Build thread: Sport-scale IRIS-T missile, 1:3.8-ish

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OK, let's a have a got at those control fins.

As you can see in a photo, the fins (which rotate to provide directional control of the missile) have smooth bulges at the bottom center where it sits on the actuator fairing:
control_fin_bulge.png

I was determined to recreate this; I have no precise specification of the curve, but I wanted it to at least look roughly correct. What follows is my third attempted technique (my pile of discards grows ever larger; I'll devote a post to it at the end of the build).

First up: cut lots of pieces. The primary fin cores are 1/16" basswood, while the rest is 1/16" balsa:
IMG_6913.jpg

The basswood cores were coated with TBII to provide a bit of a sanding barrier.

Two balsa pieces are stacked on top of the fin to create the contour. I did one side at a time, to avoid excessive handling of the balsa on the other side from where I was working.
IMG_6917.jpg

Next comes sanding. Lots of *careful* sanding. The two stacked pieces gave me a visual guide of what I was doing, rather than completely freeform sanding of a thicker piece (something I did on an earlier technique test, and I wasn't happy with the results). I roughed it out with 220 (not too aggressive, didn't want to oversand) and then worked the final shape with 440. Each side of each fin took several minutes of sanding until I was satisfied. Here's the first one, viewed from the bottom so you can see the shape I was going for:
IMG_6918.jpg

After I finished each round of sanding, I coated with TBII, again for protection.

A big question was whether this was repeatable. Could I make four fins on two sides each, and achieve consistent results? I would say the answer is "mostly". Here's the completed set; you can see the the base curves are not perfectly symmetrical but pretty good. I don't think you'll be able to notice the difference in the final model. The one on the left is not as pointy as it looks in the picture, couldn't figure out why it looks that way here.
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Thinned CWF was applied to everything and sanded down. Then, I decided that these were the one part on this rocket that I would apply filler-primer to (since these were the only components that were completely constructed off the rocket). After spraying, I could better see how the contours looked:
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I would say: pretty great, that's exactly what I was hoping for. Which is a relief given how much work they were. Finally I sanded off the filler/primer, a task which I fairly loathe, and here is the finished set:
IMG_6940.jpg

Whew. Gluing them on should be routine..... mostly. That'll be next.
 

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Fantastic result. Until someone comes up with a 20 point .1 tolerance curve, I'm saying it's scale.

I'm still at a loss as to how to recreate it 1:1 without stamped sheet metal, but I have plenty of time to talk to big builders and learn techniques.

I'm about to start my L2 build!
 
I'm still at a loss as to how to recreate it 1:1 without stamped sheet metal, but I have plenty of time to talk to big builders and learn techniques.
I assumed it would have be some sort of composite layup over a carved or maybe even 3D-printed form... but I'm really talking out my rear because I don't do composites. :)

I'm about to start my L2 build!
Excellent! What's it going to be?
 
This is what capitulation looks like:
IMG_6977.jpg

After thinking about a zillion ways to integrate the lugs with scale-like hanger structures, I gave up and put plain old lugs on. My concession to scale-ness is that the lugs are in the positions of two of the hangers and are approximately the same length. Good enough! I will focus on making the front hanger assembly as nice as possible.

Before I installed the lugs, I put each one on a small bit of 1/16" basswood to lift them above the front strake.
IMG_6973.jpg

Without doubt this was the most exciting installment of this build. You're welcome.
 
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Control fins ended up being easy. I had to decide what to line them up with, since the warp on the wings left their aft ends not perfectly perpendicular to the body. I decided to just center the control fins on the actuator fairings ant mount them perpendicular. No hugs here, all eyeballs.

Quick and Thick fillets finish the job.
IMG_6987.jpg
 
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The front hanger assembly is a weird and complicated beast. The pictures I have show it... kind of. One problem is that the hangers are rail guides, but I'm using lugs and a rod. So I needed to keep the center of the hanger open to keep clear of the rod. Here's what I did.

First, a pile of parts, the result of a bit of cutting and a lot of sanding:
IMG_6972.jpg

The little extensions are glued to the top of the side pieces:
IMG_6975.jpg

The roots are sanded so that the pieces will stand at the correct angle on the airframe.

Now the airframe is prepared. First, two pieces of 1/32" balsa are glued in front and behind the first body band, to create an even(ish) platform:
IMG_6976.jpg

Next another long piece is mounted down the middle. I did not get it quite perfectly centered, which annoyed me greatly at the time:
IMG_6978.jpg

Then the two side pieces are glued onto the outsides:
IMG_6979.jpg

Two fillet-y pieces support the sides, and blend down with the body band. Here's one of the pieces before installation:
IMG_6983.jpg

It is sanded mostly but not entirely to shape. After gluing and some more sanding, a bunch of fillets, and some CWF, the assembly is complete:
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It's a little janky but conveys the look of the real one pretty well.
 

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Good golly, it looks like the exterior construction on the airframe is complete:
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I have not yet figured out how to photograph long skinny rockets effectively. I'll try to do better when the model is finished, and it justifies the effort.

Anyway, by my count, that's 71 pieces of cut wood and 17 pieces of card stock. Undoubtedly my highest totals ever for a single build. And I must say those two bare lugs are still begging from some embellishment...

What's next? The nose cone, obviously. It's going to be a little while before I have the parts together for it. In fact I'll probably get primer and maybe even topcoat on the airframe before I get to the nose. We'll see.
 

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The fiddly bits have been so much fun, I’m kind of sad they’re mostly finished. :(

The nose cone should still be interesting though. And of course this:
IMG_6994.jpg
 
That is perfect. How does the belly conduit look with everything else on there?

Since you already know the form of the rail guides, I bet you could glue a couple pieces on the side of the Lugs. That may even reinforce them since they're on those skinny standoffs.,

For the long skinny's, I find it's best to get farther away to get them all in the shot. Admittedly, that still gets some distortion, as we saw when combing through pictures of the real thing for details.
 
That is perfect. How does the belly conduit look with everything else on there?
Like this:
IMG_6996.jpg
IMG_6995.jpg

In other words, fine, but it's certainly not the most photogenic side of the rocket. That would be more from the top/side, where you can see the front hanger assembly and the logo (eventually :)).

Since you already know the form of the rail guides, I bet you could glue a couple pieces on the side of the Lugs. That may even reinforce them since they're on those skinny standoffs.,
To match the scale profile and also match the front hanger assembly, the side pieces would actually need to a short distance away from the lugs. I'm fabricating them now, haven't yet committed in my mind to installing them. Painting in that area will be quite difficult with those pieces in place, I'll almost certainly need to do some brushwork in there.

For the long skinny's, I find it's best to get farther away to get them all in the shot. Admittedly, that still gets some distortion, as we saw when combing through pictures of the real thing for details.
Well for that I'd either need much longer arms (not likely to happen at this point in my life) or a nice-looking place on which to perch the rocket for picture taking. I should actually make a project of that: construct a halfway-decent photo setup for my rocket. My various rocket beauty shots are very un-beautiful.
 
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Eight more pieces of wood. These are the little side wings for the middle and rear hangers. They will (theoretically) mount on either side of the lugs.
IMG_6998.jpg

Of course I could not pass up the opportunity to do some papering. Though these are small they were relatively easy to do thanks to square faces and edges.
IMG_6999.jpg

At this point I’ll probably just put them on.
 
...aaaaaand nope, Mr. Indecisive has changed his mind again. Although these would look very nice, they create disproportionately annoying painting access problems, and so I will omit them for the same reason I originally didn't plan on using them. More fodder for the ever-growing discard pile.
 
Thar be primer, of the white Rusto 2x variety. Looks OK, although I saw a couple of gaps in the fillets along the skirts. I'll have to hit those with some putty once it's dry.
IMG_7004.jpg

The nose cone, having not yet been started, will obviously be painted separately. No biggie.
 
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Inspection of the primed rocket revealed a multitude of problems, most of which were fixed (?) with either Tamiya white putty or thinned CWF. One thing that sort of shocked me was that I could see spirals; apparently my spiral filling technique needs some work. I CWFed the ones I could reasonably get to; hopefully they'll be gone in the end (and if not, oh well).

The biggest problem here is the prevalence of stray glue all over the place. I knew this was happening while I was gluing and filleting, but despite my best efforts I couldn't seem to avoid it. This model will not look good from close up....

...but it still looks pretty good. I'll hopefully get all the new stuff sanded down and re-primed by tomorrow.
 
After sanding the new coat of primer, things look good enough. The area with the worst gaps that I filled with the Tamiya putty were in the area with the wings and the wire tunnel:
IMG_7020.jpg

That is in good shape now. The rear fin can looks really good:
IMG_7021.jpg

There are still a few faint spirals visible. Oh well, at this point they're staying.

We are ready for the topcoat.
 
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Haven't posted much recently because I haven't been doing much. But I have been doing *something*.

Recall that the nose of this beast looks like this:
nose.png

That is actually a non-functional unit, but the gist is the same: a large IR camera lens behind a glass dome. You can also see it in my avatar above, from straight on. I'm not going to replicate all the inner gadgetry, but I do want to get the broad strokes right, and that means a clear dome over the end of the nose.

Since February I've been searching every Target, Michaels, toy stores, dollar stores, supermarkets, 5 Below, Staples, Amazon, you name it... for something cheap with a right-sized (about 1") clear plastic dome on it that I could use. Four months into my search I finally found what I was looking for at a dollar store:
IMG_7036.jpg

Even better, for a buck I get ten of these guys to play with. Here's what one looks like:
IMG_7037.jpg

These were every so slightly larger than I wanted (about 1 1/8" diameter) but close enough to work with. With an Atlas hobby saw, I carefully cut off the dome, just a bit above the green. Then I sanded (and sanded... and sanded) on a 100 grit sanding block until the diameter was 1".
IMG_7051.jpg

Then I coated inside and out with a couple coats of Future, just to protect it from handling and such. The result is a nice looking contact lens for the rocket.
IMG_7052.jpg

Due to starting off slightly oversized, the curvature is not *exactly* what I want it to be, but I think it will still look nice... at least for the first flight, and then probably get all scratched up because the plastic is not very hard. I can live with that. And I've got plenty more so I can always replace it in the future if I can detach it.

The end of a very long and ridiculous journey. Now I need to build the rest of the nose. Soon.
 
Weather + opportunity =
IMG_7055.jpg

Every time I paint a rocket is another opportunity to reflect on what a lousy painter I am. On this occasion I think I didn't screw up anything too badly, though I'm not going to go so far as to say it's a great paint job. We'll see when it's dry. I think I at least got everything covered.

On a positive note, the color looks about right. That's Rusto 2x Winter Grey Gloss; I'll eventually coat it with matte clearcoat after decals.

Things are now going to go dark here for a little while, should resume sometime in June.
 
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OK, after five days the smell has dissipated to the point where I can bring it inside. Let's see how we did:
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Overall: not bad. I think the grey is a shade or two darker than I would have preferred, but it's OK (hard to tell from the picture above). Should look fine after decaling.

There are a few areas where the paint is not smooth, most notably the wings. This picture catches them in the light so you can see the texture:
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I'm pretty clear on the reason for this: it's the texture of the surface of the cardstock. With no paint or with primer, the surface was matte, and I couldn't detect the texture. Now with the gloss paint it's apparent. So in hindsight, the wings could have used a coat of filler/primer. Regular primer just did not have enough fill to achieve smoothness there.

After the final matte clear is applied, this texture will probably disappear again. The question I need to resolve is whether I'll need to do anything there before decals are applied. The decals that go on to the wings are very minimal, so I might be OK.

This thing needs a nose cone, stat.
 

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OK, at this point I'll come out and say it: this paint job is no good. There are two problems:
1) The surface is not smooth in many areas. As in, so unsmooth that it really bothers me, and could be a problem when applying decals.
2) The color is absolutely too dark. Apart from looking wrong, the dark color is going to be problematic with my inkjet-printed decals. Of necessity I'll be using clear-backed decals, some of them (in particular the logo) will not show well against this color, I think.

And so, I think I'm in the unfortunate position of needing to sand and repaint the whole rocket. This makes me unhappy, but the alternative is probably worse. Sanding this down is going to be very challenging due to all the nooks and crannies on the rocket; it's going to take me many sessions and I probably still won't do a great job. Honestly I can't even imagine how I'm going to do this, but I have to try.

As for the new color, the closest I can find among the Rusto 2x line is Matte Perfect Gray, which should be much closer to what I'm looking for, vs. the Gloss Winter Gray I used. Of course, using matte paint means I'll need to gloss coat the whole thing before decaling, before matte coating again. Yay. There's also Universal Matte Iced Gray, which is a bit lighter than the Perfect Gray, maybe even better. Although I've never used the Universal paint line before.

So this is going to be a project that takes a while. In the meantime, I now have the parts in hand to start on the nose cone.
 
Managed to break off a control fin while sanding tonight. Easy enough fix, but... geez. Weirdly, it seemed to be a clean glue break... shouldn't happen with TBII.

I took the opportunity to sand the fin and the actuator fairing underneath it while the fin was off. Now that it's glued back on, I'll need to apply a bit of CWF to smooth out the area.

In the meantime, sanding is coming along... slowly. *Lots* of work to do.

(first post on the new forum software!)
 
Finished sanding down the rocket. I wasn't trying to remove all the grey, just thin it out, and make it smooth. In general, once I saw primer showing through, I stopped. Sanded through to the wood in a few places, but not too many all things considered.
IrisT-624-2.jpg

It all feels pretty smooth now, including the wings. Looks like, in the end, it worked as a sort of filler/primer coat, although a lot harder to sand.

Awaiting delivery of a can of Rusto 2x "Perfect Gray" for repainting.
 
Boy, I don't envy you doing all that sanding. There's so much detail on it. Look it over good and make sure you have the surface you want. It's easier to sand a little more now than after you put the new color on.

-Bob
 
Boy, I don't envy you doing all that sanding. There's so much detail on it. Look it over good and make sure you have the surface you want. It's easier to sand a little more now than after you put the new color on.
I'm feeling sort of "sanded out" at this point, but could still do more touch up sanding before the repaint if necessary. I have found that the little areas along the body tube where the various bulges and attachments join up are really difficult, even if I use a tiny piece of sandpaper and focus on it. At this point those are the only areas left where there's a bit of gloss visible.

Last night, before declaring it "finished", I worked on a lot of those little touch-up areas, and I think it's about as good as it can get. The large areas are all in good shape (certainly much better than before); after a coat of flat paint I think everything should look pretty smooth. I hope. :)

I am definitely glad I did not try to do a coat of filler-primer on this whole thing. Leaving a bit of gloss paint in crevices is one thing; I'd not have been happy to have little bits of un-sanded filler-primer there instead.

Anyway, at this point, it'll be what it'll be. I think that even if some of the bits don't come out quite right, the positive details will outweigh the negatives. Wait until you all see the nose cone. :)
 
How have I missed this build thread?!!! Neil, this is absolutely incredible work. I need to re-read every post and take notes.
 
Wishing you the best of luck! I've been reading good things about that paint. Thinking of trying it myself.
 
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