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Making up foam wing balsa sheeting

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Old 10-02-2005, 03:58 PM
  #1
mikehannah
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Default Making up foam wing balsa sheeting

Hi
I have seen many peoples ideas on how to make up sheeting for applying to foam wings and many peoples ideas on what glue to use. ( varying from Cyno to old fashioned balsa cement)
What is the up to date thinking on what glue to use and the technique for sticking the balsa sheets together?

Mike


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Old 10-02-2005, 05:58 PM
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jmiracle
 
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Default RE: Making up foam wing balsa sheeting

I've been using polyurethane glue on all my foam parts lately with very good results. With poly glue, edge gluing the sheeting first is not necessary. The poly glue expands as it cures and will expand into the seams of the wood. I simply tape the sheets together for whatever part I'm trying to skin, then I tape the seams of each sheet to prevent the glue from foaming through.

Some guys like to then use weights to glue the skins on......i prefer to use a vacuum bag. It's quick and easy....takes me about 30 minutes to tape, cut, glue and bag both sides of a wing. Once in the bag, I let the part set overnight, or about 12 hours.
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Old 10-02-2005, 06:11 PM
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Default RE: Making up foam wing balsa sheeting

Hi JM
I didnt think you could use Vac Bagging with Poly Glue ( Gorilla Glue) as it needed the air to cure properly. I guess what you are telling me is that is not the case. Could you give me an outline of your method. This is my first attempt at sheeting let alone Vac Bagging.

Thanks in advance

Mike
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Old 10-02-2005, 08:02 PM
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Robert Bauer
 
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Default RE: Making up foam wing balsa sheeting

Mike -- I have found that a very light mist of water before applying the Gorilla Glue helps to kick off the cure.
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Old 10-02-2005, 08:36 PM
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Default RE: Making up foam wing balsa sheeting

Mike,

Easier is better and in that tone.... get all edges straight by correct sanding. Join the entire wing skin (s) together with masking tape so you can fold open the sheets. Then apply any good wood glue (Elmers...etc..) wipe off the excess... and let them sit flat till they dry. The main reason for doing it this way is that the wood glue sands easily and holds the wood together very well. Been doing it this way for years..... .. BTW.. I don't use any Cyanoacrylate because of the glue enhanced line that will not allow the sheet to be sanded evenly. Take care... I'm going to be doing 4 sets this week. I'll take some pics if you like.

Dan
Carolina Custom Aircraft
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Old 10-02-2005, 08:41 PM
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Ed Smith
 
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Default RE: Making up foam wing balsa sheeting

Before the decision is made as to how to glue the skins together one should consider the final finishing process. Using gorilla or just taping the seams and letting the glue expand into the cracks will result in a very poor surface finish on the wing. The result will be hard ridges at every seam and almost impossible to sand out.

The problem when joining sheets is that the edges are not always the same thickness, again the result will be ridges on the finished wing. So this is what I do.

I trim the edges so the fit is tight. I tape them on one side. I open them up and apply a very thin bead of Lepages Carpenters along the edge of one sheet. I close it and tape it, the join now has tape on both sides. This is to hold them as flat as possible. I make up the complete skin like this. When the glue has cured I remove the tape. I now have a skin with ridges. I then use one of those rectangular orbital sanders and sand both sides of the skin until all of the ridges have been sanded out and the skin is perfectly smooth.

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Old 10-03-2005, 05:29 AM
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Default RE: Making up foam wing balsa sheeting

No what about gluing the sheeting to the wing? What method are you using to do the vacuum bagging and where can you get the equipment?
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Old 10-03-2005, 01:11 PM
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Default RE: Making up foam wing balsa sheeting

Hi!
Best glue to use is Polyurethane glue (Gorilla glue to you Americans).
And you don't need to vacuum equipment...just press the foam core and balsa-sheets together under a pair of thick wooden plates (5-10cm thick) using 8-10 big steel woodworking clamps.
And I do recommend spraying water on the glued balsa sheets before pressing together everything.
Regards!
Jan K
Sweden
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Old 10-03-2005, 08:12 PM
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Default RE: Making up foam wing balsa sheeting

Mike,

poly glue doesn't need air to cure, it needs water. In my area, the air is generally humid enough to kick off poly glue without any additional moisture. As some others have pointed out, you can mist the foam cores with water first.

Pictures are worth a thousand words....check out my website, www.flagcityflyers.com. I detailed my build of my 35% Carden Extra. I vacuum bagged all the foam parts for that kit and took several pictures showing how I do it. (BTW, this plane now has over 60 flights on it, sitting outside all day long in direct sunlight and very high temperatures and still looks as good as the day I covered it.)

I bought a vac bag system from Aerospace Composites (http://www.acp-composites.com/acp-vbs.htm)....I've got a little over $100 in the setup, including bagging material and other supplies. So far I've been able to reuse everything many times. (I'm now finishing up a Carden Cuda, and used all the same vac bags I made up for the Extra.)

Someone mentioned pre-gluing all the sheets before skinning the foam or the finish will not look very good. While there is nothing wrong with pre-gluing, I have NOT experienced any of the problems mentioned. I do not edge-glue any of my sheeting, and every part turns out flawless. After I remove the part from the bag, I simply trim the excess wood from the edges of the foam, sand flush, then finish-sand the surface of the part with 220 grit paper and it looks great.....even over tight curves.

I've attached a couple photos of my latest project.....the first shows the turtle deck of a Carden Cuda. This is a rather tight radius....turned out great from the vac bag. The second is a top view of one wing panel from the cuda. Again, straight out of the bag, trim the edges, glue on the LE, TE, root cap and tip block. The third is a view of the wing trying to show that the sheeting is smooth with no ridges or seams visible.

Quote:
ORIGINAL: mikehannah

Hi JM
I didnt think you could use Vac Bagging with Poly Glue ( Gorilla Glue) as it needed the air to cure properly. I guess what you are telling me is that is not the case. Could you give me an outline of your method. This is my first attempt at sheeting let alone Vac Bagging.

Thanks in advance

Mike
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Old 10-03-2005, 08:55 PM
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Default RE: Making up foam wing balsa sheeting

Mike

I to use polyurethane glue Tightbond I have built one 35% extra that I have been flying for three years now. The poly is great glue it comes through the wood grains and the sheeting is nailed to the foam .I have never had a problem with sanding it and I also use a vacuum bag
once you start using one you will never know how you got along with out it . Randy
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Old 12-03-2005, 03:52 PM
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Default RE: Making up foam wing balsa sheeting

I have used polyurethane glue in the past and have had very good luck with it. I am getting ready to sheet the wings to a new Lancair and am trying to decide if the polyurethane glue will be as strong as if I were to use epoxy. The Lancair will be a speed demond, and I want to make sure my wing is as strong as possible. Any suggestions?
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Old 12-05-2005, 02:51 AM
  #12
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Default RE: Making up foam wing balsa sheeting

The way I do it is pretty ancient but it has always worked for me so I haven't tried anything new.

I make sure each sheet to be joined matches edges exactly to the adjacent sheet. This includes not only the thickness but also making sure there are no bows. I tape the joints together with masking tape on one side (let's call it the bottom joint), then allow the joint to "hinge" open. I apply a thin bead of white glue to the open joint (we'll call this one the top joint), then swing it closed and tape the top of the joint. After it's dry, and the masking tape has been removed, I sand the joint lightly.

Now what I find is I only get a very small amount of glue that squeezes out of the top joint. Since I started with a taped and sealed bottom joint, that joint generally needs only very minimal sanding as almost no glue squeezes out there. Since glue easily squeezed out of the top joint before taping over it, it will need a little more work. But here's the trick I use. To make sure I don't get any ridges later, I reverse the completed skins so the side that required more sanding is the side I stick to the wing core.

I have used Dave Brown Products Southern's Sorghum (see, I told you it was ancient!) for probably more than 30 years. For those not familiar with the product, it is a contact type cement (I believe it's the same stuff sorghum syrup is made from - very sticky). Brush a coat on the foam core and a coat on the skin. You have to make sure the skin is in exactly the right place before you let them touch. If you mess it up, you don't get a 2nd chance, but the method they recommend is to place a sheet of waxed paper between the core and the skin and allow just a very tiny strip to make contact. Then you slide the waxed paper out as you go and press the skin down down. You don't need to weight it down or vacuum bag it because once it makes contact, it's forever.

Again, this is not considered a modern method, but it has worked so well for me I never had any reason to try anything else.
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Old 12-18-2005, 05:21 PM
  #13
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Default RE: Making up foam wing balsa sheeting

Mike,

Post # 5 is the best way to make the sheeting. True the edges, tape together and use yellow glue. Squegee the excess glue off and make a light pass with a lightly damp(not wet) paper towel to clean the excess. You should sand both sides prior to sheeting. I have a large piece of glass that I lay over the stack of sheeting when I make up skins. That keeps them really flat.

A note on the Southern Sorgum...that product is a latex contact cement. Don't use regular contact cement as it will dissove foam. Gorrilla glue(polyurethane) will also work well to glue the skins. Use a credit card and spread it out evenly. Mist the foam core and put it back in the shucks and weight it and allow the glue to cure. Personally, I like the latex contact cement as it is fast!
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