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  #1  
Old 03-19-2017, 10:52 AM
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NorthernRV4 NorthernRV4 is offline
 
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Location: Prince Edward Island, Canada
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Default Really bad morning

Today started really badly. I am at the point of building my left fuel tank where I'm drilling the attach screw holes from #30 to #21 so I can prepare for dimpling. To my horror three of the inboard most holes of the aft line of #8 screws nicked the spar bar. I know this is BAD but just how bad? I'm sure tech support will have nothing definite or good to say about this. As best as I can measure the depth of the nick, the worst is about 0.001" - 0.002" at the very most.

Two questions that I need advice on

1. Has anyone encountered this same scenario? Is there a reasonable fix? I can certainly smooth the nick out to remove any stress concentrations. Yes this will reduce the strength of the spar to some unknown degree but it seems rather tiny.

2. Since there is NO room for a dimple I think machine countersinking is the only option with a K3000 corner type nut or possibly another style.

Untitled by James Soutar, on Flickr

Untitled by James Soutar, on Flickr
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Last edited by NorthernRV4 : 03-19-2017 at 12:34 PM.
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  #2  
Old 03-19-2017, 11:11 AM
pa38112 pa38112 is offline
 
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Location: Clarksboro, NJ
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I will let tech support answer your question. I'm just responding to lend you some moral support. - So sorry; but you will get through it !
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  #3  
Old 03-20-2017, 06:42 PM
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NorthernRV4 NorthernRV4 is offline
 
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Well Sterling in tech support made my day a little better today. He suggested that since the nicks were not very deep and they were between the rivets that I could buff them out and build on. This was good news!

Now I only have to worry about how I'm going to get nut plates in there. I have a little leeway on all but the inboard most hole since the taper of the bar starts to give a little clearance. I will have to grind off a bit of the nut plate but I can get a little wiggle room out of the CS too I think. It's going to be tight but there is light at the end of this dark dark tunnel.

Any suggestions on nut plate options are appreciated.
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Old 03-20-2017, 07:28 PM
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wirejock wirejock is offline
 
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Location: Estes Park, CO
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Default Build on

Glad you got the good news. Now invest in some drill stops.
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  #5  
Old 03-20-2017, 08:15 PM
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snopercod snopercod is offline
 
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Quote:
Originally Posted by NorthernRV4 View Post
Now I only have to worry about how I'm going to get nut plates in there.
Maybe the one-eared nutplates would work?
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  #6  
Old 03-20-2017, 08:42 PM
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az_gila az_gila is offline
 
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Quote:
Originally Posted by NorthernRV4 View Post
Well Sterling in tech support made my day a little better today. He suggested that since the nicks were not very deep and they were between the rivets that I could buff them out and build on. This was good news!

Now I only have to worry about how I'm going to get nut plates in there. I have a little leeway on all but the inboard most hole since the taper of the bar starts to give a little clearance. I will have to grind off a bit of the nut plate but I can get a little wiggle room out of the CS too I think. It's going to be tight but there is light at the end of this dark dark tunnel.

Any suggestions on nut plate options are appreciated.
I almost had a similar problem on my -6A spar.

I was lucky and the innermost nutplate just fit under the tapered section but I found that a shorter screw was needed in the location when mounting the tanks. You will find something similar with the screw length, but mounting the nutplate will be OK with small 3/32 nutplate pull rivets.
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  #7  
Old 03-21-2017, 06:00 AM
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NorthernRV4 NorthernRV4 is offline
 
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A drill stop wouldn't have helped prevent this really. The problem is the edge of the hole is right at the bar and any amount of the bit extending through the spar flange was catching the spar. Next tank I may put the aft screw holes 1/4" from the edge instead of the 5/16" that the plans show. Strange really because this was very carefully laid out and I'm still scratching my head as to how this didn't work out. The skin joint line is exactly at shown on the plans.

Yes, I'll be using corner nut plates on these holes with the two rivet holes at the 4&8-o'clock position. The trouble is getting the clearance for the "barrel" of the nut plate. I'm sure I'll be able to make it work.
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  #8  
Old 03-21-2017, 07:49 AM
Michael Henning Michael Henning is offline
 
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When I was getting ready to drill mine, the "little voice " said stop. I double checked, and found I would have been drilling into the spar flange.
A scotch bright pad on a angle grinder will take the nick right out. Be sure to prime that area, as the anodizing will be gone.
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  #9  
Old 03-21-2017, 10:31 AM
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JonJay JonJay is offline
 
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Sounds like you have it licked and are feeling better. There are no general rules for spar repairs so you did the right thing by calling Vans. Where I have seen spar repairs documented in airframe manuals they typically allow damage to be repaired up to 10% of the thickness of the material. I have also seen some that allow no repairs. I suspect Vans engineered a decent safety margin.
Make sure you "dish out"/polish the damage area. The rule of thumb, unless Vans directed otherwise, will leave you with an elliptical shaped polished out area with a width of 5x (transversal) the depth of the damage by 10x (longitudinal) the depth. So, if your drill penetrated 1/16" (yours doesn't even look that deep), your polished out area would be 5/16" x 5/8". This insures no stress risers. Basically you end up with a shallow elliptical dish.
A good reference is AC-43-1b Chapter 6.
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