Fuel Tank Follies
Back at it today on the tanks. Started going step by step through Section 18, Fuel Tanks making sure everything was done to plans. I was making good progress until checking that the fuel vents weren't clogged. The left tank was fine. The right tank, not so much. I couldn't blow any air through it. I initially assumed a glob of ProSeal had clogged the end of the line like the plans warn about. Further investigation revealed the AN832-4D bulkhead fitting at the wing root was the culprit. I could insert a drill 1.03" into it which was roughly halfway into the fitting. Using a light, I could see that the blockage was blue anodized aluminum like the rest of the fitting and not ProSeal or some other material. And I could see that the vent line was connected to the fitting inside the tank, and it wasn't just a cap. Apparently a manufacturing defect. And everything just....stops. I gotta figure it out. Frustrating as it was a manufacturing defect that should've been caught by Van's. I found a Safety Directive for RV-12s that warned about a bad batch of AN832 fittings. Guess I got one. That's why you go through the plans on completed QB structures. For stuff like this. I informed Van's Tech Support about it. Removing and replacing the bad fitting would've been nearly impossible without cutting an access hole in the tank bulkhead. Plus, I'd disturb the Proseal the fitting was bedded in and I didn't want to do that. Van's might replace the tank but with their supply chain issues who knows when I'd get a new one. I started thinking about drilling out the fitting in place since it's only a vent line. I ended up using a 2" length of 5/32" OD brass tubing that fit snugly in the AN fitting opening to use as a drill bushing. The I used a #31 drill bit that fit snugly inside the bushing. At this point I had no idea how thick the material was that I'd need to drill through. Only that it started 1.03 inches in. My hunch was it was pretty thin. I carefully started drilling and was through in about .150". Discarding the bushing, I upsized the hole to #21. Then I carefully removed any metal chips and cleaned the inside of the fitting and line with compressed air and Q-tips soaked in denatured alcohol. I about had a heart attack when the cotton end of a Q-Tip came off inside the fitting, trading one blockage for another. I fabricated a small spiral hook from some safety wire and was able to snag the cotton fibers and remove it. Whew. Now the right vent line flows as well as the left. Latest crisis averted but much time wasted. Aggravating. I did manage to get both aileron linkage flange bearing riveted in. Now on to the fuel senders.
