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Kevlar hinges tear off

Old 04-11-2023, 04:55 AM
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Default Kevlar hinges tear off

Hi everyone!
I am working on my rc plane project and I stumbled upon some problems with hinges. I want wings to be from carbon fiber, so it was quite obvious to me to make aileron hinges from kevlar. I made sandwich carbon - kevlar - carbon, but it was my first time doing this and kevlar orientation was 0 - 90 degress and it teared when I was moving aileron. For second try I will orientate it 45 degrees, so it should perform better, but I'm not sure what if there isn't something else that may "help" the hinge to tear: I wonder if carbon fiber behaves like knife and cuts kevlar. I'm thinkinkig of leaving space between carbon and hinge, but that would mean I would have to cut rectangle shape in carbon sheet and it will be nightmare.
My question is: can I just assume that the failure was caused by wrong orientation of the kevlar sheet and its thinness (it was 60 g/m2) and do once again sandwich carbon - kevlar - carbon? Or is there something more to do with this hinge?
I'm also thinking about filing the edge of the carbon after laminating, as it would be easier than cutting rectangles inside loose carbon sheet.
Best regards
Old 04-11-2023, 05:42 PM
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I do repairs to fiberglass, CF, Airex wings and fuselage. I have a repair that I haven’t accomplished. I have a “live” flap hinge to repair. It was recommended to me by someone knowledgeable to use Fibre Glast peel ply. It has a skin that is peeled as though there is mold release used. I am planning to laminate it into the wing skin and flap skin with 4:1 epoxy resin. The hinge seam won’t be peeled until laminate. The idea is that you don’t apply epoxy to the hinge and just apply the skins. The peel is like taping the hinge to prevent applying epoxy to the hinge.

Old 04-11-2023, 07:01 PM
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Dacron dress liner material is a great substitute for what is sold as "peel ply". It makes great live hinges. You can learn the hard way by making all the same mistakes that many of us have, or you can go to the "Composite Fabrication and Repair" thread, and post your questions there.

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