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Build Thread: Public Missiles Io

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jqavins

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I sanded off CWF today. It's not perfect, but nothing high build primer wouldn't fix.
2021-01-02 15.50.24.jpg

I also prepared for the first glue up steps, meaning I marked the location for the forward centering ring on the MMT, and reread the instructions for the piston. Then my epoxy was too cold to mix, and by before it warmed up supper was on the table and Lawrence of Arabia was on TCM, and that was it for the day.
2021-01-02 15.49.25.jpg

An update on the fiberglass front: I had decided that, since I can't really just dip a toe, and I don't feel ready to jump into tne deep end, I would not glass this one. Well, i fimally got the message that I can wade into the shallow end (am I straining the meraohore a bit? I'm no good with metaphores, and I never know when I've taken one too far) so that's what I'll do. Small quantities of materials and the minimum of tools needed for a beginner to do a good job (which inmost things is more than a seasoned worker could make do with, but less than a seasoned worker probably has.) So the spiral filling was unnecessary, but certainly won't hurt anything. Details to follow.
 
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jqavins

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It's not the first time I've used epoxy. It's not the first time I've use BSI 30 minute (did I say 15 minute earlier? Sorry, it's 30 minute) in a a Red Solo shot cup. I know what can happen, but man it happened fast this morning.

Zero the scale, dispense resin, dispense hardener,five grams each. Mix, mix, mix, scrape, mix, scrape, mix, mix, mix, scrape, mix. Maybe two or three minutes. Spread on the MMT where the forward CR will go then push the CR into position carefully lining it up on the marks. Wet the tube there the shock cord goes and press the cord in. Another two or three minutes gone. Pick up the cup to scoop up a bit more for the dges of the cord, and nearly burn my fingers, finding the epoxy has already kicked.

Alright, C'est La Vie. Mix up another batch, pour it out onto a piece of aluminum foil, and finish up the cord at the MMT end, and build the piston bulkhead.
2021-01-03 11.32.07.jpg
 

mtnmanak

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I sanded off CWF today. It's not perfect, but nothing high build primer wouldn't fix.
View attachment 445045

I also prepared for the first glue up steps, meaning I marked the location for the forward centering ring on the MMT, and reread the instructions for the piston. Then my epoxy was too cold to mix, and by before it warmed up supper was on the table and Lawrence of Arabia was on TCM, and that was it for the day.
View attachment 445044

An update on the fiberglass front: I had decided that, since I can't really just dip a toe, and I don't feel ready to jump into tne deep end, I would not glass this one. Well, i fimally got the message that I can wade into the shallow end (am I straining the meraohore a bit? I'm no good with metaphores, and I never know when I've taken one too far) so that's what I'll do. Small quantities of materials and the minimum of tools needed for a beginner to do a good job (which inmost things is more than a seasoned worker could make do with, but less than a seasoned worker probably has.) So the spiral filling was unnecessary, but certainly won't hurt anything. Details to follow.
Looks great Joe!

If you are going to give glassing the tube a shot, your spiral filling was not wasted at all. Often with those deep spirals, it can make the lightweight FG fabric dip a little bit when the epoxy is still wet, so you can sometimes see the spiral indentations a bit and need to glass it twice. This is why a lot of people will use a more "structural" FG weight first (something like a 2oz or above fabric for this size) and then a very thin (0.5oz or below) "veil" over that to make the finish look good. By filling the spirals first, you have alleviated one issue you may have encountered when glassing the tube.

Good luck on the glassing, look forward to seeing how it turns out.
 

mtnmanak

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It's not the first time I've used epoxy. It's not the first time I've use BSI 30 minute (did I say 15 minute earlier? Sorry, it's 30 minute) in a a Red Solo shot cup. I know what can happen, but man it happened fast this morning.

Zero the scale, dispense resin, dispense hardener,five grams each. Mix, mix, mix, scrape, mix, scrape, mix, mix, mix, scrape, mix. Maybe two or three minutes. Spread on the MMT where the forward CR will go then push the CR into position carefully lining it up on the marks. Wet the tube there the shock cord goes and press the cord in. Another two or three minutes gone. Pick up the cup to scoop up a bit more for the dges of the cord, and nearly burn my fingers, finding the epoxy has already kicked.

Alright, C'est La Vie. Mix up another batch, pour it out onto a piece of aluminum foil, and finish up the cord at the MMT end, and build the piston bulkhead.
View attachment 445065
If I can make one recommendation on the piston (not sure if this was already mentioned) - the instructions from PML will probably tell you to glue the piston cup so the "cup" portion is toward the strap and the "flat" portion is toward the piston buckle. I highly recommend you reverse that so the flat side is toward the strap and the buckle is inside the piston cup.

Two reasons for the this. Primary one is that the system works better if the force is pushing the piston, rather than gathering in the cup and, in effect, pulling it. I have had the pistons bind in the tube when the cup is toward the charge. I have never had it bind when it was away from the charge.

The other reason is that you then get a nice cup to put your recovery system in. I don't recommend doing this habitually, but I have packed my chute and shock cord in the cup with no protection and had it come out with zero scorching.

I also recommend smearing a thin film of epoxy around the inside of the piston cup. They become brittle over time and can crack. Here are some pictures of a cup I had to repair after it cracked. They should illustrate what I mean about putting the cup on "backwards" and how to reinforce the inside of the cup.
 

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jqavins

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Small update: I mixed up another gram or two of epoxy to fillet the top side of the CR.
2021-01-03 13.08.35.jpg

With the ejection charge below the piston, there's no way the piston can be pulled rather than pushed. I can see how maybe having it open side down could lead to jamming if the pressure inside causes it to swell. I was surprised that the piston has an open end at all, rather than having bulkheads at both ends. Had I thought a bit more before starting, I might have ordered a second bulkhead to put over the shock cord before gluing both ends of it the other things. Maye I'll make a two piece one to assemble around the cord.

As for packing recovery gear into the cup, that's not going to happen. This is a 54 mm body tube, so I couldn't pack half a dozen half walnuts in that cup.

Thanks for the tip on epoxying the inside of the cup.

Anyway, here are close ups of the bulkhead construction. The D ring is cinched down tight against the bulkhead, as per the instructions, but untouched by glue so still free to swing around the one axis.
2021-01-03 13.32.19.jpg2021-01-03 13.31.42.jpg2021-01-03 13.30.49.jpg
 
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jqavins

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Yeah, I'm temporarily stalled. I did (just now) edit post #35 to fix a bunch of typos, but that doesn't count as progress.

After deciding yes, I will do a little fiberglass on this after all, I am stymied by choices and suffering a form of analysis paralysis. I want to use 1/2 oz cloth but the place my friend found that carries small quantities of laminating epoxy doesn't carry 1/2 oz cloth, but they do carry 1/2 oz batt; is that just as good? Or I could go to 1 oz cloth but nope, they don't carry that either. If I glass the tube without the fins then I can vacuum bag it, and then I have to get into peel ply and that epoxy absorber stuff, so maybe just squeezing out as much as I can by hand would be OK, and then I can do it with the fins on so I get stronger fillets. But if I glass the tube alone, I could still lay a little glass within the fillets anyway, but that seems like more steps, but I guess it's not really, because I'll be doing those fillets whether there's glass in them or not, so it's only a little more work at that stage, really not enough more to worry about, so forget that. I should just go ahead and order some stuff and get on with it, but which stuff? This is where I came in! I guess there are other steps I could take before I'm totally stopped by all this.

My second glassed rocket will surely be a lot easier.
 

mtnmanak

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Not trying to muddy the waters, but there is another alternative that allows an easier "dip your toe in" experience - the EasyGlass sock from Giant Leap: https://giantleaprocketry.com/products/components_airframes.aspx

It is relatively cheap and makes the process very easy. Tie the sock on each end and spread the epoxy. You can get a small amount of BSI "Finish Cure" epoxy on Amazon for about $15: https://www.amazon.com/Finish-cure-...TAG950V9AF1&psc=1&refRID=YJTCPX95FTAG950V9AF1

This option is not the cheapest route per tube, but it does give you a chance to try it out with a relatively low upfront cost and not a lot of materials left over when you are done. I have used these socks before and I am actually planning to use them for a couple projects I am working on that have 7.5" and 8" cardboard tubes because they are easy to work with and quick.

In a further attempt to throw some monkey wrenches, last weekend, I tried fill some spirals on a 4" phenolic tube with regular, original formula Bondo from the auto supply store. Worked way better than CWF and was easier to sand. It is absolutely noxious stuff to work with (definitely want to work in a ventilated area), but it is my new go-to for filling spirals on larger tubes. And it is very cheap per ounce. It also worked great to smooth out fin fillets before priming.

If you glass or CF the fins, vacuum bagging is the quickest and easiest way to go.
 

jqavins

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I'll check that out; it sound like it may be the way out of my paralysis. But I'll have to look and make sure I understand it, and that it's no too far short of other options, and... AAHHHH!

It's too late for the Bondo on this one. CWF did a good job and I'm not looking back. (The CWF was super easy to sand. How do you do auto body work with something even easier to sand than that?
 

mtnmanak

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I'll check that out; it sound like it may be the way out of my paralysis. But I'll have to look and make sure I understand it, and that it's no too far short of other options, and... AAHHHH!

It's too late for the Bondo on this one. CWF did a good job and I'm not looking back. (The CWF was super easy to sand. How do you do auto body work with something even easier to sand than that?
It was probably about as easy to sand as the CWF, but, to me, it felt a little easier. Didn't clog up my sand paper as much and, more importantly, the bondo sanded smoother and stuck in the spiral better. When I use CWF, it has a tendency to chip out of the tube in places, so I always end up with gaps after I sand. Didn't happen with the bondo. I also smeared the bondo a little further out from the spiral, so when I sanded it didn't chew up the tube itself as much.

Also, I like to use these sanding blocks (also taken from the auto body world):


With some sticky sand paper, these are flexible and easy to use. Never needed them for LPR/MPR, but for HPR work, they are awesome. They are also awesome for sanding down a tube after you glass/prime/etc.

I use this little "scruff block" from them all the time - I just stick various grits of paper to the edge of my work table during a project and change them out as needed on the block. Great piece of kit for $7:

 

boatgeek

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Yeah, I'm temporarily stalled. I did (just now) edit post #35 to fix a bunch of typos, but that doesn't count as progress.

After deciding yes, I will do a little fiberglass on this after all, I am stymied by choices and suffering a form of analysis paralysis. I want to use 1/2 oz cloth but the place my friend found that carries small quantities of laminating epoxy doesn't carry 1/2 oz cloth, but they do carry 1/2 oz batt; is that just as good? Or I could go to 1 oz cloth but nope, they don't carry that either. If I glass the tube without the fins then I can vacuum bag it, and then I have to get into peel ply and that epoxy absorber stuff, so maybe just squeezing out as much as I can by hand would be OK, and then I can do it with the fins on so I get stronger fillets. But if I glass the tube alone, I could still lay a little glass within the fillets anyway, but that seems like more steps, but I guess it's not really, because I'll be doing those fillets whether there's glass in them or not, so it's only a little more work at that stage, really not enough more to worry about, so forget that. I should just go ahead and order some stuff and get on with it, but which stuff? This is where I came in! I guess there are other steps I could take before I'm totally stopped by all this.

My second glassed rocket will surely be a lot easier.
What's the lightest weight fabric your local store carries? 1/2 oz especially but also 1 oz takes a fair bit of experience to get a good surface, so may not be the best choice for a first project. The problem is that it hardly takes any epoxy to wet out, so it's easy to get puddles of epoxy over the cloth or worse, areas where the cloth floats off the surface on a pool of epoxy. 3-5 oz is probably going to be easier to work with, though a bit heavier in the final build. If you're going to be close on weight, you might need to go lighter. The sock from GLP might also be a good compromise, at approximately the same weight as 5 oz fabric, but easier to keep flat.

I would recommend just glassing the tube and not the fins. All of the joints around the fins add complexity and difficulty, which is not what you need on a first project. It's a lot easier to practice getting the fabric to lay flat when everything is convex like a tube and you're not trying to get the fabric to stick to fillets. Glassing the fillets after the fins are in won't hurt anything, but probably also isn't needed unless you're really pushing the rocket hard (like using the 38mm motor mount and J motors). It's also a lot easier to make corners fit nicely if they're small pieces of fabric.

I'd also recommend against vacuum bagging. You can get a decent surface with a brush and a squeegee. If you vacuum bag, you need to get the fabric very tight to keep from wrinkling it as the bag tightens up. That takes a fair bit of experience and equipment setup.
 

jqavins

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What's the lightest weight fabric your local store carries?
What local store?
1/2 oz especially but also 1 oz takes a fair bit of experience to get a good surface, so may not be the best choice for a first project.
Oh, no, not more options!!!
The sock from GLP might also be a good compromise, at approximately the same weight as 5 oz fabric, but easier to keep flat.
So, yeah, I guess that's the way I should go, just for simplicity. I do wish it were lighter, but oh well.

I would recommend just glassing the tube and not the fins. All of the joints around the fins add complexity and difficulty, which is not what you need on a first project. It's a lot easier to practice getting the fabric to lay flat when everything is convex like a tube and you're not trying to get the fabric to stick to fillets.
Yeah, I'd got that far. The fins are FG to begin with, so they really don't need help like the phenolic tube does.
Glassing the fillets after the fins are in won't hurt anything, but probably also isn't needed unless you're really pushing the rocket hard (like using the 38mm motor mount and J motors). It's also a lot easier to make corners fit nicely if they're small pieces of fabric.
My thinking here is that since this is partly for practice, as long as the concave corners are done as a separate step from the tube I might as well try that. The rocket does have a 38 mm MMT and while I'm not expecting to put J motors in it (my L2 cert rocket is a different project) I may well go to I motors, and maybe high thrust ones.

I'd also recommend against vacuum bagging. You can get a decent surface with a brush and a squeegee. If you vacuum bag, you need to get the fabric very tight to keep from wrinkling it as the bag tightens up. That takes a fair bit of experience and equipment setup.
OK, thanks for that.

Sock, not cloth or batt. Sock on tube only. Fiber enhanced external fillets. Sounds like a plan.

Thanks, everybody!
 

jqavins

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Today I glued in the motor mount, with the aft ring in place but still loose. I also glued the piston bulkhead into the piston body. Since I had the epoxy mixed, I also repaired the top attachment point on my coffee travel mug.

Nothing worth photographing here.

Tomorrow, I swear, I'll order the stuff to glass the tube. What do folks think about those glass cloth socks?
 

jd2cylman

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Today I glued in the motor mount, with the aft ring in place but still loose. I also glued the piston bulkhead into the piston body. Since I had the epoxy mixed, I also repaired the top attachment point on my coffee travel mug.

Nothing worth photographing here.

Tomorrow, I swear, I'll order the stuff to glass the tube. What do folks think about those glass cloth socks?
I have a PML 1/2 scale Patriot. If I ever get around to building it, I'm a gonna sock it.
 

Budro0

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Tomorrow, I swear, I'll order the stuff to glass the tube. What do folks think about those glass cloth socks?
I just tried the Soller FG sock and their heat shrink wrap. Some ups, some downs. The sock was easier than a more traditional cloth lay up, but it only comes in 9-10oz (in 4"). I would have rather used a 6oz product for my purposes. But that's about the only downside, it really was pretty simple and easy to do by myself.

The heat shrink was alright at best. If you want to try it, go for it. But I think the final product was worse than my previous experience with mylar sheets - I still ended up filling pin holes.
 

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I think you'll love that Io.
I have a Callisto (very close to the Io) that I fly frequently. Nice altitude on cheap (relatively) and easy 29mm motors.
It's nice to have rockets that straddle the Mid-power/High-power boundary comfortably.
The piston makes recovery prep a breeze.
Mine is phenolic too and I have had zero problems over 10+ years.
 

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