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Birch veneer skins for a foam wing?

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Old 01-06-2013, 02:29 AM
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jp1961
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Default Birch veneer skins for a foam wing?

I'm going to try to cover my foam wing cores with birch veneer (10 mil paper backed) from Woodcraft. The wing has no balsa leading edge (will try to wrap around the leading edge) but has a rather blunt leading edge. I will steam the leading edge area of the veneer with a steam iron (i have some experience steam bending wood for acoustic guitars). Any thoughts, ideas? Also what is the strongest contact cement around?

This veneer is roughly .025", which is slightly thinner than 1/32. I know it will be heavier than balsa, but I'm too lazy to glue 4" sheets of balsa for a 20" wide wing.

Thanks

Jeff
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Old 01-06-2013, 07:37 AM
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Default RE: Birch veneer skins for a foam wing?

From the historical perspective, 1/64 birch plywood rather than 1/32 was sometimes used rather than balsa sheeting. I'd be concerned that you are doubling the weight of an otherwise fairly weighty process.

As to adhesives. I've used sorghum contact adhesive and 3M spray adhesive and liked the 3M by far the best. Brush on contact adhesive is difficult to put on while spreading just enough to do the job. Spray adhesive on the other hand is very easy to put on lightly and holds very well. One must find the right formula however that doesn't attack foam.

As to going around the leading edge... I'm not sure I'd do so with a contact adhesive and would probably consider gorilla glue to allow some effort at get the sheeting all on before returning the core to the shucks for weighting to ensure the wing integrity. You would not want to be using contact adhesive and wrapping the leading edge with the wing out of the shucks given the danger of inflicting a warp in the wing. Normally when using spray adhesive, the core is rested in the shucks and strips layed out on the core to hold the skin from the wing. The strips are methodically withdrawn to allow the skin to contact to the core.

With spray adhesives, there is no weighted drying time in the shucks. I've for example given having pre-glued the skins together, installed the skins, leading and trailing edge and wing tip in a matter of 30 minutes. It is by far the easiest and fasted wing construction method and is strong and easy to build no warp wings. The draw back is that a foam cored wing is usually heavier than a built up wing.
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Old 01-06-2013, 08:33 AM
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Default RE: Birch veneer skins for a foam wing?

Jeff, Around 1970, there was Formula 1 racing activity in the Los Angeles area and a lot of guys were sheeting their foam wings with 1/64 plywood. After their wings began to fold in the high speed turns, they switched back to balsa. I don’t know if this has any meaning in what you are trying to do but the small extra time to make a veneer of 3/32 balsa would be well worth it. Dan.
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Old 01-06-2013, 08:49 AM
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Default RE: Birch veneer skins for a foam wing?

If you are hell bent on using contact cement then 3M 30-NF is by far the best to use, some of the guys us it on their giant scale airplanes with very good success. A couple of years ago I performed testing on this contact adhesive and wound up glueing all the skins on this airframe using 30-NF with very good results. Best of luck to you.

Bob
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Old 01-06-2013, 10:19 AM
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Default RE: Birch veneer skins for a foam wing?

Back in the 70s and 80s I would sheet my pattern plane wings with 1/64 plywood. The trick to get the skins to bend around the leading edge would be soak the area of the skin that would bend around the leading edge foam with amonia and water. While it was still wet wrap the skin around the foam core (without contact cement) and put them back inside the shucks and let sit over night .

The next morning the plywood should be dry and bent to shape.

It's a little bit difficult to work with the bent plywood, but it can be done. Weldwood water base contact cement that you get at Home Depot works really well on the foam applied with a 2 inch sponge roller. Put your favorite food coloring dye in the white contact cement and you can see the contact cement as you spread it on the white foam. It doesn't take much cement and the color will show you where the cement is too thick. Like always, a lot is too much and a little is just right.

Frank
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Old 01-06-2013, 01:45 PM
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Default RE: Birch veneer skins for a foam wing?

I would not try to go around the leading edge. I would add a balsa leading edge and shape it. Just me.
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Old 01-06-2013, 04:02 PM
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Default RE: Birch veneer skins for a foam wing?

Do you apply the contact cement to both the foam AND the wood, or just the wood?
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Old 01-06-2013, 04:58 PM
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Default RE: Birch veneer skins for a foam wing?


Quote:
ORIGINAL: jp1961

Do you apply the contact cement to both the foam AND the wood, or just the wood?
Absolutely yes, apply to both surfaces and allow to set per manufacturers directions prior to sticking both substrates together.

Bob
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Old 01-07-2013, 02:54 PM
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Default RE: Birch veneer skins for a foam wing?

Interesting blurb about the formula planes. Back in my D.N. class iceboating days, guys were making hollow runner planks using plywood skins for the top and bottom. This wasn't "normal" plywood, it was unidirectional plywood (the grain ran the length of the plank). This plywood was custom made using wood veneer and West System epoxy. For such highly stressed wing I'd say vacuum bagging carbon over foam would be the way to go. I've picked up windsurfers made by A.H.D.,,,they were EXTREMELY light (and very expensive too).
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Old 01-07-2013, 05:47 PM
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Default RE: Birch veneer skins for a foam wing?

Quote:
I would not try to go around the leading edge. I would add a balsa leading edge and shape it. Just me.
I do quite a few foam skinned wings for Q500 planes. So far my best results with glue have come from west systems and vacuum bagging. The other things work ok but bagging works much better.
As far as skin material ply will work great just not that easy to sand. Forget trying to wrap it around the LE, just put some hard balsa on there. If you want to try something different, I have also used dowel rod from the hardware store for wings that weren't as fussy as a racer. Pretty simple and bullet proof.
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Old 01-07-2013, 08:07 PM
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Default RE: Birch veneer skins for a foam wing?

Have an unbilt sr7 I used sorghum in the past what should I use now
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Old 01-07-2013, 08:25 PM
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Default RE: Birch veneer skins for a foam wing?

Anything you have been successful with should work again.
I have been on a quest to build the perfect quickiee for a long time. I have achieved a pretty good one with some of the features being as good as I think I'm capable of but not quite there yet.

When it comes to sheeting a foam wing though, I really like how a vacuum does. I know guys have used other things for decades but this is too simple and extremely effective.
I have heard of guys using gorrilla glue for skinning, I haven't done it...yet. So far the West is working exactly as I want it to.
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Old 01-07-2013, 09:22 PM
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Default RE: Birch veneer skins for a foam wing?

Bagging is the way to go. ACP composites has some great systems for pretty cheap. They have good resin as well. I have been using very thin Poplar for wing skins. 2mm. Very good results as it is a very tight grain and paints well. So many options here. I think there is no doubt that polyurethane glues are a great option. they adhere to foam as good as anything.
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Old 01-08-2013, 05:06 AM
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Default RE: Birch veneer skins for a foam wing?

I agree, if you want what is best structurally, then epoxy and vacuum debulking is the ticket, I have done many builds and tested many skinning methods over foam cores and nothing is going to be better.

Bob
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Old 01-08-2013, 07:05 AM
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Default RE: Birch veneer skins for a foam wing?

I recently did my first skinned foam core using Gorilla Glue. I just put the wing back in he shucks with weight on top. I really liked how the Gorilla glue penetrated the foam. I applied it just like epoxy with "shiny" being to much and dry, well, not enough. The last set I did I was worried I did not apply enough as I ran short. It seemed to bond as well as the other. I don't know if it would work in a bag as it does need moisture to cure and the vacuum will remove some of that moisture. I applied to the skins and did dampen the core with a VERY light mist of water. For my applications, I'll never go back to epoxy.

Ken
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Old 01-08-2013, 08:14 AM
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Default RE: Birch veneer skins for a foam wing?


Quote:
ORIGINAL: kenh3497

I recently did my first skinned foam core using Gorilla Glue. I just put the wing back in he shucks with weight on top. I really liked how the Gorilla glue penetrated the foam. I applied it just like epoxy with ''shiny'' being to much and dry, well, not enough. The last set I did I was worried I did not apply enough as I ran short. It seemed to bond as well as the other. I don't know if it would work in a bag as it does need moisture to cure and the vacuum will remove some of that moisture. I applied to the skins and did dampen the core with a VERY light mist of water. For my applications, I'll never go back to epoxy.

Ken
G/G works just fine in a bag, just go ahead and mist with water, place in bag, and get it under vacuum.

Bob
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Old 01-08-2013, 12:59 PM
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Default RE: Birch veneer skins for a foam wing?

Jeff is talking about using this stuff:
http://www.woodcraft.com/product/200...er-backed.aspx
$70 for a 4x8 sheet
That much 3/32" x 4" x 48" balsa from Balsa USA would be just under $100
Obeche: $128
http://www.oakwoodveneer.com/veneer/obeche.html
Dave
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Old 01-08-2013, 04:05 PM
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Default RE: Birch veneer skins for a foam wing?

I tried vacuum bagging paper backed veneer for my windsurfing project using epoxy, but it did not turn out well at all. Air got trapped between the foam substrate and paper causing blisters. Veneer without the paper would probably have worked.

The picture on the right looks like I used carbon fiber cloth, I did not. The black look was from mosquito screen I used as bleeder cloth. The aqua colored material is peel ply.

Jeff
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Old 01-09-2013, 04:09 AM
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Default RE: Birch veneer skins for a foam wing?

If you want to bend veneer, balsa etc around a tight curve the trick is to put masking tape etc on the outside of the bend. This stops the material bursting apart on the tension side. Even covering first with Solarfilm etc works. Try a small sample as a test piece and compare to bare wood and you will find a much smaller radius curve is possible with tape on the outside. Obviously the tape is removed after gluing in place so something like masking tape is best, but parcel tape etc also works.
If the veneer is already paper faced then this may well work better on the outside and no extra tape may be needed.
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Old 01-09-2013, 08:15 AM
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Default RE: Birch veneer skins for a foam wing?

Back in the 1980's some guys were using Bristol Board for covering foam.  I tried it with the white glue and it went wavy, so I never continued with experimenting.  Now with PU glues, and vacuum bags it may be worth another try.  It is likely a bit weaker than veneer and thicker balsa though.  Some guys are using fairly thick foam rubber and weights to sandwich the skins (or fiberglass with mylar sandwich skins.)  It is a po'boys vacuum bag, I can see issues with the leading edge maybe not coming up real pretty.                  As for bending the veneer, maybe just a light sanding for 1/2" strip where you want the bend to happen and wet it down may get the desired effect.
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Old 01-09-2013, 01:51 PM
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Default RE: Birch veneer skins for a foam wing?

Well,,,the Birch veneer arrived from Woodcraft today (for a 4' x 8' sheet, it doesn't seem that heavy, obviously won't be using the whole sheet anyway). I also picked up some 3M spray contact cement made especially for expanded polystyrene and extruded polystyrene from Menard's (will test b/4 using). Like the beer commercial "HERE WE GO"!!

Jeff
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Old 01-12-2013, 09:59 AM
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Default RE: Birch veneer skins for a foam wing?

The left wing panel didn't come out too bad.

Jeff
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Old 01-12-2013, 11:26 AM
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Default RE: Birch veneer skins for a foam wing?

Thanks Jeff!
Guys trying "outside the box" stuff like this and sharing their
results is how we can all learn new things.
Dave
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Old 01-12-2013, 02:00 PM
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Default RE: Birch veneer skins for a foam wing?

Since you're in the "thnking outside the box" mode, I'll throw this out for consideration. There was some mention earlier about the 3M 30 water based contact cement. This is really excellent glue, although a bit pricy. Try applying the glue to both surfaces and clamping the parts together when the glue is still wet. The bond is superior to the normal method of application. Years ago, I worked for a company that made laundry press tables for commercial applications. We made thousands of tables tops using this method and I can say without question, this bond is for good! These tables were subjected to constant heat and steam all day long and would not delaminate. It's not for every application, but nice to have in your bag of tricks.
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