Pratt & Whitney J58 vs General-Electric J93
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Pratt & Whitney J58 vs General-Electric J93
First of all, I'd like to clarify that the J58 that I'm talking about is not the modified bleed-bypass variants that were eventually fitted to the A-12/YF-12/SR-71, but the earlier designs which lacked it.
From what I remember reading, the Pratt & Whitney J58 was based on the J91 (which was a low pressure-ratio turbojet designed as a competitor in what would become the XB-70 program; it would ultimately lose to General Electric's J93), scaled down to 80% size for a USN high-speed high-altitude attack plane (which would ultimately emerge as the simpler A3J, powered by a pair of J79's). The projected engine thrust was to be 50% greater than that of the J75.
Okay, now here's my question. How the J58 compared to the J93 in terms of thrust?
From what I remember reading, the Pratt & Whitney J58 was based on the J91 (which was a low pressure-ratio turbojet designed as a competitor in what would become the XB-70 program; it would ultimately lose to General Electric's J93), scaled down to 80% size for a USN high-speed high-altitude attack plane (which would ultimately emerge as the simpler A3J, powered by a pair of J79's). The projected engine thrust was to be 50% greater than that of the J75.
Okay, now here's my question. How the J58 compared to the J93 in terms of thrust?
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JaneDoh
Specifically, which J93 engine are you looking for?
J93-1, build 1
J93-2, build 1
J93-2, build 2
or,
J93-2, build 3
For the J58, are you looking for:
J58X-A
J58X-B
J58X-C
Engine Thrust:
Are you looking for maximum transient thrust, steady state thrust, red-line thrust, TO thrust, maximum core thrust, sea level thrust or at altitude thrust?
How the J58 compared to the J93 in terms of thrust?
J93-1, build 1
J93-2, build 1
J93-2, build 2
or,
J93-2, build 3
For the J58, are you looking for:
J58X-A
J58X-B
J58X-C
Engine Thrust:
Are you looking for maximum transient thrust, steady state thrust, red-line thrust, TO thrust, maximum core thrust, sea level thrust or at altitude thrust?
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Brian Abraham
Because I've seen varying figures for thrust so I wanted to clarify it.
Turbine D
[quote]Specifically, which J93 engine are you looking for?
Both the J93-GE-1 and the J93-GE-3
Hmmm, I've never heard anything significant on the pre bleed-bypass J58's so I honestly don't know. Do you have additional information?
I know what takeoff-thrust, red-line thrust, sea-level thrust, and altitude-thrust mean; I don't know what maximum transient thrust, steady-state thrust (does it mean something like maximum continuous power/thrust?), or maximum core thrust (unless you're talking about turbofans in which the core is the "jet" part of the engine, but that's not applicable here as both engines are turbojets)
As I understand it the thrust figures I'd want to start out with would be full-power/full military-power (dry) at sea-level, and sea-level thrust with full afterburning (Most listed thrust figures seem to be based around full power dry and full power afterburning at sea-level)
Why don't you do your own research rather than asking others to do your leg work.
Turbine D
[quote]Specifically, which J93 engine are you looking for?
Both the J93-GE-1 and the J93-GE-3
For the J58, are you looking for:
J58X-A
J58X-B
J58X-C
J58X-A
J58X-B
J58X-C
Are you looking for maximum transient thrust, steady state thrust, red-line thrust, TO thrust, maximum core thrust, sea level thrust or at altitude thrust?
As I understand it the thrust figures I'd want to start out with would be full-power/full military-power (dry) at sea-level, and sea-level thrust with full afterburning (Most listed thrust figures seem to be based around full power dry and full power afterburning at sea-level)
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more clarification
Though having arrived "late to the dance", the "j-58/j-93" issue carries a bunch of additonal questions for me.
For openers, specs, especially physical dimensions, on both(!!) the J58 and the J91 seem to be almost imossible to come by. Bought a copy of "Advanced Engine Developement at P&W", and found only passing refernce to the J58, and nothing about its immediate predecessor, the J91, let alone the sole reason I bought the book, i.e. the JTF-17 duct-burning turbofan that was offered for the L-2000 SST.
Also curious about the "80% scale down" of the J58 from the J91. Was that a direct linear reduction or overall mass? Saw one quote where the J91 diameter was cited as "72(!!!) inches), a figure only reached by the AB nozzle of the GE-4 for the Boeing 2702 SST.
BTW, am less than impressed with the "air bleed" version of the J58, as the J57-p43WB, of which the B-52G I crewed, nearly a half century ago, had eight, featured the same thing, and for the same reason, i.e. to keep the N1 low pressure compressor (think first four stages of the single-spool J-58) from stalling when the engine was throttled back. except instead of dumping into the AB, (the BUFF didn't have any!), it simply vented straight out laterally, and would knock you on your can if you happened to be under it when it opened, as I was a couple of times. In short, any info on the J91 or the J58 would be most appreciated!. Even directions to reference sources would be good.
.
For openers, specs, especially physical dimensions, on both(!!) the J58 and the J91 seem to be almost imossible to come by. Bought a copy of "Advanced Engine Developement at P&W", and found only passing refernce to the J58, and nothing about its immediate predecessor, the J91, let alone the sole reason I bought the book, i.e. the JTF-17 duct-burning turbofan that was offered for the L-2000 SST.
Also curious about the "80% scale down" of the J58 from the J91. Was that a direct linear reduction or overall mass? Saw one quote where the J91 diameter was cited as "72(!!!) inches), a figure only reached by the AB nozzle of the GE-4 for the Boeing 2702 SST.
BTW, am less than impressed with the "air bleed" version of the J58, as the J57-p43WB, of which the B-52G I crewed, nearly a half century ago, had eight, featured the same thing, and for the same reason, i.e. to keep the N1 low pressure compressor (think first four stages of the single-spool J-58) from stalling when the engine was throttled back. except instead of dumping into the AB, (the BUFF didn't have any!), it simply vented straight out laterally, and would knock you on your can if you happened to be under it when it opened, as I was a couple of times. In short, any info on the J91 or the J58 would be most appreciated!. Even directions to reference sources would be good.
.
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OldBUFFkeeper
The bleed valve used on the J58's used on the A-12/YF-12/SR-71A/M-21 were not designed for exactly the same purpose. On the J57 as you describe, they were to deal with the fact that the LP compressor was drawing in more air than the HP stages could handle, so they put a bleed-valve in to get rid of the excess air until the RPM increased passed a certain point. Earlier engines also used bleed valves too, with single spool engines it was actually worse as they only had one shaft spinning at the same speed which made the problem worse and required either proportionately larger bleed-valves, and/or more bleed-valves to work as well. A twin-spool engine at least has the luxury of the LP spool spinning slower.
BTW, am less than impressed with the "air bleed" version of the J58, as the J57-p43WB, of which the B-52G I crewed, nearly a half century ago, had eight, featured the same thing, and for the same reason, i.e. to keep the N1 low pressure compressor (think first four stages of the single-spool J-58) from stalling when the engine was throttled back. except instead of dumping into the AB, (the BUFF didn't have any!), it simply vented straight out laterally, and would knock you on your can if you happened to be under it when it opened, as I was a couple of times.
Last edited by Jane-DoH; 7th Sep 2011 at 09:43.
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OldBUFFkeeper
Don't worry, I'm very happy to see a reply.
The J91 had an inlet diameter of 54" or 55". From what I was told the pre-bypass J58 had a diameter of 47" (which I assume is the inlet diameter)
I don't have much information on the JTF-17, though I used to know more (my memory isn't perfect). From what I remember it had a 3-stage fan, a 6-stage HP compressor, and a bypass-ratio of 1.3 with the afterburner only in the fan-duct. I do remember the engine design being relatively compact in overall design, and had no inlet guide-vanes (like modern commercial turbofans).
There was a plan to create a turbo-fanned J58, early for Lockheed's L-2000 design, but the design was not developed for one reason or another.
If you want any information on the L-2000, I have considerably more (though not absolute).
I'm not sure if the scale-down was in terms of mass-flow, or in terms of overall size. Regardless, when it comes to the listed-diameter, sometimes this means the diameter of the engine at it's widest point, not the inlet diameter.
Agreed.
Though having arrived "late to the dance"
For openers, specs, especially physical dimensions, on both(!!) the J58 and the J91 seem to be almost imossible to come by.
Bought a copy of "Advanced Engine Developement at P&W", and found only passing refernce to the J58, and nothing about its immediate predecessor, the J91, let alone the sole reason I bought the book, i.e. the JTF-17 duct-burning turbofan that was offered for the L-2000 SST.
There was a plan to create a turbo-fanned J58, early for Lockheed's L-2000 design, but the design was not developed for one reason or another.
If you want any information on the L-2000, I have considerably more (though not absolute).
Also curious about the "80% scale down" of the J58 from the J91. Was that a direct linear reduction or overall mass? Saw one quote where the J91 diameter was cited as "72(!!!) inches), a figure only reached by the AB nozzle of the GE-4 for the Boeing 2702 SST.
In short, any info on the J91 or the J58 would be most appreciated!. Even directions to reference sources would be good.
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Jane-DoH:
True, but more to the point:
After high power ops, when throttled back, the LP compressor continues to attempt to pump air into HP stages that can no longer handle all that mass flow, and the LP is thus back-pressured to the point of airfoils stalling i.e. surge. The bleed valve opens to dump the excess flow and thus permit a smooth decel.
P&W and (I believe) R-R used this method from the 1950s onward. GE found it necessary to employ a similar scheme beginning with the CF6-50 in the early 70s, although the GE system dumps into the fan discharge duct.
On the J57 as you (OldBUFFkeeper) describe, they were to deal with the fact that the LP compressor was drawing in more air than the HP stages could handle, so they put a bleed-valve in to get rid of the excess air until the RPM increased passed a certain point.
After high power ops, when throttled back, the LP compressor continues to attempt to pump air into HP stages that can no longer handle all that mass flow, and the LP is thus back-pressured to the point of airfoils stalling i.e. surge. The bleed valve opens to dump the excess flow and thus permit a smooth decel.
P&W and (I believe) R-R used this method from the 1950s onward. GE found it necessary to employ a similar scheme beginning with the CF6-50 in the early 70s, although the GE system dumps into the fan discharge duct.
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barit1
I thought prior to the J79, many single spool engines used bleed-valves of some sort, even GE ones.
P&W and (I believe) R-R used this method from the 1950s onward. GE found it necessary to employ a similar scheme beginning with the CF6-50 in the early 70s, although the GE system dumps into the fan discharge duct.
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Correct, Jane, but I was focusing on multiple-spool compressors.
Among GE's signature single-compressor-spool engines, the T58, early T64, T700/CT7, & eight-stage J85/CJ610 used bleeds for starting/low speed ops.
Among GE's signature single-compressor-spool engines, the T58, early T64, T700/CT7, & eight-stage J85/CJ610 used bleeds for starting/low speed ops.
Were it that easy...
Why don't you do your own research rather than asking others to do your leg work.
For pretty sure, I can say that the A3J was to use two J79s from the beginning. The J58 program was funded by the Navy in part to provide engines for a high-performance reconnaissance variant. It would have been powered by two non-afterburning J58s but only got as far as a mockup engine installation evaluation at North American. The F8U-3 design studies came later.
The Vought evaluation compared the J58-P-Adv to the J75 in early 1958. (The prototype had first run on Christmas Eve 1957.) Where it showed well was at altitude: much more thrust and lower SFC in afterburner. It was also intended to not have a time limit on afterburner operation, although that of course meant endurance would be badly affected.
One set of J58 specs available to Vought stated a weight of 5,900 lbs compared to the equivalent configuration of the J75 that was 50 lbs heavier. The uninstalled sea level static numbers were 300 lbs/sec air flow, Mil power thrust of 18,200 lbs at 0.925 SFC, and Combat thrust of 26,000 lbs at 2.10 SFC. Only a little better or worse than the J75. At speed and altitude, however, it was a different story. At Mach 2 and 35,000 feet at full grunt (a mass flow of 394 pounds per second), the J58 was projected by P&W to deliver 33,400 lbs of thrust (37% more than the J75 version it was being compared to) and a SFC of 2.03 (17% less).
The J58 engine diameter was stated as approximately 55 inches and the length, 18 feet with afterburner, making it four feet shorter but a little big bigger around than the J75.
The F8U-3 program was cancelled and the original version of the J58 was having development problems so the Navy lost interest in it. As noted, the A-12/SR-71 J58 was only the same engine when viewed externally in a dim light...
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Tailspin Turtle
I thought the J91 had a diameter of 55 inches, and the J58 was 80% the size of it.
OldBUFFkeeper
I found additional data for the JTF-17 turbofan
Overall Length: 215"
Inlet Diameter: 69.3"
Reverser/Suppressor Diameter (widest section): 80"
Compressor Configuration
LP: 2-Stage Fan
HP: 6-stage compressor
Combustor Type: Annular
Turbine Configuration
HP: 1-stage
LP: 2-stage
Mass Flow: 687 lbs/sec
Bypass-Ratio: 1.3:1
Pressure Ratio: 13:1
I thought the J91 had a diameter of 55 inches, and the J58 was 80% the size of it.
OldBUFFkeeper
I found additional data for the JTF-17 turbofan
Overall Length: 215"
Inlet Diameter: 69.3"
Reverser/Suppressor Diameter (widest section): 80"
Compressor Configuration
LP: 2-Stage Fan
HP: 6-stage compressor
Combustor Type: Annular
Turbine Configuration
HP: 1-stage
LP: 2-stage
Mass Flow: 687 lbs/sec
Bypass-Ratio: 1.3:1
Pressure Ratio: 13:1
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About this time of year in 1975 I attended P&W's 50th anniversary open house in E. Hartford. They had gone to a great deal of trouble to gather one each of virtually every engine they ever made, even borrowing Wasp serial number 1 (1925) from the Smithsonian. Each engine had a placard describing weight, performance, # built etc. I was particularly interested in the piston engines, but when I had my fill of that I deigned to visit the turbines.
At the end of the display was the biggest damn straight jet I had ever seen. It was missing the display placard, but I discovered the nameplate - a J58. Wow! It seemed to be about five feet inlet diameter - I'd never seen such a monster.
But then some years later at Dayton' Air Force Museum, a SR-71 (or perhaps A-12) had recently arrived. Next to it was a big engine, J58 nameplate, but it didn't seem to me as big as the one I saw out East. What I'm gleaning from this thread is that the AFM's J58 REALLY WAS smaller than the one at P&W.
At the end of the display was the biggest damn straight jet I had ever seen. It was missing the display placard, but I discovered the nameplate - a J58. Wow! It seemed to be about five feet inlet diameter - I'd never seen such a monster.
But then some years later at Dayton' Air Force Museum, a SR-71 (or perhaps A-12) had recently arrived. Next to it was a big engine, J58 nameplate, but it didn't seem to me as big as the one I saw out East. What I'm gleaning from this thread is that the AFM's J58 REALLY WAS smaller than the one at P&W.
About this time of year in 1975 I attended P&W's 50th anniversary open house in E. Hartford. They had gone to a great deal of trouble to gather one each of virtually every engine they ever made, even borrowing Wasp serial number 1 (1925) from the Smithsonian. Each engine had a placard describing weight, performance, # built etc. I was particularly interested in the piston engines, but when I had my fill of that I deigned to visit the turbines.
At the end of the display was the biggest damn straight jet I had ever seen. It was missing the display placard, but I discovered the nameplate - a J58. Wow! It seemed to be about five feet inlet diameter - I'd never seen such a monster.
But then some years later at Dayton' Air Force Museum, a SR-71 (or perhaps A-12) had recently arrived. Next to it was a big engine, J58 nameplate, but it didn't seem to me as big as the one I saw out East. What I'm gleaning from this thread is that the AFM's J58 REALLY WAS smaller than the one at P&W.
At the end of the display was the biggest damn straight jet I had ever seen. It was missing the display placard, but I discovered the nameplate - a J58. Wow! It seemed to be about five feet inlet diameter - I'd never seen such a monster.
But then some years later at Dayton' Air Force Museum, a SR-71 (or perhaps A-12) had recently arrived. Next to it was a big engine, J58 nameplate, but it didn't seem to me as big as the one I saw out East. What I'm gleaning from this thread is that the AFM's J58 REALLY WAS smaller than the one at P&W.
The JT-12 we widely know today went on to power many business type or exec type aircraft and at least one with an afterburner
The JT-11 was developed for the government as the J58 powering the SR71
The JT-9 never made it to the supersonic bomber but was the largest of these similar shapes and maybe the one that you recall. The mockup of the JT-11 (Pre J58) still sits in the museum at P&W today and it's externals look nothing like the J58 today.
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BTW - a month or two earlier, GE-Lynn (MA) had their open house, and in the test cell area a J85 was running. It was apparently on an endurance test program, and they let the kids in the crowd sit at the throttle and exercise the hell out of it.
At Pratt, when I wandered into the test cells, there was a loud noise of an engine running. I kept looking for the action, but when I reached the apparent source of the noise, two test cells were open with visitors walking in and out to see static engines. But what of the noise??
Finally I looked up in the overhead - and saw an array of very large loudspeakers...
At Pratt, when I wandered into the test cells, there was a loud noise of an engine running. I kept looking for the action, but when I reached the apparent source of the noise, two test cells were open with visitors walking in and out to see static engines. But what of the noise??
Finally I looked up in the overhead - and saw an array of very large loudspeakers...
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I concede, Barit1, you're "bang-on", as regards that "throttling back". Learned it the hard way on numerous winter launches, wlaking unerneath an engine pod, when the guy at the throttles, pulled back. But, I would submit, regardless of the specific reason why(!!) the front stages are feeding the rear ones more air than they can handle, and even with just one spool, the concept still stands.
Also, given the specs cited here, for the J-91, I would bet that the "monster turbojet" seen, without a placard, may well have been a surviving example, which for superficially resembling a J-58, except for sheer size, could have been confusing.
Would have loved to have been there and seen it myself.
In any case, thanks to all the great minds assembled here for the superb info re my questions, and does anyone know of a book containing some of this stuff in print so I don't have to keep pestering you?
BTW, has anyone noticed that the basic J-58 "gas generator"actually looks like nothing more than a J-75, with the high pressure compressor missing, and the N1 attached directly to the diffuser casing?
Last does anyone know if the J-91, carrying after all, the "in-house" designation of JT-9, was in fact the core for the high bypass ratio JT-9D, and if not why did P&W use the number twice?
Also, given the specs cited here, for the J-91, I would bet that the "monster turbojet" seen, without a placard, may well have been a surviving example, which for superficially resembling a J-58, except for sheer size, could have been confusing.
Would have loved to have been there and seen it myself.
In any case, thanks to all the great minds assembled here for the superb info re my questions, and does anyone know of a book containing some of this stuff in print so I don't have to keep pestering you?
BTW, has anyone noticed that the basic J-58 "gas generator"actually looks like nothing more than a J-75, with the high pressure compressor missing, and the N1 attached directly to the diffuser casing?
Last does anyone know if the J-91, carrying after all, the "in-house" designation of JT-9, was in fact the core for the high bypass ratio JT-9D, and if not why did P&W use the number twice?
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Tailspin Turtle
Hey -- I have your book. I'm surprised the F8U-3 was as good a performer as it was, I'm surprised it could run supersonic longer than the F-104 could. It also resolved a lot of questions I had regarding the fire-control system.
I'm surprised they couldn't do Mach 3 with the J75 as it was. There were three models that Chance-Vought built, the V-401 which was the baseline model; then there was the V-418/-419 which I think were J-58 powered (were those the advanced variants described)?
When you say 55 inches, do you mean at the widest section, or at the intake? Because IIRC the J91 was 55 inches at the inlet diameter and the J58 was supposedly like 80% the size.
I thought the J58 was said to produce 50% more thrust than the J75 (33,400 is less than 50% greater)
lomapaseo
You sure about the JT12? I looked at a picture of it and it didn't look at all like a JT9 and JT11
It was designated the J91 by the military.
It was called the J58 back then too. The versions adapted for the A-12/YF-12/SR-71/M-21 were substantially different and had little in common.
R.C.
I spent some time looking for J58 stuff when I was writing my monograph on the Vought F8U-3 "Super Crusader", for which the original J58 was considered as a way to further increase its top speed and altitude.
Mach 3 at 70,000 feet was the goal.
The J58 engine diameter was stated as approximately 55 inches and the length, 18 feet with afterburner, making it four feet shorter but a little big bigger around than the J75.
One set of J58 specs available to Vought stated a weight of 5,900 lbs compared to the equivalent configuration of the J75 that was 50 lbs heavier. The uninstalled sea level static numbers were 300 lbs/sec air flow, Mil power thrust of 18,200 lbs at 0.925 SFC, and Combat thrust of 26,000 lbs at 2.10 SFC. Only a little better or worse than the J75. At speed and altitude, however, it was a different story.
lomapaseo
The JT-9, the JT-11 and the JT-12 (I couldn't tell them apart looking at the cut-a-way drawings)
The JT-9 never made it to the supersonic bomber but was the largest of these similar shapes and maybe the one that you recall.
The mockup of the JT-11 (Pre J58) still sits in the museum at P&W today and it's externals look nothing like the J58 today.
R.C.
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Jane-DoH
There is a good history book available (somewhere) that details the history of GE's aircraft engine business from the beginning. It might go well with the history of P&W's jet engine heritage. The book's title is "Eight Decades of Progress", a heritage of aircraft engine technology. It was published in 1990 and the Library of Congress Catalog Card Number is 90-082948.
There is quite a bit of information in this book that is being discussed here plus much more and you may find it to be a very informative read.
TD
There is a good history book available (somewhere) that details the history of GE's aircraft engine business from the beginning. It might go well with the history of P&W's jet engine heritage. The book's title is "Eight Decades of Progress", a heritage of aircraft engine technology. It was published in 1990 and the Library of Congress Catalog Card Number is 90-082948.
There is quite a bit of information in this book that is being discussed here plus much more and you may find it to be a very informative read.
TD