7.7.58 More left fuel tank work.

Last night I put the left fuel tank on test again. It’s been sat for about 4 days since the ‘mega fix’ so the sealant should have cured enough for a test. Like previous times I inflated the tank to 1 PSI recorded the temperature and atmospheric pressure and left it overnight.

This morning I returned to the tank to find it had held pressure pretty well. It had only dropped from 1 PSI to 0.9 PSI but so had the temperature so it’s hard to tell if it’s a leak or just the affects temperature.

One possible place that it could be slowly leaking is the cork gasket between the access panel and tank so I decided to follow Van’s advice and seal that with tank sealant instead. I also called Nigel, my inspector, and talked through the tank leaking problems with him.

In particular, I explained the possibility of the ‘drinking straw’ affect causing air to travel along the skin to baffle seam. He agreed it was a possibility but, like me, said it was impossible to know for sure.

I saw a fantastic fix for this on another blog which involved injecting Class A (runny) sealant into the tank near the joint where the original leak was. I very much liked the theory and Nigel said there was no harm in trying it. So I did by first taking a blunt 14 gauge needle and bending it 45 degrees.

I drilled 1/8 hole in a test piece of aluminium to be sure the needle would fit which it did with good room to move it around. Next measured the length of the needle from bend to tip and marked the drill point on the tank based on that measurement. I applied positive pressure to the tank to help push any shavings outward and, with the shop vac close by the drill bit, drilled the 1/8 hole.

After deburing the hole and cleaning the area I angled the tank so that the joint was facing the ground. The theory is that the sealant would flow into place. I then mixed up a runny batch of tank sealant. I used the syringe to suck up the sealant, fitted the bent needle and inserted it into the tank. I squeezed sealant slowly out while twisting the needle left and right in an arc fashion.

I repeated that about 3 or 4 times to get a good amount of sealant in there. Once that was done I got an AD-41H closed blind rivet (as used previously on the tank baffle) and twirled it in sealant. I put the rivet in the hole and popped it with the rivet popper.

After that I gently relocated the tank at even more of an angle to encourage the runny Class A sealant to flow directly down into the corner.

All this left tank testing work had me doubting if I had properly tested the right tank so I put that on test again too just for fun. It’s ready to be fitted to the wing so I thought it best to test before I do that.

That’s enough work for today.

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