Glassing balsa mid-wing
 

I'm to the point of strengthening the balsa mid-wing joint/section of my RCM Trainer and need some advice at this point. What glassing process guarantees a smooth transition where this area is not visible under Ultracote? I read somewhere that one can use saran wrap over the area working all bubbles and wrinkles out but I don't know the specifics or if there is a different way. Any suggestions are appreciated.

swimmer

RE: Glassing balsa mid-wing
 

Get some "peel ply", which is essentially Nylon cloth. Put this over the area after glass and resin, then squeegee it down. This will produce a nice smooth surface.

RE: Glassing balsa mid-wing
 

That is exactly what I do to achieve a really nice smooth finish.

Karol

RE: Glassing balsa mid-wing
 

Does "peel ply" have a website and if so what exactly of their products did you two use? Here is what I have done so far.

swimmer

RE: Glassing balsa mid-wing
 

The Saran wrap work very well, leaves an absolutely baby bottom smooth surface and allows you to feather out the edges by carefully smoothing them out with your fingers while the epoxy is still smooth and flowing. Let the layup cure completely (over night at least) before removing the Saran wrap and it will come off very easily. I do not know if other clear food wraps will work as well as Saran or not, I hear some do not release as well as Saran does after the epoxy cures.

RE: Glassing balsa mid-wing
 

Never heard of the brand name Peel Ply, but the last time that my wife bought some white nylon cloth to make kitchen curtains, I got some from her which I use for just these sort of jobs, and it works great.

Karol

RE: Glassing balsa mid-wing
 

I think wax paper does a great job because it globally flexible but locally stiff, thus easier to get a smooth surface where you transition from glass to balsa. It is also easier if you use multiple layers of two oz cloth with staggered edges, as the thickness at each edge is thinner. Place the widest layer on first, with the last one the narrowest.

RE: Glassing balsa mid-wing
 

Rodney,

Do you need more than one application of epoxy?

Allan

RE: Glassing balsa mid-wing
 

No, but it is best to use a slow cure epoxy, at least 30 minute. I put on as thin a coat of epoxy on the area that I can then lay the cloth over it. I then take a heat gun and gently heat the area; you will see the epoxy flow out and saturate the cloth. If any area does not appear to get wet with epoxy, apply a bit more in that area and gently heat again. Now cover the entire area with one piece of Saran Wrap and smooth it out to eliminate any wrinkles or uneven areas. You can feather the edges very easily so that, when it cures and you remove the Saran Wrap, very little if any sanding is required: a glass smooth surface results.

RE: Glassing balsa mid-wing
 

Thanks, Rodney.

Your described process is the one I will use. I bought a roll of Saran wrap last night. I may have more questions but you've done a good job telling me how to do it.

Thanks,

Allan

RE: Glassing balsa mid-wing
 

RE: Glassing balsa mid-wing
 

Hi!
What you have done in the picture is fine but not the best way of doing it!
A much better way is to use thinner glass cloth (25g) and put on several layers (3-4) in different widths. That way you don't get a sharp ridge where the glass ends. What happens when you put load on the wing is that it might (will) break where the glass fiber ends , like tearing toilet papper.

And do not use the glue variety of epoxy!
Use laminating (24 hour ) epoxy! It's much thinner and easier to sand and most important ...Oracover (which is the best plastic covering) stick to it better than epoxy glue.

RE: Glassing balsa mid-wing
 

I will certainly consider your advice as I complete additional projects.

Thanks,

Allan

RE: Glassing balsa mid-wing
 

Before glassing the mid-wing I did a control sample (learned this from Mythbusters) using the Saran wrap. I expected the wrap to have a smooth surface but it does not. There are striations in the wrap. I applied 30 minute epoxy to a test strip of plywood. The epoxy went on smoothly but when the wrap was applied the wrap could not be pulled or stretched to remove the striations. Once the epoxy set and the wrap removed the epoxy had taken on the exact imprint of the wrap. Maybe there is different wrap that has a smooth surface but the Saran wrap I used does not. So, I applied the epoxy with a old credit card not using any wrap. The result is a very smooth surface. If the wrap would have worked I can see that it would have given a smooth result.

Allan

RE: Glassing balsa mid-wing
 

Allan,

I never had any luck with the saran wrap, I have also tried masking tape and other things.

However, the Peel-Ply technique works great.. Search here on RCU and there are several detailed threads. I recently posted the following information in another build thread:

I wanted to suggest the Peel-Ply method when it comes time to glass the center of your wing. I have tried several different techniques and did this the first time during my last build with a Global Skyraider kit.

Take a look Here: [link=http://www.rcuniverse.com/forum/m_7276786/mpage_3/key_/tm.htm]Global Skyraider Build[/link]on posts numbers 62 and 68.

This technique was very easy to learn and gave me a great smooth surface over the fiberglass. I have tried several techniques of thinning epoxy, layering Saran Wrap over the fiberglass and glue, even using masking tape to smooth down the finish... The Peel Ply technique worked GREAT.

Also, I had often fought with the folded fiberglass or nylon tape provided in the kit wanting to leave fold marks in the center. I did some experiments with ironing the material and reported it on the [link=http://www.rcuniverse.com/forum/m_6496478/tm.htm]King Kobra Build[/link], post # 68. It really helped keep things flat.. BTW, the Peel-Ply technique was used over the entire plane in this thread: King Cobra Build I think Mikes use of Peel Ply starts on Post #49.

Just something to check into. I use the poly dress lining cloth for my "peel ply".. I think the material is better described in the King Kobra thread.

Good Luck

RE: Glassing balsa mid-wing
 

I take a completely different approach. A high wing with dihedral will have a shallow V shape over the top of the fuselage, if the wing halves are joined in the middle. No full-scale plane I've ever seen looks like that. So I don't worry about getting the epoxy and fiberglass tape surface smooth. I just get it reasonable OK and then make a sort of cap out of balsa to put on top of it, so that the wing looks as if the part over the fuselage is really part of the fuselage, and flat on top, with the dihedral seeming to start at the fuselage edge. This covers up the rough edge and also makes the plane look better. If my computer skills were up to it I'd add a picture here.

RE: Glassing balsa mid-wing
 

Very nice Bridi trainer btw.

Advanced RCM Bridi Trainer 40?

Brian

RE: Glassing balsa mid-wing
 

I don't think peel ply is a product, but is a technique used, I use 100% polyester dress liner bought at Wally World very inexpensive. I just cut to the required size then squeege in down over the epoxy and glass, then peel it off after the epoxy cures completly. Peeling it off after cured is where you get the peel ply term.

RE: Glassing balsa mid-wing
 

I believe that Peel Ply is a product from boat fiberglassing. West Systems calls it a "release fabric" also known as Peel Ply.. I'm pretty sure that one guy using it on his planes learned it from working on boats. However, I think that the "peel ply" used on full size boats is probably a bit heavier than the polyester we use.

Yes, I go to the fabric shop and buy 100% polyester dress lining.

RE: Glassing balsa mid-wing
 

TEBerg, thanx for that info, learn something new every day.

RE: Glassing balsa mid-wing
 

I never had any luck with saran wrap either. I usually glass it then use dry wall spackling from lowes to smooth the seam between balsa and the glass tape.

RE: Glassing balsa mid-wing
 

Agree. Spackle also does it for me.

RE: Glassing balsa mid-wing
 

Hi!
Spackle is not necessary if you use thin (25g) glasfiber cloth in different widths, and saran wrap is certainly not needed to obtain a smooth surface.
I use 3-4 layers of 25g glassfiber cloth with different widths on my Q-500 racers and I use 24 hour epoxy. That epoxy gets hard as glas overnight and is easily sanded.

RE: Glassing balsa mid-wing
 

Peel Ply is a product, it is used in composite fabrication. You put it on carbon graphitelaminations before you vacuum bag, it lets excess resin out through the ply. Go to CST website, you will find it.

Good Luck

Scott