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Apr 10, 2011, 11:52 AM
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Brown Paper Towel Covering glue/wbpu


I have three planes to cover - one is a has a balsa sheeted wing and fuse while the other two are complete foam planes (edf and trainer). I want to achieve some strength and a surface that when painted, will shine without adding considerable weight. I've looked at a lot. Liquid sheeting, silk, glass, etc. Epoxy and glass is not an option - just to heavy. I've read that silk is can be just as strong and weigh less. Also, not interested in packaging tape. In this thread, I want to concentrate the discussion on brown paper cover techniques. I am looking to lightweight brown paper packing paper (u-haul) and either wbpu or glue. I am looking for the best method to achieve a lightweight, strong paintable surface that will yield an excellent finish. A few questions:

1. What are the best methods so seal the balsa and foam?
2. Wbpu or glue - pros cons?
3. What is your technique.

Thanks in advance for you time and information.
Last edited by Rocketman320; Apr 11, 2011 at 02:08 PM.
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Apr 10, 2011, 12:48 PM
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Look at masking paper available at Home Depot - there's two weights, green and tan. When it's wet it forms nicely to compound curves and it's much lighter than the packing paper.
Apr 10, 2011, 03:44 PM
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So where does the "towel" come in ?

Steve
Apr 10, 2011, 04:00 PM
Entropy is happening!
Jim.Thompson's Avatar

Brown Paper


"MattyB" has a good description of a well developed method for brown paper covering of wings. I have used it with success.
I think it is good for prototypes and for special models, such as scale, flown in ideal situations. Not a good choice for slope flyers though as it not very durable.

I'm also wondering about the "towel" part of the thread??

Jim.
Apr 10, 2011, 06:14 PM
B for Bruce
BMatthews's Avatar
The heavy brown paper used by butcher shops and likely the same as your packing paper would be too heavy. You don't need that much "fiber" for a surface. I'd suggest using newsprint instead. You can buy bundles of decent size newsprint from the same packing supply outlets. Using the newsprint as a skin and bonding it down with water based Poly Urethane varnish should work out well. Another option for bonding it down would be well thinned wall paper paste that you soak the paper panels in and then lay it onto the foam.

Here's a sketch of how I did some .15 powered control line combat models many years ago. The glue I used at the time was thinned white PVA wood glue. But since then I've thought that either wall paper paste for the initial bond and then polyurethane for the top coat would work. And then the water based PU came along and I figured that I could likely cut out the "middleman" glue and use the WBPU for the whole treatment.

Keep in mind that wet newsprint shrinks a lot. I found that I needed to keep misting the side already layed up with a plant mister to avoid the PVA glue and paper drying on the one side while working the second side. Keep the whole mess evenly damp until you're fully done and then stand or hang it in such a way that both sides are clear and can dry at the same rate.

For sheeted balsa I would not use a water based solution on the balsa. Instead I'd suggest art store tissue and clear aircraft dope. Or if you can't obtain or don't want to use aircraft dope then use a locally acquired clear brushing lacquer. The lacquer will have much the same charactarisitics of easy sanding as the dope. PU varnishes don't sand worth a hoot. Also the film builds quick and is quite heavy as a result. Another option that may be worth experimenting with would be shellac thinned with methyl alcohol. Two thinned coats on the wood with light sanding to remove the fuzz, a third coat laid on and then lay tissue over once just barely dry to the touch and use pure methyl alky through the tissue to soften and re-activate the shellac to bond the tissue down. Follow with two more well thinned coats of shellac and let dry fully for a few days until there's no more smell of alky at all. Then top coat with colour enamels of some sort.

This all supposes that these models will never see glow fuel. Although I did find that the newsprint over foam with the original solvent based Flecto Varathane varnish for a top coat on the combat models resisted glow fuel very well.

In any case it definetly would pay to try out all these ideas on some scrap pieces to both see what works and to develop the skills needed to work best with each material.

Here's a sketch of the combat wings I did showing how multiple layers of the paper served as wing spars and engine mount reinforcements. The models turned out to be very tough and damage resistant. In the end all three models I built using this method were brought down by the "buzzsaw" factor when other models mid aired with them. Along the way two of the three easily survived a lot of powered "landings" into foot high grass with no signs of damage. The third was "bellcranked" on it's first operational mission following one short trim check flight so it didn't get a chance to live long enough to see if it was a durable as the others.

"Bellcranked" is the term used when one model slams prop nut first into the engine bearers and bellcrank mount of the other model. The one so struck pretty much explodes into shards since nothing will withstand being struck that way. The one doing the striking seldom survives unscathed either.
Apr 10, 2011, 07:20 PM
treefinder
springer's Avatar
I've had good results with using WBPU and coffee filter papers. I haven't tried the thinned glue yet, though many in the scratchbuilt foamies forum have, and like it. I happen to have about a quart left from a floor refinishing that's my wbpu varnish stash. The urethane actually "cures" or chemically crosslinks, so I'd expect will be more durable long term. The filter papers absorb the varnish really well, and are soft and conformable when wetted, but they don't come apart like tissue does, and don't add as much weight as brown paper. Only disadvantage with them is they are circular and not too large (even if you use the commercial ones). However, creative layups make the joints look like panel lines.....
Apr 10, 2011, 09:53 PM
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Xanadu's Avatar
Have you thought of Minwax polycrylic and super thin fiberglass?
Lots of guys use it for their GWS foamies with great success. I bought some to do my GWS P-38, waiting for warmer weather first.

https://www.hobbyking.com/UNITEDHOBBI...dProduct=10905

http://www.minwax.com/wood-products/...ve-finish.html
Apr 11, 2011, 03:33 AM
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Quote:
For sheeted balsa I would not use a water based solution on the balsa. Instead I'd suggest art store tissue and clear aircraft dope.
Yes Bruce, I understand what you posted, but for the newbies that don't, DO NOT use Dope and thinners on Balsa sheeted FOAM structures, ie. Balsa sheeted foam cored wings etc..

Really creates a lightweight wing.

Regards Ian.
Apr 11, 2011, 12:18 PM
Registered User
Quote:
Originally Posted by Xanadu
Have you thought of Minwax polycrylic and super thin fiberglass?
Lots of guys use it for their GWS foamies with great success. I bought some to do my GWS P-38, waiting for warmer weather first.

https://www.hobbyking.com/UNITEDHOBBI...dProduct=10905

http://www.minwax.com/wood-products/...ve-finish.html
Can you thin minwax for lighter weight?

Trying to put things into context. The glass is 18g/sq m which I think comes out about 1.7g per sq ft. Yeah, mixed units, but it's something I can relate to. How much will the minwax add per sq ft?

Trying to toughen up an EPP flying wing that some bozo keeps putting into the ground.
Last edited by WAM74; Apr 11, 2011 at 12:32 PM.
Apr 11, 2011, 02:19 PM
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Thread OP

Many Thanks


Thanks for all the replies and the excellet information. I'll take a look at all. One of the planes is an old Sig Mustang 450 kit that I want to convert to electric and use as a fast sport plane - no pylon racing in my near future. Do you recommend the paper method or perhaps lightweight silk and poly?
Apr 11, 2011, 03:30 PM
B for Bruce
BMatthews's Avatar
If it's one of the pylon racers that you just want to finish as a fun fast flyer then it'll be a sheeted foam wing. For that I'd suggest the shellac and tissue base. You don't need to add any significant strength, you're just trying to produce a smooth surface that to some extent strengthens the wood from splitting. And tissue with a minimal bonding agent does that in fine style. As a bonus shellac sands very nicely with even fine grit paper and doesn't clog the paper. So any "fuzzies" are easy to smoothen out. It also makes a nice base for a sanding primer. But test this first for compatibility to whatever you're using. The surface you'd get with a tissue and shellac base would be lighter and easier to fill any remaining grain than would a cloth and Minwax Poly option. And a fabric option would require more of the heavy sanding primer to fill the weave as well. All in all a lot of weight where you only need a minimal solution to give a nice base to paint over.
Apr 11, 2011, 03:53 PM
Entropy is happening!
Jim.Thompson's Avatar
Quote:
Originally Posted by slipstick
So where does the "towel" come in ?

Steve
I'm still wondering??
Apr 11, 2011, 07:29 PM
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Thread OP
Someone described a covering method that used brown paper towels like those found in a public wash room.
Apr 12, 2011, 03:32 AM
Registered User
Normal use for a "Towel" when covering is to use a Kitchen towel (Paper absorbant type) or a good old bog roll for mopping excess epoxy resin off a coated surface after covering.

Regards Ian
Apr 12, 2011, 02:45 PM
B for Bruce
BMatthews's Avatar
Quote:
Originally Posted by Rocketman320
Someone described a covering method that used brown paper towels like those found in a public wash room.
If it was used as the actual covering material in some odd "paper mache" method similar to my own newsprint treatment can you find it and give us a link? Otherwise I'd say that it was likely in connection with mopping up excess resin as CirClip described.

If it was used as the actual covering material I'd suggest you go for the newsprint instead. The finish you'd get from hand towles would be a lot more rough than that from newsprint due to the surface of the paper towels being deliberately rougher and more random for fibers so it works well for soaking up water. Meanwhile the newsprint is finished to a smoother face in order to take ink better without bleeding. So it's a better option for a "paper mache" skin over foam and would require less material and work to get a smooth finish.


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