Author Topic: fiber glass cowls (Read 1738 times)

Bootlegger · « **on:** February 08, 2013, 04:39:12 AM »

Guy's I am looking for methods to make a fiber glass cowl, what I want to do is make the cowl over foam (florist, blue, pink and styrofoam like wings).
What kind of epoxy resin and what weight and type of cloth should I use.
This is all new to me also I need all the suggestions and help that I can get...
Thanks a lot...

Robert Zambelli · « **Reply #1 on:** February 08, 2013, 07:17:51 AM »

Gil - I did an article a while back on this exact subject. It was in Control Line World.
If you wish, I can scan or copy the article and send it to you.

I have made around 50 cowls by this method with very good results.

Bob Z.

Paul Wood · « **Reply #2 on:** February 08, 2013, 08:57:53 AM »

Gil,

Do a search in "building techniques" in the June 2011 time frame. I did a three part series of this method while building a cowl for my Nobler. ("Alternatives to carving balsa", parts 1,2,3). I tried to post a link to the articles here, but it would not load. If you need more info, let me know. It's actually a very easy process.

Paul

James Mills · « **Reply #3 on:** February 08, 2013, 11:16:39 AM »

Pat Johnston did an article in Model Aviation some time back on his Mustang. He covered how to build a fiberglass cowl. Sorry, but I don't remember the year.

James

Pat · « **Reply #4 on:** February 08, 2013, 11:21:24 AM »

There is also a very good series on youtube on molding fiberglass, one of the things they make is a model airplane cowl.

Pat

Tim Wescott · « **Reply #5 on:** February 08, 2013, 11:30:48 AM »

Links to "Alternatives to Carving Balsa". Or, at least attempts.

http://stunthanger.com/smf/index.php?topic=22194.0
http://stunthanger.com/smf/index.php?topic=22195.0
http://stunthanger.com/smf/index.php?topic=22196.0

SteveMoon · « **Reply #6 on:** February 09, 2013, 09:04:34 AM »

I also wrote about making fiberglass cowls in my Furias 96 article in
the March 2010 issue of Flying Models.

Steve

Avaiojet · « **Reply #7 on:** February 09, 2013, 09:30:07 AM »

I made this cowling with pink foam.

Spun the foam block on a drill press using a hand held sanding block to shape it. Only because it's round.

Three layers, I believe, of glass cloth and Polyester laminating resin. K&B cloth, back then, eons ago, was available as "heavy," no desinated weight.

Washed the foam away with laquer thinner and scratched the inside up a bit. Also applyed a coat or two of resin before applying any cloth. Sanded before applying the cloth.

Made a few cowlings this way. Works for me.

Because of the way a particular cowling is shapped, that is, curves, angles, cheek cowels, etc., these character lines can add strength, like character lines on a car door.

So, a lighter layup of cloth could possibly be used. If you have interest in saving weight.

Charles

Larry Renger · « **Reply #8 on:** February 09, 2013, 09:49:52 AM »

There is a thread on the 1/2A forum where I made a 'glass cowl for my Zippiee racer. Foam base, 3 hour Epoxy, 2 layers of 4oz 'glass. I used the balloon technique to both smooth the outer surface and squeeze out the maximum amount of resin.

Bootlegger · « **Reply #9 on:** February 09, 2013, 05:37:17 PM »

Bob Z, would you scan and send me that info from the C L W mag? Thanks a lot

Gerald Arana · « **Reply #10 on:** February 10, 2013, 04:42:51 PM »

Robert Z.

Was that the article with the XL condoms? If it was, where do you get "unlub'ed XL condoms"?

I've tried a couple stores (got some funny looks) but they didn't have any "unlubed" ones. Then when I told them (her) what I wanted them for, she had a look of relief on her face.........

Jerry

Avaiojet · « **Reply #11 on:** February 10, 2013, 04:54:26 PM »

Quote from: Gerald Arana on February 10, 2013, 04:42:51 PM

Robert Z.

Was that the article with the XL condoms? If it was, where do you get "unlub'ed XL condoms"?

I've tried a couple stores (got some funny looks) but they didn't have any "unlubed" ones. Then when I told them (her) what I wanted them for, she had a look of relief on her face.........

Jerry

Jerry,

You should have told her nothing else fits, you may have gotten a date.

Charles

Mark Scarborough · « **Reply #12 on:** February 10, 2013, 09:15:32 PM »

I recomend against polyester resin,, if the cowling has to align with other parts,, be aware that polyester resin SHRINKS,, its also very volatile,, and the catalyst is particularly unhealthy for you.

epoxy CAN have some issues, but shrinkage is not one,, nor is killing you,, ( though some people do aquire an allergic reaction to epoxy)

Tim Wescott · « **Reply #13 on:** February 10, 2013, 09:29:09 PM »

I believe that epoxy has better mechanical properties once it's cured, even if you dodge the shrinking problem.

Polyester resin shrinks enough that if you're building a mold for a part, you need to compensate all of the sharp angles: they tighten up as the resin shrinks, so you have to open them all up in the mold.

john e. holliday · « **Reply #14 on:** February 11, 2013, 08:16:06 AM »

Epoxy in my experience is much stiffer than Poly-ester resin.

Gerald Arana · « **Reply #15 on:** February 11, 2013, 09:13:44 AM »

Charles,

My wife won't let me out of the house after 5:00 PM!

And besides, what would I do with a girl the same age as my grand daughter?

I don't plan the computer games very well and my 8 year old (grand daughter) beats the crap out of me, so...........

Jerry

Dennis Toth · « **Reply #16 on:** February 11, 2013, 09:34:14 AM »

Gil,
You asked about the type/brand of epoxy - I have used ZAP finishing resin- this works but it takes a month or so to get ridget. The better epoxy would be the "West System" brand.

The cowls I molded I did a simple foam male mold and put the glass over it then took a large round balloon and pushed it over it to retain the shape.

Another approach was to take the male mold part and make a simple plaster female mold by having a sealed box, put a release wax on the male part then put it in the box and fill with plaster to the level about 1" higher then the part. Once it sets (several hours) you can carefully remove the male mold part. Wax the inside of the mold and lay up the fiberglass, leave about 1/2" overhang around the edge. I used three layers of 1/2 oz glass worked well.

Best, DennisT

Robert Zambelli · « **Reply #17 on:** February 11, 2013, 10:55:16 AM »

Hi, Gil - I just sent you the original word document of the article, complete with pictures.
I hope it's helpful.

Anyone else want it, let me know.

Jerry: Unlubed XL?

?? They would be good if you're making a full size cowl for the Enola Gay!

I just asked for plain old unlubed condoms, as pictured. They work perfectly except for very small cowls, in which case I use a small balloon.

And, I always use epoxy, the thin kind used for finishing. It penetrates and really soaks into the fiberglass cloth.

Bob Z.

Avaiojet · « **Reply #18 on:** February 11, 2013, 11:10:46 AM »

Anyone know what's lighter?

Polyester resin or Epoxy resin?

When my can of Polyester resin is gone, really soon, I'll move over to Epoxy.

Using it does have drawbacks.

Charles

Robert Zambelli · « **Reply #19 on:** February 11, 2013, 11:48:12 AM »

DO NOT USE polyester with condoms - they will dissolve, as will may styrofoams.

Believe me, weight is not an issue.

Bob Z.

Gerald Arana · « **Reply #20 on:** February 11, 2013, 12:47:38 PM »

Bob Z.

No, I just want to try it (molding!) with a Nobler size cowl. I didn't know they would stretch that far.......

Thanks, Jerry

PS: Now I'll look for them. The wife won't care as long as I use them in the garage!

Pat Johnston · « **Reply #21 on:** February 11, 2013, 01:13:45 PM »

My Mustang construction article in MA June 2006 has a section on how to do fiberglass cowls. This is the only way to go for cowls.
Pat Johnston
Skunk Works