Making fiberglass cowl
 

Been reading several posts and I may be going to show my ignorance... I know that you use about 3 layers of cloth... Do u cover each layer with resin or do you put all three layers on then put the resin... Or is it a put some cloth on put some resin on...

Hi Coach...I just finished building a cowl for a modified Corsair. I built mine over a foam mold and used varying thicknesses of fiberglass. I'm not exactly sure how many layers I used but I did use resin between each layer.

Thanks B-Squared... I've never tried it but I like to scratch or plan build and a lot of the planes I've been looking at have no after market cowl.. I'm gonna try a canopy too.. Oh well we'll see... I had some resin one time I used on a center section of a wing and I think it took like 45 minutes to set, would that be something I would use to have time to work with it

Coach, can you give more details please? Are you using the lost foam method? Building a plug and making a mold? What size airplane?

Yes I'm gonna use the foam plug... At some time or another it will be different size planes but probably a 60 size or a 40 size first...

On the canopy I will probably build a balsa plug

For a cowl that size 3 layers of 4 oz cloth will work well. Apply one layer at a time, it's easiest to apply in 4 pieces. Sand smooth before dissolving the foam.

Coach,
I apply one layer of cloth and then "paint" with resin till the cloth is wet through, then apply another layer of cloth and ("paint") wet the cloth. Apply just enough resin to wet the cloth, any more is just excess weight. I am not an expert but have had good success, see my web site for my scratch build of the F-94C.
http://www.sidgates.us/HOBBIES/F-94C/F94C%20PROJECT.htm


Sid

With the lost foam method, I would use a 6oz first, brush on epoxy resin, then a 4oz ,epoxy, then maybe another 4oz,epoxy, then a nice fine weave, maybe 2oz,epoxy to finish. And sop up excess epoxy if too much.

The fine weave will make it easier to eliminate the weave when finishing.

When making your cowl, consider if the model is tail heavy. Like a Zero. A Zero (every one I have ever had)

could use a heavier layup on a cowl to add ballast to the nose.

Steve

To help smooth out the resin and fiberglass roll a toilet roll across the part once you have the resin applied.
You want to roll it such that the paper doesn't unroll.

Then let it set and do another coat.
Means less sanding in the end as rolling the toilet paper across the surface will help whet the glass and also remove excess.

Roll it until the top couple of layers saturate, unravel the paper until you get to fresh paper then repeat.

If the cowl is 40-60 sized and your plug is solid, there is an easier way to smooth out the resin. We do this with Quickie 500 front ends after we reinforce them to hold the cloth tight, as well as give a smooth finish. The fuselage front is 2 1/4" square (rounded corners) and goes back 5" or so with a rear size of around 3 1/2" (about the size of a 40 cowl). All you need is a medium to large round balloon. Once all the cloth & resin has been applied, blow up the balloon a couple of times to stretch it out some. Blow up the balloon one last time, but this time, place the end of the balloon on the front of the cowl and push the balloon down over the cowl as it deflates. This will force the balloon over the cloth and basically shrink wrap it. you can even rub out any spots that look odd thru the balloon and not get your hands dirty! :) Let the resin totally cure (24 hours or longer) and then tear the balloon off. You should have a very nice finish with minimal sanding left to do. ;)

As I said, make sure your plug can take the pressure of the balloon, and test this a couple of times before you have the resin on the plug. It works like a charm on small parts.

Best wishes,

How I do it.
1. Make a foam plug,
2. sand and shape to suit,
3. get it smooth as ya can,
4.apply a coat epoxy reisin thin caot. I've used west systems, U.S. exopy 88 and a couple others.
5. let it set to tack
6. cover with fiberglass cloth 3oz to 6 oz depending on size,
7. mix more resin apply a few coats serveral in some spot for stengh
8. let tack
9. apply peel ply fabric, you'll have to cut it in pieces to apply to your compound surfaces.

The peel ply acts in two way, first it soaks up the extra resin ,
second it smoothes out the cloth and will virtullay eliminate the need to sand much.
Once you peel it off you are left with a fabric like surface, its great I think.
I'll have to post some photos soon

I show a cowl layup in my Monocoupe thread here: http://www.rcgroups.com/forums/showthread.php?t=2011807

Start at post #72

I also show how to get some quick fiberglass wheel pants made up. Same thread right after I do the cowl.

Tom

Tom thats a great constuction artical. I have question, Why do you make a mold if your only making the one item? or are you making several copies?

First, I just like working with composites. Second, the cowl is usually the very first thing ever damaged on a model (assuming it is not totaled). I can turn out as many as I can destroy. :) Last, replacements always fit perfectly.

I never understood the upside of the lost foam process anyway. If I go to the trouble of making a nice plug, I do not want to have to repeat that process if I ever need another part. So I go just the one simple step further and use the nice plug to make a permanent mold.

Tom

I usually build a master model, then a layup block followed by laying up parts from the inside of the molds, but for quick and dirty...

1. I made templates for the front of the airplane.
2. Glued in foam blocks.
3. Shaped the foam with a wire brush, and 80 grit sand paper.
4. Fished foam plug gets glassed, a bondo surfacing treatment, primed and sanded until smooth.
5. For this shape I laid up an upper half and a lower half from the outside of the plug, then seamed them together.
6. I then glue in the cowling with CA.
7. check fitted.
8. I then prime fill, sand and base coat.
9. I then clear coated.

Bob

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