Right Fuel Tank Build

It’s been over 2 years since I built the first fuel tank. The right side fuel tank skin arrived with a big dent when I originally received my wing kit, and it took a few tries and a lot of waiting to get a replacement skin. But, with everything in hand now I decided to build this fuel tank and finish the right wing.

I already did some work back in early 2019 preparing the closing ribs, but in the interim I had procured sealed M4 rivnuts for the fuel sensor cover. Sealed M4 rivnuts were very hard to find, I think I found them someplace on eBay. So, my first task was to drill out the old rivnuts, and then install the new ones along with the AN6 fuel line fittings to rib 101. I completed these tasks during my first session on Sunday 8/15.

One thing to note, since I’m putting the 915iS engine on my plane, I needed a bigger AN6 fitting for the fuel return fitting – the kit normally uses an AN4 return fitting with the 914 engine. I used a step drill to upsize the hole to 9/16”. Unfortunately I didn’t put an AN6 fitting on the other fuel tank (finished that one before I decided to go with the 915), so I’m going to have to look into reworking it, which will be a pain since it’s already riveted onto the wing!

Drilling out the original open-ended rivnuts
I removed the old sealant with a single edge razor blade and then sanded the rib clean
Installing rivnuts and AN fittings to the rib
Drilling additional holes on the fuel vent tube to ensure it doesn’t get clogged
Vent tube looks good
Dry fit check of rib 101, looks good
View of rib 101 from inside the tank

Sealing the ribs onto the skin is a long task and requires uninterrupted time, so I saved that work for another day. The next session was on 8/20, which started with preparing the skin: deburring the holes, cleaning/degreasing, sanding the areas where sealant is applied, and masking off the areas next to the ribs, to ensure nice clean lines of sealant. As before, I mixed up a batch of Flamemaster CS3204 sealant and used a syringe to lay down the ribbon of sealant on the skin along the rivet lines. I made 100g of sealant and that was just enough for this part of the job. It took me the full 2 hour working time of the sealant to set the ribs and stringer in place and shoot in the rivets. Cleanup took another hour and a half, which largely involved wiping down the excess sealant around the rivet heads and cleaning the sealant off my clecos with acetone.

Unfortunately I don’t have a lot of in-process photos, the sealant is incredibly gooey and sticks on everything! I was wearing gloves and an apron the entire time, and left my phone safely out of reach.

Rivet lines masked off and ready for sealant
Folding the taco
I used a caulking tool to form a nice chamfered bead of sealant on the end ribs
Clecoed and ready for rivets
Just about done, the back close out channel will get attached next, here it’s just temporarily attached so that the sealant for the ribs sets properly

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