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Slightly elongated hole

Everwild

Well Known Member
Elongated hole

Hi all. I was drilling one of the upper attach holes on the rear spar of the vertical stabilizer to 3/16". When I broke through the spar cap, the assembly walked up the drill, slightly elongating the hole on the forward side of the spar doubler. The hole is still round on the aft side on the spar cap where the AN3 bolt head will ultimately insert and rest. So it's only elongated slightly on the forward face of the VS rear spar assembly. The elongated side will end up in the middle of the sandwich when bolted to the tail cone.

I think a slight elongation will remain even after match drilling it to a #12, called for when attaching it to the completed tail cone assembly later.

So, continue on with the assembly of the VS, and live with a slightly elongated hole here?

Or can / should I go up to an AN4 in this location thus removing any elongation? I wasn't sure about edge distance where the rear bulkheads and flange on the aft deck all come together to receive the AN3 bolt from the rear spar of the vertical stabilizer.

I would be going from a AN3 3/16" to AN4 1/4" bolt which is 1/16" wider or only 1/32" closer to the edge of the tailcone assembly in that area.

(Post was edited with a better photo)
 

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Elongated hole

I did something like that on the main spar and I checked with Vans support, they said it was OK to have slight elongation in that situation since the bolt is working in tension, and to not enlarge it to the next size bolt.
Based on the picture yours doesn't look too bad, especially if it is on one side only.
 
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Yeah, it's not horribly elongated, but I have no idea how important the tolerance is for this particular attach point. I was thinking about the forces put on this bolt. When you stomp on the rudder, it seems like there's lateral force on the VS rear spar as well as forces in tension. All of the other bolts holes are good so I don't believe that there will be any tendency to moved laterally + the compression forces holding a sandwich of 6 pieces of aluminum together but want to double check.

Sent a note into Vans but was wondering what feedback I would get from the group.

I don't want to continue with the VS build if I need to scrap this spar (again) and start over. :( Or at least replace the spar doubler as the spar and spar caps are still salvageable IMO.

I've been down this road before though and trying to match drill a new doubler to the existing caps, spar and hinge that are all already match drilled can leave me with a bigger mess than this one elongated hole. I messed up a countersink on my first VS spar, tried to put the match drilled parts onto a new spar and buggered it all up. So this goof is to a second set of new VS spar parts. Maybe the third time will be the charm?
 
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Vans said there is not enough edge distance to go to an AN4 bolt, but in this specific case I do not need to replace.

That said, due to OCD a new spar doubler has been ordered. The spar caps and spar have only a very slight elongation which should be minimal when I final drill it to #12. The spar doubler is the most screwed up. It should be fairly bungle-proof to cleco and re-match drill, but somehow I managed to mess this hole up so...

The learnable moment here is to always secure the work piece regardless of size. I've been drilling the spars and spar doublers for the HS and made it through all of the holes without any issues.

Frustrating, challenging and fun all at the same time.
 
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Use of double margin drills and clamping things tight will help prevent that.
 
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Use of double margin drills...

Didn't know such a thing. Will grab a set and see how they go!

I've been drilling things small where the pilot hole isn't already final size and using reamers everywhere possible. Bought them for #8 and AN3 finished hole sizes vs using a drill. I find the finish and control is way better with reamers.
 
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