Scratch question

[HBpilot]

Did a search on scratches but surprisingly did not come up with a lot of info.
The process of fixing has been explained pretty clearly, but I am still trying to define, what is a bad scratch and how much you need to take care of it ? Does the scratch needs to be gone, meaning you can't see it, or does it just have to be smooth ? What about minor scratches, do you have to take care of those too ?


Thanks.

[Bob Kuykendall]

Originally Posted by HBpilot

Did a search on scratches but surprisingly did not come up with a lot of info.
The process of fixing has been explained pretty clearly, but I am still trying to define, what is a bad scratch and how much you need to take care of it ? Does the scratch needs to be gone, meaning you can't see it, or does it just have to be smooth ? What about minor scratches, do you have to take care of those too ?

It all depends on what is scratched, and where. AC43.13 offers some good guidance for the most critical items (canopy and transparencies, propeller blades, highly stressed aluminum parts).

[HBpilot]

sorry I should have been more specific. I am just starting the project and working on the vertical stabilizer.

[Bob Kuykendall]

Originally Posted by HBpilot

sorry I should have been more specific. I am just starting the project and working on the vertical stabilizer.

Ah, thanks, that helps narrow things down.

In general, search the forum on the word "scratch" and the name of the part you are working on.

In specific, this is the thread that comes to mind as regards good guidance for how to dress out scratches in highly-stressed components. See Dan Horton's diagrams, they're a good explanation of what you're looking for when dressing out scratches in critical parts.

For scratches in the middle of a skin, away from edges and rivet holes, unless they are very long or go through a substantial percentage of the skin thickness, the advice is usually "build on." But it is best to approach them on a case-by-case basis. You'll find it easier to get specific advice if you post a photo of the scratch in question.

Scratches to be especially careful of are those in the edges or corners of cyclically stressed components (shear webs, spar caps and flanges, etc), or passing through fastener holes of same.

[HBpilot]

Thanks. I didn't see this thread. Great info.