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mis-drilled tie down

dbhill916

Well Known Member
Hi guys,

I'm looking for advice as how to proceed from a major mistake. The first thing I did with my new wing spars was mis-drill the tie down extrusion on the upper surface of the L spar. (I got cocky after the 1st 3 and drilled & tapped with the spar positioned such that extrusion was underneath the spar where I couldn't see everything that I was doing. Learn from my mistake!)

The image is a bit blurred, but you can see that the drill was angled toward the surface the extrusion and has surfaced. For the photo, I re-inserted the tap and you can see it in the surface.

So far, I have identified 3 paths to pursue. Easiest (and therefore of greatest suspicion) is to ignore it and use the tie down as if nothing happened. The threads are intact along the upper (as oriented in the photo) and lateral walls of the long axial hole, but probably non-existent on the lower edge of the hole directly under the unwanted opening. As a total WAG, I guess that there's a 30? arc x 1/2" where there are no threads. Is that lack of contact enough to compromise the strength of that bolt? (What is the function of that bolt, anyway? I'm further guessing that it's to suspend the wing in maintenance actions.)

2nd option is to ignore it completely. That is to say mark the tie-down as InOp and never use it.

3rd option is to re-drill with a larger bit and re-tap with larger threads. To ensure good strength, I would tap 2" to obtain a full inch (original spec) of completely engaged threads. Will there be sufficient aluminum to accept the larger bolt?

Any and all inputs on how to proceed are certainly welcome!


IMG_2689.jpg
 
If its on the upper surface of the spar, you can ignore it. The tiedown ring will screw into the other end, on the lower surface of the spar.
 
If the piece is symmetrical end to end you could reverse it. If it's not, for the price and effort I would replace it. I think most of us end up with a couple of unusable parts. Drill and start the tap in a drill press if you can before attaching it to the spar.
 
I'd replace it on ethical grounds.

Here's why. Proper tiedowns are as much about protecting the planes near you as they are protecting your own plane.

Drilling out the rivets won't take long and the part is cheap.
 
I would want to replace it, but since this is an RV-12, the associated issue becomes one of re-setting those 3/16" rivets. Unless you have a heavy duty pneumatic squeezer and experience with this larger rivet size, you may want to shop locally for professional help. In any case, a quick note to the Mothership would be appropriate before diving into the spar.
 
As already mentioned... Is this the one for the top of the spar or the bottom.
If it is for the top, I would just move on. It is very unlikely it will ever be used for any purpose that would apply a high pull load.
If it the bottom position, I would replace it.
 
I went through a few tie-down extrusions after mis-drilling them to the spar on my 9. I would replace, and ask Van's about the option of replacing those 3/16 rivets with bolts if you can't find somebody handy to re-rivet. It would probably be an acceptable repair, as I believe it is bolted on all the other models.

Chris
 
I was never really sure of why we even messed with tapping the top tie down. Unless there's something I'm missing (often the case) it just doesn't make sense.

Bob
 
Drill and tap one end. then come back a week later, pick it up and install it. months later comes time to drill out the bottom skin in order to install the tie down only to discover u screwed up and put it in upside down,,,,,,,,,,,,,,, now if you'd d&t both ends, you'd never know if you installed it upside down................. all is not lost because you can d&t it where it is, but then you break off the tap,,,,,,,,,,,,,,,,,,,,,,,,:cool:
 
I never even drilled or tapped the top one after researching it here. Couldn't see a need for it...the wings are removable after all.

Label me a slacker I guess.
 
Drill and tap one end. then come back a week later, pick it up and install it. months later comes time to drill out the bottom skin in order to install the tie down only to discover u screwed up and put it in upside down,,,,,,,,,,,,,,, now if you'd d&t both ends, you'd never know if you installed it upside down................. all is not lost because you can d&t it where it is, but then you break off the tap,,,,,,,,,,,,,,,,,,,,,,,,:cool:

It comes pre-installed...although in the beginning that may not have been the case...

Bob
 
Drill and tap one end. then come back a week later, pick it up and install it. months later comes time to drill out the bottom skin in order to install the tie down only to discover u screwed up and put it in upside down,,,,,,,,,,,,,,, now if you'd d&t both ends, you'd never know if you installed it upside down................. all is not lost because you can d&t it where it is, but then you break off the tap,,,,,,,,,,,,,,,,,,,,,,,,:cool:

Then you can use "tap-out" , a nitric acid based tap dissolver. It won't harm the aluminum. I looked it up for a different issue, but hope I never have to use it on a plane.
 
"Tap out". Dang never heard that one before. Don't know when I'd use it nowadays but the first thing I flashed on was busting a tap on an exhaust port. Sure would've saved some agony.
 
Thanks for the feedback guys. To clarify, yes, the tiedown in question is actually on the top of the wing (so should I call it a "tie up");)? If it was not an integral portion of the wing spar (factory riveted with 6 large rivets that I can't re-set) I would replace it out of principle. Since there's no apparent need for it, then it is a non-issue and I'll just put a plug in it and call it InOp. (Last chance for someone to tell me what it's used for!:D)

Thanks again,
-dbh
 
The only use I have come up with is a lifting point for a one man wing removal rig. I have not seen a rated weight limit for the tie-up point, but I suppose you could use them to lift the entire aircraft for overhead storage in a high enough hanger.

John Salak
RV-12 #120116
 
I think those top fixings are meant to be helium balloon attachment points to get some extra lift on those high density altitude days. These little LSA's need all the help they can get sometimes, and Van's have put a lot of thought into this design. ;)
 
I had been told they were armament attach points. Keeps the machine guns from sliding off the wing in high speed dives.
 
Would probably have to be on a swivel mounting then Don. Doesn't sound very plausible to me.
 
Thanks for the feedback guys. To clarify, yes, the tiedown in question is actually on the top of the wing (so should I call it a "tie up");)? If it was not an integral portion of the wing spar (factory riveted with 6 large rivets that I can't re-set) I would replace it out of principle. Since there's no apparent need for it, then it is a non-issue and I'll just put a plug in it and call it InOp. (Last chance for someone to tell me what it's used for!:D)

Thanks again,
-dbh

Dave,
It is not used/intended for anything specific (at this point anyway)and plans don't specify to enlarge the hole in the top skin during assembly.
The design aspect of the bracket meant it would be full height on the spar, so in consideration of future plans for wing storage, trailering, etc. is was specified to tap it also, since it was easy to do.
You should be fine leaving it as is.
 
Dave,
Scott is right as usual, but just keep in mind that you'll be limited to either one balloon or one machine gun from now on. :(
 
There was a prepunched #30 hole above it on my top skins. I just put in an LP4-3 blind rivet before painting. Figured I would never need it and if I do I'll drill out the rivet on each side.
 
Not really, the RV12 steps are ideally suited to attaching the gun barrel and feeding the ammo from inside the cockpit. Just don't have the unique swivel option.
Dave,
Scott is right as usual, but just keep in mind that you'll be limited to either one balloon or one machine gun from now on. :(
 
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