Crack in F671 skin (fuse top in front of canopy)

[java]

In my recently purchased RV6, there was a crack in the F671 skin. It is in front of the canopy, mid-line of the fuse, just before where the cowl joint is.

There is a stiffener (F643 channel) along the mid-line of this skin. In my 6, this stiffener terminates before meeting the firewall, and wasn't attached to the firewall. It was cracked at the last rivet (most forward) of the stiffener.

The crack occurred before I bought it (and yes, I was aware of it). The builder stop drilled it, but did so through the paint from the outside and so didn't "hit" the end of the crack (hard to see through the paint) and it propagated. I stop drilled it again from the inside (no paint to hide the end of the crack), and riveted a piece of angle in to tie the stiffener to the firewall (there was way too much flex at the end of the stiffener without it being tied into the firewall... it could be seen vibrating in flight at high RPM's).

The pic shows the original crack and stop drill before I completed subsequent repairs. You can just see the joint where the cowl starts on the left side of the pic, and the canopy is out of the pic but to the right.

My plan, now that I know I have the ends of the crack stop drilled accurately and have firmed things up with tying the stiffener into the firewall, is to watch it and if I have to, put a patch on it later if it keeps going. I'd rather not mess up my nice paint though!

Anything else I should consider?

Has anyone else seen this problem?

[Pat Hatch]

Just a suggestion: you might want to have your prop dynamic balanced if you haven't already. Can't think of any other reason for there to be that much vibration in this area. Just knowing how much out of balance there is might be a clue about what is going on.

[krw5927]

I'm certainly no expert, but I think I heard somewhere that stop-drilling was best performed beyond the end of the existing visible crack, letting the crack propagate into the stop drill. Something about the grain structure at the end of the crack may already be disturbed beyond the visible portion of the crack?

Welcoming the chance to learn from all the experts out there!

[jbagley]

I've heard of this happening with another builder in the local area here. He did the same as you.

I was advised to rivet that support to the firewall and did so before the skin went on. It still has more movement than I would like, but as long as it doesn't move in flight then it should be ok?

We'll know in 3 or 4 weeks. :-)