Buff upgrade
Another reason for keeping 8 engines was the design of the systems to get multiple redundancy from several sources for hydraulics, electrics, air etc.
Losing 1/2 of the electrics for an application is better than losing it all.
Losing 1/2 of the electrics for an application is better than losing it all.
That would mean a total pylon/ wing redesign along with hydraulics, electrics etc along with flight testing for engine out performance etc.
They opted for swap 8 for 8 to minimise the changes required.
https://theaviationist.com/2022/09/2...nacelles-test/
https://www.airandspaceforces.com/ar...-for-the-b-52/
While USAF once considered four large-fan commercial engines instead, it stuck with eight to avoid substantial redesign of the wing, cockpit, and other components, and to minimize risk and delay.
They opted for swap 8 for 8 to minimise the changes required.
https://theaviationist.com/2022/09/2...nacelles-test/
https://www.airandspaceforces.com/ar...-for-the-b-52/
While USAF once considered four large-fan commercial engines instead, it stuck with eight to avoid substantial redesign of the wing, cockpit, and other components, and to minimize risk and delay.
Looking just at the thrust numbers of the new B-52's and the B-2's engines (and assuming the latter will be similar in B-21) I wonder why they decided not to use the Raider's engines as replacements.
Last edited by Bahrd; 13th Jan 2023 at 08:06.
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"I wonder why they decided not to use the Raider's engines as replacements."
IF they are different its probably because the B21 engines have to fit in a stealth airframe and environment
The B-52 is so unstealthy you just fit the ones that are the best deal on cost, maintainability, economy etc as it makes no effective difference to the radar signature
IF they are different its probably because the B21 engines have to fit in a stealth airframe and environment
The B-52 is so unstealthy you just fit the ones that are the best deal on cost, maintainability, economy etc as it makes no effective difference to the radar signature
I am sure US AF, together with Northrop Grumman and Boeing, have examined the single engine type option in both bombers and just wondered what the reason would be not to choose it.
Ecce Homo! Loquitur...
Not sure why, two centrally mounted engines with a centreline exhaust shouldn’t prove a major issue with a single engine failure.
Might need a titanium divider between them though - as in the F-111.
Might need a titanium divider between them though - as in the F-111.
""one of the reason B-52 has (and will have) eight engines is the redundancy"
no - when it was designed/built (70 years ago) they needed 8 engines of the time to make it work
no - when it was designed/built (70 years ago) they needed 8 engines of the time to make it work
According to 'former' poster Ken V, the big issue with going with four engines was messing up the ability to carry wing mounted weapons.
Engine maintenance was not considered to be much of a concern. The time-on-wing between overhauls is so high on modern engines (15-20,000 hours between overhauls being pretty common) that the airframe would wear out before the engines...
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That would mean a total pylon/ wing redesign along with hydraulics, electrics etc along with flight testing for engine out performance etc.
They opted for swap 8 for 8 to minimise the changes required.
https://theaviationist.com/2022/09/2...nacelles-test/
https://www.airandspaceforces.com/ar...-for-the-b-52/
While USAF once considered four large-fan commercial engines instead, it stuck with eight to avoid substantial redesign of the wing, cockpit, and other components, and to minimize risk and delay.
They opted for swap 8 for 8 to minimise the changes required.
https://theaviationist.com/2022/09/2...nacelles-test/
https://www.airandspaceforces.com/ar...-for-the-b-52/
While USAF once considered four large-fan commercial engines instead, it stuck with eight to avoid substantial redesign of the wing, cockpit, and other components, and to minimize risk and delay.
Yeah, I'd say having to incorporate landing gear into nacelles represents a ground clearance issue and extensive engineering effort in the solution. It sounds like a bad solution to me.
You are correct, weapons carriage on wing was another issue that was mentioned.
You are correct, weapons carriage on wing was another issue that was mentioned.
The outrigger gear on the BUFF wingtips are not intended to carry significant load - they are basically there just to support the wing statically - the main body gear are intended to take all the landing loads (they don't even touch the ground unless the wing is carrying lots of fuel). So in short, the structural requirements were not that big of deal - the mass and thrust of the engines was a far more significant design consideration (for example, the gyroscopic loads of a rapidly spinning turbofan engine at rotation are massive).
Testing Underway for New B-52 Engines | Air & Space Forces Magazine (airandspaceforces.com)
Testing is underway of two Rolls-Royce F130 engines to confirm how they perform close together and to test new digital engine controls. Rolls is conducting the tests at NASA’s Stennis Space Center, Miss., the company said.
“We want to be wrapped up by the middle of the year with this testing … because confirming that we’ve got the right inlet paces a lot of things, in terms of finalizing what the nacelle is going to look like,” Rolls-Royce B-52/F130 program director Scott Ames said in an interview.
The program is “marching toward” a critical design review in early 2024, he said. These tests will ensure “we’re ready to go with the next phase of the development program, [and] flight testing, etc.,” Ames said. “We want to make sure we get this locked in.”
The two-engine nacelle test was “a part of the Rolls-Royce proposal from the get-go,” he said. “Coming to a decision finalizing what the inlet mold lines look like for the nacelle by the middle of the year is our overarching objective.”
“We want to be wrapped up by the middle of the year with this testing … because confirming that we’ve got the right inlet paces a lot of things, in terms of finalizing what the nacelle is going to look like,” Rolls-Royce B-52/F130 program director Scott Ames said in an interview.
The program is “marching toward” a critical design review in early 2024, he said. These tests will ensure “we’re ready to go with the next phase of the development program, [and] flight testing, etc.,” Ames said. “We want to make sure we get this locked in.”
The two-engine nacelle test was “a part of the Rolls-Royce proposal from the get-go,” he said. “Coming to a decision finalizing what the inlet mold lines look like for the nacelle by the middle of the year is our overarching objective.”
From the flight manual.
FLIGHT CHARACTERISTICS WITH ENGINE FAILURE
MULTI-ENGINE FAILURE ON ONE SIDE
During inflight emergencies involving multi-engine failures on one side, applications of large amounts of rudder and lateral control are necessary in order to maintain control when extreme amounts of asymmetrical thrust exist or are applied, Application of this control creates severe loads on the aircraft structure. These loads vary in magnitude in accordance with the degree of thrust dissymmetry, degree of deflection of corrective rudder. rate of rudder application, amount of yaw/roll displacement that has taken place prior to rudder application, abruptness with which engine thrust is removed, indicated airspeed, gross weight, center oi‘ gravity, fuel distribution, amount oi air turbulence present, aircraft configuration including flaps and landing gear positions, missile loading, external tank loading, etc. If these variables occur in certain combinations, critical structural loads can result. In view of the difficulty in controlling these variables, close observance of the following procedure will minimize the possibility of structural overload.
1. If asymmetrical thrust develops abruptly, the resulting yaw/roll tendency should be counteracted with lateral control followed by steady rudder application. Trim as required to balance control forces.
2. If thrust requirements permit, readjust the power on the remaining engines to minimize control surface deflections‘ Power adjustments should be applied slowly and simultaneously with control surface movement.
3. Avoid turbulent air and limit bank angle to 20° maximum.
PERFORMANCE - WARNING - Nonzero lateral trim resulting from inoperative engines must not be compensated for by fuel manipulation because an uncontrollable roll may occur when power is reduced on approach for landing.
This aircraft is unique in its ability to handle asymmetrical thrust conditions provided the prescribed procedures are followed. See "Multi-Engine Failure on One Side, " this section. The takeoff and climbout performance of the aircraft with inoperative engines is shown in Parts 2, 3, and 4 of the Appendix, In each case, the inoperative engines are assumed to be in the most outboard positions and all on the same side. This is the most adverse condition from the stand point of trim drag which is associated with control surface deflections. Advancing the throttles to full travel in an emergency situation will give maximum thrust. This may exceed normal engine limits. Overthrusting the engines will accentuate the aircraft control problems and reduce engine life. All instances of overthrust. as indicated by excessive EGT and/or rpm will be recorded can Form 781. See "Engine Limitations," Section V.
FLIGHT CHARACTERISTICS WITH ENGINE FAILURE
MULTI-ENGINE FAILURE ON ONE SIDE
During inflight emergencies involving multi-engine failures on one side, applications of large amounts of rudder and lateral control are necessary in order to maintain control when extreme amounts of asymmetrical thrust exist or are applied, Application of this control creates severe loads on the aircraft structure. These loads vary in magnitude in accordance with the degree of thrust dissymmetry, degree of deflection of corrective rudder. rate of rudder application, amount of yaw/roll displacement that has taken place prior to rudder application, abruptness with which engine thrust is removed, indicated airspeed, gross weight, center oi‘ gravity, fuel distribution, amount oi air turbulence present, aircraft configuration including flaps and landing gear positions, missile loading, external tank loading, etc. If these variables occur in certain combinations, critical structural loads can result. In view of the difficulty in controlling these variables, close observance of the following procedure will minimize the possibility of structural overload.
1. If asymmetrical thrust develops abruptly, the resulting yaw/roll tendency should be counteracted with lateral control followed by steady rudder application. Trim as required to balance control forces.
2. If thrust requirements permit, readjust the power on the remaining engines to minimize control surface deflections‘ Power adjustments should be applied slowly and simultaneously with control surface movement.
3. Avoid turbulent air and limit bank angle to 20° maximum.
PERFORMANCE - WARNING - Nonzero lateral trim resulting from inoperative engines must not be compensated for by fuel manipulation because an uncontrollable roll may occur when power is reduced on approach for landing.
This aircraft is unique in its ability to handle asymmetrical thrust conditions provided the prescribed procedures are followed. See "Multi-Engine Failure on One Side, " this section. The takeoff and climbout performance of the aircraft with inoperative engines is shown in Parts 2, 3, and 4 of the Appendix, In each case, the inoperative engines are assumed to be in the most outboard positions and all on the same side. This is the most adverse condition from the stand point of trim drag which is associated with control surface deflections. Advancing the throttles to full travel in an emergency situation will give maximum thrust. This may exceed normal engine limits. Overthrusting the engines will accentuate the aircraft control problems and reduce engine life. All instances of overthrust. as indicated by excessive EGT and/or rpm will be recorded can Form 781. See "Engine Limitations," Section V.
The oddity with the Buff is they had a marginal structure at the rear end, and a rudder that was designed to give excessive torsion for the amount of lateral force that may be needed. Couple that all with the design decision to go with spoilers for roll control, and you are endowing the plane with the qualities of being a bit of a beast, and not just to the other team, but to the poor schmucks that are cocooned in the plane. Design constraints in the late 40s led to the configuration that was chosen, and they have lasted some time with only a modest loss of personnel.
How bad the inherent handling of the B52 is is exhibited in the Fairchild practice disaster. While the driver and the command system got beaten up for the event, it is interesting to note that the spoiler response was being saturated quite early in the left turn that Holland entered. The speed and the bank resulted in exceeding the authority of the spoiler system, and the rudder, well, we have just commented on the rudder's authority. Occasionally, limits are there for very good reasons, bank limits on the Buff were rational, and needed to be respected. Asymmetric thrust was the last resort remaining to come out of the steepening bank, and that has not been indicated as having been attempted by the crew. Pity, McGeehan died ensuring that no other pilot in his squadron had to fly with a pilot who has a known history of operational violations.
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Good news. Just don't do aerobatic displays with it, eh? It's not a Vulcan!
Ecce Homo! Loquitur...
https://www.airandspaceforces.com/re...ed-b-52-b-52j/
It’s Official: The Re-Engined B-52 Will be the B-52J
Once they receive their new Rolls Royce F130 engines, B-52Hs will become B-52Js, according to the Air Force’s fiscal 2024 budget documents.
The designation resolves a question that had been debated for several years, as the B-52 undergoes some of the most significant improvements in the H model’s 61-year service life.
“Any B-52H aircraft modified with the new commercial engines and associated subsystems are designated as B-52J,” the Air Force said in justification documents for its 2024 budget request.
The service had been considering various designations for the improved Stratofortress, because in addition to new engines, the B-52 will also be receiving a new radar, as well as new communications and navigation equipment and weapons, among other improvements intended to keep it credible and capable through the 2050s.
Given the number of major changes, Global Strike Command had considered using interim designations—“J” model aircraft would have then become B-52Ks.…
It’s Official: The Re-Engined B-52 Will be the B-52J
Once they receive their new Rolls Royce F130 engines, B-52Hs will become B-52Js, according to the Air Force’s fiscal 2024 budget documents.
The designation resolves a question that had been debated for several years, as the B-52 undergoes some of the most significant improvements in the H model’s 61-year service life.
“Any B-52H aircraft modified with the new commercial engines and associated subsystems are designated as B-52J,” the Air Force said in justification documents for its 2024 budget request.
The service had been considering various designations for the improved Stratofortress, because in addition to new engines, the B-52 will also be receiving a new radar, as well as new communications and navigation equipment and weapons, among other improvements intended to keep it credible and capable through the 2050s.
Given the number of major changes, Global Strike Command had considered using interim designations—“J” model aircraft would have then become B-52Ks.…
