Internal foam??

[exprditer789]

How many of you guys/girls use foam inside the fin can after internal fillets?If you do what kind of foam do you use?Is it worth doing?Thanks Alex

 

[Handeman]

I used foam in my L2 bird because I expect to use up to L motors and Mach 1.4+. Even with that, I'm not sure it really adds anything to the rocket except weight. I just used the expanding foam in a can from Home Depot.

 

[GrossApproximator]

I used foam in my L2 bird because I expect to use up to L motors and Mach 1.4+. Even with that, I'm not sure it really adds anything to the rocket except weight. I just used the expanding foam in a can from Home Depot.

What kind of foam was it? I know PML sells special expanding foam. I've never used it though.

 

[troj]

The foam folks use is a two-part expanding polyurethane foam. PML sells it, as do several other vendors.

That said, I've used it, but I don't use it often.

My most common use is to hold nose weight in place in rockets that need it.

-Kevin

 

[GregGleason]

If you have good fillets with a good adhesive (such as Aeropoxy with amendment like Kevlar pulp) I don't think you get much for your trouble. But there are those who do use expanding foam because they have had good experience with it.

If I were to use foam, it would possibly in the nose cone to void fill around recovery electronics/CG management cavity. I would buy stuff from:

https://www.uscomposites.com/foam.html

Greg

 

[blackjack2564]

I have built fincans with wire ties and foam only. Turned right around and flown them on K-805's . You cannot get the fins out period! We use it mainly for the "how fast can you build it " contests. You should have at least 1inch between MM and airframe or it's a bust. In properly built rockets it has no use in a fincan but can save a glass NC from popping the gel coat loose on hard landings and for tracker placement in the NC also.

Use the 2-part PML or Wildmans pro-line around 12.00 for the 2 bottle kit.

NEVER use the stuff in the can. Some that have are lucky, most are not. It is a moisture cure and should be exposed to the air to cure correctly. Made to be used for insulating around windows etc. in construction.
When sealed up in a rocket it never fully cures. Exposure to sun and heat can cause it to continue to expand for months or years after initial use splitting or deforming airframes and NC.

 

[Pantherjon]

Also, the stuff in the cans is 'open cell' foam and the 2 part foam is 'closed cell' foam. Meaning? Even after the open cell is fully cured, it will collect moisture and expand, very detrimental to airframes, fin cans and nosecones...

 

[powderburner]

I have used foam from aerosol cans for a lot of different things, rocketry included, and I have never seen problems even remotely close to the comments posted above.

Years ago I used hardware-store canned foam (supposed to be for weather-sealing and insulation) in a 4 inch NC. It cured just fine. It cured fully, overnight, plenty hard enough to lock in a BT50 center tube I put up the middle. I have had similar results every time I have used it. Oh yeah, it works great between 2x4s around windows and doors, too.

I have used canned foam on many projects, home-building among them, and have never seen the stuff require more than a few hours to cure no matter what kind of cavity it was placed in. Occasionally the canned foam (inside a large cavity) will even begin to "skin over" on the outer surface before it expands to fill the space.

I think the canned stuff is cheaper if you only have one little job. You can buy a can for like $3-4 locally, same day. You don't have to mail-order a gallon-sized jug. OTOH, if you are doing LOTS of foaming, the two-part foam is probably more economical than buying dozens of cans of canned foam.

What I can complain about is that it is difficult to guesstimate how much it will expand, and the expanded foam squirts out of any available hole, and it sticks to EVERYTHING (normally a good thing), and it doesn't clean off easily.

The two-part foams are probably better. They probably expand more predictably. You can mix a little of the stuff and save the rest (whereas the canned stuff is pretty much shot after you "open" the can, no matter how much you use). From what I have seen of two-part foams that other people have used, it seems to foam up with a more uniform density.

Two-part foams appear to be a bit more expensive. They are usually not as easy to find as the hardware-store canned stuff (and if you need it today, not next week, that may make a difference for you).

And from what I have seen, both of them are open-celled foam.