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Jul 11, 2019, 09:02 AM
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What is a good technique to prevent, or lessen the curling effect around the edges of the foam? I cannot seem to find a good way to bond the paper at the edge.
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Jul 11, 2019, 10:11 AM
Space Coast USA
hoppy's Avatar
Thread OP
Hi Tom,
Don't know as I ever had that problem.
Describe how you are applying the paper and the materials you are using. That might help explain the problem. A picture of the curling would help.
Jul 11, 2019, 05:38 PM
Entropy is happening!
Jim.Thompson's Avatar
Hi Hoppy,

I recall you or someone else mentioned using this covering method on open framed structures. Is my memory correct?
If so, I would like some indication that it is worth a try.
I am day dreaming about giving it a go on my next model...............later in the year.

Jim.
Jul 11, 2019, 05:58 PM
Space Coast USA
hoppy's Avatar
Thread OP
It wasn't me. You might try an experimental piece. I would like to know how it works.
Are you talking about balsa framing or foam framing?
Jul 11, 2019, 06:01 PM
Entropy is happening!
Jim.Thompson's Avatar
Quote:
Originally Posted by hoppy
It wasn't me. You might try an experimental piece. I would like to know how it works.
Are you talking about balsa framing or foam framing?
I plan to try it on a foam frame.
Yes, I will do an experimental piece.
Jul 12, 2019, 03:31 PM
Registered User
Quote:
Originally Posted by hoppy
Hi Tom,
Don't know as I ever had that problem.
Describe how you are applying the paper and the materials you are using. That might help explain the problem. A picture of the curling would help.
I am using 50/50 Titebond II and water. I soak brown paper in water and lay on towel to blot excess. I then paint the foam with the glue/water mix. I then place the paper on the foamboard, the wipe with cloth to remove wrinkles. I do one side, then immediately turn the piece over and do the other side. I then stand the piece up to dry. After it dries, there are spots, especially corners, where the paper has lifted from the edge of the foam. I'll try to get a picture of a dried piece to demonstrate.

Thanks,
Jul 12, 2019, 05:22 PM
Space Coast USA
hoppy's Avatar
Thread OP
A picture woud be nice. Brown paper like from a paper bag? Heavy wrapping paper?
Jul 12, 2019, 05:24 PM
Entropy is happening!
Jim.Thompson's Avatar
Quote:
Originally Posted by Tom Sawyer
....................... After it dries, there are spots, especially corners, where the paper has lifted from the edge of the foam. I'll try to get a picture of a dried piece to demonstrate.

Thanks,
Did you de-grease and scuff up lightly with sandpaper?
Jul 13, 2019, 11:21 AM
Registered User
Yes, I scuffed the foam and cleaned with rubbing alcohol. Here is a pic.
Jul 13, 2019, 12:07 PM
Space Coast USA
hoppy's Avatar
Thread OP
I cut my paper about 3/4" oversize on all sides and cut slits in the paper when it goes around a curve. The paper is wrapped around the foam to the back side.
Heavy line = foam, thin line = paper.
The bottom paper is cut just a bit less than the foam shape. It covers the top wrap around.
Jul 14, 2019, 06:33 PM
Registered User
hoppy, I know you've been using various methods to glue various papers to foamboard for years. Can you give us your best techniques/materials? It would save a bunch of searching.
Jul 14, 2019, 09:35 PM
Space Coast USA
hoppy's Avatar
Thread OP
Post #1.

One pointer not in there...if the paper is torn rather than cut, the seams are almost invisible.
Last edited by hoppy; Jul 14, 2019 at 09:45 PM.
Jul 14, 2019, 11:22 PM
Entropy is happening!
Jim.Thompson's Avatar

Pre-made paper/PVA sheet.


Hoppy,

I am day dreaming about an experiment in making pre-made paper/PVA sheet.
The reason for me exploring this possible option is the aim to obtain a satisfactory trailing edge on a wing.
The general idea is to borrow from epoxy/glass pre-made laminate sheet as has been done by me and many others with some success.
I won't give too much away, as it might be a total flop!
However, that is what I am thinking. I will not be able to do any trials until after September....................(and our annual Manilla Slope Fest).
More later if it shows any sign of success.

Jim.
Jul 15, 2019, 09:58 AM
Space Coast USA
hoppy's Avatar
Thread OP
Looking forward to your experimental results.
Jul 15, 2019, 11:13 AM
Registered User
tspeer's Avatar
Quote:
Originally Posted by Jim.Thompson
Hoppy,

I am day dreaming about an experiment in making pre-made paper/PVA sheet.
The reason for me exploring this possible option is the aim to obtain a satisfactory trailing edge on a wing....
I've been thinking of something similar, but in my case, it's to make a flexible trailing edge with a specified stiffness. This post shows why I'd want such a thing. It could give a RES glider the benefits of a flapped wing with a substantial reduction in drag while thermalling.

One possibility would be to lay up a paper trailing edge on a curved mold to a thickness that would be a little stiffer than the desired stiffness. Then use a whiffle tree to apply a force to the trailing edge while I sanded it to get just the right amount of deflection. For the mold, I've been considering PVC pipe, a flexed sheet of Plexiglass, or a 3D printed mold. I think paper might be a good candidate material because the stiffer the skin, the thinner it has to be to get the right flexibility, and it can be difficult to get precisely the right thickness if it is too thin. Paper is also a pretty consistent product (unlike balsa), making it easier to reproduce sample test configurations on an actual build.

Another reason to make a pre-made skin would be to lay it up on a smooth surface. The finished sheet could be used as a skin over a built-up framework. Even if glued to a foam core, it would require less effort and paint to get a good finish. Laminating film could be ironed onto it while it was flat, without worrying about overheating the foam underneath.

Finally, paper might be a good choice for a molded leading edge. The leading edge is far and away the most critical part of an airfoil, but most building techniques require hand shaping of the leading edge. Even if you use templates, it's almost impossible to get an accurate leading edge shape. A paper leading edge laid up in a 3D printed mold (either female or male) could be a way of getting an accurate shape. Back it up with polypropylene foam, and it might be damage resistant as well.


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