turbine inlet. The overall fuel / air ratio is lean of stoichiometric, but the localized rich area would generate soot particles that passed through the turbine and seen as exhaust smoke. 99+% of the fuel was burned, but you still got soot formation.

The rich front end was to enhance cold start and altitude restart capability to meet specifications for those characteristics. Better design tools and understanding of combustion flows inside the combustor allowed for leaner burning front ends, resulting in the current “smokeless” designs.
 
I did not realise that the early turbojet B-52 also used water injection? Was that to increase thrust?
 
Water injection cools the compressor discharge air and increases its density, as well as increasing mass flow, allowing more fuel to be burned before reaching the turbine temperature limits and increasing thrust. More fuel means a higher Fuel / Air ratio (i.e. richer), which makes the soot formation even worse than before, making a smokey engine worse with water injection.
 
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So in other words it was a double edged sword, increase the thrust but also increase the smoke. Something that the USAF will be glad to get rid of after all those years with the new smoke free and more powerful engines.
 
Water injection thrust augmentation was used only on takeoff where the J57 powered B-52 and KC-135 were thrust challenged, so the really heavy smoke was only an issue around the runway. But any smoke trail is a high visibility arrow in the sky that makes the aircraft easy to locate for an adversary.
 
So no more nasty smoke trails in the Sky to alert the potential enemy to where the B-52s are coming from that is another plus point.
 
FighterJock said:
So no more nasty smoke trails in the Sky to alert the potential enemy to where the B-52s are coming from that is another plus point.
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True, but the TF33 engines on the B-52H were pretty good in regards to smoke. Of course, contrails when operating at altitude is another operational consideration, for any fuel burning engine.
 
F119Doctor said:
Water injection thrust augmentation was used only on takeoff where the J57 powered B-52 and KC-135 were thrust challenged, so the really heavy smoke was only an issue around the runway. But any smoke trail is a high visibility arrow in the sky that makes the aircraft easy to locate for an adversary.
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The J75 in the F-105 had it too.
 

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