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Old 08-14-2019, 07:40 PM
N546RV's Avatar
N546RV N546RV is online now
Join Date: Aug 2010
Location: Houston, TX
Posts: 765
Default Horizontal stab SB failure, and a question about hole spacing

I've reached the point in my -8 build where it's about time to fit the tail feathers to the fuselage. This seemed like a good time to undertake the service bulletin, prior to making my h-stab and fuselage a matched set, so to speak.

Unfortunately, in the process of drilling the doublers to the spars, a wandering dull drill bit enlarged several holes in the spar channel, too large to even open up for a -5 rivets. So I've resigned myself to replacing the spar, splice angles, and other associated parts. Obviously not happy about it, but I knew this was a risk going into the SB, which is one reason I did it sooner rather than later.

The real question I have is pertaining to all the holes in the spar doublers. I've seen multiple discussions about edge distance issues with these holes - and I ran into issues with this too, but I can see in retrospect where I wasn't careful and caused those problems.

The less-clear concern involves the spacing between the rivet holes in the "main body" of the doubler. Minimum acceptable rivet pitch/spacing for 1/8" universal rivets is called out at .500" center-center, but in many spots the pacing between the prepunched holes in the doubler and the holes drilled using the spar/angles as a guide are far closer than that. There are many spots where it's under .350" and one where it's barely over .300".

The thing is, I don't see how it would be possible to position the doublers such that this spacing issue could be avoided. If I'd moved them further inboard, I think that would have helped, but then they'd interfere with the vertical stab splice plate.

Maybe the solution when I get to rebuilding this is to place the doublers such that the spacing is good as well, and then trim inboard to clear the splice plate? I have that plate on hand, so I can easily use it as a guide.

Mostly I'm just wondering if others have run into this hole spacing issue while doing the SB, since I haven't yet run across a reference to it.
-8 fuselage in progress (remember when I thought the wing kit had a lot of parts? HAHAHAHAHA)
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Old 08-14-2019, 08:18 PM
Rallylancer122 Rallylancer122 is offline
Join Date: Aug 2013
Location: Oconto, WI
Posts: 115

I ran into the same issue. I called Vans tech support and they said trim the vertical stab splice plate. Just make sure you to keep enough edge distance on the mounting holes. On mine there was really no way to even get this close without trimming that plate. I assumed this was in the instructions or drawings for the later kits (I was repairing a plane built in 2000), but maybe not. Call Vans tech support tomorrow to verify.

BTW, re-sparring the stab is not that bad. I had to do that as well after the original builder screwed up the SB. In fact doing the SB gets you about halfway there already. By using a handful of cherrymaxes you can get away without completely disassembling the stab.

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Old 08-14-2019, 08:57 PM
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N546RV N546RV is online now
Join Date: Aug 2010
Location: Houston, TX
Posts: 765

Yeah, while I'm not happy about the re-sparring, it's not bothering me a ton. Part of this is because I feel I'll be able to do much better work on the SB area (doublers and such) this way. It's just going to be a lot of rivet-drilling.

I figure the rough procedure will be:
  • Drill out rivets common to the rear spar and stab skins
  • Drill out rivets common to the rear spar and tip/center main ribs
  • Remove the rear spar
  • Drill out rivets common to the center main rib and skins
  • Drill out blind rivets common to the center main/nose ribs and the forward spar channel
  • Remove the center main ribs
  • Drill out rivets common to the fwd spar and skins
  • Drill out rivets common to the fwd spar and tip ribs
  • Remove the fwd spar

I think that should be enough. It may be necessary to partially separate the skin from the tip ribs to make it easier to extract the spar, I'll work that out as things go along. Really, the main concern I have is damaging one or both of the skins and making this a more expensive repair.
-8 fuselage in progress (remember when I thought the wing kit had a lot of parts? HAHAHAHAHA)
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Old 08-15-2019, 08:55 AM
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SeanB SeanB is offline
Join Date: Dec 2006
Location: Colorado Springs
Posts: 477
Default Yep


I can empathize. I was virtually finished with the SB on a completed HS when I got holes that were over-sized beyond recovery. You are fortunate not to have drilled it to the fuselage yet. That's a whole other set of challenges trying to match drill that and risk yet another HS rebuild.

I ended up just biting the bullet and losing some $$$ by starting from scratch with a new HS, rather than trying to salvage parts of my existing one. was tons easier to install the SB and I'll bet I saved time overall. I know I have a stronger and better part because of it.

Just one other data point. Good luck!
Colorado Springs, CO
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