Having completed the S-II Aft Interstage for my previous post on this build log, I’ve now progressed to the Big Beast of the S-IC.

This stage is composed of Revell’s usual combination of moulded cylinders for the skirts and intertank, and printed styrene sheets to be rolled into cylinders for the tank sections. The stage also has two service tunnels running along its length, each one provided in two sections in the kit:

As with previous stages, my plan was to turn the printed sheets inside-out, paint them white to match the other structures, and then detail them using the decals provided in the detail set by New Ware. The kit service tunnels are both too long and too large, so need to be replaced—I’ll come to that in my next post.

For this post, I’m going to describe a small modification to the forward skirt, a rebuild to the aft skirt, and a wide-ranging replacement of the kit’s engines, fairings and heatshield.

As usual for this kit, the S-IC needs to be rotated to bring it into correct alignment with the rest of the stack. So the locating lugs on the forward skirt need to be moved. This is complicated by the fact that I have previously rotated the aft part of the S-II stage through ninety degrees so as to be able to conceal an unrealistic kit feature. Not having undone that rotation when I modified the S-II Aft Interstage (because that kit part is rotationally symmetrical), I need to reverse that rotation now. A corrective quarter turn would amount to moving the locating lugs 3⅜″ clockwise around the rim, looking down. Instead, judging from the position of the S-IC service tunnels, I found I need only three-and-a-sixteenth. (So it seems to me that, if you build this kit without rotating the aft part of the S-II, you’ll need to move the S-IC locating lugs five-sixteenths of an inch anticlockwise to fix the stage alignment. But please check my working.)

As usual, the colours of the skirt interior and LOX dome are hard to ascertain. I used zinc chromate yellow-green for the tank on this stage, which matches the colour photos I’ve seen of the stage being assembled, as well as the apparent colour visible in the familiar footage of Apollo 4 staging.

At the other end of the stage, the big problem with the fairings and heatshield provided in the model kit is that they are rimmed with multiple air scoops, designed to drive cooling air across the heatshield between the engines and the fuel tank. These featured in early designs (on which the kit was based), but on operational Saturn V launch vehicles the scoops had largely been removed, leaving only a pair at either side of each engine fairing. So both need to be replaced with much plainer resin versions from New Ware.

The kit engines also need to be replaced. Revell provides bare F-1 engine bells of the kind seen on the small number of Saturn V vehicles that are on display. But in reality, the F-1 engines on operational launch vehicles were swathed in external insulation called “batting”, to protect the engine bells from hot gases billowing back from the rocket exhaust. It looked like this view of a test item:

(This picture rattles around the internet uncredited, but thanks to Fons Bingen, whose comment appears at the end of this post, I can now provide a source and photo credit. It appears in The Saturn V F-1 Engine: Powering Apollo Into History by Anthony Young, credited to Saverio “Sonny” F. Morea, F-1 Program Manager at the Marshall Space Flight Center.)

Resin versions of the batted F-1 engines are available from RealSpace Models. Here’s a comparison of the kit version and the resin replacement.

The batting consisted of both generic pads applied to the bell, and shaped sections which surrounded more complex structures. As the photograph of the real thing shows, there was a slight difference in the reflective properties of these two kinds of batting. I aimed to reproduce this by applying chrome-finish paint to the resin, and then adding bright chrome Bare-Metal Foil detail.

RealSpace’s resin engines are adequately shaped to locate them accurately on the kit heatshield. And New Ware’s resin heatshield is adequately shaped to locate the kit engines correctly. But the two detail kits don’t have enough locating studs to align them precisely with each other. So I sawed the locating studs off the kit engines, and cemented them to the resin parts, ready to engage with the holes in New Ware’s heatshield; and I drilled out the gimbal mounts on the resin heatshield, and added short sections of brass rod to engage with the sockets on RealSpace’s engines.

Then I needed to attach the gimbal actuators to the engines. In reality, these “fueldraulic” pistons steered the outer engines, and were supported on structures concealed inside the engine fairings. Each outer engine had two gimbal actuators, attached to its base by an open pyramidal outrigger. The kit provides each actuator and its engine outrigger as a single, poorly detailed part.

I used the kit heatshield as a jig to get the correct relative positions of each resin engine and its pair of actuators. Then I filled the open pyramid of each outrigger with clear glue, allowing the glue’s surface tension to gather it into a pyramidal tent-like structure—that was my way of reproducing the appearance of the real engine outriggers, which were wrapped in foil batting along with the rest of the engine.

After painting and the application of foil detail, here’s what the engines looked like:

You can see that the centre engine sports a couple of vertical rods in place of gimbal actuators. This engine was not steerable, but still had outriggers attached, which were supported by rods attached to the heatshield. I scratch-built outriggers and rods for this engine, since the kit neglects that detail.

The New Ware heatshield is light on detail, providing only the outlines of the various tiles. In reality, the heatshield was dotted with rivets and other details, which you can see in this view of the Apollo 11 S-IC:

Guided by this photo, and John Duncan’s excellent reference photos of the heatshield of the S-IC displayed at the Kennedy Space Center, I drew up and printed a set of custom decals, which I applied, tile by tile, to New Ware’s resin part.

The next problem was the subsidiary heatshields positioned within each engine fairing. Both Revell and New Ware provide simple rectangles, supported at their outer corners by the base of the gimbal actuators. These certainly match the appearance in the Apollo 11 photo, above. But notice how many panels have been removed in the Apollo 11 view—engineers were gaining access to the interior of the Saturn V until late in the pre-launch period. So in fact, the whole interior of each engine fairing was eventually blocked off by a lunate heatshield built up of several panels—the rectangle in the Apollo 11 view is only the central part of a larger structure, as shown here:

The complete structure is visible in the S-IC at Johnson Space Center—see, for instance, this photograph by Kevin A. Boudreaux.

So I scratch-built replacement fairing heatshields using styrene sheet.

A little experimentation with paper revealed that these needed to be cut from discs 22mm in radius, if they were to fit New Ware’s replacement fairings at heatshield level. (In fact, they should have been slightly elliptical, since the fairing heatshields were tilted a little from the horizontal.) These little lunes then got their own custom decals, reproducing what I could see of the panelling in various views of the JSC Saturn V.

Finally, the whole lot could be assembled:

The Revell aft skirt also needed to be seriously modified, since it lacks hold-down posts. These were important components of the real launch vehicle, since they supported the entire weight of the Saturn V on the launch-pad, and at launch engaged with hold-down arms which prevented the Saturn V taking off until full engine thrust was achieved.

New Ware provides four resin parts, each of which requires a large, shaped slot to be fashioned to accommodate it. Starting with a series of hand-drilled holes, I expanded and shaped each slot before fitting the hold-down and epoxying it in place, only moving on to the next slot once the glue was dry.

 

 

Finally, a dry assembly to ensure that everything fitted together. Notice the internal fairing support struts, which are photo-etched parts from New Ware.

Next time, I’ll complete my build of this stage.

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