I've seen on multiple occasions people mentioning that the engine intended for the F5D was the J79. In fact, it is one of the leading narratives in the other thread about possible alternatives for Vietnam Wat fighter. Still, I cannot find any hard data on this engine swap, the "Naval Fighters vol. 35" by Steve Ginter only briefly mentions that on the very first page, and then never comes back to this subject, except for a technical drawing of the proposed J79 tail at the end of the book. With the common notion that the J79-engined F5D would be a world-beater, does anyone have any information about the expected performance, or in general, the planned development path of the Skylancer?

Also on the same subject, the "Naval Fighters vol. 13" about the F4D Skyray, has a short section about the F4D J79-powered testbed (the rebuilt XF4D-1 no. 587). It mentions that the engine mount was reconstructed and that a new inlet duct extension was designed (see the installation below), yet, despite the quite detailed description of the history of the fight test, there is no information about the concluding remarks of the project if it was indeed an improvement and by what margin. If anyone could share any info, I would be grateful.
J79.png
 
Many people believe that the Skylancer was a faster and better choice than its competitor the Vought F8U Crusader. They believe that it had inherently better stretch potential to the point where it could have outperformed the F-4 Phantom if the J-79 engine had been installed as envisioned by Ed Heinemann.
Steve Ginter, "Naval Fighters vol. 35 Douglas F5D Skylancer".
 
Steve Ginter, "Naval Fighters vol. 35 Douglas F5D Skylancer".
And that is exactly the only mention of the subject in the whole book I was referring to. There is no other data or description provided except for this particular sentence. Maybe somebody with access to "Killer Rays: Story of the Douglas F4D Skyray & F5D Skylancer" book can provide some more details?
 
The XF4D was simply a testbed for the J79/CJ805 to gain in flight experience/cycles with that engine - not meant to be a J79 powered Skyray as a fighter or testbed for a J79 powered F5D. Some excellent photos of the XF4D and other GE test aircraft at:


Enjoy the Day! Mark
 
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This one is also spectacular (F-4H):

Screenshot_20250219_233148.jpg

Jason Chapman
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Installation of J79 with liquid nitrogen-cooled conic nozzle
From a GE research paper: "A special test program was conducted on the F-4A to evaluate the IR suppression characteristics on a cooled plug nozzle. The exit lip of the aircraft engine bay was modified and a test engine with a plug nozzle was installed. An LN2 tank was designed to hang from centerline stores position. An LN2 system was installed in the aircraft to allow the LN2 to cool the plug."
 
And that is exactly the only mention of the subject in the whole book I was referring to. There is no other data or description provided except for this particular sentence. Maybe somebody with access to "Killer Rays: Story of the Douglas F4D Skyray & F5D Skylancer" book can provide some more details?
There was a Douglas proposal for a J79 engined version with revised intakes, but the Navy weren't interested.
 
How well would a J79 powered Skyray likely have performed compared to the J57 powered production version?
Airframe was distinctly subsonic - fuel load was always problematic without external tanks so maybe the better SFC would have helped a bit. By then though, it would have made more sense to follow thru with the F5D.
 
F4D-1 (F-6A) max speed @ sea level = 722 mph (M1 = 761 mph)
F4D-1 (F-6A) max speed @ 36,000 ft = 695 mph (M1= 660.5 mph)

39 mph below M1 @ sea level, 34.5 mph above @ 36,000ft with the afterburning J57-P-8 (10,200 lb.s.t. mil, 16,000 lb.s.t. afterburning).

For comparison:
The FJ-4 Fury could do 680 mph @ sea level, 631 mph @ 35,000 ft (42-64 mph less than the F4D at both altitudes with the non afterburning J65-W-16 [7,700 lb.s.t. mil]).

The F11F-1 (F-11A) Tiger could do 753 mph @ sea level, 727 mph @ 35,000 ft (31-32 mph more than the F4D at both altitudes with the afterburning J65-W-18 [7,400 lb.s.t. mil, 10,500 lb.s.t afterburning]).

Yes, the F11F-1 was faster with only 72.5% (mil) and 65.6% (a/b) of the thrust.

The F11F-1F Super Tiger hit 836 mph @ sea level, 1,325 mph @ 35,000 ft, and 1,400 mph @ 40,000 ft with a J79-GE-3 (9,600 lb.s.t. mil, 14,800 lb.s.t. afterburning).
Still less power than the F4D and just over twice the speed at 35,000 ft!

Yeah, the F4D wasn't great aerodynamically.


The F5D was planned for the "available in 1957" J57-P-14 (10,700 lb.s.t. mil, 16,900 lb.s.t. afterburning).
The F-102A, in 1955, had the J57-P-25 (11,700 lb.s.t. mil, 17,200 lb.s.t. afterburning).
The F8U-2 (F-8D) in 1960 had the J57-P-20 (10,700 lb.s.t. mil, 18,000 lb.s.t. afterburning).
And by 1965 the RF-8G had the J57-P-420 (11,650 lb.s.t. mil, 19,600 lb.s.t. afterburning).

The J79-GE-10 of the F-4E & F-104S, in 1966, produced 11,430 lb.s.t. mil & 17,860 lb.s.t. - less than the contemporary J57-P-420, but smaller and lighter.

Only with the J79-GE-119 of 1980 (for the F-16/79) did the J79 finally exceed the power of the strongest J57 - by producing 12,050 lb.s.t. mil & 18,725 lb.s.t. afterburning [@ sea level, 20,840 lb.s.t. @ 35,000 ft and M2]).
 
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Yeah, the F4D wasn't great aerodynamically.
Could be transonic drag, combined with (non FBW) delta wing drag ? delta wing really shines at mach 2+ .

Only with the J79-GE-119 of 1980 (for the F-16/79) did the J79 finally exceed the power of the strongest J57

Interesting. So the J79 would be to the J57 / J75, what the F404 is, to F100/F101 ? medium-power engine for compact fighters ? Imagine how much scaled up a Phantom would need to be, with a pair of J75.
 
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