XF8U-3 Performance Comparison with F4H-1/F-4B (1 Viewer)

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I'm rechecking my numbers for the F8U-3 but otherwise it seems that everything's good. I've finished up a set of spreadsheets which basically illustrate turning radius and rate of turn between the two aircraft. There's obviously some very basic limits owing to information available of the XF8U-3 (since it never entered service) and other matters such as sustained agility.

These are merely figures for peak agility as if it were applied continuously. Still, it is illustrative.
 
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It turns out I made an error for the early F-4B variants since I have to correct for the load-factors being 8.5g instead of 8.0g (something that applied to RF-4B's only).
 
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Okay, everything's complete. There's of course going to be some obvious limitations owing to the following
  1. This presumes a steady-state turn held throughout 360-degrees of turn. This isn't something that would likely happen (and the F-4 could sustain 7g in turns).
  2. C/G affects stall-speed and I don't really have any real information as to how the F8U-3's C/G would shift in flight; the F-4B's C/G was stated to shift forward. However, I don't recall listings for stall speeds at the various C/G positions. As a result, all data just assumes no shift in the C/G.
  3. With both aircraft, there's differences in stall-speeds owing to transonic effects: With the F-4B, this varies from low-speed to transonic by around 15 knots. I have no idea how the F8U-3 would compare in these flight-regimes and, while arguments could be made that the F8U-3 would perform better, it's really just conjecture. Figures cited here are based without this being factored in.
  4. The L/F for Mach 1.05 is really only there for measuring the plane's turning circle at 6.5g. This doesn't really factor in supersonic performance or the radii would be way higher and the degree per-second rates would be way lower (and with it not possible to achieve 0.72 while pulling ultimate load so I only included figures for 9.75).
While the data listed is more accurate than somebody simply pulling numbers out of their ass: It's not perfect.

Starting with the F-4B Phantom: There's two basic charts that I made. The first one was based on another spreadsheet on the F-4B & F8U-3 which was used to factor in stall speeds. There was an error in this in that I'd made the faulty assumption that, without g-load data for the F-4B: I'd ended up using data for the RF-4B....

F-4B_ROT-1.png


... It turns out most of the RF-4B's weren't built to the same structural standards (thanks for that detail BiffF15 BiffF15 , I really appreciate it). This graph involves a correction with the adjusted L/F in the early operational variants being listed correctly. I'm uncertain why my initial figures had variations in the turning radius and the later ones didn't, it's probably the result of me bungling something. I can't seem to figure out exactly where, though it would be logical to conclude with weight and C/G differences there would be variations that would occur.

While I'm not sure why the initial graph had differences in turn radius with weight and this one doesn't: While calculating g-load to weight and varying speeds needed to pull the load-factor, the radius theoretically should be the same, but that probably doesn't happen in practice.

F-4B_ROT-2.png


Continuing onto the F8U-3 Crusader: The XF8U-3 1958 program review came right from Tommy Thomason's book. I included it as a reference because the aircraft would be lighter than an operational design and would be interesting to compare the prototype with both the operational F8U-3 and the F-4B. I listed two sets of turning radii and rates of turn for each configuration based on the fact that there's some guesswork to the stall-speed. These were derived from earlier F-8 variants and some data from the preliminary flight-manual and seemed to indicate speeds ranging from 1.15-1.22 Vs. Based on what was said on about the F8U-3 from the USN, test-pilots, and so on, I figured this seemed to indicate 1.2-1.22 Vs, and that's what I included.

The operational F8U-3 had provision for a semi-submerged/conformal store which could include a special store, an additional fuel-tank, or a gun-pack. While I'm not sure how seriously the USN looked into it, the RN:FAA was given some proposals that included this. Since this was largely proposal work, I'm not sure how much this weighed, so I used the SUU-23 as a baseline since there are weight figures.

F8U-3_ROT-1 copy.png


When it comes to comparisons: I compared the performance figures in terms of ratios/percentages as well as direct comparisons to turning radius and rate of turn. Though it requires no real mention: Green indicates a superiority and red indicates an inferiority.

Overall, the F-4B has an advantage in turning rate at or below 0.72 Mach whether or not the XF8U-3 is flying clean or has its droops extended to the cruise/combat position regardless of the air-to-air configuration of either aircraft: This advantage largely owes to it having a higher L/F (8.5 vs 6.4); when these numbers are brought down to 6.5g (which is actually why I listed it): The XF8U-3 ends up on top in the basic mission (3 x AIM-7C) over the F-4B, and retains an advantage when droops are extended into the cruise-position even when carrying an additional 2 x AIM-9B and the associated pylon.

F-4B-v-F8U-3_1.png


This compares the projected weight figures for the operational F8U-3 had it entered service.

The aircraft gained some weight and this would have had an effect on performance: As before, the F-4B wins the rate fight at or below 0.72 mach regardless of whether the F8U-3 has its droops retracted or extended. When it comes to a radius fight, the F8U-3 wins when its droops are extended in the basic mission; depending on which stall-speed figures are correct: The F8U-3 always comes up at a disadvantage when the droops are up and may be at an advantage or disadvantage with them extended depending on how willing the pilot of the F-4B would be willing to get to the ragged edge of a full-on stall. When the F-4B's load-factor is limited to 6.5g, it ends up either losing outright or loses when the F8U-3 pilot extends the droops to the cruise-position.

F-4B-v-F8U-3_2.png


The final comparison below is of the later F-4B variants. While it's unclear what would change with the F8U-3, I just left the figures as they were, but I did include both airplanes carrying either a gunpod or gunpack and AIM-7D and AIM-9D's instead since that seems something that would have likely changed.

The F-4B seems to gain weight more gracefully than the F8U-3 and the performance shows it. I guess with the gunpack being semi-submerged, should the F8U-3 pilot be able to get his nose on the F-4B, he would probably do better than the other way around because of the gun likely to wobble less.

F-4B-v-F8U-3_3.png


There are of course some factors that aren't really accurate included in here such as the fact that these figures are based on maneuvering performance that would be seen right on the deck instead of up at altitude -- these limits were based on an inability to compute mach effect on speed. I suppose as a basic estimate I could just use TAS figures at higher altitudes. I guess it'd be more honest a comparison with the F-4B above 0.72 M doing Mach 0.85 (which would see a load-factor of around 7.5g)

There's also the potential possibility that the F8U-3 might have had a faster roll-rate than the F-4B and that would have offset things to some degree. While this is an extreme example (and one involving older aircraft): The P-47 actually had an inferior rate of turn to the P-38 when both aircraft were stabilized in the turn and at peak rate, but the P-38 rolled considerably slower and that meant from 90-180 degrees, you'd often see the P-47 beat out the P-38. The F-4B seemed to generally have a pretty good roll-rate so this wouldn't be as extreme, but there would be some difference in this regard.

The F-4B seemed to do better when carrying 2 x 370 gallon tanks instead of 1 x 600 gallon centerline tank, which was almost always carried off the decks of carriers. The USMC seemed to use either arrangement (though I don't know what the statistics are) and sometimes carried all three tanks as the USAF did
 

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BiffF15 BiffF15 , drgondog drgondog I'm curious if the F-4B's effective limit was at the point of nose-slicing since that had to do with (as I understand it) the rudder becoming ineffective owing to the fuselage blanking the tail.
 
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BiffF15 BiffF15 drgondog drgondog I'm curious if the F-4B's effective limit was at the point of nose-slicing since that had to do with (as I understand it) the rudder becoming ineffective owing to the fuselage blanking the tail.
Zipper,

Im not familiar enough with the F4 to answer your question. I do know the Eagle could get some blanking from the fuselage (which the speedbrake exasperated) and this was solved on the Hornet with its outward canted vert tails. There was some talk of doing this to the Silent Eagle (lower RCS variant) which supposedly changed the weight and balance quite a bit (nose ballast removed).

Cheers,
Biff
 
BiffF15 BiffF15

From the limited research I've done it seems that might very well have capped the limit of what the F-4B would do. The aircraft appears to basically have departed at that point.

X XBe02Drvr

I'm curious if you're aware of whether the F-8 had any issues with tail-blanking at high AoA? I'm curious because the F-4B seemed to have issues with the fuselage affecting the airflow over the tail.
 

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