Hahahaha!

Yeah that stuff snuck up on me. There I was staring down at the gap by the motor mount- nothing...nothing...nothing....WHAM!!!!

Yep all over the hands, airframe exterior, motor mount interior...

Ahh, live and learn eh?!

Hahaha....

I use GLR expanding foam, and I haven't had that experience, but I learned early on to use only a little at a time. A lot is asking for disaster.

Makes for some great stories though 😆

I have used PML foam on several of my birds. I have yet to have a problem with it. As long as you use a small amount at a time, it shouldn't get all over.

There are a variety of formulations of 2 part urethane foams out there. PML happens to be a pretty agressive formula with approximately 25:1 expansion ratio for the straight up 50:50 mix. I ALWAYS foam any thru the wall fin can assembly. Might be overkill, might be a good idea - I can't prove it either way except to say I had an EZI-65 kit come in ballistic from a J350 flight and the only part of the bird that was intact and flyable was the section of airframe that was foamed. Fins, motor mount and airframe around them was 100% intact and the rest of the bird was essentially fragmentary.

DON'T use too much at a time. Never mix more than a full cup at a time because you will barely have time to place it given it will be reacting before you can even get it properly mixed. You literally have 90 seconds or less from the moment you pour the materials together to stir AND place the foam. At 90 seconds you'll almost certainly have a mess on your hands. I wrap masking tape on all surfaces that can't get foam on them so I can peel it off cleanly afterwards. By the way, don't breath the vapors of this stuff before or after its mixed... these are urethane cyanoacrylates... VERY bad juju for your eyes, nose and lungs.

There are also a number of less aggressive formulations out there; slower reacting AND less expansive. The 4:1 ratio foams give you as much as 8 or 10 minutes to place the foam.

Warren

Sounds like it's the same stuff as the GLR foam then. Very fast, and I have yet to mix more than 1/2 of a dixie cup at once. Still foamed up quickly and aggressively.

No idea what foam you guys are talking about but I use the foam from Fort Collins Plastics it awsome. When you put a little bit in it goes slow but when you do alot ot expands really fats be careful. XD

I know I'm not as experienced as anyone on this topic, but I learned my lesson real quick. The first rocket I used foam on, I did so without really testing how it would react. I tried a little bit in a paper cup and it was slow, so I figured that increasing the amount would be the same. Big mistake. It was more like soda and vinegar. Got all over everything and I ended up sanding the inside of the MMT with the handle of a long socket wrench wrapped with sandpaper, the fins, the outside of the airframe. Everything. It was a royal pain and took forever. The last rocket I built I papered and taped every surface that shouldn't be exposed to the foam - inside and out - fore and aft. Poured the foam, let it cure, cut it down, Dremmel'd what I didn't need and removed the paper and tape. Other than some very minor sanding It worked great. The only cleanup was the garage floor - easily scraped off with a putty knife.

The great thing about foam is that my kids love watching it blow up all over the place - it's a great science experiment!

I've gotten much better at judging foam volumes... small amount take a lot longer to cure as the stuff is exothermic like epoxy. More in one place results in greater heat, greater bubbling, greater volume. Oh yeah, newspaper on the garage floor and masking off any parts of the rocket I don't want covered with foam generally makes it a bunch easier. The foam from the plastic supply place in Fort Collins is about 7:1 expansion and takes 2-3 to minutes to react.

Warren

Have to get me some of the ft collins foam as this particular project and one I'll be starting soon for LDRS involved injecting foam into 8 cavities thru a syringe to make a conical transition section--very tricky to mix, draw into a 60 cc syringe, get the delivery tube on, and get in the right spot with the right volume, before blowing up or clogging the syringe delivery tube.

4 hands helped but a slower cure would have been much less messy. Thanks for the info! (Warren you're an amazing source of info.)
JS

If you're going to do the syringe thing, don't draw it back into the syringe, get the syringe all set, remove the plunger and then fill the barrel directly, reinsert the plunger and go. You really don't have the time to do it by drawing up into the syringe. Pour and plunge immediately.

Warren

Warren,
Makes sense tho I was taught never to do so for other reasons. We actually got it to work pretty well as w/o the fill tube, you can draw thru it up pretty quickly--at least in a 60cc with the nozzle nipped. Took some trial and adventure, amazing stuff.

PS off topic but I recently tried the Devcon 60 sec epoxy today for tacking on fins. When used with one of the 2 mixing chamber needle nose extensions supplied, worked fabulously. A big honking fin was tacked in place w/in 90 seconds. I know CA can be used for this but I don't like mixing adhesives for some likely irrastional reason. Not as good when merging puddles. the othe rproduct (man I love/hate McGuckens--always buy more than intended) is an epoxy putty sandable w/in 20 minutes. Worked well.
John S

I'm looking for the right expanding foam application for my "Estes size" rocket project that has some 1/4" gaps. -Any suggestions?

-Robby

A 1/4" gap would be something I would try to resolve with epoxy or sandable filler. Foam would be great in between the airframe and the motor mount tube as a filler. If you have a visible gap in the airframe, the foam will expand out of it after pushing it out of shape. If you have a big gap along a fin root, use PC7 Epoxy or one of the other thick paste epoxies first to close the gap before putting in foam to fill the fin can.

Warren

PS: I may have totally mis-visualized what you're talking about here, so if I have, just ignore me - won't be the first time I've said something without knowing exactly what I'm talking about.

Warren,

Having never used expanding foam before, I imagined that maybe there was a brand out there that would be useful as lightweight filler for small rocket projects. Maybe it is not lightweight at all, I don't know. I realize that most "high power flyers" use this application in between the body tube and motor mount.

I'm thinking of using the foam in a gap 3" long with a girth of 16mm that is inside the forward end and hard to reach. I would say It's inside the nose cone, but it is unique and not a typical nose cone. The foams' purpose is to not let the gasses go in the 2 gaps and cause unneeded stress in the form of pressure. I would like that pressure to flow uninterrupted out of the cockpit releasing the window. I figure if it's hard to reach use foam, but using sandable filler looks like a good option. What's the weight difference compared to foam?

-Robby