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Old 07-08-2018, 06:49 PM
cacflyer cacflyer is offline
Join Date: Feb 2008
Location: Columbus, GA
Posts: 15
Default HS replacement and fuse match drilling...

What is the best method to match drill pre-existing holes for the AN3 bolts in the fuse for a newly built HS? This seems one of those critical operations with no do over capability. I need to align the new HS perfectly to the existing holes in the fuse, and perfectly drill the HS and not enlarge the existing holes.

The back story is I am replacing a HS that I acquired as part of the kit from another builder. Oh, and also replacing the VS. These are the only two structures not built by me. This is not just for fun, I discovered an issue with the HS that is not easily fixed...


Chris Cook
N261CC Reserved
RV8-QB Finishing
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Old 07-09-2018, 03:37 AM
chris mitchell chris mitchell is online now
Join Date: Jul 2006
Location: near Harrogate, England
Posts: 376

Now that's a challenge. Its not easy just to drill through from below, tempting tho it might seem. THere are two sets of things to align - the holes in the angle, and the location of the angle relative to the fuselage.

First, I would not - at this stage - rivet the angle to the HS - cleco and clamp so that its easy to remove if you need another go.

Second - make up some little transfer punches on a lathe - they could project the same amount as the spacer - IIRC 1/8". You won't get to much of a collar but as they will be single use only that shouldn't matter. Maybe 1/16 collar and 1/16 point. Alternatively make them up so that they go i from below, project 1/8" and then work out some way of locating them securely enough that you can use them as punches and not just knock them out of position.

Put the four transfer punches in place, then position the HS - insert and tighten the bolts through the "ears", securely clamp the front so its correctly located, then give the angle some smart taps at the locations of the transfer punches.

Remove the whole lot, inspect the angle - you shpould now have four punched marks. Drill out starting small and working up. Verify locations of holes before rivetting to HS.

I think I remember that you could, if essential, go up to 1/4"bolts or at least use oversize 3/16 bolts if necessary.

I'll be really interested to see other suggestions. Good luck.

Chris Mitchell

Repeat offender;
RV-8, QB, built, flown 150 hours, sold;
RV-4 - attempted repair, rebuild and remediation - abandoned and junked ;
RV-4 fuselage and wing kits - both at QB stage;
2015-2018 dues paid!
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Old 07-09-2018, 09:48 AM
JonJay's Avatar
JonJay JonJay is offline
Join Date: Jan 2007
Location: Battleground
Posts: 4,149

There is a really good thread on how others have done this but I canít find it. I believe it was Tom Martin. He essentially uses a template indexed to the longeron and transfers the hole locations via the template.
I hope someon can come up with that thread. If it wasnít Tom it was another serial builder who has done it a lot.
Sorry I canít find it.
Smart People do Stupid things all the time. I know, I've seen me do'em.

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Old 07-09-2018, 01:05 PM
SuperCubDriver SuperCubDriver is offline
Join Date: Feb 2011
Location: Germany
Posts: 344

I replaced the horizontal stab on my RV-7 and the way I did it would work on the RV-8 as well.
I clamped a flat 1" aluminum bar to the old stab and matchdrilled the four mounting holes. Then I made sure the for-aft location of the new stab front spar is the same as the old spar was. A little for-aft adjustment of the drilled aluminum bar on the new spar for matchdrilling the spar might be required making sure edge distances according to the plans are satisfied. When matchdrilling the spar the left-right position of the bar must also be checked. After drilling each hole I inserted a bolt to make sure the bar did not move when drilling the next holes. This is one way to do it - worked for me.
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Old 07-09-2018, 02:02 PM
JRichichi JRichichi is offline
Join Date: Mar 2013
Location: League City, TX
Posts: 65
Default Strap Duplicator

I had to do this when I made a new HS because I screwed up SB14-01-31. I used a "strap duplicator" to locate the holes in the F-714 Aft Deck and F710B Angle. The thickness of the strap duplicator almost perfectly matched the thickness of the F-798 Shim. I bought the strap duplicator from Brown Tool. Once I got the HS positioned correctly and clamped to the fuselage (with the strap duplicator in an existing hole) I then used a pancake drill attachment to drill the hole in the HS-714 Attach Angle. I needed the pancake drill attachment to clear the HS-710 Reinforcement Angle. After drilling a hole I took everything apart, deburred the hole and reassembled everything with the strap duplicator in the next hole to be drilled and an AN3-10A bolt in the holes I drilled.

For the VS, if you're starting from scratch, just follow the plans for installing the VS. If you have an existing VS (like me), I needed to drill the four holes in the HS for the F-781 Vertical Stabilizer Attach Plate. The four holes in the F-781 were already there so I used them to locate where I needed to drill into the HS assembly. After getting the VS located properly and clamped in place (it was already bolted into the fuselage via the VS rear spar), I made a small "drill bar" from a piece of scrap aluminum. I put a #12 drill bushing in the drill bar and used the "shank" side of a #12 drill bit to pick up the existing #12 in the F-781. I clamped the drill bar in place and then swapped out the #12 drill bushing with a #30 drill bushing. I drilled the #30 hole, and then just kept swapping out drill bushings and opening up the hole until I got to a #12. After the hole was full size, I installed a AN3-5A bolt to hold everything secure and moved on to the next hole.

Both jobs are very time consuming but I was able to match drill the HS to fit perfectly with the existing holes in the fuselage and the VS.

I hope this helps.


Last edited by JRichichi : 07-10-2018 at 06:40 AM.
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Old 07-09-2018, 02:32 PM
xblueh2o xblueh2o is offline
Join Date: Apr 2011
Location: SF East Bay
Posts: 781

Transfer punch.
Secure the stab in the correct position and then mark the spar from below through the structure with a transfer punch.
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Emp completed except for glass work
Wings completed except for bottom skin and glass work
Fuselage underway
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Old 07-09-2018, 08:27 PM
Rallylancer122 Rallylancer122 is offline
Join Date: Aug 2013
Location: Oconto, WI
Posts: 109

I just did this on our -8. I clamped it in place, and match drilled up from the bottom, installing the bolts as I went. If the plane is complete, getting here is a royal pain as you have to crawl into the tailcone. A smarter guy than me would use drill bushings as lining up the drill with your arms over your head and the elevator bellcrank lodged firmly in your....ahem, inner thigh, is nearly impossible. I would be very leery of using transfer punches or templates. Getting them straight is no easier, and if that bit walks even a bit..... I like the strap duplicator idea if you can get in there. As I was working on completed plane I couldn't.

DO NOT oversize the outer holes!! My holes were oversized from the previous builder, and Vans really had heartburn over it. Apparently that part of the longeron is pretty highly stressed, and a lot of builders already have edge distance issues there. Oversizing the holes just makes it worse. We ended up engineering a strap to reinforce the longeron, but installing that was no picnic (call Eric at Vans for details on this repair). By the way, if you do end up oversizing the holes, the special NAS oversize 7/32 bolts are only available from Spencer Hardware, and they are $40 a piece. My airplane is now stronger than ever, but getting there was not fun.

For the vertical stab you should be able to just follow Vans normal instructions. The F-781 is really cheap, so if you aren't starting with a blank one you may want to consider it as that will make it a no brainer. Depending on the vintage of your stab, you may have to cut this down anyway to fit within the new spar doublers (the old were ones were something like 4" wide, and the new ones 3.75" I's a quarter inch smaller anyway).

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Old 07-15-2018, 07:09 PM
cacflyer cacflyer is offline
Join Date: Feb 2008
Location: Columbus, GA
Posts: 15
Default Thank you

First I want to thank everyone for the ideas on how to proceed. I have made a transfer template based on the old HS. Cut a piece of fairly thick aluminum that fits tightly between then two inboard ribs. And snugs up to the front spar. After clamping marked the center of each of the four 3/16 holes on the transfer template. I first did the outboard holes, carefully drilled the center with #40, then #30, #20 and finally 3/16Ē. I then checked then template against the fuse to ensure the AN3 bolts fit. They did and the template did not move.

Now for the real challenge... fortunately for me the holes in the fuse are round and sized properly. The inboard holes in the HS are oval. Iím not sure how this occurred, but it means I canít locate the center of the inboard holes using the HS.

Tried anyway, sure enough then inboard holes on the template did not align to the fuse. I thought about upsizing the inboard holes, but iím not there yet. Instead. I oversized the holes in the template, by marking the area to remove and slowly expanding and re-checking against the fuse. I finally got the inboard holes in the template to allow the AN3 bolts to pass through the fuse.

I then took four AN460 washers, and attached them to the template using JB Weld, inserting the AN3 bolts through the washers, template and fuse to align the washers attached to the template. Now I have four round holes in my template that I plan to use the transfer to the new HS.

And this is not even the primary reason I am replacing the HS... the old HS has a partially mis-drilled hole for the left inboard AN3 bolt, and a few other issues not done per the manual. Once I complete the task Iíll update here to let everyone know if this was a good idea, or not.

Again, thanks everyone!!

Chris Cook
N261CC Reserved
RV8-QB Finishing
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