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Tiny crack in fuselage skin, drill it or leave it ?

Good day, after rolling the mid side skin (F-1070) l observed a tiny crack above the relief notch, the crack is less than 1/16 of an inch long. Would you leave it as it is or drill a hole (1/16 or less) at the end of it ? Thanks in advance..
 

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Hi Yannick

In my opinion you really need to stop drill that. I don't know if 1/16" is large enough to ensure it doesn't spread but it may be. Is that area under a fairing or anything? If so, I would be inclined to use a #30.

I'm sure others will chime in shortly with more (and probably better) advice :)
 
Hi Yannick

In my opinion you really need to stop drill that. I don't know if 1/16" is large enough to ensure it doesn't spread but it may be. Is that area under a fairing or anything? If so, I would be inclined to use a #30.

I'm sure others will chime in shortly with more (and probably better) advice :)

That sounds like sound advice, per AC43.13-1B 4-59 (a.) drill small holes 3/32 or 1/8 inch at the end to help stop the crack. Or, simply file out the crack with a small round needle file, the technical effect will be the same but it may look neater and more deliberate.
 
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If you don’t stop drill, a tiny crack grows into a big crack. That is the only thing I remember from my material science class on the theory of crack propagation in college but probably the most important.
 
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I would probably enlarge the relief area to include/capture the crack, will not leave it as it is.
 
Recreate a relief

I’d recreate a significant bend relief, going at least 0.03” deeper than the visible crack. You’ll never see it later. 1/8 bit or better. Nice clean edges, please! Just a stop drill at this stage is ...correct, but incomplete, IMO. I might have a similar situation in my 9A....maybe. ;)
 
Would a sheet-metal hole puncher work instead of a drill.

Just wondering if the hole-puncher would set up another failure mode.
 
Had this crack on a 6 built years ago, flush riveted a doubler on the back side. This was back before pre-punched.
 
If you do use a punch, you'll need to ream the hole anyway to avoid the micro-cracks from the punch.

Also, it looks like there are a number of other scratches on the skin. It might be better to leave the blue film on until immediately before permanent assembly. Some people remove the film only where rivet lines go, since the vinyl is decent protection.

Canoe Upright S.jpg

(Ignore the red tape, that was to remind me not to drill that area until the top skin is fitted).

Dave
 
Thanks again, so i won't take the chance and stop drill it now, apply a dab of mastic on the inside face (as it is not subject to further tension or forces l believe a doubler will be excessif). Then fill the hole flush with mastic from the outside when painting time comes. That should do it.
 
What do you expect to accomplish with the mastic?

If you're placing the mastic as a paint prep, there is no good reason for NOT stop drilling the end of the crack.

I know others have observed no propagation, but do you have the same grain orientation? Temp cycles and normal airframe vibration is enough to continue propagation of the crack.

Ounce of caution . . . . .
 
What do you expect to accomplish with the mastic?

If you're placing the mastic as a paint prep, there is no good reason for NOT stop drilling the end of the crack.

I know others have observed no propagation, but do you have the same grain orientation? Temp cycles and normal airframe vibration is enough to continue propagation of the crack.

Ounce of caution . . . . .

I think that Yannick IS going to stop drill the crack, there may be just a tiny language barrier here! :D
 
indeed, l will stop drill the crack. I was then thinking of a way to threat this hole as it will be on a visible part of the fuselage. The idea is to fill the hole with flexible mastic just before paint and for now to "close" the hole with a little dab of flexible mastic on the inside face of the skin. (as you would glue or rivet a small doubler on the inside) if someone has another idea or if the hole must stay unfilled i would appreciate further comments..
 
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