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wsimpso1

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Tough to tell from a photo usually. Let's start you telling us what was the original part, and I will now call this the substrate, what the substrate is made of, what kind of damage was to be repaired, how it was prepared, and then what the repair is in terms of type of cloth and how it was applied.

It does look like there was some sort of joint that has had layers of cloth put on over it. There is dense pattern of white spots that do look like the weave of a layer of cloth with what looks like air (the white spots) trapped between layers. In addition, along what looks like a seam, there is an area where the two pieces were not aligned or sanded to blend together well, and a long line of air appears to be trapped between the substrate and the upper layers of cloth.

Why do I mention what appears to be air? Each spot of air is both an area where the substrate and the glass cloth are not bonded to each other AND a shape with an infinitesimally thin edge all the way around that is perfect for growing a crack in the resin. This makes for a part with somewhat reduced strength immediately, but more importantly a tendency to grow a crack into the hardened resin and delaminate the new cloth from the substrate over time and with load cycles. In the Rutan Aircraft Factory booklet Moldless Composite Homebuilt Sandwich Aircraft Construction, a maximum of 10% of any 6"x6" surface may show air in laminations.

If that is air between substrate and laminate or between layers of the laminate, that would constitute an unacceptable airplane structural component. If it is something else, with far less critical issues with failure, it might be acceptable. But you have to tell us what the big picture is and how we came to have this "repair" in front of us.

Billski
 

TFF

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Looks like it’s been sanded down a little too much first. The large white streaks either look like air or something broken underneath. Depends on where this is and if it’s a repair or original. Looks like a repair to me.
 

Foundationer

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Nov 29, 2016
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Thanks everyone. Had to start over! Failed to seal the back properly and air displaced resin around the original crack (sanded to almost nothing). Would have been fine if I was sensible and just did an open layup.

Your replies are almost like a textbook that opened at exactly the right problem billski. I don't remember having a textbook that explained things so well though.
 

Foundationer

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And as to the what's and why's... Putting fully extended brakes away also puts the 15 degrees of flap away. Which I didn't consider while trying to arrest my excessive sink rate. Good job it's a grass field or there'd be more than just the seat pan to fix! I try to make these mistakes just the one time.
 

wsimpso1

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And as to the what's and why's... Putting fully extended brakes away also puts the 15 degrees of flap away. Which I didn't consider while trying to arrest my excessive sink rate. Good job it's a grass field or there'd be more than just the seat pan to fix! I try to make these mistakes just the one time.
Ouch!
 
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