SR-71A Blackbird (Testors) Build #18 – Fuselage Tedium Continues…With a Much-appreciated Detour on the Engine Nacelles

After taking August off and away from the bench, I’m back at it. And since the fuselage isn’t finished, yet, I’m back at that, too.

I’ve done so much work on sections of the fuselage and, more importantly in terms of my ancient eyes, have used so many different materials that my ability to see the surface has diminished. To work around that, cue the primer! Normally I tend to not use primer as each coat of paint (of whatever type) fills in details, some of which I have labored to include. But this time, what the light does as it reflects off a surface that is mostly black, some white, and the green of putty, makes getting things correct has become a struggle.

Sod that…grab the rattlecan of primer (Tamiya Medium Gray):

Once under a uniform gray coat of primer, areas that still need work become evident (for me, the most important part of priming). These areas still need further sanding for filled areas to become invisible:

Some areas need just a little bit of filling (the holes will show you where they are):

Not everything needs more work, though:

And one spot needs just a little tweaking (note how a thin coat of primer, just enough to cover, has almost completely filled the two grills at the bottom-center of the photo):

After sanding and another touch of primer, one spot still needs more work:

Putty takes care of the small holes and surface imperfections:

With those small sections attended to, I wanted to check the…well…”fit” isn’t quite accurate, but it’s the least foul word I can think of…of how the engine nacelles and outer wings…well…yeah. Look closely. Where the nacelles attach to the inner wings has a LARGE GAP and those sections are supposed to meet:

Yeah…that’s going to need some work (and it’s going to take enough work that in contrast, I didn’t even mention the gap that runs the length of the attachment point between nacelle and wing). But before any fitting of these parts can happen, there are a number of details and modifications that have to be done to the nacelles/wings, first. It will be MUCH easier to do the work and make the modifications before these parts are attached.

About this time, the upgraded engine afterburner sections arrived, giving me a sincerely appreciated break from the ongoing fuselage diddling. The white conical parts (fuel spray assemblies) are 3D printed parts (something I expect I’ll be seeing more of as that technology becomes more affordable and commonly used) and the remainder of the parts are nicely cast resin:

I checked fitment of the provided parts and I like them much more than the modified kit parts I had done. It’s interesting in that I like the PE afterburner feathers much more than I do the resin parts that came with this set and they fit the kit parts more precisely. When it comes time to add these to the nacelles, the combination of both AM parts sets and kit parts will really dress up the business ends of the engines.

One of the things I wanted to see was how easily (or not at all) the engine intakes are going to fit. That AM set is very nicely cast resin and requires a bit of modification to the nose of the engine nacelles. For the resin intakes to fit, the molded-on lips had to be removed and the leading edge of the intakes cut back (the AM set provides a new, more accurate, part).

These are the intake parts:

The resin parts were cleaned up and everything fitted, then glued into one unit (twice):

With the resin parts assembled, it was time to cut, carve, and sand the nacelles to slide these things into place. The nacelle on the left is unmodified, the nacelle on the right has had its lip removed:

Once I had one side cut back and cleaned out, I slid the resin parts into place to see how they fit. There will be some work required (big surprise) to make them fit correctly but the overall effect is good:

I cut, carved, and sanded the other nacelle and the other intake “fit” equally “well”. Each side is specific to its location and I dry-fitted the shock cones to see how it all worked together. Again, some work required but the end result will be worth the effort:

There are replacement grills to add. Looking at references show that these panels fit flush with the surface on the Blackbird. That means I have to socket them into the nacelles. I started by taping the grills in place, tracing them with a needle, and then using a chisel blade to remove plastic.

This is what the kit parts look like:

I determined where the PE grills needed to go and taped them in position, then outlined the exposed grill with a needle:

Then I added tape to the exposed end:

And repeated the tracing process:

This is the result:

Now that I know where it goes, it’s time to cut plastic, leaving me with this:

Which enabled me to glue the grill into position:

Yeah…there’s a gap around the grill. I taped over the subtle surface detail and applied putty:

There are eight places on each nacelle where this had to be done. (Some of them came out better than others, requiring varied ways of filling gaps around them.) After seeing how easily the grills packed up with paint when I applied a light coat of primer under the nose, I wonder just how much of these details will be visible once everything has been painted. But having started this process, I saw it through until all the molded-in details had been replaced.

Scribing panel lines is an annoyance. I don’t like it. One little oops and things have to be fixed. (“One”…that’s funny!) In the process of socketing the grills and panels into place, I needed to scribe the panel lines of the nacelles. One little oops and this line isn’t quite straight:

Panel lines. ::heavy sigh:: If they’re correct, they’re mostly unnoticed. If they’re not correct, they’re as obvious as a hooker’s wink. To fill that one little oops with putty will result in the putty breaking out when the area is re-scribed. To avoid that annoyance, instead of using putty to fill the bobble(s), I use stretched sprue. It’s the same material as the surrounding area and the scribing tool cuts plastic, not putty and plastic. So a piece of stretched sprue gets glued to the bobble and let sit for a couple of days to be completely hardened:

Once that’s completely hardened, the sprue is trimmed and then sanded so that the surface is smooth:

A straight edge is laid down to connect the grooves and this time no bobble occurs:

The area is sanded through progressively finer grits until it looks like this:

Yes. Each time I bobble a scribe (something that happens MUCH MORE than I like) (hell, once is more than I like!) in a spot that will need to be re-scribed, I go through this process. (I also curse a lot.)

When I assembled the upper part of the nacelle/wing to the bottom part, the gaps were substantial. Also, note that the panel lines below the corrugated sections in the photos don’t match, so that had to be fixed as well:

MUCH FILING AND SANDING ENSUED. The white plastic I used to fill the gap below was .015″ (.381mm) thick. The step from the trailing plane of the elevator to the body of the elevator was a LOT more severe than the above photo showed. I didn’t measure it but it was about 3/16″ (4.76mm). “Was” is the operative word, here:

While I was making the two surfaces evenly meet, I kept looking at the trench between the strake (leading edge of the wing along the side of the engine nacelle) and the nacelle. The gap was huge and my initial intent was to stretch more sprue, fill the trenches, and spend many hours sanding, filling holes, and more sanding. I really wanted a structural putty, but making my own by partially dissolving styrene scraps in plastic cement resulted in something a lot more porous than I wanted. “Gee,” I thought, “I wish I had structural putty.” Milliput would work, but it doesn’t store well after opening the package and goes hard, so that was out. And then I remembered I’d purchased some epoxy putty to do something with the Gemini build that I ended up doing differently. I put the epoxy putty in the drawer and promptly forgot about it. Well, if you need epoxy putty, allow me to mention Apoxie Sculpt.

The gaps and spaces in the two nacelle/wing parts have been filled with Apoxie Sculpt and it works VERY well. It’s structural, bonds well, and thin sections don’t blow out or lift up. Once hardened (overnight, though you could work it after a couple of hours for general shaping), it’s hard:

Apoxie Sculpt saved me tens of hours of work to fill the trenches and I suspect it’s going to save me a metric (or Imperial) butt-load of work getting the wings to meet the nacelles properly!

4 responses

  1. Hi, I am reading your build with great interest as I am doing the same build with the same additional detail and a few other bits I 3D designed and printed myself. I encountered all the same issues you have and wish I had addressed my hideous scribed panel lines as you had. I have not yet fitted the landing gear as I am still adding wire detail but I am applying decals- 10 sheets purchased but only 4 viable.
    My next address is the red lines which I figure are about 1mm too thick. I am building 17972 but as it was at the 1974 Farnborough Airshow.
    Happy to share build with you and discuss the millions of issues with the kit.


    1. OH boy! Is the build improving your colorful invective?


      1. You could say that!!! I’ve basically done everything twice at least- that includes two kits, and just about two sets of each of the metallic detail parts too. My nose cone took 7 3D prints to get right! The only bit I did just once was the build and paint of my 3D print afterburners!
        I have not checked fit of main landing gear so am now wondering if I will have to cut and fit as you have- thing is, my painting is done (well, i’d hoped so)….
        Happy to share photos of my wip


        1. Yep…that’s about right. NOTHING is easy about this kit.

          Check the spam filter of your email account. Sent you a note.


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