Lightest glue for foam wing sheeting?
 

Is spray adhesive the lightest way to go when sheeting foam wings? If so which one? 3M?

There is only 1 way that I would sheet a foam wing. Epoxy laminating resin and vacuum bag. Some will tell you that it will add too much weight, if it does you are using too much resin.

Scott

Exactly!

Bob

Don't have vacuum. Still looking for lightest way. Anyone help me ?

No vacuum then go with 3M 30-NF contact adhesive, you can spray it, brush it or roll it, heat makes it only stick better unlike many of the other contact ahesives like 3M 77 spray adhesive that heat tends to soften the bond line. Place 30-NF on both surfaces allow to dry per manufacturers specification and lay your skin down. NOTE: Make sure you properly place the skins down on the core the first time because there are no second chances, just saying... after all sheeting is done then use a clothing iron, NO STEAM and iron the sheet down real well, trim and cap.

Bob

Laminating epoxy or polyurethane glue are far and away the best choices for sheeting foam core wings. You don't need a vacuum bagging system, weights work just fine.

http://www.mackrc.net/patternwings2/index.htm


Mark

If you are going to use epoxy laminating resin or polyurethane glue like Gorilla glue, use vacuum, its that simple. if using 3M 30-NF no vacuum needed. There are IMAC guys that have been using 3M 30-NF for years, here is a picture of one of my scratch built models using the 30-NF as the contact adhesive used for skinning my cores.

http://www.rcuniverse.com/forum/atta...mentid=2068806http://www.rcuniverse.com/forum/atta...mentid=2068807

Bob

Vacuum is preferred but it is not essential. My biggest issue with contact adhesives is that they are harder to get a straight wing with. They work fine, but you only get one shot at attaching the skins. Epoxy and PU both give you time to set things up and make sure everything is OK before they cure. If OP is doing his first ever set of foam core wings some forgiveness in the process is a good thing.


Mark

Thanks all. My biggest concern is weight. I sheeted a foam wing years ago, can't remember what glue I used, and it came out HEAVY. Much heavier than the same built up wing would have turned out. Now I need to sheet again on a small plane where weight is important.

That is probably a technique issue more than the glue itself. You only use a couple ounces of glue per wing half (on a 2m sized pattern plane wing) for either epoxy or PU and the 3M 30-NF is likely similar. The biggest mistake people make is wanting to use too much glue "just to be sure". In the link I posted Terry Brox uses a tiny amount of glue and then really works it to cover the entire skin. No matter what method you use you will need to be ruthless about resisting the urge to use more than the absolute bare minimum amount of glue or it will end up heavy.


Mark

POLYU glue question: In the link above he is using elmers probond and misting the cores with water to apparently activate the glue. I know you need to do this with gorilla glue, but I can't find anything that says you must do this with elmers. If I'm not mistaken, elmers probond was a precursor to the current probond Advanced (?) Could it be that water was required with probond but not with advanced? Elmers says nothing about using water, and am waiting from their tech for a response.

I can tell you this from experience, the poly glues can activate from just the moisture in the air and in the wood and core. They also can expand with enough hydraulic pressure to push the skins off the core during it's drying period without the use of a vacuum bag. Just saying.

Bob

Since you are in Florida I would suggest not using any water at all. The glue will cure just from atmospheric moisture, it just takes a bit longer. I live in a near desert with very low humidity levels and seldom use extra moisture to kick off PU glues and have never had it fail to cure properly, just at a slower rate. As sensei notes, too much water can cause problems because the PU foams too much and can move things around.


Mark

I've built foam wings for over 40 years for pylon racing. I tried spray on contact glue, brush on contact glue, epoxies, acrylic tape (3M 465), and poly glues. The poly glues wins hands down. To minimize weight, glue your sheeting together with model airplane cement and sand both sides. Clean well and spray the side that you are gluing to the foam with a light coat of cheap hair spray to partially seal the wood. Sand the cores lightly and vacuum clean. Roll on the poly glue with a small closed cell roller as thin as possible. Spritz on a very small amount of water on the cores if you are in low humidity. You can do this by shooting a fine mist into the air and waving the cores through the mist. Place the sheets and core into the shucks and place between a flat board and a flat surface and add about one to two hundred pounds on top. Turn off the lights and do something else for a day.

I flew through another airplane about two weeks ago (150 mph quickie 500). Hit hard enough that all four wing bolts sheared off, his molded wing exploded, mine is lightly damaged along the leading edge on the left panel, though the three Dubro hinges on the aileron ripped in half. While wings built with tape do almost as well, nothing I used in the past is this strong for the weight.

On stuff this size 100, or 200 lbs. is not going to get it done, there is just too much hydraulic area advantage for numbers that low, it takes more like 7000 lbs. pressure from a bagging and de-bulking operation @ 4 lbs. per sq, in. besides even with two experienced guys the foaming action happens too fast from poly glue. Anyway I do use Gorilla glue on my builds that there is foam core utilized for things like wing tube sockets and false ribs, servo mounts, spar extenders, leading and trailing edges, and wing root and tip cap ribs. I love it for that stuff but to each his own. Anyway the question was: Is spray adhesive the lightest way to go when sheeting foam wings? If so which one? 3M? Answer: the right stuff to use if you are going with contact adhesive is again 3M 30-NF. To answer your other question they will all be to heavy if you over use the adhesive. Try some sample tests for yourself and you will have the best data of all. Best of luck to you.

Bob

http://www.rcuniverse.com/forum/atta...mentid=2069060http://www.rcuniverse.com/forum/atta...mentid=2069061http://www.rcuniverse.com/forum/atta...mentid=2069062http://www.rcuniverse.com/forum/atta...mentid=2069063http://www.rcuniverse.com/forum/atta...mentid=2069064

i find that about a pound per square inch is enough pressure to do the job. Certainly not practical for a wing like you are holding. At that size I start thinking amount rivets and rib stitching.

Here is PDF form is the 3m product adhesive description for applicable 'foam adhesive's'.
It appears the "78" and the "30NF" series are the products to consider. Pages 4,5 and 7 show the specific of the adhesives listed here.

Link: Attachment 2267097

Mike