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Fuel tank dimple vs countersink question...

Rich Pulman

Well Known Member
Sponsor
On the RV8 fuel tank, the destructions call for the skin to be dimpled where it attaches to the ribs and countersunk where it attaches to the rear baffle. Both the skin and the baffle are 0.032" thick.

I'm having a hard time understanding why the difference between the ribs and the baffle. Especially since the thickness of the head of a -3 rivet is greater than 0.032". This will clearly leave a hole >3/32" in the tank's skin with a knife-edge to boot.

Can anyone help me understand this? Thanks.

Richard
 
If you dimple the skin for the rear baffle, you both make it harder to get the baffle on and hinder the associate seal.

Carl
 
The rear baffle is the most common place, possibly the hardest part of ensuring no leak since it is done blind
By countersinking the skin, it ensures that there is no gap between the skin and the baffle whereas if you dimple those, unless those dimples are prefect, it could leave some gap between the baffle and the skin which could add to the risk of leaking.
You will not have this risk with the ribs as you have access to the inside while riveting the ribs and could seal from inside.

Hope this make some sense.
 
I did my RV10 tanks the same way your directions describe. Just don’t overdo the countersinks. If the countersinks are slightly shallow you can always flush the rivets with a shaver. Dimpling the aft baffle is a good way to have leaks.
 
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