gluing wing foam together

[Big Steve]

I have been cutting wing cores for the last couple of weeks. I have learned a couple of intersting things. It has been pointed out that urethane pour in place foam can be hot wire cut. This I have found to be true. The problem is that it cuts at a different rate than my wing foam. This is not a big deal but it did leave a ridge where I cut through it. I sanded it down. I have decided to glue all my foam pieces together using pour in place instead of micro. The reason for this is I am a cheapskate and used extra blocks of foam in cutting that made it different than the plans. I have foam joints where the torque tubes need to be cut out. Micro does not hot wire cut very well so I used pour foam. Just something to think about in the future when cutting your foam cores another reason to stick to the plans. If I would have stuck to the plans I wouldnt have a foam joint where I need to cut out the elevator hinge area. I did save about $300 in foam doing it that way. I bought a varize project and used its foam to make my wings. A stack of varieze foam to supposedly make 2 varieze wings makes one cozy wing barely. I still have to buy some foam to make my left wing. STeve build on

 

 

[Waiter]

My concern with using "Pour-In-Place" for this purpose are two fold;

 

1) The wing cores are part of the structure. They make up one giant continous wing rib that transfers skin loads into the the spars.

 

 

2) Pour-in-place foam shrinks, outgasses, and becomes brittle with time. How will this impact the bonding of wing cores.

 

Waiter

[TMann]

Aren't most folks using 3M 78?

[longez360]

The easiest way to do it is to use micro and 5 min epoxy/microballoon mix. You simply add micro to your cores BUT DO NOT put it near the edge. Plan that once it is clamped in place, it STILL doesn't go near the edges. This protects you from sanding foam/micro (which doesn't produce good results), ridges on your glassed part (i.e. fibres that are crimped) and allows a trick. That is, the use of 5minute epoxy (with microballoons) dollops around the edge where you did not use micro.

 

Result: A jigged solid part in 5 minutes that allows you to work on your part while the micro cures.

 

Pour foam is not good stuff from an outgassing perspective. Raise the temp and get bubbles in your layup...

[Big Steve]

The problem with using micro is that it cannot be hot wire cut. so if you need to cut in an area where you have put micro you have problems. I have odd sized foam and have to use the pour in place because I cant cut micro with a hot wire.

[Marc Zeitlin]

...It has been pointed out that urethane pour in place foam can be hot wire cut...

Yes, and it has also been pointed out that doing so releases incredibly poisonous gasses, and is a REALLY bad idea.

 

Search this and other fora as well as the COZY archives for information on this topic. Don't do it.

[Big Steve]

Yes, and it has also been pointed out that doing so releases incredibly poisonous gasses, and is a REALLY bad idea.

 

Search this and other fora as well as the COZY archives for information on this topic. Don't do it.

to late already done

[Steve Innova]

Looking at the picture, that doesn't appear to be the standard 3lb foam. What is it?

 

Also -- the pour-foam can react with aluminum to cause substantial corrosion. Not sure if it's an issue with the wings, I've seen a picture of the canard where pour-foam ate away the tabs.

[TMann]

Looking at the picture, that doesn't appear to be the standard 3lb foam. What is it?

Wing foam is 1.6 - 2.0 lb

[steve]

The problem with using micro is that it cannot be hot wire cut. so if you need to cut in an area where you have put micro you have problems. I have odd sized foam and have to use the pour in place because I cant cut micro with a hot wire.

i needed to sand my hot wire after a cut or two, the pour foam was burned on and was mucking up the cut.

a lite sand and all was good. i do believe the smell is very bad.

out gassing is not a problem when you crush the foam joint so all the air is gone and you have just glue. we...i don't use it as a filler ,just a mastic.

[longez360]

I am about to cut new winglet cores. In my case I will be using 1 peice of foam to make the cut. Had I not been able to do that, I would still use 5minute epoxy and temporarily join the cores, strategically locating the 5min/micro mix. Just takes some time and a little thought. Then I would micro & 5 min per previous post.

 

On a part with taper, you will tend to burn in further at the small end where the rate you advance the wire through the foam is so much slower. You don't have to accept that.

 

Nowadays I use the Ronneberg Berkut process of hotwiring oversize (0.080 for mine), and then adding blueprint sized templates (with same nail holes + a few) and sanding back to them with a rectangular alum extrusion with 120grit sandpaper attached with 77 spray adhesive.. This removes any burned in notches and accounts for variations in sweep rate between two individuals cutting etc, and provides dead straight cores. Any notches in your foam does not allow straight fibres. I will also be cutting my extended winglet spar caps with separate hotwire templates like the Roncz plans - if you don't and your partner is not at the same % location on the foil, you will not get a straight spar trough.

 

Just thought I'd add what works for me. When I made my wortmann FX LV 153 gear leg fairings, it got pretty thin at the trailing edge and tended to burn through. This process eliminates those problems.

[Marc Zeitlin]

out gassing is not a problem when you crush the foam joint so all the air is gone and you have just glue...

That is incorrect and extremely bad advice. Whether there are air bubbles in the urethane or not is immaterial - the hot-wire goes through the urethane and releases isocyanurates.

 

You really shouldn't address issues on which you are not in the least conversant.

[steve]

That is incorrect and extremely bad advice. Whether there are air bubbles in the urethane or not is immaterial - the hot-wire goes through the urethane and releases isocyanurates.

 

You really shouldn't address issues on which you are not in the least conversant.

plz note in my post 'BAD" . i was referring to the air expansion the prier post was addressing, not the part you are so concerned about. but thanks for staying on top of it !