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Nov 24, 2010, 10:19 AM
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tzyoung's Avatar
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Cool

Gorilla glue wing


Hi,
I recently got a call from my dad asking for some blue foam wing cores to use on a couple of small electric parkflyers that he was going to build. I decided to do one better and bag a fiberglass skin on one of the wings for him.

Being no stranger to vacuum bagging I planned to use epoxy and incorporate some nylon into the skin to act as a live hinge; however, school got in the way and I barely had enough time to cut the cores, but there was no way that I would be able to bag the wings and have the epoxy cure before it was time to make the trip home for Thanksgiving when I planned to deliver the parts. (My epoxy is very slow curing, fibreglast 2 hour cure hardener).

So inspired by this thread, https://www.rcgroups.com/forums/show....php?t=1334077, I grabbed a huge bottle of the original gorilla glue that I had lying around and decided to see for myself if this crazy notion of using polyurethane instead of epoxy was real.

If you skip ahead to the attached pictures you will see that grouch wasn't lying to us about how well this works. You can actually use the stuff as a matrix in a fiberglass skin. I went ahead and gave the mylars a good heavy coat of white paint reasoning that my dad could apply the color scheme of his choosing with a nice white base coat.

My process was as follows. I cut my single layer of 2 oz cloth just over sized for each mylar half. I squirted glue over the cloth and worked it in with the same type of foam roller that I use for epoxy. It took about 30 minutes for me to wet out both mylars to my satisfaction. The wing area is 252 inches. The leading edge strip was generously wet with glue using an acid brush and I dampened the cores with an atomizer bottle before putting the mylars on the cores.

A few notes about the process. I have no idea how long you have before this glue starts grabbing moisture out of the air and begins convert itself into foam. Judging from the tools it is about an hour.

Gorilla glue is quite viscous compared to good laminating resin so it will take a bit longer to get the skins wetted out. With that comes a greatly improved surface tension. The glass seemed to stay stuck down much better to the mylar than with epoxy. Also the initial grab to the cores was much stronger when assembling everything before bagging. It was nice to not have everything sliding around as it tends to do with epoxy; however, I intend to play around with thinning the glue with mineral spirits to make the wet out easier ( any experience anyone might have here would be appreciated).

The cure time is unbelievable. I have heard 4 hours quoted as the cure time. I un-bagged the wing after about 10 hours because I was asleep 4 hours after bagging. There is no way that I could pull parts that quickly with my epoxy. And when I have used west systems resin to make bagged wings on the university's dime (senior design project/ research) there is no way that I would have pulled parts that soon.

I would imagine there is a size limit where this technique would not be feasible due to cure time, but If you are on the fence about whether to try vacuum bagging this is a good way to do it with an $12.00 bottle of glue rather than buying a $100.00 gallon of epoxy and finding out that this technique isn't for you. Although I agree that epoxy Gorilla glue is not cheaper per unit volume compared with epoxy for doing this kind of work it just happens to be more readily available.

So there it is. I tried it, and I think that this is a perfectly viable way to build wings. Many thanks to the folks that tried this before me and inspired my to try it myself.

-Trent
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Nov 24, 2010, 12:53 PM
there is no spoon...
Cap232ac's Avatar
That's impressive. Both your work and that of Grouch. I'm new (read don't know a thing) to vacume bagging. Is this something I could learn with or is more experience needed to get this done?
Nov 24, 2010, 01:53 PM
Entropy is happening!
Jim.Thompson's Avatar

PU glue


That looks quite impressive TZ. There is a short thread on these forums somewhere discussing this method. I tried it out on a small sample and achieved patchy results myself. Excessive foaming in places and poor adhesion in others. At the time, I drew the conclusion that the brand of PU glue available here in Australia it thicker (more viscous) than that available elsewhere. That may not be the case, I am only guessing. I found my glue to be very difficult to get to spread out and wet out the cloth, even though I warmed it first.
So I have gone back to using West Systems epoxy and only in warm conditions. That way I can achieve a thorough wet out with minimum pinholes etc.

Anyway, good luck with that. You seemed to be getting good results.

Jim.
Nov 24, 2010, 02:16 PM
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tzyoung's Avatar
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Cap232ac,
The only way to get experience is do it. If you know what to expect, I think that using this glue as a resin would be a fine way to learn the basics of bagging wings.

A few points to keep in mind
As I said before, Gorilla glue is much more difficult to work into the glass than epoxy

First attempts should be done with as few layers of cloth as you can get away with

A good vacuum is required for this to work as PU and water react forming CO2 as it cures. I suspect the vacuum pulls this away as the glue cures which makes it cure clear and shiny.

Every other procedure for vacuum bagging work exactly the same whether you are using epoxy of polyurethane glues.

With all of that out of the way, I think that this is a fine way to get started. Try bagging a skin over some 6mm depron or fff to practice and save the nice cores for when you have the procedure worked out.


Jimbello,
Thanks for the complements. I will confess that after sanding out the leading edge I masked it to spray some white spray paint. The tape pulled up paint in places. It looked like I had some air bubbles between the skin and paint film (i will post some pictures soon). To be fair I have seen this happen with epoxy as well. I was using a continuous run pump with no vac gauge so I have no clue how many inches of vacuum I actually had. I am just going to fill the spots with something and my dad will just have to decorate over the "boo boos."

-Trent
Last edited by tzyoung; Nov 24, 2010 at 02:24 PM.
Nov 24, 2010, 03:26 PM
Entropy is happening!
Jim.Thompson's Avatar

Air bubbles


Quote:
Originally Posted by tzyoung
It looked like I had some air bubbles between the skin and paint film (i will post some pictures soon). To be fair I have seen this happen with epoxy as well. -Trent
Trent,

That surely happens with epoxy too, as you say. I have been plagued with this problem and I am only 90% sure I have solved it by rolling out the assembled mylar/resin/glass assembly when vacuum is first applied. I have one to do again soon, so its a case of fingers crossed!

Jim.
Nov 24, 2010, 04:09 PM
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tzyoung's Avatar
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Here are the pictures of the defects I discovered. I also cut the ailerons and got them moving freely.

-Trent
Nov 24, 2010, 04:32 PM
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tzyoung's Avatar
Thread OP
Jim,
I have seen my fair share of those types of bubble too. The good news is those are an easy fix because the paint generally stays attached to the skin and the delamination is between the skin and foam. I have had good luck fixing those by slitting the bubble with an xacto, injecting some epoxy with a syringe, patching a piece of mylar over the area and putting the whole thing back in the bag.

-Trent
Nov 24, 2010, 06:54 PM
Registered User

Pinhole cure


Get some powdered silica gel from a paint supply store or fibreglass outfit, add a small amount to the paint or the surface gel coat.(Thats why its called GEL coat"). Result, no pin holes and better adhesion all round.
Nov 24, 2010, 11:23 PM
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tzyoung's Avatar
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Macboffin,
Is it possible to get enough silica into the paint to get a gel effect and still have it go through a paint gun? I think hand painting a waxed mylar would be difficult at best. The paint needs to lay down pretty smooth for this.

I have found that a catalyzed urethane auto paint is the best paint for this technique. The high amount of crosslinking allows the paint film to bridge pinholes with plenty of toughness. It just isn't so friendly when you are trying to build in an apartment bedroom.

-Trent
Nov 25, 2010, 01:13 AM
Just fly it!
wyowindworks's Avatar
The real downside to a gel coat is the added weight and increase laminate brittleness.
Nov 25, 2010, 08:47 AM
Red Merle ALES VII SJ
Curtis Suter's Avatar
Quote:
Originally Posted by Cap232ac
That's impressive. Both your work and that of Grouch. I'm new (read don't know a thing) to vacuum bagging. Is this something I could learn with or is more experience needed to get this done?
I labored over two winters making an instructional DVD just for someone like you. I've taken all the research and in a couple hours of watching your TV you can obtain all the tips necessary to cut foam core wings and vacuum bag them on little expense while still obtaining excellent results.
It's as if you're in my workshop with me while I make some beautiful wings and fuselages using composite materials.

Please visit www.TailwindGliders.com
There is a Holiday sale through the end of the year too!

Curtis Suter
Montana
Nov 25, 2010, 08:56 AM
Red Merle ALES VII SJ
Curtis Suter's Avatar
Trent,

Very, very nice!

Happy Holidays from Montana
Curtis
Nov 25, 2010, 10:46 AM
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tzyoung's Avatar
Thread OP
Thanks Curtis,
I should give credit where it is due. I did get the gorilla glue idea from some of your threads here on rcgroups. My gravity foam cutter is also pretty much copied from your article in soaring digest. I appreciate you taking time to get info like that out to the rest of us.

-Trent
Nov 25, 2010, 01:32 PM
Entropy is happening!
Jim.Thompson's Avatar
Quote:
Originally Posted by tzyoung
A good vacuum is required for this to work as PU and water react forming CO2 as it cures. I suspect the vacuum pulls this away as the glue cures which makes it cure clear and shiny.

-Trent
This is precisely the reason that I abandonded this method after some small trials. The production of the gas caused a very uneven surface to result. In places it was glossy and others quite porous. There is no way the vacuum can possible vent all the gas out with the viscosity of the adhesive locking it in. I even tried using a notched spreader to spread the glue after warming it for ease of application.

Jim.
Nov 25, 2010, 01:42 PM
Entropy is happening!
Jim.Thompson's Avatar

Gravity hot wire cutter


Quote:
Originally Posted by tzyoung
My gravity foam cutter is also pretty much copied from your article in soaring digest. -Trent
Trent,

After some development and experimenting with several configurations for hot wire cutters, I have now build one mostly along the lines of "JoeMach 1" example. It has several advantages, and I am extremely happy with it. One of the big breakthroughs though is the template design, especially the entry and exit ramps! The exit ramp slope is my idea, and avoids totally any scalloping or mid span distortion of the TE.


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