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Poly Fiber Fabric Overlap Seam

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Posted

Has anyone effected this type of fabric repair and can share your results/thoughts?

I have read the Poly Fiber Manual regarding overlap seam repairs on leading/trailing edges and unsupported areas such as fuselage sides (my application). I know the recommended procedures mentioned there for E-AB and in AC 43.13 for certified aircraft. However, I can not locate any youTube or builder videos actually detailing the procedure and showing end results.

So, some additional questions come to mind:

  • I am particularly interested in repair procedure/tips with 2k poly topcoats (vs. PolyTone) and paint blending techniques.
  • After sanding off the 2k topcoat, does removing silver down to pink w/ M.E.K. result in the original fabric 'tautening' being reversed?
  • Should one or both (old or new) fabric layers being joined be tautened prior to gluing and at what heat setting?
  • Should fabric reinforcing or cover tapes be fully or partially pre-shrunk prior to application?

Again, any insight is appreciated. I have already decided my next project will be PolyTone...

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Posted (edited)

Sanding, stripping ,poking, etc. around a hole tends to make the fabric slack. And, if you are in the middle of a unsupported bay, the patch will tend to be a bit on the saggy side (at least when I've done it.).  Shrinking a patch needs to be done carefully to avoid heat loosening the seams - but I would stick it in place first then shrink enough to take up the slack.

I would not think you would want to shrink the reinforcing tape.

Big area? Small area?

The only video I have is one where I replaced the fabric over an entire bay.

Edited by Geoffrey Thorpe

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Posted

Not patching a hole, replacing approx 30"x36" sections of fabric over the fuse sides aft of the doors. Three sides terminate at structure so no prob there, but the one vertical seam from lower to top longeron on the fuse sides require an overlap seam. I'd be interested in seeing your video if it deals with joining a sheet of new replacement fabric to existing old fabric still in place using an overlap seam. Thanks.

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Posted

I was just looking in my Poly Fiber manual, and it says on a large patch of 8" or more in diameter, you need a 2" overlapped seam.  That means 2" wide old fabric under 2" of new fabric in the seam.  They also say that it may require a 2" wide finish tape centered over the seams of the patch.  I would take that last sentence to mean center the tape on the outside edge of the new fabric.  Then there would be 3" of glued fabric on the repair.  This info applies where you aren't glueing patch edges to structure.  In my opinion, with that big a patch, I would think your fabric should tighten up well enough when you shrink it.  I would try not to have any excess material in the patch, pull all the wrinkles out of it as much as possible.  YMMV.  JImChuk

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Posted

Thanks Jim, I have the book and understand the min fabric and tape overlap requirements. Unfortunately there's very little additional 'how-to' detail beyond the requirements and I can see some potential differences on how to approach a large hole patch vs. joining two fabric panels together. I have some extra fabric and PolyTak thanks to another Jim (aka. Neloner), so some experimenting is probably in order.

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Posted

 

Not patching a hole, replacing approx 30"x36" sections of fabric over the fuse sides aft of the doors. Three sides terminate at structure so no prob there, but the one vertical seam from lower to top longeron on the fuse sides require an overlap seam. I'd be interested in seeing your video if it deals with joining a sheet of new replacement fabric to existing old fabric still in place using an overlap seam. Thanks.

So you have room to do the shrinking - I suspect that you won't have any issues at all. If memory serves me  correctly, that's about what I did on the wing that I did not video. You can put a little heat on the overlap seam if necessary - again from memory - I think that 250F does not melt the polywhatever. I used parchment paper where I had to iron over existing polystuff to keep the iron from sticking. The video I did had ribs / leading /  trailing edge on every side. fwiw https://youtu.be/F02Qkl7VRck?list=PL3ea3YrO-K5hlHDwFTh4KCwlKzn8BrDQE 26 minutes of your life you will never get back. You have been warned!

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Posted

Thanks Geoffrey. I actually did watch all 3 of your vids a while back, which I did find helpful! And, glutton for punishment that I am, I went back and re-watched the section where you did an overlap seam on one of the wings. Yes, that is pretty much what I am doing. One difference is that my existing fabric edge, where sanded down to bare fabric, is no longer flat and taut. It is wavy and wrinkled, not with creases but rather simply seems to have lost the original tautness. That is one reason I was wondering whether I should put an iron on that old fabric edge to flatten/tighten before gluing the new fabric panel to it. In my mind, as you note, there should be more than sufficient new fabric to pull the whole area tight but that might help prevent any potential unevenness of two unlike fabric conditions being shrunk together.

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Posted

If the old fabric wasn't shrunk to 350 degrees originally, you might get the wavy edge to shrink some more by going up to that maximum heat setting.  I would try at lower temps first, and work my way up.  If you don't go over 350 degrees, you shouldn't hurt the fabric at all.  JImChuk

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Posted

Jim, my thoughts exactly. My new Black Baron iron arrived yesterday so we should know pretty quick. :)

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