Microcrack in spar dimple

[Captain Sacto]

So, I?m having a great time, riveting my front VS spar to the skin (7A). As I look approvingly inside at the line of shop heads beading along the spar flange, I notice that one of the little volcano-shaped dimples has a teensy crack (starting where the shop head was a possibly slightly over-driven). I think that it?s too tight a fit to get y?all a decent photo.


Two questions for the learned folks here.

First, is this common? Might there a certain percentage of spar flange dimples that might have a short, hairline crack?

Second, what to do? I honestly think that if I try to dig this out, it just might turn out with more defects, or at least not as strong, than if I just let it be. I?d genuinely hate to drill out all those rivets (a few dozen), and I?m not sure what I?d do with the flange once I removed it.


All comments and suggestions welcome.

Thanks in advance - - Tom in Sacramento

[Geico266]

You could drill out that rivet and "do over".

[TerryWighs]

Personally, I would leave it alone and build on....and be more careful with hole preparation. If you really really have to do something with it....carefully drill out the microcrack.....and put an "oops" rivet in its place.

[grantcarruthers]

I'd replace it with a -4, 0.02 cents.

Micro crack turn into real crack at wrong time, maybe, maybe not??????? Easy fix going to -4 with clean uncracked hole.

[Captain Sacto]

All great suggestions, and thanks!

For some added info (and in the interest of full disclosure) this was a "do-over" and it was a -4.

When dimpling the skin, I moved the c-frame slightly and got an off-center dimple. I corrected this by expanding the hole, and enlargening the dimple with a larger pop-rivet dimple die, matching the holes and dimples.

I'm thinking that the larger rivet, and expanded dimple diameter stressed the flange hole edge enough, so that slight over-driving caused the dimple to get a hairline crack at the hole.

So, I can't "oops" my way out of this, I'm afraid.

I'm now thinking of trying to put a teensy "stop" hole at the front of the microcrack. (It is not in a convenient place to try this, however, and visibility while drilling would be poor.) I also think (make that rationalize) that most airplanes flying have such undetected cracks, and that trying to make this one better might mess up a H S subassembly.

I'll experiment with the stop-drilling technique before deciding to just build on.

Thanks again for the help!


- - Tom

[thallock]

Tom,

With all due respect, without a picture, there is no way that anyone can give you any useful advice on this. If it is a visible crack, then it probably needs to be fixed. I agree with Grant, here, small cracks turn into big cracks. However, if it is truely a "micro" crack, then maybe build-on is good advice. It all depends upon what "micro' means. Honestly, if the crack is visible, then it is not really a micro crack.

Tracy.

[cytoxin]

a teensy stop hole may not be any better than the teensy crack. if your gonna stop drill it then do so in a way that is acceptable....i would call vans for sure.

[Norman CYYJ]

Crack in a spar. Either fix it according to acceptable air worthiness standards or scrape the spar and replace it regardless of how much work it will take.

[brenegan]

Originally Posted by thallock

Tom,

With all due respect, without a picture, there is no way that anyone can give you any useful advice on this. If it is a visible crack, then it probably needs to be fixed. I agree with Grant, here, small cracks turn into big cracks. However, if it is truely a "micro" crack, then maybe build-on is good advice. It all depends upon what "micro' means. Honestly, if the crack is visible, then it is not really a micro crack.

Tracy.

Ditto.... and another theory is this could just be the anodizing? But take a picture and check with Vans.

[cytoxin]

Originally Posted by brenegan

Ditto.... and another theory is this could just be the anodizing? But take a picture and check with Vans.

unless things have changed, the tail feathers are not annodized.