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

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neil_w

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How did I get here?
It's all Nytrunner's fault. And maybe Steven's, a little.

I'm not normally a scale modeler. Although I admire a lot of the typical scale modeling subjects, I've never had the slightest interest in building any of them. Then Nytrunner mentioned his interest in this missile in another thread and I went and looked at the pictures and I thought that looked like fun and to our knowledge it hasn't been done before (at least not on TRF), and well... here it is, leapfrogging my other designs onto the top of my build pile.

I give Steven some credit too because I've been in awe watching him methodically working through all the details on his Saturn V made me want a little piece of that action, but on a (much!) smaller scale. And so here we are.

About the IRIS-T
The IRIS-T is an infrared-homing air-to-air missile deployed widely in Europe (and elsewhere), intended to replace the AIM-9 Sidewinder. It's dimensions seem to be 9.5' long, and 5" in diameter (say, that would make a great subject for an L3 rocket at 1:1, don't you think?). This model will be BT55 and about 27.5" long, which puts it somewhere around 1:3.8. Neither Nytrunner nor I could find any official drawings for it, so everything is derived from a bunch of photos we have scavenged from around the web. And hence "sport-scale".

Here are a few pics that we've used to derive all the dimensions and such:

iris-t_and_sidewinder.jpg

A very good side view:
side_reference.jpg

And finally a good bottom view:
bottom_view.jpg

The Design
Nytrunner provided a good starting ORK file, which I've subsequently tweaked quite a bit. Here's the summary side view:
iris-t_ork_side.png

And here's the latest render. Some aspects of the decals are still work-in-progress, but at this point it already looks pretty good:


Notes
1) Standard build thread disclaimer applies: I do not work quickly. This will take a while.
2) Due to OR limitations, the above render does not have all the features that the finished model will have. Although it would still be a fine looking model (and a great kit) as shown. I'm not going the crazy obsessive route on this, but I do intend to capture as much of the detail as i can, within reason.
3) There will be some fun stuff here. :) This should be a pretty cool model when completed, if I can pull off everything I have planned.
4) I've spent the last month or so experimenting with techniques to make this model happen. So I'm pretty sure this is all gonna work. I think. ;)
5) If I can pull this off it'll be pretty cool.

And finally:
6) C11 is the ideal motor for this. Rats. :(

Next post starts the build.
 

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Nytrunner

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C11? What happened to the D12!?

Good overview, I look forward to seeing more than one piece at a time now :D
 

Andrew_ASC

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Buwhahahah....... Blaming Nytrunner...
 

Andrew_ASC

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And finally:
6) C11 is the ideal motor for this. Rats. :(
Hey, it's economical, and you should recover your fine model. Rats would be a wimpy "A" motor...
 

neil_w

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Sequence of construction took quite a bit of thought before I was satisfied with my approach. We'll see how it works out. Anyway, first up is the conduit that runs almost the entire length of the underside of the missile, shown most clearly in this picture:
bottom_view.jpg
[This is probably as good a time as any to notify readers that I haven't really the slightest idea what a lot of these parts are called. I call this a conduit because... well, it's just a guess. If anyone knows the proper names of these parts please let me know.]

[This is actually called the "wiring tunnel".]

This piece, as well many pieces on this build, be shaped balsa. I started with two ~12" pieces of 1/8" x 7/16" balsa. I split the whole thing into two pieces because I didn't think I'd be able to wrangle one extremely long piece. Then I hollowed out one side so it'd sit cleanly on the body tube. My tool of choice turned out to be 400 grit sandpaper wrapped around a 3/4" dowel:
IMG_6713.jpg

Eventually I achieved a decent shape:
IMG_6712.jpg

Then I beveled the two sides of each piece to achieve the profile from the picture (approximately). My sandpaper-wrapped dowel was called on again, this time held at an angle and run side-to-side.
IMG_6717.jpg

After working on this slowly and gently for a while, I ended up with this:
IMG_6715.jpg

That looks pretty good to me. Final shaping would take place on the body tube, I just wanted to get it in the ballpark for now.

The pieces were glued on. The ends wanted to lift so I taped them down to dry.
IMG_6727.jpg

Then came more sanding, a coating of TBII, more sanding, some CWF, sanding, more TBII, more sanding. End result, viewed from the end:
IMG_6736.jpg

The angle accentuates the unevenness; when you look at it from the side it looks pretty good. Here are the two ends:
IMG_6741.jpg IMG_6740.jpg

I beveled off the rear end (right) a bit too much, oh well.

Some Quick and Thick fillets on the sides finishes off this piece.
 
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neil_w

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Next up are the "body bands", four bulges on the airframe on which stuff is mounted. Three have hangers mounted to the top, and the fourth... well it just seems to be along for the ride. Anyone know what these are *really* called, if in fact they have a name?

I determined pretty early on that they seemed to be about 1/32" thick at this scale, and so I nabbed a sheet of 1/32" balsa at Hobby Lobby. I was relieved to see that, as I had hoped, the wood would bend with the grain and comfortably wrap around the BT55, with no Windex or special measures required. Unfortunately the sheet is only 3" wide, so I needed to use two pieces to cover the full circumference (minus the conduit).

Here's after the first piece is installed, with another piece on the bench in the lower left:
IMG_6743.jpg

And here's how it looks after all four bands are installed (total of 8 balsa pieces):
IMG_6744.jpg

So far so good, and now the airframe is starting to look recognizable as an IRIS-T. What comes next? Naturally, I had to paper the bands. This didn't seem so crazy when I first decided it, but by the time I finished I was truly questioning my sanity. But every one of my builds must in some way push the papering envelope as it were, and so here we go. Of course I did a test of this, and it went... "OK", but I figured I could do better on the real thing. Ha!

First I wrapped around a piece of label paper, with some extra on each edge.
IMG_6752.jpg

Here is the hard/insane part: sanding off the excess. There's very little sharp edge to work with on a 1/32" thick band, and so sanding around the edge was a really frustrating process. And I was using 400 grit, to avoid damaging or oversanding anything. Here's after I sanded one edge, ready to remove the excess. The label paper shows black through the white coating when it is ready to be separated:
IMG_6754.jpg

And here it is after removal:
IMG_6755.jpg

Not too bad I guess; that's actually one of the better edges I achieved. Honestly I was just relieved to get it over with without damaging anything. As always, I finished by sealing the exposed edges with TBII (that'll also help fill and smooth the rough-sanded bits at each edge) and sanding with 800 grit. The edges don't look beautiful but I think they'll be good and smooth after primer is sanded.

Here's all four of them, finished:
IMG_6757.jpg

Now, to confirm size and placement (as if I could do anything about it at this point). Here's a paper template of one of the main fins, with cutous along the root edge for three of the bands. And the fit is...


...perfect! Now I'm getting psyched.
 

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neil_w

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This first part of the installation of the (very) small forward vanes is preparing what goes underneath them. The side vanes are mounted on bulgy things that look like this:
vane_bulge.jpg

[edit: Actually these are "strakes".]

The top and bottom vanes are mounted on small plates that are not really pictured well anywhere. For these, I cut small pieces of 1/32" balsa; after mounting they will be sanded down even thinner.

But lets get back to those bulgy things. I started with pieces of 1/8" x 1/2" balsa, and marked the future cut lines:
IMG_6749.jpg

Then, once again, I hollowed them out underneath so they'd sit nicely on the BT55. Once again, 400 grit sandpaper wrapped around various cylindrical objects was called into duty. The big trick to this process is to get the curve properly centered on the piece of wood, and as symmetrical as possible. It is not easy. My results are good but not perfect (not perfect as in, they don't sit 100% flush on the BT).
IMG_6750.jpg

Next I cut the pieces to shape:
IMG_6751.jpg

Then came the fun part. I started sanding them to shape while holding them in my hand, but realized there was a better way. I fastened some blue tape sticky-side up on a piece of BT55, and stuck the piece down onto it:
IMG_6760.jpg

Then I went to work, curving the top sides down and generally thinning the part down. The finished parts are very delicate and quite lovely; being affixed to the BT like that kept them safe from harm during sanding. Eventually I removed them; the finished cross section looks like this:
IMG_6761.jpg

I love that, what can I say.

Next they are glued to the BT in routine fashion. Here are top and side views with all four vane bases attached.
Top:


Side:


At this point they look good but are still a bit thick, and the edges are not blended into the BT as well as they need to be. Fillets and/or CWF will take care of that, along with the small chunk missing from the lower left "corner" of the side bulge piece showing in the picture (a minor sanding casualty).

The next installment will cover final shaping and filling, and attachment of the vanes themselves (once I get around to actually doing it. ;))
 

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viciouspeanut

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Awesome missile! Will watch this one closely, a 3 or 4" one would be wicked.... :wink:
 

boatgeek

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I admire your craftsmanship on this project. I wish I had the patience to put that many little fiddly bits on to my rockets.
 

neil_w

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I admire your craftsmanship on this project. I wish I had the patience to put that many little fiddly bits on to my rockets.
You ain’t seen nothin’ yet. ;)

Still, this is a toddler toy compared to stuff like Steven’s Saturn V or that crazy new N1 kit.
 

neil_w

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OK, we'll get back to the vanes. In the meantime, here is the first part of constructing the supports for the rear control fins. I do not know what these things are called. They are shown reasonably well here, but I will note that they look a bit different in different pictures:
Screen Shot 2018-03-17 at 8.58.32 PM.png

[edit: they are probably called "actuator fairings"]

Time for more balsa sculpting. These pieces are interesting because they need to hug the transition. We'll get to that in part 2. Here is far too much detail about how I sculpted the main part. I really needed these to all be as precisely the same as possible, so I added some extra technique to ensure my desired result. In hindsight, I wish I'd built the conduit and side bulges this way also. Oh well!

First, four pieces of 1/8" x 1/2" balsa (I sure am getting good milage out of that stuff on this build). One side is covered in black sharpie.
IMG_6765.jpg

Similar-sized pieces of 1/16" balsa are laminated on top. Each piece is now 3/16" thick. If you click to enlarge the image you can see the lamination at the edges where the black sharpie peeks out.
IMG_6766.jpg

Now I sand out the underside curve, on the side with the 1/16" balsa. My tool of choice this time is 220 grit sandpaper wrapped around a 3/4" PVC pipe coupler. In general, whenever doing this sort of thing, you want to use a slightly smaller tool than the BT you're going to mount to. Also, using a rigid tool like this (vs. a piece of body tube) ensures that it won't deform when sanding. This time I think I got it exactly right.

So: back and forth and back and forth ad nauseum. When I made it all the way through the 1/16" balsa, the black sharpie would start to show through, and it would make it easy for me to make sure that (a) the entire channel is consistent depth, width, and well-centered, and (b) that all four pieces would be exactly the same. Here's the first piece:
IMG_6767.jpg

You can see I have a very even, consistent channel, and it is well-centered on the piece. Also note I didn't go all the way to one end, since that end is going to hang over the tail transition so the channel was not needed there. So on to the next three. But I encountered a small problem. The amount of sanding required to do this was kind of crazy. After finishing the second piece, I looked at it closely and saw that only about 1/32" of the laminated piece was left at the thickest part at the edge. And so I made two new pieces for my last two, this time laminated with 1/32" balsa instead of 1/16". This gave me much less wood to sand through, but due to the sharpie system I was able to still end up with exactly matched parts:
IMG_6768.jpg

Next I cut the front of the pieces to shape:
IMG_6769.jpg

This was done after sanding out the channel underneath because it would have been hard to sand the channel into the pointed tip. Then I sanded down the front point, so it would taper to just about blend with the BT at its tip. No special tricks here, just slow and careful sanding (didn't want to oversand and have to start one of these pieces over again!). Here's the profile I ended up with, looking from the side:
IMG_6770.jpg

And, at long last, here's how the piece looks fitted on a BT (this is not the model itself, just a piece of scrap tube):


All that careful sanding seems to have paid off: that looks pretty great, and indeed all four pieces looked really consistent.

It is not yet time to glue these to the model. More pre-assembly needed.
 

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neil_w

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The motor mount is ordinary:
IMG_6746.jpg

[edit: this really is called the motor mount. :)]

I'm not allergic to hooks, so I put one in. It's positioned at the top of the rocket, in line with where the lugs will go. The rear centering ring is recessed a bit so...
IMG_6794.jpg

A (messy) fillet of Quick and Thick goes in the back, and then while wet I pressed in a ring of cardstock like so:
IMG_6797.jpg

That'll provide the anchor for the large end of the transition. Which looks like this BTW:
IMG_6799.jpg

That's a single ring of 65lb cardstock with some CA reinforcement.

TBII was applied to the tail end of the motor mount, and to the tabs on the anchor...
IMG_6800.jpg

And then the shroud was pushed on. Finished:
IMG_6801.jpg

I filleted around the seam and will probably do a bit of CWF to really smooth it out. Most of the shroud will be covered by those control fin mount platforms, and that includes the seam, so I didn't worry about trying to smooth out the seam or anything.
 
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neil_w

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Let's finish up those strakes.

The side bulges were a bit too prominent, so I sanded them down quite a bit. They're probably still somewhat larger than scale, but that's going to be a general characteristic of this build: some subtle details are going to end up less subtle, just due to practical reasons. I also sanded down the little rectangular pieces under the other two vanes so that they really are quite subtle (final judgement will come with the paint).

Anyway, the vanes themselves are barely slivers of wood. After not doing a great job creating such things in any sort of consistent way with my knife, I broke down and blew 39 cents on a piece of 1/16" square basswood dowel. That made things easy. Here's the result:



Note that the strakes on the side bulges (first picture) taper a bit from front to back to keep the tip edge of the vane parallel to the airframe. I sanded them down with a sanding block after gluing to get as close as I could.

I am very happy with how these turned out.

IMG_6818.jpg


IMG_6820.jpg
 
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neil_w

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This is part two of three on the actuator fairings.

First, the tail pieces. The exact shape of these is not clear from the pictures I have seen, so I just picked a shape and am going with it. Start with some pieces of 1/4" x 1/2" balsa and beveled off one corner:
IMG_6809.jpg

Then I hollowed out the ends, this time with 220 grit wrapped around a spend D engine:
IMG_6811.jpg

Finally they are attached to the ends of the pieces from the previous posting.
IMG_6812.jpg

Now they are glued onto the airframe:


The spacing around the motor hook is tighter than I expected, just barely fits!

From this angle they look great. I am not showing from directly behind because from that angle they look like garbage. Despite all my checking and double-checking, they are not sitting even, and as a result they are perfectly placed and oriented. You can't really tell unless you look from directly behind, so it's not a disaster, but I am still pretty pissed off about it. I'll have to do something to flatten the tops so the fins stand straight on them, but I'm not sure there's much more I could do. I'll just take solace in the fact that most folks won't ever notice. But I will. :bang: No pics of the f-up until I cool down a little and/or have a plan to deal with it.

Other than that, they are looking good ("Other than that, how did you enjoy the show Mrs. Lincoln?"). There is still one more step to complete them.
 

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Nytrunner

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Those are looking good. That backend has always been a little questionable. Especially when we started to think the structures are actually offset instead of sitting centered on the tube lol
 

neil_w

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Hmm, I have thought of one way to address this issue: cut off the entire rear end (about 3.5" worth) and build a completely new one, using a new technique (TBD) that will not suffer the same problems as the last.

Upside:
  1. Good chance to make the end result much closer to perfect

Downsides:
  1. I'll need to cut through the conduit -- make that the "wiring channel", as I have been informed by a highly knowledgeable reader over on YORF. I'll need to construct a new piece and try to match it as closely as possible to the existing one. I think that's doable, and anyway the wiring channel is not the side that most people will be looking at anyway, so if it's not 100% perfect no biggie.
  2. The required coupler will add some unwelcome weight towards the rear of the rocket.
  3. Lots of work thrown away. That's more of a simple bummer than a real problem though.

I'll need to think about it. And so, I shall focus on other tasks until I make my decision.
 

neil_w

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I've now taken enough chill pills and meditated sufficiently to achieve inner peace with this screw-up, and so I am ready to disabuse the world of the notion that I am any sort of craftsman. Mind you, at this stage it's only really noticeable when you look from behind the rocket, but this is what it looks like:
IMG_6827.jpg

Click for screen-filling horribleness. The piece on the bottom of this picture is especially heinous, although the top one is pretty bad too.

I have come up with several possible reasons how this went so far wrong, but right now I need to decide how to deal with it. As far as I can tell there are three options:
  1. Cut off the whole rear end and make a new one, as previously mentioned. In this case I will have to apply all my alleged learning here and do it right the second time.
  2. Attempt to flatten the surface of each piece so that at least it will be appropriately perpendicular to the, ah, whatever it's supposed to be perpendicular to. Then the fins should mount normally. This will not be easy.
  3. Leave as-is, and do what's necessary make sure the fins are oriented correctly, even though they might not be perfectly perpendicular to the platforms they're on. Most important (I think) is for the control fins and the main fins to be in line with each other. Will it look even worse with a fin mounted non-perpendicular and maybe even not quite centered on its platform?

I haven't decided yet. Fortunately I have lots of other stuff to do in the meantime.
 

neil_w

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To my surprise, I was able to remove the worst of the four pieces without too much drama. I will replace it and see if the end result is satisfactory. Otherwise...

IMG_6836.jpg
 

neil_w

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And so I made a new piece:
IMG_6842.jpg

Getting better at it, going faster. I installed it, and now the new piece (shown at top in picture) looks pretty good, but the one opposite now sticks out like the proverbial sore thumb.
IMG_6843.jpg

And so I am now attempting a different fix on that one. It's looking a little iffy right now, might end up needing to make a whole new piece again. At least now I know it's possible...
 

neil_w

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My attempted non-destructive repair of the remaining “bad” structure was clearly headed for failure, so...
IMG_6846.jpg
 
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