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Old Jan 27, 2013, 11:13 AM
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Repairs with Dow "Great Stuff" Insulating Foam.

I just finished repairing a badly crashed 3 meter molded sailplane wing that I use on the slope. It had about ten significant leading edge injuries after it landed in our local La Bajada, NM site lava boulder slide far below the rim.

https://soarabq.googlegroups.com/att...?view=1&part=2

Everyone I talked to said not to try and use hardware store expanding foam and gave all kinds of reasons, from "too messy" to "the nozzle clogs so you have to do all the repairs at once."

I decided to try anyhow and was quite happy with the result. I went to Ace Hardware and after discussion with a very smart old guy who actually had some experience with these products, I decided to use Dow "Great Stuff" Insulating Foam Sealant "Big Gap Filler". Dow makes five of these products, but this one seems to produce the lowest density foam.

http://building.dow.com/na/en/produc...ggapfiller.htm
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Old Jan 27, 2013, 11:32 AM
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Albuquerque, nm
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So here is a list of the things I learned.

Stuff you'll need:
1. 12 oz can of Dow "Great Stuff" Insulating Foam Sealant "Big Gap Filler".
2. Latex or Nitrile gloves.
3. At least two packages of pipe cleaners.
4. Isopropyl (rubbing) alcohol.

The repair:
1. It takes less of this foam than you think. Do a small repair first. Be stingy.
2. Repair only a single area at a time.
3. Cover the repair with 3" wide masking tape after the foam is in. This will keep the foam from coming back out of any holes. The tape comes off quite easily after the foam is set up.
4. Cover the taped repaired area with plastic wrap (I used 'Glad') and put it into the foam "shucks" if you still have them. If not, prepare a properly shaped bed of foam or other material beforehand to accurately maintain the airfoil shape..
5. Weight down the whole thing with about 20-30 pounds of phone books, metal, etc. I use baby food bottles filled with lead shot on the phone book.
6. Leave the whole setup untouched for at least 12, better 24 hours to avoid later unwanted expansion.

Cleanup:
1. Wear gloves during the the repair.
2. When your are done, wipe the outside of the nozzle and tube with paper towel pieces and isopropyl alcohol.
3. Clean out the tube and nozzle with pipe cleaners moistened with isopropyl alcohol.
4. Use doubled up pipe cleaners to clean out the can's nozzle.
5. Put some isopropyl alcohol in the nozzle and tape it shut until you need it again.
6. This will keep the can of foam just like new for the next step in the wing repair.
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Last edited by Tandberg; Jan 27, 2013 at 03:16 PM.
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Old Jan 27, 2013, 11:47 AM
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Cleaning the tube

I forgot to mention that the screw-on nozzle extender and the 6" tube can be taken apart for easier cleaning. The pieces are connected with a fitting which can be pulled apart and put back together easily.
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Old Jan 27, 2013, 02:58 PM
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Albuquerque, nm
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Here is a picture of the two nozzle parts with pipe cleaners.

Tape the can nozzle with some alcohol in it after cleaning thoroughly.

The product will keep indefinitely if you clean it up good.
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Old Jan 27, 2013, 05:56 PM
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Tandberg, have you ever tried 2 part foam or mixing water with Gorilla Glue?

The twopart is much more structural, gases out better, and is a chemical cure. The GG does a great fix on bagged wings. I have used the two part foam on more projects than I can count and it is a great product. Used the can foam twice, and that was it.

Marc
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Old Jan 27, 2013, 08:10 PM
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Foam repairs

When using this stuff for repairs you should allow some opening for the excess to "weep" out of. I used to use it on Sagitta 600 fuses and would make some holes for the expanding foam to weep out and i would also put some Kevlar tow wrapping on the boom.This stuff will try to bust out of a confined area. Also heat will make it expand more. BTW those Sagitta 600 tail booms were really tough with the foam fill.
Stew
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Old Jan 27, 2013, 08:40 PM
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Stew, a tailboom was my first use too, on a Southwind. When it augered in, the only complete part left was the boom. I am working on a 1/5 scale Fw-190 and the entire LG structure is foam filled and I also foam filled around the engine box, really gets stiff. The 190 build thread is in Fuel Warbirds on RCG. KMP Fw-190 D9

Marc
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Old Jan 27, 2013, 10:22 PM
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I've heard horror stories about the foam continuing to expand. (I've heard that about two part as well. Story by a guy who was using it on his full scale homebuilt and ruined some parts.) If I was using it, I'd make sure that everything was a little damp as that makes it cure faster. And I'd keep it damp for a long while before shaping it.
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Old Jan 28, 2013, 11:17 AM
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Lincoln, I work incrementally as I can only mix so much. If you could keep flowing the foam in some sort of pump/mix system could get you in trouble. You do not want to dump a bunch in a bunch and hope.

Marc
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Old Jan 28, 2013, 06:04 PM
SlingWinger
San Bernardino, California, United States
Joined Oct 2004
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I played around with this stuff a few years ago.

I found that I could squirt a bunch into a container, such as a box, bucket, or plastic bag, and as it foams I stir it up and this reduces it's volume and increases it's density.

I let it foam up some more, then stir it again. If I keep doing this it eventually will almost stop foaming, and I end up with a very dense, and of course heavier, material.

I used it to partially fill an old balsa fuselage that was really busted up. Also I repaired the leading edge of an Obechi sheeted foam core wing.

Using a plastic bag inside a bucket works well. After you've stirred it up a time or three, You can close the bag up tightly around some plastic tubing, and use it as a dispenser. While wet the stuff is very sticky and potentially messy, but when cured it's not difficult to clean up.

I never got around to trying this idea: Using cement make a mold using an old wing as a plug. Then put poster board in the mold and squirt the high density foam into it.

I thought this might work to make some cheap wings, but like I said I never got around to trying it. A hot wire is just too easy to use.
Steve
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Old Jan 28, 2013, 06:33 PM
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Didn't use two part because I couldn't figure out where to buy small amounts cheaply. The can was less than 10$ and was way more than enough.
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Old Jan 28, 2013, 06:39 PM
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This was a hollow molded wing, so no relief holes were needed.
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Old Jan 28, 2013, 06:40 PM
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Dayhead, my idea was to keep the foam density as low as possible.
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Old Jan 28, 2013, 06:40 PM
ShOP loCAL FaRMers
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http://www.rcgroups.com/forums/showthread.php?t=1804245

I ordered the 2 part from this thread...I really like it.
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Old Jan 28, 2013, 06:43 PM
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My two part comes from Aircraft Spruce, and the smallest container size goes a while.

Marc
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