Tanks 18-03 Step 6

Fuel Tank Sheet 18-03 Step 6. Do I really need to Machine countersink the row of holes in the T-0001L Fuel Tank Skin that attach the skin to the T-00002 Tank Baffle to fit the head of an AN426AD3 Rivet?

Or can I just Dimple the Tank Skins and the Tank Baffle Flange. We dimple all the other holes why not these?

The theory is that dimpling will interfere with the insertion of the baffle, thus affecting the quality of the filet seal applied to the skin that is pushed forward during baffle installation. Some have dimpled with no ill effect IIRC. Had I to do it over, I would give more consideration to dimpling.

Follow the plans!

On my RV-3B, I accidentally dimpled the skin and baffles for my first set of tanks. Man, that was a mistake. I had to make two entirely new tanks. Set me back considerably, both time and money.

The baffles curved and that stressed the various parts. It was very difficult to install the dimpled baffles, and worse (and this might be an RV-3B issue and not an RV-14 issue) some of the dimples interfered with the spar caps.

Lesson learned: follow the plans!

I found that a one-flute countersink bit made smooth countersinks with no chattering. It wasn't a big job. A micro-adjustment cage makes it easy to make consistent countersinks.

Dave
RV-3B

Actually it is a number of reasons....

One is that this is a critical seal point that is done blind (no access to work the sealant after assembly like it is on the end ribs). Years of experience has shown that it is also one of the areas most prone to leaks.

Since the quality level of dimpling (particularly on .032 skins) is a variable among builders (this will effect how flat the parts are, and how well they mate together), machine countersinking is recommended.

Just thought I'd check in before I started this step. Thanks guys!