Foam Question

I have a project in which I want to use some expanding foam to fill and stiffen a part. It's a pod that I want to stick on the outside edge of a long fin. The rocket will most likely land on the fin pod, causing a lot of stress. I'm considering having a tab on the outside edge of the fin that will extend through a slot in the tube of the pod and contact the inside of the tube opposite the slot (sort of like a TTW fin tab, except it contacts the other side of the tube, not a MMT). I'll add fillets at the slot and where the tab contacts the opposite inside wall. To make the whole thing more rigid, I'm considering filling the entire pod with foam.

My question is what kinds of foam work for this kind of application? Is it necessary to use 2-part foam? Or can you use the expanding foam that comes in a can and is used to fill gaps in construction? It seems like canned foam would be easier to work with and control than the 2-part kind, and I think I have a can of the stuff already. But I do not want to use it if it won't help with strengthening the part or if it will cause other problems.

Let me know what you think. Thanks!

the tinned stuff has a bad habit of continued expansion long after you use it.
Rex

ThirstyBarbarian said:

My question is what kinds of foam work for this kind of application? Is it necessary to use 2-part foam? Or can you use the expanding foam that comes in a can and is used to fill gaps in construction? It seems like canned foam would be easier to work with and control than the 2-part kind, and I think I have a can of the stuff already. But I do not want to use it if it won't help with strengthening the part or if it will cause other problems.

Let me know what you think. Thanks!

Click to expand...

Use only 2-part foam for rocketry. The can stuff is moisture cure and when confined it will continue to expand when ever moisture is present & sun heats the tubes, usually resulting in a split or expanded tube.

2-part foam is designed to cure rock hard and can be sanded, shaped, cut etc.

Some have reported using canned stuff with success, I write that off as not completely filled or just plain stupid luck.

Is your project worth taking the chance? Once you have some foam, you will find many uses for it!:grin:

Yikes! I do not want my rocket pods to explode! Thanks for the info.

So, what kind of retail store might carry 2-part expanding foam? I know I can order it online, but I have a nice block of rocket-building time this weekend, and it would be great to be able to get some now without waiting for shipping. Any ideas? Does a place like Tap Plastics carry that kind of thing? I was in Hobby Lobby today and asked about it, but they said they do not carry it.

Do you really want to use foam? An alternative would be to use a moisture-curing poly glue like Gorilla Glue. You would put just a drop or two of water in the pod, then shake as much of that as you can back out. Follow that with a drizzle of the glue. It will foam up and should cure rock hard. I've used this method to secure BBs used as nose weight in hollow plastic nose cones. Several have survived falls from altitude onto hard surfaces (some onto paved parking lots) when the parachute failed to operate properly (or was left safely packed away in the range box...).

(Yee-Haw - my 1000th post!)

sooner.boomer said:

Do you really want to use foam? An alternative would be to use a moisture-curing poly glue like Gorilla Glue. You would put just a drop or two of water in the pod, then shake as much of that as you can back out. Follow that with a drizzle of the glue. It will foam up and should cure rock hard. I've used this method to secure BBs used as nose weight in hollow plastic nose cones. Several have survived falls from altitude onto hard surfaces (some onto paved parking lots) when the parachute failed to operate properly (or was left safely packed away in the range box...).

(Yee-Haw - my 1000th post!)

Click to expand...

This foam idea is for this project: https://www.rocketryforum.com/showthread.php?64212-REVIVED-Pods-on-Mega-Der-Red-Max

It's a Mega Der Red Max with pods on the fins. Most likely it will land on a pod. So that's a lot of weight coming down on a pod made of BT60 and Estes nosecones. I'm thinking if I fill the pod with foam, it will form a much more solid pod for landing and there is less likelihood of damage, but I am open to suggestions.

ThirstyBarbarian said:

I'm thinking if I fill the pod with foam, it will form a much more solid pod for landing and there is less likelihood of damage, but I am open to suggestions.

Click to expand...

It would be more solid. Don't know if it would be stronger. Would also make it heavier - both heavier in the aft, and heavier at the fin tip. If you use pointy cones on the pods, you could really stick the landing. What about attaching part of the recovery harness to the aft end so it would come down sideways? A so-called "squid line".

a shop that caters to model railroaders ought to carry it, used be named 'mountains in minutes' (IIRC). an alternative to using plaster of paris for making scenery hills etc.
Rex

Or you make the pods replaceable if needed but a BT60 based pod can't be cheap. Oh, the canned Great Stuff comes in 2 formulas. The old formula is the one the other's speak of and there's a newer type that's low expansion. You'd have to test but I'm going to give it a try sometime next year for my projected 3rd level.

Oh, I once got the 2 part kind at Home Depot, worked pretty good.

I found Alumilite Super Foam 320 at Hobby Lobby. Is that what I want? It is described as 3 lb density self skinning foam that expands up to 20 times the original liquid volume.

Anyone? Alumilite 320?