foam

I've got to fill the space between a 4" body tube and a 54 mm motor mount with foam to lock the fin tabs in place. Does anybody know of a one part foam that will do the job? I was looking at this and the review said it was used to fill a cavity in a boat by drilling a hole and shooting it it. That's what I want to do but I've always thought that one part foam needed moisture to cure and I remember making a gooey mess using Great Stuff years ago. Or does anybody have a good source for two part foam in a small quantity?

I think Giant Leap sells two part in a smaller sized kit.

Be very careful with the 1 part spray foams. They have been known to expand in the summer heat and split fiberglass rc boats at the seam... We use the two part for floatation.

Do you have the materials on-hand to do a mock-up of the fin can? You could even try different foams on the sections between fins if the fits are tight enough.

Section it when you're done, see what the best product is and then you get to throw something away. :wink:

KennB said:

Do you have the materials on-hand to do a mock-up of the fin can? You could even try different foams on the sections between fins if the fits are tight enough.

Section it when you're done, see what the best product is and then you get to throw something away. :wink:

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I wanted to use 1 part foam because I'm too cheap to use the $50 two part foam that we use under fiberglass bathtubs. Well, not exactly too cheap. More like unwilling to waste 90% of it because it doesn't last long once you start using it. I could build a mock-up and then try five different cans but the one part stuff has an even shorter life once you start using it and it's $10 a can. That warning about splitting the boat with one part has me concerned so I guess I'll order two part from Giant Leap

I have some US Composites 2 part foam that I was going to offer to bring with me to the TARC launch, but it has been on my shelf for a couple of years and the Part A has started to harden. I have a number of projects that I want to foam the fin can for, so I guess I will be buying new as well.

guywad said:

I have some US Composites 2 part foam that I was going to offer to bring with me to the TARC launch, but it has been on my shelf for a couple of years and the Part A has started to harden. I have a number of projects that I want to foam the fin can for, so I guess I will be buying new as well.

Click to expand...

I have found you will get less expansion when part A hardens but it will still work. It helps to pour it when the product is 70F or warmer to help with expansion. Also adding a drop or two of water to the mix seems to help also.

I have been thinking about doing this to the same size bird. Will check out Giant Leap.


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guywad said:

I have some US Composites 2 part foam that I was going to offer to bring with me to the TARC launch, but it has been on my shelf for a couple of years and the Part A has started to harden. I have a number of projects that I want to foam the fin can for, so I guess I will be buying new as well.

Click to expand...

If you can wait a few weeks you can have my leftovers. I have nothing else in mind that I might use it for so you can be sure it will just sit on the shelf hardening.

And taking up space in the basement? . I wouldn't want that to happen!

billspad said:

If you can wait a few weeks you can have my leftovers. I have nothing else in mind that I might use it for so you can be sure it will just sit on the shelf hardening.

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And if he doesn't want it I do.


Matt

blackbrandt said:

And if he doesn't want it I do.


Matt

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I have used both the 2 part from PML as well as the 1 part spray foam from the local hardware store for the fincan. Luckily for me I got away with the 1 part foam but from what I understand you can have issues so it's not advised.

One word of advice on the 2 part. Some of them allow you to add water to reduce the density (trade of of weight savings for rigidity), they say 1 drop or 5 drops etc., depending on the amount you require. Trust me when I say if you add water make sure you follow that advice, it is literally 1 drop etc. The first time I mixed up a batch I accidently put too much water in and the foam expanded quite a lot but at the expense of strength it would literally crumble like dust to touch it, so I had to clean the fincan and start again.

In my case I decided not to add water as the cavity was small enough and the design of the rocket was such that it is a shorter style, PML 3" bull puppy with a 38mm MMT, that I was not so concerned with the extra weight as I wanted a workhorse instead of a delicate race car.

So I bought the foam from Giant Leap, carefully calculated the volume I was trying to fill, divided by 25 and mixed a little less. I poured it in through four holes in the aft centering ring. Not much happened after the first three pours but by the fourth one it must have heated up enough to get the reaction going. Evidently my math was off a little. At least I'm confident I filled the entire space.

Nasty stuff to clean up. I use us composites. It works slower in cold temps.

billspad said:

At least I'm confident I filled the entire space.

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That looks like your "No Mass". You rebuilding it (again)?

GuyNoir said:

That looks like your "No Mass". You rebuilding it (again)?

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No, the No Mass is still in one piece although it does need a new paint job.

But you've seen that rocket before. I flew it twice at the NARAM in Michigan a couple of years ago. Both times I got the drogue but no main. The second time it knocked a fin loose when it landed. I fixed it and flew it in Maine last year. I totally rewired because I could never find out why the main charges didn't fire. Evidently it wasn't the wires since it did exactly the same thing. So this year I'm fixing the fins so the epoxy joints don't crack and replacing both altimeters.