Pratt & Whitney J58 vs General-Electric J93

[Jane-DoH]

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?

[Brian Abraham]

Why don't you do your own research rather than asking others to do your leg work.

[lomapaseo]

The Pprune Tech Forum is an excellent place to do research providing the questions are well posed and specific.

[Turbine D]

JaneDoh
How the J58 compared to the J93 in terms of thrust?

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?

[Jane-DoH]

Brian Abraham

Why don't you do your own research rather than asking others to do your leg work.

Because I've seen varying figures for thrust so I wanted to clarify it.


Turbine D

Specifically, which J93 engine are you looking for?

Both the J93-GE-1 and the J93-GE-3

[quote]For the J58, are you looking for:

J58X-A
J58X-B
J58X-C

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?

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?

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)

[OldBUFFkeeper]

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.
.

[Jane-DoH]

OldBUFFkeeper

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.

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.

[Jane-DoH]

OldBUFFkeeper

Though having arrived "late to the dance"

Don't worry, I'm very happy to see a reply.

For openers, specs, especially physical dimensions, on both(!!) the J58 and the J91 seem to be almost imossible to come by.

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)

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.

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).

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.

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.

In short, any info on the J91 or the J58 would be most appreciated!. Even directions to reference sources would be good.

Agreed.

[barit1]

Jane-DoH:
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.

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.

[Jane-DoH]

barit1

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.

I thought prior to the J79, many single spool engines used bleed-valves of some sort, even GE ones.

[barit1]

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.

[Tailspin Turtle]

Why don't you do your own research rather than asking others to do your leg work.

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.

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...

[Jane-DoH]

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

[barit1]

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.

:8

[tmusser]

Frontiers of Flight Museum, located at Dallas (TX) Love Field, has (or had) a J-58 on display.

[lomapaseo]

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.



In the 50's there were three similar engine mockups in shape. 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-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.

[barit1]

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... :}

[OldBUFFkeeper]

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?

[Jane-DoH]

Tailspin Turtle

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.

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.

Mach 3 at 70,000 feet was the goal.

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)?

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.

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.

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.

I thought the J58 was said to produce 50% more thrust than the J75 (33,400 is less than 50% greater)


lomapaseo

The JT-9, the JT-11 and the JT-12 (I couldn't tell them apart looking at the cut-a-way drawings)

You sure about the JT12? I looked at a picture of it and it didn't look at all like a JT9 and JT11

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.

It was designated the J91 by the military.

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.

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.

[Turbine D]

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

[OldBUFFkeeper]

The beginning of your text makes me want to scratch my old, grey, head in wonder, as I have heard it before, and many times. Given that the J-58 and the J-93 were roughly the size, to hear that the J-58 was an 80%(!!) "scale model" of the J-91, originally offered as a competitor to........... the J-93, as a B-70 powerplant, one must wonder just how much of a monster that engine (the J-91) must have been, and what was P&W thinking when they offered it as a J-93 alternative? Perhaps, there was a FOUR(!!)-engined version of the Valkyrie that no one, (certainly not I), has never seen! But then again, when one hears the thrust figures for the J-91, (approx. 41,500lbs w/AB) they're not that much greater than the most powerful versions of either the J58 or J-93, both of which "clocked in" at around 33,500/35,000lbs. To add insult to injury, the weight, around four and a half TONS(!!!), gave a T/W ratio that, even in the '60's, was almost pitiful. Anyone have any further specs on the "P&W MONSTER(!!!)", or, even better yet, know eher we can find pics?


OldBuffkeeper

[lomapaseo]

OldBUFF
Ther are an awful lot of paper engines that never found a home. It's pretty hard to make comparisons between engines.

Along the way the paper engine actually morphs into development hardware with many chaqnges depending on the whims of the guy with the pocketbook (mostly Uncle Sam). After the entrance into the commercial jet age a designer might even produce drawings that mimic actual for sale hardware for commercial service, hence some of these engines that get the JT prefixes in the P&W world.

The development hardware lots of times starts with some modules (compressor, burner, Turbine, afterburner) that are tested separately against possible combinations that might sell. Thus a collection of like modules might end up with an afterburner or not depending on the mission it might fit. The hardware still in the P&W museum in East Hartford only mimics a few of these combinations. Many other combinations have already been sold for scrap.

I've heard stories of stuff 50-60 years ago of giant burners that were 2-3 times the diameter of the high turbine. I never saw any signs of these on an aircraft.

[OldBUFFkeeper]

Great info there, and now recall that the first two stages of the, by then defunct, J-91 became the fan for the turbofan version of the J-57/JT-3, i.e. the TF-33/JT-3D. Since the inlet diameter of the that engine was around 53 inches, your figure for the J-91 seems borne out.
Still would like to find some pics of the J-91, and am also still wondering how/why P&W managed to use the same designation, JT9, for what now seem to be TWO COMPLETELY SEPARATE(!!!) gas generators, since there is no way the core for the JT-9D turbofan could have been 50+ inches in diameter at the first stage after the fan? BTW, does anyone out there know where one can find cutaway views of any of these powerplants?

[OldBUFFkeeper]

Upon measuring off a photograph of an operational version of the JT-11D-20, it became excrutiatingly self-evident that the total cross sectioal area, and, by definition, delivery capability, of the six bypass tubes coming off the compressor just after the fourth stage, was substantially less than the similarly tasked area available with a fully annular bypass duct in a classic turbofan. Which leads to my question: does anyone know what the claimed "bypass ratio" of the JT-11"D" actually was?
When looking at the respective bypass ducts of F-100s, F-110s, and F-135s, measuring the available areas there, dividing by six, then PI, extracting the square root, and multiplying by two, i.e. the reverse figuring for the area of a circle, I came up with tube diameters more than TWICE(!!!) the diameter of those on the J-58, thus exposing the JT-11D as not much more than a "leaky" turbojet, and leaving me to wonder just how useful such an arrangement could ultimately be above mach-3 when ANY(!!!) rotating machinery in the way of ramjet/afterburner airflow is about as desirable as a drag chute?

[lomapaseo]

Upon measuring off a photograph of an operational version of the JT-11D-20, it became excrutiatingly self-evident that the total cross sectioal area, and, by definition, delivery capability, of the six bypass tubes coming off the compressor just after the fourth stage, was substantially less than the similarly tasked area available with a fully annular bypass duct in a classic turbofan. Which leads to my question: does anyone know what the claimed "bypass ratio" of the JT-11"D" actually was?
When looking at the respective bypass ducts of F-100s, F-110s, and F-135s, measuring the available areas there, dividing by six, then PI, extracting the square root, and multiplying by two, i.e. the reverse figuring for the area of a circle, I came up with tube diameters more than TWICE(!!!) the diameter of those on the J-58, thus exposing the JT-11D as not much more than a "leaky" turbojet, and leaving me to wonder just how useful such an arrangement could ultimately be above mach-3 when ANY(!!!) rotating machinery in the way of ramjet/afterburner airflow is about as desirable as a drag chute?


Agree,

but how else would you get the vehicle up to that speed to begin with where the compresor becomes useless?

It's not the relative efficiency of the parts that's important, it's the mission objective being met

[Jane-DoH]

OldBUFFkeeper

The beginning of your text makes me want to scratch my old, grey, head in wonder, as I have heard it before, and many times. Given that the J-58 and the J-93 were roughly the size, to hear that the J-58 was an 80%(!!) "scale model" of the J-91, originally offered as a competitor to........... the J-93, as a B-70 powerplant, one must wonder just how much of a monster that engine (the J-91) must have been, and what was P&W thinking when they offered it as a J-93 alternative?

The J91 had a pressure-ratio of 7:1, and the J58 had a pressure-ratio (IIRC) of 8.8:1 so the J58 would get more thrust for it's size. I'm not sure if the J91 had a variable IGV or the airflow-controlled nozzle, but the J58 had both of these. The former may have been to keep the turbine inlet temperature in line at high mach-numbers; the latter, might have been to squeeze extra AB performance out of the engine.

I'd like to make note that I'm not sure if 80% scale meant 80% the weight, 80% the diameter, 80% the mass-flow.

Perhaps, there was a FOUR(!!)-engined version of the Valkyrie that no one, (certainly not I), has never seen! But then again, when one hears the thrust figures for the J-91, (approx. 41,500lbs w/AB) they're not that much greater than the most powerful versions of either the J58 or J-93, both of which "clocked in" at around 33,500/35,000lbs.

That's because of the lower pressure ratio. I actually didn't know the thrust was that high actually.

To add insult to injury, the weight, around four and a half TONS(!!!)

The J91 weighed 9,000 pounds?

Great info there, and now recall that the first two stages of the, by then defunct, J-91 became the fan for the turbofan version of the J-57/JT-3, i.e. the TF-33/JT-3D. Since the inlet diameter of the that engine was around 53 inches, your figure for the J-91 seems borne out.

I'm not sure if the two compressor stages were exactly the same or simply derived from the J91. Still there's a connection between the two.

am also still wondering how/why P&W managed to use the same designation, JT9, for what now seem to be TWO COMPLETELY SEPARATE(!!!) gas generators, since there is no way the core for the JT-9D turbofan could have been 50+ inches in diameter at the first stage after the fan?

Manufacturers have their own proclivities when it comes to designating their products. For example the JT3C was a J57 variant that powered the 707 and DC-8. When they made a turbofan; they called it the JT3D. After that point, virtually every turbofan they developed had a -D after it.

Upon measuring off a photograph of an operational version of the JT-11D-20, it became excrutiatingly self-evident that the total cross sectioal area, and, by definition, delivery capability, of the six bypass tubes coming off the compressor just after the fourth stage, was substantially less than the similarly tasked area available with a fully annular bypass duct in a classic turbofan.

Because it wasn't designed to use the fan to produce thrust like a propeller -- it was meant to dump excessive air around the engine as a way of lowering the pressure-ratio at high-mach as a means of lowering the turbine-inlet temperature.

The airflow was fed into the afterburner as a way of making use of that compressed air. It increased the pressure of the airflow in the afterburner inlet and also increased the air-percentages (60-65% of the engine exhaust is air -- the bypass air is 100% oxygen)

Which leads to my question: does anyone know what the claimed "bypass ratio" of the JT-11"D" actually was?

Allegedly 65% of the airflow was routed around the engine, and fed into the afterburner. So the bypass was 2.86:1

When looking at the respective bypass ducts of F-100s, F-110s, and F-135s, measuring the available areas there, dividing by six, then PI, extracting the square root, and multiplying by two, i.e. the reverse figuring for the area of a circle, I came up with tube diameters more than TWICE(!!!) the diameter of those on the J-58, thus exposing the JT-11D as not much more than a "leaky" turbojet, and leaving me to wonder just how useful such an arrangement could ultimately be above mach-3 when ANY(!!!) rotating machinery in the way of ramjet/afterburner airflow is about as desirable as a drag chute?

The idea evidently was to basically operate as a turbojet (which you need for takeoff and landing), and progressively relieve the excess pressure more and more as you went faster and faster and feed it into the afterburner which doesn't have the same limits as the turbo-compressor (the core of the engine) -- plus I'm not 100% sure of this, even without turbine temperature limits, there might be a point of diminishing returns as to your ability to compress air and get propulsive efficiency out of it (without cooling the air, which is used with the SABRE and Scimitar engine designs used for SKYLON and the Reaction Engines LAPCAT A2)

Regardless there's only a certain degree of efficiency you need to accomplish a task -- the rest is gravy.

[OldBUFFkeeper]

Brilliant work, from both of you! I'm impressed! HOWEVER(!!!), given the actually inability of a one-inch hose to deliver the same flow, all other factors being equal, of a two-incher, I must continue to scratch my head as to the actual bypass ratio of the JT-11"D", especially as the cited figure of "2.86(!!!??) to one" not only exceeds that of the very much below mach-3 F-101 on the B-1, but also, (again) considering that pressures at that longitudinal point, just aft of the fourth stage, would be, more or less, uniform from hub to casing, the combined amount of area of the six tubes just doesn't provide that much relief as to provide the bypass ratio you cite. Maybe I'm missing something.

Also, as to the common use of a designation, "JT-3" remained that "D", or no "D". Why not the same for the "JT-("?


OldBUFFKkeeper

[lomapaseo]

Also, as to the common use of a designation, "JT-3" remained that "D", or no "D". Why not the same for the "JT-("?



Come again :confused:

[OldBUFFkeeper]

The point I was trying to make, in my clumsy way, was that if only for some semblance of corporate continuity, designations have tended to be contiguous, with "JT", i.e. "jet turbine" being the same for P&W until a few decades ago when they went to a new system based, among other things, on the thrust of the engine. Until then, the sequential arrangement was quite clear, i.e. "JT-3" (J-57), followed by "JT-4"(J-75), etc. Of course, even this can still be confusing when one notes that the next developement, the "JT-8", has a LOWER(!!) military designation "J-52" than either the J-57, and J-75, both of which it is clearly a technological successor. In any case, as if that wasn't enough, I'm having a serious problem with the allegation, offered in several sites, that BOTH(!!!) the J-52, and the J-58 were scaled down descendants of the massive J-91.

As I've noted before, externally, the basic J-58 looks roughly like a J-75, minus the N-2 casing, as well as the distinctive "bump" in the diffuser casing of the J-57. By contrast, the J-52 (i.e. JT-8) looks like nothing more than a "miniature J-75 (JT-4)", at least as it appeared to me in the "dash-4" for each engine, as I gleaned when thumbing through each. Not insignificantly, the site claiming common ancestry with the J-91 then shows a cross section, allegedly of the JT-8 (J-52), that looks nothing at all like what I saw in the tech manuals. Specifically, the JT-3 through JT-8 had an N-1 in which the hub was parallel to the axis and the casing tapered inward, moving rearwardly, and an N-2, in which the casing was of a constant diameter while the hub increased as one moved towards the final stages. In the view provided at this one site, the arrangement was REVERSED(!!), giving an external profile unlike anything I'd even seen from P&W, and roughly resembling a RR Avon, but with the compressor divided into two separate sections.

Having been "professionally aquainted" with the JT-8 from both extremes, beginning with its first employment as the J-52, still too "hot" and unreliable to be used on a manned aircraft, instead driving the GAM-77 Hound Dog missile, of which the B-52 I crewed carried two, and its "fully tamed" ultimate application as the JT-8D turbofan, three of which, drove the B-727 airliner, countless numbers of which, I serviced, while employed at United Air Lines, after leaving the service, not to mention watchng the RM-8 afterburning version of the turbofan, drive the Saab J-37, a spectacular demonstrator at air shows of the real meaning of "specific excess power", I know what one looks like, and now stand even more confused about the P&W lineage than before. HELP!!!

P.S. Have also learned of a planned genuine turbofan version of the J-58 that was the first proposal for propulsion of the L-2000, along with other claims that the core of the actual JTF-17 was, in fact, nothing but a modified J-58.

Any info there, anyone?

Am at least realising substantial savings on haircuts, as ripping it out over this stuff seems to work fairly well.

[lomapaseo]

One can only imagine what it must have been like in the smoke filled rooms in the back offices of P&W back in the 50's when all this was going on.

On one side of the room you have the cigar chomping military sales guys stating what the latest paper airplanes were being drawn up in the far off skunk works, and that millions of development money would be there for the asking if P&W would offer up product designs on paper to match the paper airplanes the government had already decided to fund for study.

It wouldn't have taken much for the P&W advanced engines groups to dust off a previously desgned and protyped model, add some stages, and afterburner and then claim that they could easily extropolate a performance and thrust size increase based on old data and with a few million actually commit some componet (scale hardware) on rigs to verify the feasibility in a step funded program.

Then on the other side of the room the fleldgling commerical applications dream merchants were saying that some of the military big guys like Douglas and Boeing were thinking of entering the jet age if an engine might be avialble in 5 years or so.

Not to worry it would be relatively easy to move some accessories around take off an afterburner and offer up paper model like the JT3 series and then a b then c as the specs tried to keep pace with the same dreams in the commerial sides of Douglas, Lockheed and Boeing. Actually with enough development money it actually worked as the Collier trophy for the J57 attests.

By the time the commecrial airplane guys finally settled on a plane that matched the available thrust to weight, then the various development models finally settled on a compressor and turbine combination that would match and a salable model would actually be sold in quantity like the JT3c

This went back and forth through the 50's and other models jumped in like the J60/JT12 and the J52/JT8 J58/JT11, even though the actual sales numbers might actually have been low and the model itself stored as a development only machine for future possibilities.

So when the first concept of a commercialy viable fan came along all they did was trot out a bigger compressor blade and bypass part of the air and calim better fuel consumption and quieter noise4 signature. While at the same time changing the4 model number by one charcted from a "C" to a "D". This was such a hit with the JT3c moving to a JT3D that they figured they could do the same thing with the orphaned JT8 by adding a new compressor and a fan and since the "D" change meant oodles more performace they just decided that was te way to desgnitae any ne4w commecial engine with a fan and two separate compressor sections.

Now as for the mysterious J57, J60, J58 designation you need to ask the airforce how they came about in their smoke filled back rooms. Remember since the government was spending their money their were a lot of number combinations that existed on paper both in the government offices as well as the engine manufacturers design and component development groups..

Some of these combinations even had hardware like tiny turbines behind boron fuel tubes and gears between the turbine and the large compressors, with afterburners 6 ft in diameter. I never heard of one finally coming together as a full engine though.

One of my neighbors worked there in the test department straight out of college, but sadly he died just before this thread was started so I can't trot over there for a beer and questions anymore:sad:

[kilomikedelta]

"The airflow was fed into the afterburner as a way of making use of that compressed air. It increased the pressure of the airflow in the afterburner inlet and also increased the air-percentages (60-65% of the engine exhaust is air -- the bypass air is 100% oxygen)" Do you mean that the engine exhaust is 60-65% air and 35-40% combustion product gases and the bypass air was 100% air (21% oxygen) with no other gases? Regards, KMD

[OldBUFFkeeper]

Am still curious as to the actual efficacy of those six "tubes" and wondering if they collectively had the air delivery capacity of an "honest" classic bypass duct (eg. F-100/101/110/RM-8/M-53, F-414, et.al.), and, why, even if they somehow did, the concept was not precluded by energy loss intrinsic to the no less than FOUR(!!) right-angle turns,(i.e. out of the compressor after the fourth stage, and, by definition, essentially perpindicular to the longitudinal axis, then back parallel to the axis to head aft past the high pressure stages, combustor and turbines, back in, at the AB, and perpindicular again, with a final turn to match the prevailing gas flow), and the issue resolved with a "simple" radial extension of the low pressure stages, ala Snecma M-53?

Not to "Monday morning quarterback", but, given the sheer aerodynamic elegance of the Blackbird, the tubes seem appalingly crude.

[barit1]

Well, if the Mach in the ducts is low enough, pressure loss is minimized, but then so is the flow minimized... :ugh:

[OldBUFFkeeper]

You make a very good point here. But it still seems to make more sense to have the "fan" stages feed a classic circumfirential duct, allowing both the harnessing of that airflow for "propeller" thrust at low speeds, i.e. dragging a full fuel load off the runway for once, rather than just enough to allow one to clear the runway and scramble to the nearest tanker, and then allow the air exiting the fans to simply follow the "path of least resistance" in the intervening space between the low and high pressure sections, flowing into the N2 as needed and going around through the fan duct when either quantity or pressure are in excess. Also, noting the degree to which the French aero engine industry, specifically SNECMA, has benefited from liasons with BOTH(!!) GE and P&W, I'm surprised and a bit disappointed that that "river" could not flow the other way as well, a "J-58-as-scaled-up-M53" still looking extremely good as the quintessential Mach 3+ powerplant.

[barit1]

Ah yes. Some years ago I worked some preliminary design stuff on such an engine - Low-bypass fan, twin spools, variable shutters to gradually close down core airflow and divert more to the afterburner, so the machine migrated toward a ramjet system. Similar in principle to what OldBUFFkeeper describes.

Very complex, but should have performed well past Mach 3. It could even be used as a reusable orbital-insertion booster vehicle with fly-home capability. NASA might be interested if they only had some $$$. :sad:

[OldBUFFkeeper]

A variable-cycle turbo-ramjet, did you say, with possible TSTO capability? Then you're just the person to answer my next trivial question.

Given that aside from propelling the aircraft, another significant function of the powerplant is driving all those other devices (eg. generators, via CSDs, and hydraulic pumps), crucial for auxiliary capabilities, not to mention "small neccesities" such as fuel pumps, all of which derive their motive power from a tower shaft PTO of the turbocompressor drive shaft, just what do all you "RTA"-types have in mind for a substitute when the main powerplant has transitioned completly to ramjet/scramjet mode, or is it an unspoken consideration that the core will even then still be allowed to "windmill" in a small portion of the airflow as the qunitessential "RAT"?

[barit1]

OldBUFFkeeper, as best as I can recall, the gadget was as you described. A more-or-less conventional accessory package, lube & fuel pumps etc. The core kept operating if for no other reason than to pump fuel for the afterburner. :ooh:

[OldBUFFkeeper]

Ah yes, yet another "what if" project!! Have done much the same in desktop "doodles", but rather than taking the gas generator completely out of the loop, my "bypass relief doors", situated just foward of the HP compressor, opened outward, thus allowing excess air to go around and into the ramburner through what was otherwise the fan exhaust duct, while a "smidgeon" of the remainder still went through the core. My theory was that, by providing such a relief, both the quantity and the ambient pressure of the air just foward of the core would be reduced, allowing it to continue to perform some useful function, however limited, throughout the envelope, including accessory drive. That way, one can have it all, fan thrust at takeoff and climb, with gradual transition to ramburner as the mach number mandates. Again, "what if........................................."

[peter kent]

Hi folks,
Sorry this is a bit cryptic but I'm scared to spend too much time typing words in case I lose the whole lot with one wrong mouse click. It's already happened.

Good news for oldBUFFkeeper,
Six tube BPR is 0.25 as they passed 20%. See below for this and much, much more

http://www.enginehistory.org/Convention/2005/Presentations/LawPete/SR-71Propulsion2.pdf

Hope this new revelation on low flow reqd raises your opinion of the elegance or lack of it for the tubes.
BTW Jane-DOH had already summed them up in one line although I think the relevance of the statement was missed, ie "there's only a certain degree of efficiency you need to accomplish a task. The rest is gravy" or big waste of money actually.
The apparently crude tubes were engineeringly elegant I'm sure ie reqd min mods to min # of components They did what was reqd cheapest and lightest and durable.

Following answers come from "The Engines of Pratt & Whitney, a Technical History" by Jack Connors

There are 3 pages on J91.
J91 compressor, in order to pass req flow for M3 with smallest size, hadnew low level of hub-tip-ratio, about 1/3 re previous 1/2, and also transonic blading so no IGV reqt. JT3D fan was slightly scaled down 1st 2 stages.

Finish off with thought for the day:
overall PR of subject matter above at M3 is today attained by your big fan engines at zero flt speed, ie over 40:1

That's about it for now.
Any more P&W Qs I can look up for you in the book.

Thank you all for renewing my interest in above details.

PK