Shim between upper fuse channel and side skin?

[tims88]

I'm curious if anyone else has needed a shim between the F-1040 upper fuse channel and the F-1069 fwd side skin and if you have any tips on how to do it if you did?

The WD-1002 upper firewall bracket was not welded with the correct alignment so the face of the channel does not match up with the flanges on the firewall. I've contacted builder support and was told to use a shim to bridge the gap so that the skin can make a nice transition to the firewall.

You can see in the pictures below that the face of the channel is offset inboard of the firewall flanges and is slightly rotated, so the shim I make will have to be wedge shaped so that it is thickest at the upper forward corner and will have to taper off towards the bottom and towards the back. This also means that the rivets will be going through the WD-1002 bracket at a slight angle and I'm not sure if that is something to worry about or not. It seems like that would cause the shop heads if the rivets to want to tip over.

 

[Mikeyb]

I had a similar nightmare on a -8. Mine might have been worse. Ive edited this a few times as it was something I wanted to forget. I made tapered shims with a belt sander and a file in 3 sections. It was too hard to do it in one piece. I used a feeler gauge to measure the thickness at each shim end point and guessed at the other angle. To handle the shim during the shaping process I glued it to a piece of angle with contact cement.

The other part of the nightmare was that the offset of the weldment meant the rivet holes that you match drill through the top bracket ended up very close to the inside corner of the steel angle and were exceedingly hard to buck. I used wing-nut/screw cleco’s to pull the whole mess together.

Good luck and sorry

 

[tims88]

Thanks Mike. Glad I'm not the only one who has had a problem like this but I wish you were able to tell me that it was no big deal. You've given me some ideas on how to get started making a shim though.

I almost feel like it would be easier to just replace the steel bracket at this point.

 

[Mikeyb]

I tend to exaggerate my discomfort with problems. Every aluminum part in my kit was perfect and slid into place. Half of the steel fuselage parts required some rework and/or compromise.

There is a recent RV8 thread on a fit problem on the landing gear mount weldment that is amazing. I had a similar issue with that part as well. If I was ever to build another one I would cleco the whole forward fuselage together to check the alignment before I riveted them.

I was hoping some big kid would respond to your post with an easier solution.
Maybe just stacking thin sheet stock to approximate the taper.

 

[Raiz]

Looks like you haven't already riveted the WD-1002, upper channel and upper firewall angle together. If so, consider putting a shim between the WD-1002 and the channel instead of between the channel and the skin. This can be a constant thickness shim because the arm of the WD-1002 easily bends away to take up the difference. However, if you do go this route, make sure you still have adequate edge distances when you drill through into WD-1002.

Good luck!