Mis-drilled the Rear Spar of the Horizontal Stabilizer

[bacstabber]

Everything was going along perfectly as I installed the Horizontal Stabilizer. Good readings all around. I drilled the #30 holes into the rear spar using the holes in the stabilizer attachment bar as guides. Squared the Stabilizer before going to drill the front spar and spacers. Something looked wrong! There wasn't enough attachment angle covering the spacers to drill for the attachment bolts! After reviewing the drawings, I discovered that I had layed the Horizontal Stabilizer on the aft deck upside down. When I read the drawings at the beginning, I had seen only what I wanted to see, not what I needed to see. The top angle has tapered ends, an important clue, thus not enough material to drill.

[IMG][/IMG]

I flipped the HS over and started all over again. I drilled one matching hole into the rear spar, hoping that it would be far enough from the original hole to be useable. What I got was a "figure 8" pattern.

[IMG][/IMG]

There is a good chance that all of my re-drilled holes will yield similar results. The final drill out of these holes will be a #19 hole for some bolts. My questions are:
1. Should I rivet these holes to fill them then re-drill the correct holes or;
2. Do I need to rivet a patch over the holes and then re-drill? If so, How thick does the patch need to be?

Thanks

[Mike S]

Jack, this is definitely a call Vans issue.

[Rivethead]

I'm so glad someone else posted before me. I don't think you're going to skate by on this one. Definitely call Vans. You don't have to be defiant about it though.

[Aden Rich]

You have enough meat on the rear spar and the bars on F-13? to get some good holes in there. Get the thing jigged back up and very carefully drill some #19 holes in there. Once this is done, drill to 3/16". If there is still some of the hole that has some of the cresent from the smaller holes, they could be drilled to 1/4". It's an over kill for the application but there is plenty of edge distance on the spar flange strips. I've seen half moon holes drilled into the firewall on Van's original RV-4 when they didn't like the position of the engine mount. The only big thing is make sure there is no wobble in the hole. Drill good straight holes that are slightly undersized if you have the drill bits. If you need to you can get close tolerance NAS bolts to go in there to fit real nice.

[Mike S]

Originally Posted by Rivethead

I'm so glad someone else posted before me. I don't think you're going to skate by on this one. Definitely call Vans. You don't have to be defiant about it though.

Thanks for the correction.

Dang spell checkers------I shouldnt be trusting them late at night

[bacstabber]

Thank you for all of your responses to my troubles.

I called Van's today and it doesn't look like I'm going to skate one bit on this one.

The Good News is that it can be fixed!

The Bad News is that the engineers suggest that I replace the rear spar stiffeners I don't particularly look forward to drilling out all those rivets and undoing my beautiful stabilizer, it is such a step backwards. Trying to make what I have work by drilling out the holes to a larger hole and still end up with a well drilled hole with good edge distances all around looked less practical after our conversation. In the attempt to drill larger holes to encompass my errors and still fit an appropriate bolt size, I would have to also enlarge the stabilizer mounting bar holes. In the end, should I fail to make acceptable final holes, I would now have to repair not just the rear spar stiffeners but also the stabilizer mounting bars. I will just bite the bullet and replace the Spar stiffeners.

I believe in the building of experimental aircraft for the purpose of Education and Recreation. This time it is purely and education.

Thanks again for your comments...It is nice to be part of such a great community!

[Aden Rich]

I don't know who you talked with at Vans but that spar is fine and drilling up to a 1/4 hole is perfectly acceptable repair. If you are not comfortable drilling, get someone who is and save yourself hundreds of hours of work. If you have to replace anything, I would replace the bars on the fuselage bulkhead. There is only a fraction of the rivets to drill vs the rear spar stiffeners. If you need to make a jig make one from wood in a drill press first, clamp it in place over your already drilled holes. This will help in alignment and guide your drill without it walking around the existing holes. I've seen much worse than that repaired and flying. Whoever you spoke with a Van must not have understood the whole picture here. I would tend to think you have more potential to screw up some holes in your rear spar by trying to drill it out then worry about getting two holes drilled right in the rear spar attach to the fuselage bars. As I stated before, make drill jigs to keep you square to the hole and proceed in incremental steps. If you have to, but some undersized bit at the local bolt shop, just in case. You could also use a long center drill bit to help drill the holes in conjunction with the drill jigs. These are stepped bits and have only about 3/8" drilling area. This keeps augering out the hole down to a minimum. I've seen this situation on rear spar attach fittings on the wing. The holes got off and we drilled oversized with jigs and got some oversized bolts from A.D. Swayne in Seattle. It saved the wing and rear spar attach bars. This can be saved too! Call me if you need any more help. 1-360-560-5822.

[Ironflight]

With all due respect to Aden (yes, it CAN be fixed the way he suggests, if a person has the experience and skills to not make a mistake in drilling. But as you give up edge distance, you use up the extra margin designed into the structure...), I'd go with the factory advice. Why? Well, you're going to be flying that airplane for a lot of years, and seeing how it's an -8, you'll probably be yanking and banking more than a little. And every time you do that, you're going to want to know that by gum, that tail is on there exactly the way the designer intended it to be! If the tail comes off, you're dead - it's not something you can recover from, and you probably won't get out.

You can blow a jug off the engine and still fly. You can have an avionics fire, put it out, and land. You can have your fuel system block up and still glide to a landing. Go ahead and experiment with whatever you want...except Primary Structure. I am a degreed aeronautical engineer, but it's been years since I did structural analysis, so I would trust the guys that designed it to give conservative advice.

That's just my two cents. Do whatever makes you feel comfortable that you will never worry about the tail strength.

Paul

[Jamie]

In the grand scheme of things, it's really a small repair. Just swap it out and build on. You should be able to do it on one evening! Just take that one evening and as Paul said, never, ever worry about it again.

[jmartinez443]

Originally Posted by Jamie

In the grand scheme of things, it's really a small repair. Just swap it out and build on. You should be able to do it on one evening! Just take that one evening and as Paul said, never, ever worry about it again.

First of all, I would listen to the Vans engineers.

This is definitely repairable, though one evening may be a bit optimistic unless Vans approves the use of cherry rivets to attach the new doublers and brackets.

Otherwise, since the doublers are attached with solid rivets, here are the steps he would have to take:

1. drill out all the rivets in the trailing edge of VS
2. drill out all the rivets attaching the ribs to spar and remove rear spar assembly
3. drill out all the rivets attaching the doubler to the spar web
4. drill out/unbolt the elevator brackets
5. prep and match drill the new doublers
6. re-rivet all of the above.

If I were doing this repair I would chuck the entire rear spar and build anew. The difference in parts count is a new spar, and two sets of elevator brackets. The elevator horn bearing can just be unbolted and reattached.