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How many layers of 4.25 ounce glass is needed for a cowl

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Old 08-17-2011, 07:19 PM
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flyingagin
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Default How many layers of 4.25 ounce glass is needed for a cowl

Any suggestion on just how thick or how many layers of 4.25" glass cloth I will need to have a usable cowl?

I am just about to start a fiber glass engine cowl. I already have the foam mold made. I need to seal it with white glue yet. Once I dig out all the foam the then the white glue can be dissolved out in a pan of water.
I have 4.25 ounce glass cloth. As a test I laid two layers down on a waxed flat surface and worked the epoxy (30 minute) thru. It has cured about 8 hours now.
Lifted the panel and it is very flexible and weak. It will take more than that to make a descent cowl.
Any suggestion on just how thick or how many layers I will need to have a usable cowl? It measures about 4” wide by 4.5” tall and is about 5” long to the firewall. It will extend 1” beyond the firewall onto the fuse for a total length of 6”.
The engine (pictured) is a K&B K&B .65 Sportster .65
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Old 08-17-2011, 08:05 PM
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Default RE: How many layers of 4.25 ounce glass is needed for a cowl

First to answer your question. 2

The epoxy will get a little harder as it fully cures, You are deflecting air not water, it doesn't need to be real strong.

If you use thin packing tape over the foam you can tape it right to the front of your plane, then lay up your glass over the foam and about 1/2" of the fuse, you'll have a perfect fit to you plane/cowl.
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Old 08-17-2011, 08:05 PM
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Default RE: How many layers of 4.25 ounce glass is needed for a cowl

30 minute epoxy makes for a pretty rubbery part. A true laminating epoxy will make a more rigid feeling part. Also most resins don't start to really polymerize until it cures for 24 hours. In my testing most room cure epoxy resin don't reach maximum stiffness until 6 or 7 days.

I would think that 2 or 3 layers of the 4 ounce would be adequate...unless you dork it a lot. If there is lead in the nose of your plane, then you can do a beefier layup and remove some lead.

Adam
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Old 08-17-2011, 09:15 PM
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Default RE: How many layers of 4.25 ounce glass is needed for a cowl

thanks soarrich and wyowindworks
I will buy laminating epoxy and add one more layer
I can always add reinforcement if I need to after the cowl is cleaned up.
The project this is part of is here
http://www.rcuniverse.com/forum/m_10...m.htm#10675596
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Old 08-18-2011, 06:25 AM
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Default RE: How many layers of 4.25 ounce glass is needed for a cowl

Also note that the shape of the glass, like curves ,bends, and humps increase the "stiffness of those immediate areas and help support flat sections. A flat sheet is not the best method to conclude that the glass is too pliable. Also note that your fire wall is really playing a big role in keeping the cowl shape.

As mentioned earlier, correct resins will also play a big role.

I use west systems resin in all my composite models. I have a BF 109 all composite running a fully cowl enclosed nitro engine/muffler and the resin has yet to soften from the heat generated. Even after flight with no air circulating.

You can even look into post curing with heat. this will add additional stiffness. Search online for methods that suite your needs.

Steve
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Old 08-25-2011, 07:42 AM
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Default RE: How many layers of 4.25 ounce glass is needed for a cowl

Hi flyingagin,

I built the cowl of my Giles using laminating Epoxy, WEST SYSTEM. One layer of 2-oz and one layer of 6-oz. Since you have 4-oz cloth, I would use just two layers. The cowl I build has a lot of flights now and the final result was a semi rigid cowl. It is still flexible at the long sides but never rubbery. Flexible enough for not craking or breaking.

My 2 cents.

Pedro
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Old 08-25-2011, 08:57 AM
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Default RE: How many layers of 4.25 ounce glass is needed for a cowl

Hey thanks to all the answers. I will use laminating Epoxy, and just 2 layers of my 4.25 ounce cloth. The mold is ready to seal and then lay up. I have a ply nose ring in it.
I ended up having to remake the make the original mold. After much effort I found there were a places that just did not match up to fuse correctly and the lack of a ply nose ring concerned my, so I made a new one. I like the shape of this one a lot more. I changed how I roughed out the foam block. Did it while it was attached to the fire wall. I will say it so far has been a learning experience.
I up dated my construction thread on this airplane to include redoing the mold.
http://www.rcuniverse.com/forum/m_10...m.htm#10675605

Thanks again all for all the help.
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Old 09-25-2011, 06:28 PM
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Default RE: How many layers of 4.25 ounce glass is needed for a cowl

Well I made the cowl. There is still a lot of work to do on it, but here is what I got at this point.
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Old 09-26-2011, 05:20 PM
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Default RE: How many layers of 4.25 ounce glass is needed for a cowl

Looks good!

Nothing better than reviving an old airplane.

Bliksem
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