Scott Smith

My Feedback: (4)

First time making a fiberglass part...

I working on a canopy plug that I'll be using for a fiberglass mold. If it's all "positve angles" from the deepest point, any reason not to do a one piece mold?

My plan is to end up with a 'fiberglass skin' (just the top surface) that I will attach to a ply frame.

Thanks for any advice!

Scott

Mike James

You can make it one piece, but then you'll have to add some sort of frame internally, or a "flange" around the bottom, to attach it to the plane. (If you want it easily removable, rather than just using screws to attach it.) As it is now, it's just "open at the front, back, bottom and sides.

I usually do these left and right, so that a flange can be built into the part, but it's a tradeoff, since you then have a seam to join, too.

Ed Smith

Looking at the picture of your plug I would do this. To the plug I would screw three plates say 3/32 or 1/8 thick aluminum. One on each end and one on the bottom. Then make the glass mold. Ensure you have a flange against the aluminum plates. Before the whole lot is taken apart glue some pieces of ply to the mold flange and drill screw holes through plates into the wood. Take it all apart and cut out the centres of the plates about 1/4 smaller than the inside mold profile. Before you mold the part screw the plates back to the mold. You can now easily reach into the mold and lay up parts that will have a flange on all three open faces. When cured remove the plates and pop the part out.

I mold a canopy shell this way for a mid wing airplane. I do not bother with the bottom as it has to be trimmed to fit the top wing curve. Doing the ends this way gives me a perfect fit with the fuselage. It requires a little more work at the mold making stage but gives a perfect part with no ends or seams to fix.

Ed S

Scott Smith

My Feedback: (4)

Thanks Mike. I need to do three canopies; one for an existing plane (where I hope to save a few ounces over the butyrate canopy), one that's in the bones and one for this winter's project.

I figured doing a ply frame with a glass skin would be the easiest way to get a good fit on all three.

I guess it comes down to am I willing to risk the plug. If I go one piece and its not positive angles, I'd have to start over.

Scott Smith

My Feedback: (4)

I'm with you Mike...good idea! I was planning on adding 3/4" foam to the front, bottom and rear to make it oversized. I like your idea except that one of the canopies needs to go on a finished plane and there some variations between fuse #1 and #2.

I don't think I could get a perfect fit for #1 if the dimensions were set by the mold.

Scott Smith

My Feedback: (4)

Finished my plug today. Went to wax it and my mold release wax has dried up! Any way to rejuvenate mold release wax (it's the green stuff from CST)?

Mike James

The plug looks good, Scott.

Not sure about the wax question.

Ed Smith

I cannot offer much help with dried out wax. For future reference, I always leave the dampened pad in the wax container.

Ed S

Scott Smith

My Feedback: (4)

Thought I'd post some pictures of my progress. I sure hope that plug pops out like they say!

I got 5 or 6 layers of 6oz cloth, do you think that's enough?

Mike James

Plug is looking good.

Mold thickness is personal preference, depending on your needs for rigidity and durability. I usually make mine about 1/4" thick, which would call for about twice as many layers as you have. But if you don't plan on making a milliion canopies, it's probably ok as it is.