In my previous post of this build log, I eventually got the heavily modified parts of the Revell S-II stage assembled, and had replaced all the kit fairings with more correct versions from New Ware. A good coat of white paint brought all the disparate parts to the same shade, and then I added the black chequer pattern to the aft skirt, using the same masking techniques I used for the S-IVB aft interstage. Then it was time to add the five J-2 engines (which I prepared when working on the S-IVB stage) and the aft heat shield, supplied as a resin part by New Ware.
This heat shield was suspended about halfway down the J-2 engine nozzles, completely surrounding the central engine and housing the outer engines within cut-outs around its edges. Its job was to protect the underside of the liquid oxygen tank from the heat of the engines immediately below. Each engine was attached to the heat shield by a flexible skirt, to accommodate vibration and to allow for the steering of the outer engines. The New Ware resin part imitates these flexible skirts with rigid collars.
As I’d previously discovered when trying to fix up and paint the S-II thrust structure, the heat shield of the S-II is poorly recorded photographically. It seems to have been added in sections after the engines were installed—it’s certainly absent from delivery photographs of the S-II. And it’s omitted from the three surviving S-II stages that are on display.
One of the best photographs we have comes from the stacking of the Apollo 6 launch vehicle, though the flexible curtains are not yet installed:
Here we get a good view of the intricate support lattice that suspended the heat shield below the thrust structure. (You can also see a slab of something dangling off the underside of the heat shield—we can only hope it was a protective cover of some sort, rather than a structural component.)
In terms of colour, we have the interstage separation video from Apollo 4, which shows the upper surface to be brick red:
And for the underside there’s an image from the stacking of the Apollo 13 launch vehicle, slightly obscured by the presence of a work platform around the engines:
So it looks like the aft surface was very dark, if not black, and the flexible curtains were very pale, if not white.
That’s the colour-scheme I used, anyway.
The next problem was figuring out how to get the position of the heat shield correct, while still being able to insert all those support members. The solution I came up with was to epoxy the heat shield to the central engine, at the correct height (taken from David Weeks’s invaluable drawings). I built a little cardboard jig to keep things level while the glue set.
A millimetre or so needs to be shaved off the protruding elbow of the engine’s fuel line to allow it to sit centred in the heat shield. I also used the fuel line as my landmark to get the heat shield correctly rotated, so that it would align with the other engines once assembled in place—careful dry fitting and a pencil mark was the low-tech solution to that problem.
After that, I installed the central engine and levelled the heat shield.
This gave me a nice space into which I could insert the support structure, a strut at a time, modelled in 0.5mm brass rod.
Finally, the outer engines were set in place, and I added the various control packages provided by New Ware to the outside of the thrust structure. (In themselves, these are problematic, since there seems to be little consistency between the early Apollo 4 and Apollo 6 photographs and the three surviving S-II stages on display. I went with what New Ware provided, which was consistent with David Weeks’s drawings.)
The New Ware decals consisted of the vertical motion target (a black dashed line on the S-II which faced the launch tower) and four vertically printed “UNITED STATES” labels. All of these, being long and narrow, were excruciatingly difficult to get sitting perfectly straight and vertical. Eventually I hung a plumb bob from my modelling light, and used that to give me a vertical alignment against which I could gently nudge the decals into position.
Finally, I added the LH2 vent lines to the tank dome, so that they aligned correctly with LH2 vent valves on the forward skirt. (I also scratch-built a little rectangular telemetry package to sit on the tank dome.)
And here’s the Position II view with the S-IVB aft interstage on top, just to check alignments.
And that’s it for the S-II. Next up, the S-II aft interstage—which (you guessed it) needs considerable modification.