Shimming A Tail Rib That's Too Short?

[Spaceman]

Hey guys, long time lurker first time poster here!

I'm working on my Waiex tail kit and today I put together the internal structure of the RH stabilator. I started by drilling and clecoing the four parts around the perimeter to get the overall dimensions correct, and then I started adding the four ribs in the middle. First I attached all four to the rear spar, and then started attaching them to the forward spar.

Anyway, I drilled/clecoed the longest one first (second from the right in the picture below, it's part number T11-09), but then I found that the other three ribs seemed a little too long. So I took the longest one out and then the other three fit perfectly. Turns out the -09 was a little short so it was pulling the forward and aft spars together a little and causing the other three to not fit.

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So my situation is, my -09 rib is a little too short, AND I already drilled the holes in the flange so I can't really adjust the bend to compensate. Short of rebuilding the rib entirely, I figured the best solution was to just put a shim between the flange and and the forward spar channel so the holes still line up and the rib is still square with the aft spar. I cut up some scrap pieces of channel stock and found that two layers of 0.032" material (i.e. 1/16") filled the gap perfectly.

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Is this an acceptable thing to do with pop rivets? I feel like I've seen it done before but I want to be sure I'm not doing anything too crazy. I don't see why not, but I don't have a ton of experience...

This whole stackup adds up to 0.371" (0.25 hockey stick + 0.032 spar channel + 0.064 shim + 0.025 rib), and the CCP-46 rivet grip range spec is 0.375". So it seems like I can even get away with using the spec'ed rivet.

Is this a bad idea? Would I gain anything by using a single piece of 1/16" material rather than two 1/32" layers sandwhiched together?

My other options that I can think of are:

1) Cut the flange off the rib and rivet on a new one, like Bryan Cotton did on his build. http://sonexbuilders.net/viewtopic.php? ... 8&start=10 (awesome thread BTW!)

2) Just push the rib over until the flange meets the channel. However then I'd have:
2a) the rib not quite square with the aft spar
2b) two sets of holes real close to each other (I think they would clear, but just barely)

So I don't think I'll do #2

3) Just re-make the whole -09 rib!!!

Any opinions? Thanks!

[Sonex1517]

Just my two cents, but always check with tech support at the factory! They are there to help you through this adventure.


Robbie Culver
Sonex 1517
Chicagoland
Tails and Wings complete - finishing fuselage.
N1517S reserved

[Bryan Cotton]

In general adding a shim to improve fit is ok. You will see shims everywhere in cessnas, boeings, Sikorsky helicopters, and my Waiex. Of course Robbie is right regarding tech support. But I'll bet a dollar they say a shim is ok!

P.S. Thanks for the compliment!

[Bryan Cotton]

One other thing- I would cleco it to the skin before you do anything. Otherwise how would you know which side needs the shim?

[Spaceman]

Thanks for the replies guys! I'm thinking the shim method is the way to go.

I'm actually surprised how well this assembly went together. When I was building the ribs I figured there was no way I was locating the bends precisely enough for it to work. I guess three out of four is better than I expected!

Good point on checking with the skin too. I think it'll be fine since the whichever side the shim is on will just move the rib fore or aft, and it's square and in the right place left to right, so the flange should catch all the holes in the skin... I think. But since you mentioned it I'll hold off on riveting that rib in for good until I have test fit the skin!

Bryan I was actually just reading your thread and I got to where you put some shims under the turtleneck skin, and that's what reminded me to come back here and see if anyone replied to my question! Nice!!