ORIGINAL: doxilia
Good stuff.
I made a "pull tab" cut into one of the ply plug formers with the idea that once the layup has cured, I could simply pull the plug out of the cowl bottom. Is some "wiggling" usually required with the wax and PVA or will the cowl simply slip off the plug?
I also want a light but firm part. I plan to put a couple of lite ply rings at either end, the front to provide a little thickness and a contour to open the front to (I realize this one is usually not needed) and the rear to keep the shape and provide a flush mount point to the fuse (possibly with magnets but likely screws). I was thinking two layers of 2oz cloth followed by a top layer of 3/4 oz to close the weave. How does that sound?
David
Suggestion... If you have the male mold ready but not quite finished yet, you can do a quick finish job with adhesive backed teflon tape. Just stick it to the male mold, smoothening as you add more pieces. For simple molds, I use 2" wide material and for more complicated, I use 3/4" wide, striping the tape if you will. You want a reasonable surface underneath that won't telegraph too much
The cured epoxy will no stick and it pops right off with minimal effort. But before you pop it off, sand it and prime it at least.
As you suggested, 2 layers of 2 oz with a top coat of 1/2 oz will produce a reasonable outcome. It will be heavier than necessary but would be hanger rash proof too. Vintage models only need maybe 1 layer of 2 1/2 oz and maybe 1 layer of 1/2 oz as fill for canopies or chin cowls. Some strips of balsa layed inside maintain the shape. You can get a little fancy if you want by laying the second layer on bias. Produces more stability over time, but isn't absolutely necessary
I make fairly large canopies for the EF 78" Extra for example. Not apples to apples since mine is a cavity mold but it is close in comparison. The canopy is laid-up with 1 layer of 1/2 oz as fill and 1 layer of 3 oz, close weave glass. This is very large compared to vintage canopies, about 9" wide, 19" long and 7" deep. I lay in balsa strips to hold the shape while the canopy is curing. The cavity mold also allows me to shoot the primer first into the mold. The ready primed and otherwise readyto install canopy comes in at less than 5 ozs. Balsa-glass composite done this way, is surprisingly stiff and strong but super light