Thorp Air Command - T18.net

Hi everyone! New T-18 owner here. One of the fiberglass tips on the stabilator was loose and therefore removed. It was attached with two bolts that screw into the outside rib. Does anybody have a different attachment method for these tips? It seems like a pretty cumbersome way to do it.

I asked this on the Facebook group yesterday, but thought I should repeat here for more feedback and better history for everyone. Lee Walton replied on FB as follows: "Most of us (99%) have a flange on the outboard rib that we use to attach the tip (either aluminum pops, sheet metal screws or machine screws/nutplates). Looking at your stab I'd cut a strip of aluminum, drill out the existing rivets on the outboard rib and install a flange and attach with pop rivets."

I would appreciate it if anyone has details (pictures, drawings, or good explanation) of this install or any other method. If I understand correctly what Lee said, do I slip an aluminum strip between the skin and the outer rib? I would assume it would be too tight to do that. If I am to mount this strip inside the rib, I'm having trouble seeing how to attach it due to all the crimps in the rib.

Thanks all!

Hi there ‘Slayton’,

If you wanted it looks like you could drill out rivets and slip a narrow strip between rib and skin on stabilator to make a tab to attach tips. Don’t try to make it all one piece to go around the leading edge. Depending on thickness of the tips it should make a nice flush joint. Take a look at my project photos in my album in the gallery. See page 1 and 16 for both main wing and stabilator application.

I know what you mean about flutes on the rib flanges. I glued a separate strip, top and bottom, to the red fiberglass main wing tips with extra holes included for epoxy to bite (it shows up as black dots). Best to use a ‘soft’ epoxy with a little give when joining aluminum to fiberglass for changes in temp. In this case, the attaching strip goes below both the skin and wing rib flange; not between. To accommodate flutes on the wing rib I added larger holes, I think 3/8” or 1/2”. This is instead of cutting notches for each flute which would lose strength and make it difficult to get all the tabs to slide in all at once during installation.

Finally, add holes for screws or pop rivets. Dimple the parts and you’ll have a nice looking joint.

Hope this helps.
Les

Kind of what Les said . My ribs did not have the flutes so it made the job a little easier . Aluminum strip between the skin and the rib . Riveted the strip to the AC and then the tip . Another solution for your situation (since you have to drill out the skin rib rivets) would be to get a rib that is not fluted and replace it .

RB

Ok guys .. not between the skin and the rib ... that changes the rivet hole alignment between the rib and the skin and shifts things undesirably ... the only option here is to add the attach strip on the outside of the rib (under/over however you want to put it) ... also fiberglass is thicker than .025 so there is a better chance of the tip ending up flush. I would not worry about the flutes ... just mark the attach points in between the flutes on the high points.

_________________
Lee Walton
Houston, TX
N51863,N118LW
KEFD