More peelply and plastic questions

[rhofacker]

I've used a similar technique on "stich-and-glue" boats. Basically you cut a series of pannels from plywood, stich them together along the edges with safety wire, flox the inside corner and put fiberglass tape over that. Let cure. Remove all the wires and cover the out side of the boat with fiberglass cloth and epoxy. Sanding as needed, of course . Now, the peelply and plastic works very, very well over the flat and/or simple curves of plywood and I would expect it to work as well on flat (like bulkheads), or simple curves (like the wing) surfaces. But how do you do it on compound curves or concave surfaces? the plastic wrinkles around the compound curves and in the concave corners

[Jon Matcho]

But how do you do it on compound curves or concave surfaces? the plastic wrinkles around the compound curves and in the concave corners

You wouldn't be able to use the Plastic Pressure Bagging technique here, but you might be able to use peel ply in thin strips. In either case, it may be best not to use either and just do a little sanding. Chances are you won't need peel ply in these areas, and your only bagging option would be Vacuum Bagging. You could consider sandblasting.

 

Peel ply also adds weight, and so I am actually considering peel plying ONLY the seams, and hand-sanding where necessary (or lightly sand blasting with this dream machine).

 

With the little experience I have right now, I feel the anti-sanding rhetoric may be a bit outdated. Get yourself a set of the sanding tools from www.permagrit.com, available everywhere, and see what I mean. They have every shape imagineable, are indestructible and have so far made sanding a non-issue for me.

 

Of course, these are my "famous last words".

[Marc Zeitlin]

.....Peel ply also adds weight.....

You state this as if it's a well known fact. Actually, there is substantial disagreement as to whether PP adds weight or saves it. I'm in the "saves it" camp, and AFAIK there are NO controlled studies that prove the claims one way or the other. Be careful stating categorically things that aren't so, or at least are not proven to be so.

 

"Some folks claim that PP adds weight" would be an accurate statement, as would the opposite.

[Jon Matcho]

Actually, there is substantial disagreement as to whether PP adds weight or saves it. I'm in the "saves it" camp, and AFAIK there are NO controlled studies that prove the claims one way or the other.

Agreed. I should have indicated my statement to be my opinion (as well as Burt Rutan's), and that I'm in the "spends it" camp.

 

How's this for the controlled experiment:

• foam, glass, squeegee treatment
• foam, glass, squeegee treatment, peel ply treatment
• foam, glass, squeegee treatment, pressure bag treatment
• foam, glass, squeegee treatment, peel ply treatment, pressure bag treatment
• foam, glass, squeegee treatment, vacuum bag treatment
• foam, glass, squeegee treatment, best non-vacuum bag treatment, sandblast treatment

Controls would be a 12" x 12" foam piece, micro the foam (same volume for each piece), 1-ply of UNI glass, same epoxy type (with volumes driven by the needs for each experiment #), pieces trimmed and cut to exact dimensions.

 

Ideally the pieces would be made larger to get a better contrast of weights, but 12" x 12" is all I could afford throwing at this right now (unless I make shelves for that fiberglass bookcase I designed...). Regardless, I cannot perform tests 5-6, so I'd gladly let someone else do this in order to prove Marc wrong.

 

In the end, proving Peel Ply = Added Weight is not on my top list of priorities and I may do as everyone else has done in the past -- go forward with what I feel is the best technique to produce the lightest parts. With all that said, I'm afraid to weight my seatback bulkhead tonight and compare against the Cozy Builders Web stats.

[Dan Tomlinson]

I'm firmly in the Peel-Ply = Lighter camp.

 

As are many experts - who advise "against" peel ply cloth!

 

Peel Ply REMOVES epoxy from the layup and may remove too much and make the layup too dry - so you have to be careful with it!

 

Several composite books suggest 100:100 by weight (EPOXY:GLASS) is best,

with MGS and warm I can easily achieve 80:100 without trying hard,

after peel-ply, 68:100 can be checked by weight after peeling - but 65:100 looks dry!.

 

Weigh your cloth, your epoxy, and foam if you want an accurate basis, OR

just weigh or calculate the cloth weight, mix the same total weight of epoxy (use part for micro) and you will almost always have leftover epoxy!

 

If you then squeegee to where you are "done" and have got it all out, add peel-ply (weighed of course) and squeegee it down.

 

Weigh your peel-ply after you've removed it, and let me know how much weight the peel-ply "added" to the layup!

 

Use the grams scale for accuracy, or a more accurate scale if you can.

 

/dan

[rhofacker]

I've got a composit learner's kit on order from Aircraft Spruce. I was actually thinking about making two of the desrtuctive test samples Burt tells how to make in his book that I got with my veri eze plans. Make one with and one without the peel ply/plastic routine. weigh them both and break them both. I'd sure like to be confident in a process used throughout the project

 

weighing the peel ply before and after should tell me how much resin I pulled off...

[Jon Matcho]

I thought about this topic while laying up my F28 and F22 bulkheads this weekend. I have come to realize that major factors for part weights must involve technique, particularly:

• Micro-slurry density (affects how much epoxy soaks into the foam)
• Micro-slurry partial cure (if it's wet, it may dilute a bit with the incoming epoxy; it it's tacky, it may stay where it's at)
• Optional non-glass coverings (peel ply and/or plastic)
• Squeegee techniques (from light-to-hard pressures)

Personally, I've found that I like to keep my layups on the damp-wet side, apply plastic and squeegee fairly agressively. Ideally, I will pull the plastic off and let cure, unless the part needs to cure flat while weighed down. Pulling the plastic at layup-time lifts a residual amount of epoxy from the fabric voids, as well as allowing inspection for areas that have become too dry. If too dry, I just stipple a small amount of additional epoxy.

 

I do think that using peel ply and/or plastic reduces weight over glass alone, but suspect a small weight advantage of using plastic and peeling off at layup-time. Which, however, isn't always possible when parts need to be weighed down -- use peel ply AND plastic, with the plastic here functioning as a non-stick surface.

 

If it sounds like I know what I'm talking about -- I apologize in advance. I don't.