by Tommy H. Thomason

Saturday, June 1, 2013

Things Under Wings: F4H (F-4) Phantom External Fuel Tanks

6 June 2013: Revised 600-gallon and McDonnell 370-gallon tank illustrations in accordance with McAir drawings provided by Mark Nankivil

3 June 2013: Updated with additional pictures and information.

The McDonnell F4H Phantom was delivered with unique external tanks, a big 600-gallon centerline tank and somewhat smaller but still unusually large 370-gallon wing tanks. The two General Electric J79s enabled it to lift a heavy load but required a lot of fuel, particularly in afterburner.


The 600-gallon tank with the "long" pylon fairing (which suggests that there was a short one; I don't know what it looks like yet):

Forward is to the left. Note that there are two small brackets on the aft part of the tank mounted at a 45 degree angle to vertical. These functioned as sway braces (and probably insured that the tank departed cleanly when jettisoned) because when the tank was attached, they were set into brackets that were mounted on small access doors on the belly of the F-4.
Craig Kaston provided this closeup of the aft sway brace (the hose provided the air to start the J79).
This Bill Spidle picture shows how little clearance that was between the 600-gallon tank and the fuselage.

There were supplier or at least design changes to the 600-gallon tank. (McDonnell short fairing, nestable, and welded; and Royal Jet are some of the configurations listed in the flight manual; the drawing above is the "welded" version) Note the flange on the lower left side of this one. I await comments and further information...
At some point, some operators of the F-4 (for example the USAF but not the Navy/USMC) adopted the F-15 610-gallon tank that did not have this aft sway brace arrangement and was not mounted at a nose-down angle.

The first 370-gallon tanks were provided by McDonnell. They can be distinguished from the subsequent Sargent Fletcher tanks by 1) the continuous increase and then decrease in cross section and 2) the flange on both sides of the tank where the upper and lower halves were connected together.
I'm pretty sure that this tank was 240 inches long and about 26 inches in diameter based on scaling a McDonnell stores drawing provided by Mark Nankivil.

Strictly speaking, the pylon and McDonnell tank were separate items, unlike the later tank. I had wondered why there were no sway braces involved or gap between the pylon and the tank (there was a small gap between the pylon and the wing—see picture in the discussion of the later tank) until Rex Droste provided this illustration, which shows that the tank was bolted to the pylon, not simply hung from it:
Installation of the tank on the pylon was obviously not as simple as hanging it and connecting the fuel and pressurization lines...

As you can see from the above picture and the following one, the forward mounting flange of the pylon was not symmetrical.
The reason was undoubtedly the need to transfer the weight of the tank directly into a wing spar, which was swept. Note that the outboard flange in the picture of the lower wing surface appears to be smaller than one in the illustration, possibly one of the differences associated with the later 370-gallon tank.

The later tank was supplied by Sargent Fletcher. You will see statements to the contrary (the early tanks were Sargent Fletcher and the later tanks, provided by McDonnell) in print and on the web but I'm all but certain of this.

The later tank is distinguished by having a constant cross section for much of its length and only one flange, which was on the lower left side of the tank.

A view of the right side of the Sargent Fletcher tank, showing that there is no flange. (The line on the tank is a painted pin stripe.)

The shape of the aft lower side of the pylon had to be different due to the changed shape of the tank and in this case, the pylon and the tank were a single unit.
Craig Kaston provided the following picture of an installed Sargent Fletcher pylon/tank and noted that there was a gap between the pylon and the wing.

The McDonnell tanks were on the first operational F4Hs. I'm not sure when the changeover to the Sargent Fletcher tank was made, but I vaguely remember there being two different tanks while I was a flight test engineer for McDonnell in 1966. According to an illustration of Sargent Fletcher history, it began delivering F-4 tanks in the late 1960s, roughly corresponding to the changeover in production at McDonnell to the F-4J. Rex Droste reports that there are dated pictures of the McDonnell tanks being used as late as August 1974, at least on USMC F-4s. I'm sure that there was nothing fundamentally wrong with them other than they were probably more expensive than the Sargent Fletcher. As a result, they would have been used until they were no longer economical to repair.

Note: For a possible third version of the 370-gallon tank, see http://tailspintopics.blogspot.com/2014/02/f4hf-4-370-gallon-external-tank-redux.html

8 comments:

  1. Hi Tommy,

    having done some research (using printed pictures as reference) of the earlier Sargent Fletcher tanks, I am also sure the length is the same as the later McDonnell tanks, that is, 240 inches. There is a drawing in the Squadron #1065 book that states the McDonnell tank is 260 inches long, but that is obviously a mistake. Note I am naming the tanks as I had always thought they were called in respect to their manufacturer. Your statement that it's the other way around is completely disconcerting to me! :)
    As for the 600 gallon tank, your drawing looks too symmetric to me. I think the forward part is OK but the rear should be a bit more "streamlined", kind of replicating the shape of a drop of water. The old Hasegawa and Monogram kits in 1/72 show them thinning at the rear, but in contrast the new Hasegawa 1/72 kit shows it to be quite symmetric, with the front and rear cones the same shape. That is a bit disturbing and I cannot be sure it is entirely correct. HTH,

    Jorge R. Figari

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  2. Jorge,

    Thanks very much for your comments. I feel on pretty firm ground with respect to the Sargent Fletcher tank being the later one. There's some discussion of this on the interweb that comes to that conclusion as well.

    I slightly revised the line of the 600-gallon tank and added the pylon based on McDonnell drawings just provided to me, mainly making both the front and rear tips more pointed. Based on dimensioned drawings, I agree that it is slightly teardrop shaped but the midpoint of forward half of the tank is only about two inches wider than the midpoint of the aft half. Since my line weight is on the order of 0.5 inches, that is visible but only just.

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  3. Also, that Phantom in Action error in labeling the tanks is easy to check on.
    The F-4C had the same tank options, and the correct names are used in the F-4C TO,,,,the two flange tank that removes from the pylons is called the "McDonnell tank on the Fuel tank pylon",,,,,and the one flange tank is called the "Sargent Fletcher tank with Integral pylon"

    Logically it makes sense,,,,,the removable fuel tank and early "USN style" weapons pylon would have come first,,,,,,before the additional tanks from Sargent Fletcher and the USAF "weapons only" pylons were invented

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  4. DUDE!

    I owe you a favor - thank you for this post.

    John Mollison
    johnmollison(dot)com

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  5. A bit late, but I can confirm that the Sargent Fletcher tanks were the later tanks. I was a crew chief on F-4Ds and Es in the mid 1970s and that was what was used on the aircraft at that time.

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  6. An interesting development on the tank issue. I just received Danny Coremans book by DACO - Uncovering the US Navy Q/F-4B/J/N/S Phantom. A great wealth of information. His claim is that the first tanks were the Sargent Fletcher tanks and the second tanks were by Royal Jet. Now saying that, my experience is just the opposite because in the Air Force we only had one type of outboard tanks and we always referred to them as Sargent Fletchers.

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  7. I have one of the 260" Sargent Fletcher tanks in my back yard, if anyone needs dimensions etc.

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    Replies
    1. If you have any nice detailed digital photos of the tank and pylon I would appreciate the info. (simmelink.kim@gmail.com) Always nice to see some detail for my drawings.

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