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Old Apr 30, 2007, 04:25 PM
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jrbackus's Avatar
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Fiberglassing a balsa fuselage...

I have been reading on here about fiberglassing fuselages and I have the whole process dialed in i think...
-light spray of super 77
-lay glass on as smooth as possible (1.4oz ish)
-wet out the glass with thinned epoxy
-blot with paper towel
-let it set
-fill the holes with a cote of light weight spackling (good filler???)
-sand smooth

Here's where I have questions:
1. I was told to put glass from the nose to about 4 inches behind the TE of the wing... What should I do aft of the glass??? Just cote with thinned epoxy??? Or should I just put a layer of glass on the whole fuse and put a second layer on the forward section (too much weight??)

2. How should I put the glass on the fuse? What I mean be this is should it be in one piece? One piece per side?? Right/Left or Top/Bottom??? Lots of small strips???

3. Should I put a second coat of epoxy over the glass before I fill the holes with the lightweight spackling

4. Is lightweight spackling actually a good filler???

Thanks in advance for the help!!!

--Jeremy
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Old May 01, 2007, 09:22 AM
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Anyone???
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Old May 01, 2007, 10:23 AM
the-plumber
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Quote:
Originally Posted by jrbackus
I have been reading on here about fiberglassing fuselages and I have the whole process dialed in i think...
I think most folks would agree that .5 oz. cloth is more appropriate over a sheeted structure; certainly lighter.

A chemical engineer friend pointed out that acetone is the preferred thinning agent for epoxy.

I like to use a full roll of paper towels to blot up the excess epoxy. I use a scrap length of PVC pipe through the roll of paper towels, and go over the entire surface with the paper towel "paint roller". In tight quarters I blot with a wad of paper towels.

Quote:
1. I was told to put glass from the nose to about 4 inches behind the TE of the wing... What should I do aft of the glass??? Just cote with thinned epoxy??? Or should I just put a layer of glass on the whole fuse and put a second layer on the forward section (too much weight??)
I 'glass the entire structure, except over open bay areas where I use Coverite Super.

Quote:
2. How should I put the glass on the fuse? What I mean be this is should it be in one piece? One piece per side?? Right/Left or Top/Bottom??? Lots of small strips???
When using thinned epoxy, your best bet is to cover an entire "top" surface. For the fuse, you can cover the top and sides in one piece if the fabric will layout nicely without having any puckers. Otherwise use multiple pieces, as large as possible. The reason for doing a "top" surface is that the thinned epoxy WILL run off to some extent, and you need to keep those drips blotted up - unless you really like sanding off epoxy blobs at the bottom edges.

Quote:
3. Should I put a second coat of epoxy over the glass before I fill the holes with the lightweight spackling
I use a second coat, but only after the first coat has fully cured (sometimes 3 to 4 days, for thinned epoxy).

You may find that you don't need spackling. Depending on the paint you plan to use, filling/spackling may not be required at all. I just finished a 33% L-4 and used exterior latex over Coverite Super. Needed three coats for full opacity (because latex thinned for spraying is -pretty thin stuff-), and when the color was fully opaque the paint had filled the weave completely.

Quote:
4. Is lightweight spackling actually a good filler???
Indeed. Make sure it is NOT vinyl-based spackle. Vinyl spackling compound has compatibility issues with a number of paint systems and other model finishes. For example, polyester finishing resin will not cure if applied over vinyl spackle - what you get is a semi-cured gooey mess that is almost impossible to remove and there is no way to get it fully cured. DAMHIKT.
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Old May 01, 2007, 10:29 AM
hul
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I would glass the whole fuselage, not just the forward half, and use as big pieces of glass as possible. This depends on the shape of the fuselage, rectangular cross sections probably need 4 separate pieces (top, bottom, left and right) to prevent wrinkling. Overlapping the glass is not a problem, can't see that in the end.
Wouldn't put any more epoxy on it than necessary, epoxy is heavy. Never used spackle to fill the weave, not sure it will stick and I think you still need to prime it before paint. I used baby powder/varnish mixed to make a paste last time around (at the recommendation of RC group members). That worked well, but you'll have to see if your color coat will stick to that (my water based acrylic did).
Don't think you really need the super 77 (this is spray on glue, correct?). It probably causes more wrinkles than it cures.

Hans
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Old May 01, 2007, 03:05 PM
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Bondo Lite instead of spackling?
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Old May 01, 2007, 03:32 PM
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Originally Posted by TheSaint
Bondo Lite instead of spackling?
Bondo Lite??? I've never seen that before...
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Old May 01, 2007, 03:39 PM
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By the way, What is the concensous on the best weight of glass???

I have heard that .5oz is the best but i've also heard that 1.4 is perfect...

Anyone out there that has used both have any suggestions??? Or should I just go with .7???

--Jeremy
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Old May 01, 2007, 04:42 PM
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I think I got some in a tin recently, premixed with some kind of material (probably chalk or pummice) to bulk out the epoxy and lighten it up a bit. A bit like putting glass microbaloons in regular bondo.
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Old May 01, 2007, 04:51 PM
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I'll try microballoons and bondo but i'm also going to give the lightweight spackling a try. I've heard a lot of good things about it.

--Jeremy
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Old May 01, 2007, 04:58 PM
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Epoxy has a cured specific gravity of about 1.2. The glass weights are quoted in ounces per square yard, so I'll wager a pint, well maybe just a half, that the glass mat has only a small influence on the finished weight, although it depends on the percentage of glass to epoxy. One figure I was able to pluck out the air (well out of old Westland Helicopters training notes) is a specific gravity for GRP of 1.8 with 22% glass. More likely to effect the finished weight is the amount of epoxy you use and how much you blot/sand off. For example, 0.1 mm (4 mils) thick epoxy over 1 square yard weighs 100 grammes (3.5 oz), 0.2 mm (8 mils) weighs 200 grammes (7 oz). Compare this to half an ounce per square yard for the glass mat and i think you see my point.
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Old May 01, 2007, 11:41 PM
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3/4 oz cloth has a closer easier to fill weave than 1/2 oz.
I would do the entire fuselage with 3/4oz and then add the heavier cloth from the wing T.E. to the nose.
My own preference is to do the bottom first, then the sides, then the top. Blot with toilet paper.
Filling has to be last. I have had good luck with Krylon H2O Primer.
Buy some titanium blade sissors..they are in the $8 range and work well for cutting the light weight cloth.
Make up a couple of sticky side out masking tape 'loops' to control the odd strands that happen.
Acid brushes work well...buy a dozen at a time.
Please consider this with the other excellent advice.
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Old May 02, 2007, 09:03 AM
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Thanks everyone for the advice!

I actually already bought the .58 glass yesterday but I think that should work well. I'm going to cover the whole thing in .58, then put a second layer from the TE to the nose.

I still don't know how i'm going to fill the weave after i'm done but I'll try the lightweight spackling, epoxy/micro balloons, bondo/micro balloons and anything else I can think of. I'm sure something will work.

--Jeremy
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Old May 27, 2007, 11:20 AM
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use primer paint.spray a thin coat on.sand with 300 put on a thin coat sand with 300,after a couple of coats the weave will be filled and after sanding the weave is all that is filled,then one very light coat before you put on your color coat
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Old May 28, 2007, 01:29 AM
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another way is to put somthing over the glass and let it cure because it will draw the epoxy to the surface kinda like a mold would and you will have less weave to fill in.
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Old May 28, 2007, 09:18 PM
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The light clothes like .5 to .75 are great as a finishing cloth but do only a little for strength. If this is for a glider of some sort then I'd be using a layer of 2 oz to 4 oz depending on the size. And a "short" layer would be put on over the nose and belly back to just behind the wing's trailing edge. A layup of this sort would add an appreciable amount of muchly needed strength to the long whippy glider fuselages.

And if it was me I'd be worried about the 3 making it hard to position and smoothen down the cloth. Especially the super light stuff. If it's not stuck it's much esier to make it flow around the curves.

If this is for finishing an excellent superlight cloth bonding agent is water based varnish. YOu can brush it on and carefully spread it around and a lot of the weight dries away. Similarly good old model airplane dope also makes an excellent bonding adhesive. Either of these options is lighter than the Epoxy.

And since this is your first run thru doing this you may want to try it on something else to get a feel for the procedures. Use something with compound curves to get a feel for drawing the weave of the cloth around the curves. Then you'll see why I don't like the idea of the 3M mist. Besides the surface tension of the stuff you brush on will suck the glass down like it's vacuum packed.
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