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Hi Guys

I need a little direction, I'm planning on making a fiberglass cowl. What should i use for the plug? Foam, wood, I was thinking on using a plaster for the mold but i hear that plaster of Paris is not the plaster to use, so which one should i use. the cowl is a pretty simple oval shape something like a PT 19 cowl. Should i do it in two pieces or one? and are there any good books on this subject. I would really appreciate any help

thanks Louie

Mike James

If you do a search right here on RCU for "fiberglass cowling" or "cowling mold", etc., you'll find a variety of discussions we've had here in the past, some of which include links to web sites with tutorials, etc..

Check these composite suppliers' sites for online info and tutorials:

http://www.fibregast.com/

http://www.freemansupply.com/

http://www.acp-composites.com/

https://www.cstsales.com/Epoxy_&_Mol...est-system.htm

I've got a tutorial on my site as well, showing how to make a cowling plug and mold, from a recent project. http://homepage.mac.com/mikejames/rc...t_cowling.html

It doesn't matter what you make your cowling plug out of, as long as it's chemically tolerant to what you're going to put on it, and as long as it's durable enough for your needs. Whether it should be one or two parts depends on what you need, attachment-wise, and how easy (or difficult) it would be to make the parts. Sometimes a small cowling is easier in a one-piece mold, but that's up to you.

You could also use the "one-time-only" lost foam method, where you make a plug from foam, glass it, then remove the foam afterward. It's a little more work on the exterior finish when you use a male "mold", but is simpler if you only need one part.

hnesitd1

I just finished making a fiberglass cowl for a bi-plane. The kit's cowl was a segmented (3) piece unit that looked extremely flimsy. I used the kit's cowl to produce a female mold out of plaster-of-paris - worked fine but I hear that something called UltraCal is more ideal. There are (2) types of resins; Epoxy and polyester. Poly is what I used but be advised it stinks and does not have a long pot life; mix in 1 ozs amounts and in a well-ventilated area. Epoxy is just the opposite but costs more. As you can imagine, the fiberglass wants to stick to the mold - I waxed the mold and then sprayed on PAM (wife uses it, eh?). Something called PVA is what the industry uses - stay clear of spray-on parting agents - you'll never be able to remove it from the finished product. I used 3/4 oz cloth, cut in strips and laid into the mold; this weight follows the contours nicely. After the 3/4 oz dries, lay in 2 oz cloth the same way. For the cowl I fabricated, this is where I stopped laminating and the finished product seems plenty strong. I used a dremel for trimming. For my next project I intend on starting with Gel-Coat - reputed to really help the finish.

Scott Smith

My Feedback: (4)

Just curious why you say this...PVA is water soluble and my experience (although limited) is it washes right off. Not only that, when trying to get the finished part out of the mold, a little water practically makes the part jump out (I did this just this morning with a canopy and it literally popped out with no effort)

Scott

hnesitd1

A misunderstanding - PVA supposedly is great stuff. However, my first experience with parting agent was a sample spray-on substance (NOT PVA). It worked great but I defy anyone to paint over it - I could not remove it using acetone, etc. Again, I understand PVA is great and as you say, water soluable, eh?