Patrick's Sling TSi

Weeks 31-33: Fuel tank leak testing

While waiting for the sealant to cure, I replaced all the pulled rivets on the right wing rear skin support with the solid rivets. This fixed the issues with some of the rivets rubbing on the flap, and since they were all accessible with a squeezer it was easy to do.

After waiting a full 6 days I did another leak test on the assembled fuel tank. I found a couple leaks around the corners of the rear channel. I patched those up with additional sealant, then let it cure for another 4 days. I never disconnected my homemade manometer after the first leak test, and the day after making the repairs I noticed that he manometer was indicating a small amount of pressure in the tank. I did the repairs with the AC on (which was blowing directly on the tank), when the temperature in the tank increased the manometer indicated about 4" w.g. in the tank. This was a very promising sign, as I would expect any amount of leak would let the pressure equalize.

Once I was convinced the last sealant was cured well enough I tested up to the full 1.5 psi (40" w.g.). After letting it set for an hour, the pressure actually increased slighted due to temperature change. Satisfied that the tank is finally not leaking (I started on this in April), I started to work on assembling the tank to the wing.

When I first fit the tank in place, I noticed the part of the skin that has the jog in it was not sitting very flush. I removed the tank and cleaned off any excess sealant that I thought might be causing the issue. That didn't completely fix it, so I ended up gently bending the skin inwards to try and minimize the issue. After a couple attempts of this I did get it flush enough that I am happy with it. Happy with the fit, I went ahead and permanently riveted the tank in place.

I am still waiting to find out when my replacement skin for the left fuel tank will arrive. While I am waiting I decided to start filling the rivets on the right wing. I am using Poly-Fiber Super Fil, which I already had to potentially do some minor body work on the rudder cap (it looks like the base of the beacon is slightly larger than the fiberglass mounting point).

The best method for me seems to be mixing a small batch (a total of 5oz part A + 2.5 oz part B) and putting it in a 10 ml syringe (I bought a pack of 100 for $14 on amazon). I place the tip directly over the rivet hole and fill until I see it start to sqeeze out. Then I pull back slightly on the plunger to limit how much oozes out uncontrolled. After filling a syringes worth of rivets I smooth the top with a body filler spreader, then come back and clean the top of the rivets and the surrounding area with MEK.

I had been putting this part of the process off, but it is easier than I expected. I finished the top side of the wing, now I will flip it over and do the bottom side before moving to the next step. If I can get the left tank skin in the next couple of weeks I will move on to that, if not I am going to start on the fuselage and come back to the left wing when I get the tables cleared up again.

This post is from Patrick's Sling TSi