Fiberglass + Foam: A Tutorial and Discussion

Tench745

Master member
Sorry, yes, I should have been more clear. I meant only to present another way to fiberglass; the way I learned/developed. There is no one right way to fiberglass, everyone will figure out what works best for them and the finish they're trying to achieve. That said, there are definitely wrong ways. Starting with Willsonman's tutorial here is a great way to bypass a lot of the wrong ways. Thanks for sharing.
 

Craftydan

Hostage Taker of Quads
Staff member
Moderator
Mentor
There is no one right way to fiberglass, everyone will figure out what works best for them and the finish they're trying to achieve. That said, there are definitely wrong ways. Starting with Willsonman's tutorial here is a great way to bypass a lot of the wrong ways. Thanks for sharing.

+1

Also echo the squeegee -- in any layup with glass you need to control where the resin is and isn't and a squeegee or brush (if disposable) is a great way to spread it where it isn't and to get rid of as much excess as you can without snagging or stretching the cloth. Typically I use a dulled-but-not-dinged razor blade. Drag don't push, watch the blade corners, and use something else on a convex surface, but on a concave or flat surface it's great for getting down to the glass.

Quite a few people who do the wax-paper bagging also blot with a paper towel, but they're using straight resin.

As for resin . . . I hate to admit, I use what I have on hand -- 30min epoxy, thinned 65/35 with isopropyl alcohol. Comes out like a thin syrup, but wets and spreads very well. Alcohol evaporates off as it's worked, so as the resin thickens, it also looses bulk. 50/50 still works, but when it gets that thin, porous surfaces (balsa/ply/some foams) tend to soak it in more than I care. If you thin, take care to get the good stuff from the paint thinner aisle. Rubbing alcohol at the pharmacy can be 30% water -- fine for sterilizing things, but you *don't* want water in you resin :eek:

I'll admit, the 30 min stuff doesn't cure as hard and slows WAY down between final strength and final hardness, but it works. If you keep it thin, the glass/carbon/kevlar/unobtanium cloth is still the source of the strength. The resin just holds it in place and gives you the finish . . . when it eventually cures.
 

wilmracer

I build things that fly (sometimes)
Mentor
Old decks of cards work great as squeegees. If you need something more firm you can always laminate two or three of them.

I prefer to use Z-poxy brand finishing resin but there are lots of good options. The finishing resin doesn't set up nearly as fast as the WPBU but it is harder/stronger.
 

mrwzrd59

Old Guy Geek
Forget about squeegees and use 2" foam brushes when using polyurethane resin. I use Varathane wood sealer as my resin and don't have any issues with smell or mess. Cleans up with water!

I buy my glass cloth from Fiberglast and use mostly 1.5 oz. single weave with only one layer if it's over foam board or depron. Your airframe can be as stiff as you like if you take the time to lay down several layers.

Wet the glass out on a suitable surface and lightly wet the foam before wraping/applying the cloth over your shape...If you want 100% fiberglass construction, you'll need a female mold and release agent like a good carnuba wax. I use real mold release that we have at work.
The parts pop out of the mold with as good of a finish on them as your mold! Very little sanding for finish with the exception of seams where the parts are joined.

Anyway, Varathane is cheap and really nice to work with! It works for sealing the edges of FT foam board too! 20150414_202618.jpeg
 

AdamV

New member
Can you also glass a plane after it's built? Presumably, you have to if you're glassing a hotwire wing.

Are there advantages to glassing before vs after the plane is built?

Lastly, if the advantage of WBPU is for surface text, not strength, why glass both sides?

Appreciate any feedback, i'm looking to try this technique out
 

bstanley72

Member
It's crazy how this topic has just come up. I've been thinking about trying glassing for the first time on a FT Spitfire speed build kit I have.

So, my first question (I'm not quite clear on this) is you do the first step above with the WBPU and cloth on the parts before you assemble the craft, then you do the second step (in post #5) after the plane is built, to get it ready for paint, right?
 

willsonman

Builder Extraordinare
Mentor
GREAT question. Applying the glass to both sides does increase your strength. The idea is to replace the paper. The glass with WBPU is more stiff than paper so it provides better rigidity. Doing it to both sides will make your model last longer. Also, larger surface areas will bow and warp with fluctuating heat and temperature. This risks changing the aerodynamics of your model. In dryer climates you may be able to get away with it but its fairly humid here in MD.

You indeed can glass the outside after construction. So, say you were to use standard foam board with the paper on, construct each part, remove the paper on the outside, and then glass. It would work but the paper on the inside will de-laminate from the foam over time. Then you risk the same bowing and warping mentioned above. Not to mention glassing flat surfaces is much easier.

Also, you will want to apply the WBPU + BP mix after a part has been constructed. I don't think I made that clear. So, make your fuselage, tail surfaces, wing(s), and before you assemble them, apply the mix first. It will make sanding much easier. Painting can come later, or not. That is up to you and how much detail you wish to add (panel lines, rivets, etc.)
 

marc60

New member
Can you also glass a plane after it's built? Presumably, you have to if you're glassing a hotwire wing.
Are there advantages to glassing before vs after the plane is built?
Lastly, if the advantage of WBPU is for surface text, not strength, why glass both sides?
Appreciate any feedback, i'm looking to try this technique out

Hi Adam.
When I glass polypron (that's like depron) I glass the the polypron sheets that I use for wings/tailfeathers after cutting the shape but before folding the wing. I made two FT spitfire's, one with wings glassed only on the outside, one both on in and outside.
Both are really, really stiff. I always glass the fuselage after construction, that way it's stronger where I glued it together.
In this you tube video you can see me diving and pulling up the spitfire, with the wings glassed only on the outside; they stay on the plane, quite an achievement I think :p And the doublesided wing is even stronger


I did some tests in glassing polypron with light glassfibercloth and acrilic paint (no smell, speeding up dry-ing with hairdrier)
http://forum.flitetest.com/showthread.php?4288-FT-Spitfire-Build/page34

I also build a P51 and a B25 with glassing. I glassed them because I wanted to paint them. You can't paint on tape. If you paint and tape after that, the tape won't stick
http://forum.flitetest.com/showthread.php?14781-Scratchbuild-polypron-P51-Mustang
http://forum.flitetest.com/showthread.php?7219-Scratch-building-a-B25-look-alike

My last build was the frankenstorch. I wanted that to be a quick build, strong, no paint needed as it was a pure FPV plane: so I didbn't really care to paint. I use packing tape there; it turned out to be just as strong. I know because I crashed it. You can read that here
http://forum.flitetest.com/showthread.php?19976-The-frankenstorch-plane

Greets Marc
 
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abieex

Member
Mentor
I'm pretty excited about all this info and Josh B's input would be great. We currently have pod casts etc, what about monthly training vids on subjects like this or maybe every other month. Maybe workshops at FF are a better idea.
 

earthsciteach

Moderator
Moderator
So details such as panel lines easy to press into the surface even after you've glassed it? Or are you meaning details using paint?

Panel lines are added with paint. Tape them out with Chartpak tape then apply three layers of primer on top. Sand down until the tape is exposed and peel off.

Rivets can be added with drops of CA glue applied with a toothpick.
 

willsonman

Builder Extraordinare
Mentor
Maybe workshops at FF are a better idea.

Oddly enough I have started to put together some plans to do just that. With all the interest in the Sikorsky build I figured there was a real interest in this process. I've modified a set of plans for a BW that includes a hot wire cut airfoiled wing. The airplane is complete at this point awaiting maiden. If it all goes well I may have something to propose to the FT team and see if they can get behind it. They would be in 1-hour sessions. and give hands-on work with hot wire cutting and glassing. That is the hope anyway. I am getting some guidance from CraftyDan on this. If there is higher interest posted here they may go for it more.
 

willsonman

Builder Extraordinare
Mentor
So details such as panel lines easy to press into the surface even after you've glassed it? Or are you meaning details using paint?

See post #5. Its all outlined there. While CA glue does work, I prefer wood glue. Its cheaper for the amount that you will be using, and does not have fumes like CA. I hate that stuff and honestly use very little of it. Again, are you doing raised or flush rivets? The techniques differ. Flush are fun because when you are done its one of those details you do not see until you get REALLY close and it blows people's minds. Its fun, and I think its fun to do that kind of detail work.
 

abieex

Member
Mentor
It seems that there is enough interest to move ahead with some sort of presentation to the FT guys. Many of us are moving beyond the basic stuff now and want to learn more. We are very fortunate to have talented people in the community to teach us! Dan, Monkey, can you guys help open a door or two for this idea?
 

willsonman

Builder Extraordinare
Mentor
So, a little side project I've been working on is a fully composite version of the Bloody Wonder. The wing is hot wire cut with a carbon fiber arrow shaft spar embedded in the wing and the flat parts are glassed using WBPU. The spar is glues with gorilla glue and lightweight spackle used to smooth it out again. I used the same heavy glass on the flat parts that I featured in the tutorials. The wing was glassed with 0.56oz. glass and epoxy, sanded smooth. Everything was glued using gorilla glue. I'm using a 9g servo for the elevator and a full size servo for the ailerons. Prop is a cheapie 1900kv motor swinging a 7x6 prop. 30A ESC and a 1300mAh 3S battery. I did have to add lead to get the CG right but a 2200 3S battery would fix that... I honestly do not have any of those.

Flying characteristics are good. She is fast for the small power setup she has. No trim needed. Inverted needs a little push but other than that she is just a raw combat ship.

The intent here is that the plane is simple to teach the very basics of hot wire cutting and glassing. If there is interest here I will gladly post the plans, as they are now proven and need no adjustments.

 

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saiga556

Full of...
Have you guys been using spars in your foam/fiberglass wings? I have seen it done both ways and I'm a fan of having a spare in there.
 

marc60

New member
Have you guys been using spars in your foam/fiberglass wings? I have seen it done both ways and I'm a fan of having a spare in there.

In the spitfire and B25 wings I only used the foam spar, which main purpose is shaping the wing. Of course it adds some strenght too. But I'm in the impression that most of the strenght of the wings is from its shape in combination with tape or glassfiber.
In the storch I used a flat carbon strip glue-ed against the foam spar. It survived a rather nasty crash :p