It’s been a while since I made any progress on this kit. Last time, I described building the Spacecraft/Lunar Module Adapter and Instrument Unit assembly. Moving down the launch vehicle, this time I’m building the S-IVB stage, which was the third stage of the Saturn V—the “small” one that pushed the Apollo stack into Earth orbit and then into translunar orbit.
The Revell kit has three parts for the main body of the S-IVB: moulded pieces representing the forward bulkhead and forward skirt; the aft bulkhead, thrust structure and aft skirt; and a printed piece of styrene card to connect the two, representing the hydrogen tank external wall. The styrene card is intended to be wrapped into a cylinder, and held together by a plastic strip representing the systems tunnel, which in the real rocket carried all the electrical connections between the aft and forward skirts—so it handily spans the full length between the two skirts.
There are a few problems with this basic assembly. One is that the styrene sheet is “helpfully” printed with the letters U S A. The only Saturn V S-IVB stage to be lettered in this way was the 500F Facilities Integration Vehicle, a dummy that never flew. (Unfortunately, that’s the Saturn V from which Revell derived the markings for its model, which it has never updated through numerous reissues.) So this needs to be flipped inside-out to conceal these markings. I blocked the locating holes with pieces of styrene card, so that they could be filled and sanded.
Another problem is that the moulded locating strips within the forward skirt, which fit into the Instrument Unit above, are (as I reported last time) out of place by about 10º, and need to be relocated so that the SIV-B is correctly aligned with the Apollo stack. The necessary displacement is by a quarter inch (six millimetres), to the right as you look at the inside of the skirt. This moves the systems tunnel of the S-IVB two scale feet to the right of the -Y marker on the Instrument Unit, and the same distance away from the Position II coordinate of the launch vehicle (which faces the launch tower).
And finally, the systems tunnel provided in the kit is the wrong shape and size, and needs to be replaced—the replacement part being carefully aligned so that it conceals the seam in the styrene cylinder, above.
For replacement parts, and additional detailing, I’ve been using New Ware’s Saturn V Detail Set. As well as a properly shaped systems tunnel, this also provides replacement and additional parts for various fairings in the aft skirt, and photo-etched parts for the umbilical attachments, fore and aft.
Getting these parts into position requires a degree of chipping away at the moulded stringers in the kit parts, to create space for the new resin and photo-etch parts. I first marked up the parts to be excised with reference to photographs and plans, and by dry-fitting the new parts. The curvature of the kit parts was just sufficient to allow careful paring of one stringer using a sharp blade, without damaging neighbouring stringers. The number of new gaps and new parts began to get a little difficult to keep track of, so I ended up numbering the spaces and parts with a felt pen.
Once all the parts that were going to be white on a white background were in place, I placed bits of masking tape to protect areas where parts were going to be attached that have colours that contrasted with the fuselage, then primed the model. The bulkheads, thrust structure and inner skirts were primed with white Alclad, because they were going to have a metallic finish applied. The outer surface was primed with Tamiya white primer, which was also going to be my basic white colour. Here it is with the masking partially in place for the black paintwork on the forward skirt:
Once the black paint was in place, I added four white antenna fairings to the forward skirt, and then gave the whole thing a coat of silk varnish.
While I was doing this, I assembled the J-2 engine. In fact, I assembled six J-2 engines, because the second stage requires five, and I thought I might as well do them all at once. There were problems with the seams where the two halves of each engine bell come together—I thought I’d done a reasonable job of concealing them, but they’re unfortunately still quite visible in some lights, courtesy of the metallic finish.
The colour of the thrust structure is a bit of a vexed problem. The Revell painting instructions suggest a matt mid-green finish, but the photos I find online, of S-IVB stages on display, suggest a sort of brassy metallic sheen to the green. I ended up applying Alclad brass, with a transparent green Alclad lacquer on top. The end result was a bit of a mixed blessing—looking satisfactory under direct illumination, but too dark a green when it’s in shadow. Here’s the final effect (looking too dark!), with the stage waiting for its final details to be added—the silver metallic Auxiliary Propulsion System modules and umbilical connectors:
And here’s the thrust structure under direct illumination to show the colour I’d aimed to achieve:
(In reality, the thrust structure was partially covered by a complex tangle of wires and pipes, but my enthusiasm faltered at the prospect of spending so much time detailing an area that will be hidden inside the final model, most of the time.)
Here’s the completed model, with the Instrument Unit and lower part of the Spacecraft/Lunar Module Adapter attached, which is the way we see it in photographs taken in orbit.
And here’s the kit’s astronaut figure, to give a sense of scale to what we often think of as a “small” rocket stage:
Next time, the S-IVB aft interstage—which despite being just one kit part promises to be a real pain in the neck to model.
Note added retrospectively: I was never particularly happy with the paint job on the thrust structure of this stage. I felt I produced a better effect on the S-II thrust structure, so I came back and revised the S-IVB paintwork at that time, with a mix of Tamiya Cockpit Green and Titanium Gold.