Carbon Cub Preemptive Modification

[Steve Pierce]

I keep finding cracks in the boot cowl where the pulley cover blister is attached to the cooling tunnel. They seem to emanate from the sharp corners of the the Tinnerman clip nuts. Today, instead of waiting for my buddy's new FX3 to crack I went ahead and drilled for Tinnerman nuts plates, dimpled and riveted them in. Should have used my blind dimple dies that work with a pop rivet gun and some counter sunk 3/32 pop rivets since it is hard to get the river squeezer in there but it worked and he shouldn't have any cracks. Just an FYI for those Carbon Cub owners out there.
Cracked SS I patched.
PXL_20220306_225859385.jpg
What appears to be the culprit.
PXL_20220306_194412354.jpg
Tinnerman nut plates riveted in.
PXL_20220306_210829457.jpg

[ceslaw]

Thanks for the tip.

[Daveembry]

Thanks for the heads up Steve. I’ll start doing that in mine. Might be easy to just use these small pop rivets like we use on the nut plates for the fuel tank covers. Easy to pull.

3CC1B5EA-3934-4502-BEBE-E46993002820.jpg

I keep finding cracks in the boot cowl where the pulley cover blister is attached to the cooling tunnel. They seem to emanate from the sharp corners of the the Tinnerman clip nuts. Today, instead of waiting for my buddy's new FX3 to crack I went ahead and drilled for Tinnerman nuts plates, dimpled and riveted them in. Should have used my blind dimple dies that work with a pop rivet gun and some counter sunk 3/32 pop rivets since it is hard to get the river squeezer in there but it worked and he shouldn't have any cracks. Just an FYI for those Carbon Cub owners out there.
Cracked SS I patched.
PXL_20220306_225859385.jpg
What appears to be the culprit.
PXL_20220306_194412354.jpg
Tinnerman nut plates riveted in.
PXL_20220306_210829457.jpg

[aflyer]

Steve, thank you for coming here to post this!

Having just done this on my EX-3...the manual shows that you should notch out of that smooth curve so the nutplates will fit. But on mine, there was no notching required, it was apparently cut out larger, perhaps to stop this?

Could it be just the notches that cause the problem, or the nutplate as it rotates and pushes on the aluminum?

Thanks, John

[Steve Pierce]

The cracks I have seen seem to start at the corner of the clip nuts where it is compressed against the fairing and the bootcowl skin.

[aeroaddict]

I have an extreme dislike for Tinnerman clip nuts. Why not just use a nut plate?

I did not use the Tinnerman's on the belly blister and instead installed nut plates during the build (EX-2). Another place, if I recall correctly, is the little inspection door where you can access the thru firewall fuel connection to the gascolator (this may be EX-2 specific).

If already built, use a pop rivet counter sink tool and then use the C/S pop rivets as mentioned above.

Thanks for the heads up.

[Dan L]

I put nut plates in mine from the start. No issues.

I also put some D shaped door seal on the inside of the tear drop cover where it contacts the tunnel to help keep out carbon monoxide. When I installed my belly pod weird airflow was brining in CO and I thought this might be one of the culprits.