Replacing the Pratt & Whitney J57 with the General Electric J79?

Christopher Wang

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The following United States military aircrafts of the Cold War were equipped with the Pratt & Whitney J57 axial-flow turbojet engines:
  • Convair F-102 Delta Dagger
  • Douglas A3D Skywarrior
  • McDonnell F-101 Voodoo
  • North American F-100 Super Sabre
  • Vought F-8 Crusader
Douglas, McDonnell, and Vought would later submit proposals based on their existing military aircraft designs which swapped out the Pratt & Whitney J57 for the General Electric J79:
  • Douglas D-790 (Air-to-air variant armed with AAM-N-10 Eagles for fleet air defense)
  • McDonnell F-101D/E (Proposed tactical fighter variants with variable ramp inlets)
  • Vought V-1000 (Land-based export fighter offered to replace the F-5 Freedom Fighter)
Although none of these proposals ever made it past the blueprint stage, the designs seem to imply the technical feasibility of replacing the J57 with the J79.

Could other J57-powered military aircraft designs such as the F-100 Super Sabre and F-102 Delta Dagger be outfitted with the J79?

Hypothetically, could these J57- / J79-powered military aircraft designs also be upgraded with modern low-bypass turbofan engines such as the Pratt & Whitney PW1120 or General Electric F404?
 

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tomo pauk

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Could other J57-powered military aircraft designs such as the F-100 Super Sabre and F-102 Delta Dagger be outfitted with the J79?

They probably could. The J79 was lighter and shorter than J57, with almost an identical diameter. Some shuffling of ancillaries will happen, though. We can recall people were re-engining aircraft in the Cold War and beyond, like the Israelis did the engine installation from Dagger into Kfir, or the Americans with F-16, or when XF-104 became the F-104.
Should've been far easier job than stuffing the big Spey in the Phantoms.

Hypothetically, could these J57- / J79-powered military aircraft designs also be upgraded with modern low-bypass turbofan engines such as the Pratt & Whitney PW1120 or General Electric F404?

Such a thing was mooted - the 'Super Phantom' by Boeing and P&W, supposed to be powered by PW 1120. A silently shelved project.
 

Christopher Wang

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Could other J57-powered military aircraft designs such as the F-100 Super Sabre and F-102 Delta Dagger be outfitted with the J79?

They probably could. The J79 was lighter and shorter than J57, with almost an identical diameter. Some shuffling of ancillaries will happen, though. We can recall people were re-engining aircraft in the Cold War and beyond, like the Israelis did the engine installation from Dagger into Kfir, or the Americans with F-16, or when XF-104 became the F-104.
Should've been far easier job than stuffing the big Spey in the Phantoms.

Hypothetically, could these J57- / J79-powered military aircraft designs also be upgraded with modern low-bypass turbofan engines such as the Pratt & Whitney PW1120 or General Electric F404?

Such a thing was mooted - the 'Super Phantom' by Boeing and P&W, supposed to be powered by PW 1120. A silently shelved project.
But the Super Phantom does illustrate that it is technically feasible to swap out the J57 or J79 for the PW1120 or F404?
 

apparition13

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Yes. IAI flew them in a Phantom. I believe the plan mooted was to upgrade Israeli Phantoms with PW1120 engines when the Lavi program went forward since that was to use the PW1120, but when the Lavi was cancelled the economy of scale for purchasing PW1120s disappeared as did plans to install them on F-4s.

Article:
https://www.19fortyfive.com/2021/07...antom-the-killer-fighter-jet-that-never-flew/

Video, with dodgy music and narration, of some of the 1987 Paris Air Show demo of the PW1120 Phantom.

View: https://www.youtube.com/watch?v=aePzMZbImNU
 

BlackBat242

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You forgot the Douglas F4D-1 Skyray (J57*)... 419 built, in-service from 16 April 1956 to 29 February 1964... including many aircraft carrier deployments across the world. http://www.joebaugher.com/navy_fighters/f6_2.html

There were two prototypes of the F4D-2N (redesignated F5D-1). This had a thinner wing and 8' longer fuselage (incorporating "area rule" design), significantly reducing drag (particularly in the trans-sonic and super-sonic regimes), and almost doubling internal fuel capacity. They were fitted with J57s for their flight tests, but this aircraft actually WAS planned to have the J57 replaced by the J79 - but the program was cancelled before this could be done.


* The aircraft was designed to use the Westinghouse J40 - but designer Ed Heinemann was dubious about this in-development "uber-engine" and designed the engine bay to take a larger engine. The two prototypes initially flew with J33s, and later got developmental versions of the J40 - but that engine was eventually cancelled, and the decision was made to use the J57 in the production Skyrays. http://www.joebaugher.com/navy_fighters/f6_1.html
 

SSgtC

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In theory, sure. You could follow a path of J57-J79-F404 (or PW1120). But eventually, you hit a point of diminishing returns. How much life are you really getting out of a 30+ year old fighter with a new engine?
 

BLACK_MAMBA

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In theory, sure. You could follow a path of J57-J79-F404 (or PW1120). But eventually, you hit a point of diminishing returns. How much life are you really getting out of a 30+ year old fighter with a new engine?
Most countries seemed to rather extend the service life of a fighter with an avionics upgrade, rather than engines. German F-4F, Israeli Kurnass, Greek Phantoms, Spanish F1M etc. All aircraft where service lives were extended through avionics as that is where the real gains lie. Performance is always welcome but a better radar & weapons are more economic ways of prolonging useful service life.

The Super Phantom also had the issue that Lavi fell (PW1120 gone) and it sort of competed in MDD and the Hornet's world! Why spend big bucks for an avionics and engine upgrade if you could either - just do avionics (cheaper than doing both) or buy a new aircraft and gain an extra 10 - 20 useful service years over an upgraded type.

As a side note - I often wondered if the Phantom could take the F404, but then you really need to start asking if a Hornet isn't a better choice...
 

1635yankee

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One problem with replacing the J57 with the J79 is that the first generations of the J79 were, reputedly, quite susceptible to FOD. After all, a Luftwaffe F-104 was taken down by a dumpling. The J57, as a twin spool engine, didn't need variable IGV or compressor stators. In other words, if the J57 was replaced by the early variants of the J79 the aircraft would likely have significantly lower availability or higher maintenance requirements. Of course, later variants of the J79 did improve, but then the J57 didn't stand still in that regard. In another thread, I posted the USAF loss rates due to engine failures, and the J79-powered F-104 had about 70% greater loss rate due to engine problems as did the J57-powered F-100. I think it's telling that the only single-J79 aircraft to see US service was the F-104. The Israeli-developed J79 powered derivatives of the Mirage III were fielded about 20 years after the J79 entered service.

Also, if you want to replace the J57, you'd want to replace them with an engine that is significantly more powerful, at least 14,500 lbst or so without afterburning and 20,000 lbst afterburning.
 

apparition13

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Since this is secretprojects, my ideal engine upgrade path for this class of engine would be J57/J79 -> (cancelled) RB.106 (20k lbs afterburner, which could get some of these aircraft over unity) -> PW1120 (turbofan, so more range) and then -> (proposed but not developed) EJ270, for 17/27 thousand pounds of thrust, preferably with thrust vectoring, just to tic all the boxes.

Assuming, as I've sometimes read, that the projected EJ270 somewhat larger, so it would better fit the space and deal with weight balance issues. Just think of it - 54000 lbs of thrust in an IAI/Boeing Super-Phantom, preferably with Boeing's conformal weapons and fuel pallet. Or an F-104 with 60% more thrust and TV, although I would certainly want the Dogfighter mod Lockheed proposed in the late 70s that enlarged the wing and moved the horizontal tail down to the fuselage. Fuel might become an issue though. ;)
 

1635yankee

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Since this is secretprojects, my ideal engine upgrade path for this class of engine would be J57/J79 -> (cancelled) RB.106 (20k lbs afterburner, which could get some of these aircraft over unity) -> PW1120 (turbofan, so more range) and then -> (proposed but not developed) EJ270, for 17/27 thousand pounds of thrust, preferably with thrust vectoring, just to tic all the boxes.

Assuming, as I've sometimes read, that the projected EJ270 somewhat larger, so it would better fit the space and deal with weight balance issues. Just think of it - 54000 lbs of thrust in an IAI/Boeing Super-Phantom, preferably with Boeing's conformal weapons and fuel pallet. Or an F-104 with 60% more thrust and TV, although I would certainly want the Dogfighter mod Lockheed proposed in the late 70s that enlarged the wing and moved the horizontal tail down to the fuselage. Fuel might become an issue though. ;)
The Lockheed Lancer proposal.
 

Archibald

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One problem with replacing the J57 with the J79 is that the first generations of the J79 were, reputedly, quite susceptible to FOD. After all, a Luftwaffe F-104 was taken down by a dumpling. The J57, as a twin spool engine, didn't need variable IGV or compressor stators. In other words, if the J57 was replaced by the early variants of the J79 the aircraft would likely have significantly lower availability or higher maintenance requirements. Of course, later variants of the J79 did improve, but then the J57 didn't stand still in that regard. In another thread, I posted the USAF loss rates due to engine failures, and the J79-powered F-104 had about 70% greater loss rate due to engine problems as did the J57-powered F-100. I think it's telling that the only single-J79 aircraft to see US service was the F-104. The Israeli-developed J79 powered derivatives of the Mirage III were fielded about 20 years after the J79 entered service.

Also, if you want to replace the J57, you'd want to replace them with an engine that is significantly more powerful, at least 14,500 lbst or so without afterburning and 20,000 lbst afterburning.

The Atar might have been a dated relic for way too long, but compared to that early J79 misery, it worked like a clock, was rugged, reliable, even in the worst possible environments.

I would say the Avon was probably the best of both worlds.
 

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