In histories of the Apollo programme, the S-II stage of the Saturn V is often referred to as “troubled”. There were difficulties with weight reduction that led to a delay in delivery of the first functioning S-IIs. That may be why Revell’s rendering of the S-II is so poor—it’s clear, from the paint scheme and other aspects of the model, that they were working from very early iterations of the Saturn V stack, and perhaps they didn’t get very long to look at the production S-II.

The main body of the Revell S-II comes in three parts—one piece for the forward skirt and the dome of the LH2 tank; one piece for the aft skirt, thrust structure and rear dome of the LOX tank; and a printed styrene sheet to be rolled into a cylinder to form the outer wall of the combined tanks.

The first problem with the forward part is a familiar one, if you’ve been following this build log—the locating strips inside the skirt, which engage with a gap in the flanges of the S-IVB interstage above, are misaligned, and need to be shifted so that the S-II is correctly aligned within the Saturn V stack. Unfortunately, the two features of the forward part that allow its orientation to be checked are in disagreement with each other, too—the notch that marks the location of the service tunnel is in the wrong position relative to the vent tubing on top of the LH2 tank. As described in my previous post in this build log, I chose to move the locating strips 11/16″ (17 mm)  to the right so as to get the service tunnel in the right place, and then went on to fill and smooth the circular depression that is the locating point for the vent tubing, which I’ll position correctly later.

I also removed the raised edges of the fifteen gores into which the kit divides the tank dome, and replaced them with the correct number—twelve.

Next, there’s the problem of the appearance of the tank dome. The Revell kit has an odd annular structure surrounding the dome, which doesn’t appear in David Weeks’s excellent Saturn V drawings set. It turns out to be difficult to check against reality, because finding an image of the front end of a complete S-II ready for launch is remarkably difficult. They were generally moved around with something called the Forward Hoisting Frame Assembly attached to the top end (there are some nice images of that in action over at Heroic Relics), which completely obscured the LH2 tank dome. And when the Saturn V was being stacked, the photographic views show the underside of the S-IVB being lowered into position, rather than a top view of the S-II. Two of the three surviving S-IIs on display have the Forward Hoisting Frame still attached, leaving the one at the Kennedy Space Center providing the only clear view. It’s a late model, from the cancelled Apollo 18 mission, by which time the method of insulating the LH2 tank had changed, but it’s the best I can find. There’s no structural ring around the tank dome. (That said, displayed Saturn V stages often omit components, like the S-II heat shield, which were added only late in the stacking process.) I suspect Revell have mistakenly moulded in a removable work platform or handling ring, but unfortunately it’s impossible to remove without having to scratch-build a new tank dome.

One thing I could fix is the fact that the stringers on the kit’s front skirt extend too far back. On the real thing, they disappeared into an odd raised external cuff of insulation surrounding the top of the LH2 tank. So I took my measurements off David Weeks’s plans, created a demarcation line around the forward skirt using Dymo Tape, chiselled and sanded to remove the offending parts of the moulded stringers, and then created the appearance of the insulation by wrapping with a couple of strips of styrene sheet. While I was at it, I removed stringers from a few more areas, so that I could later add New Ware’s photoetched details (a personnel hatch, LH2 vent valves, and telemetry antennae). Here’s what I ended up with:

Finally, a puzzle—the right colour for the tank insulation. Again the lack of contemporary colour photographs makes it difficult to know. The material covering the Kennedy Space Center S-II tank has aged to a shade of brown, but the fresh finish is generally described as having been yellow. Many modellers use a zinc chromate yellow-green finish, which was widely applied as an initial coat to protect the metalwork of Saturn V components, and which was certainly applied to the bare external metal of the fuel tanks. However, David Weeks’s drawings contain this piece of information:

Exterior of LH₂ tank dome is covered with insulation and is painted FS 33558 Orange-yellow.

That’d be handy, except for the fact that there is no Federal Standard 33558 colour. There is, however, an FS 33538 orange-yellow, and I assume that’s what was meant. I used the Luftwaffe’s RLM 04 Gelb, which appears to be a close match.

If the front assembly is merely inaccurate, the rear assembly is a disaster. Really, Revell should have moulded this in at least two parts—the aft skirt and tank dome; the hollow conical thrust structure and cruciform engine support. Again, there’s nothing short of massive scratch building that can fix the unrealistic wall within the thrust structure, or the fact the cruciform is plastered on to the tank dome, rather than standing free.

The stringers on the aft skirt extend too far forward, so again there was a need for Dymo Tape, chisel and sandpaper to trim them back to their correct extent.

And the aft skirt should also bear a number of fairings protecting various bits of prominent piping—Revell manage to place a few of these, but of the wrong size, shape and position. I can replace the kit parts with more realistic resin parts from New Ware, but first I needed to get rid of the attachment points for Revell’s aberrant LH2 feed line fairings (only one of which aligns with the pipe on the thrust structure it’s supposed to be supplying), and fill the gap left by Revell’s LOX vent fairing.

For reference, here’s the offending item in its raw state:

Having first trimmed off the forward part of the stringers, I then applied myself to getting rid of the raised fairing attachment points. I protected the stringers on either side with Dymo Tape, then used a razor saw and a 2mm chisel to remove the offending part and restore the gap between the stringers.

The vent fairing gap was repaired with white filler, and the missing stringers rebuilt with 1mm styrene strip.

The thrust structure in the real world bore a number of control packages, which are supplied in resin by New Ware. Unfortunately, the Revell thrust structure has one little moulded package in place (at the left side of the image above, in partial shadow), which bears scant resemblance to anything in the real world. It’s also impossible to fully remove without leaving a hole in the thrust structure.

After a bit of pondering, I decided to rotate the entire kit part through 90 degrees anti-clockwise (when looking down from above the Saturn V). This moved the remnant of the unrealistic package from a location next to the A-quadrant engine to the same position in the B quadrant, where it can be almost completely concealed under an engine actuator assembly and an electrical system assembly from the New Ware detail set.

All that was required to achieve this rotation was to fill and sand the locating slot for the service tunnel, and to remove the (in any case unrealistic) attachment points for the central engine, which needed to be counter-rotated through 90 degrees to restore its correct alignment with the rest of the stage. After all I’d already done to this kit part, that was a completely trivial task.

Then I used a grinder to remove the spurious moulded pipework that bedecks Revell’s version of the rear tank dome (just achievable, with care—the plastic was so thin in places that it was translucent by the time I’d finished). I added my own pipework using styrene rod—the LOX fill line, and the LH2 feed for the centre engine, both of which had been omitted by Revell. Then, with the orientation of the aft skirt pinned down, I was able to do a final bit of chiseling to make space for the fairings, umbilical connections and the new position for the service tunnel.

Here’s the final item, still some way from being entirely accurate, but a great deal better than I started with:

The correct colour for the thrust structure was another problem. Again, photographs of the final assembly are rare, and apparently restricted to the S-II stages of Apollo 4 and Apollo 6. The Apollo 6 S-II thrust structure looks sort of white-ish in the NASA image. A good quality photo at Drew Ex Machina (scroll to about halfway down the post) shows the S-II of Apollo 4 with a metallic yellow-green thrust structure. The thrust structure of the very early S-II displayed at Huntsville is flat green, while the late models at Johnson and Kennedy are white.

Essentially, then, I’ve scant idea what colour I should use to realistically depict the SA-506 launch vehicle of Apollo 11. In the end, I mixed up a pleasing yellow-green shade using Tamiya Cockpit Green and Titanium Gold, which ended up about halfway between Apollo 4 and Huntsville*.

The pre-printed styrene sheet that connects the fore and aft skirts was only a little problematic. As with the S-IVB stage, I turned it inside-out so that I could paint it uniformly white and then apply New Ware’s decals. It’s supposed to be held in shape by pins on the service tunnel assembly, but that would leave an exposed edge visible. So (again, as with S-IVB) I glued it together and filled the locating holes, so that I could completely cover the edge with the service tunnel part. At this point, I discovered that aligning the locating holes properly resulted in a part that was very slightly too small to fit on to either the fore or aft skirt. So I pried it gently apart, and reassembled with holes misaligned by a half millimetre or so.

Finally, the whole thing fitted together, and I was able to start placing New Ware’s resin and photoetch details.

I’ll pick up the story from there, next time.

• Go to next post in this build log

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* While I was at it, I revisited the thrust structure of the S-IVB stage, which I’d previously left with a greenish metallic tint that looked right in some lights and very wrong in others. The real colour for this structure seems to have been about as variable as that for the S-II. I’m slightly more satisfied with the Tamiya recoat.