Friday, March 23, 2018

Fixing a fuel tank baffle leak

As I mentioned in the previous post I had a baffle leak on the right fuel tank.  This is the process I went through to repair that leak (two actually).

First step was to cut two 5" holes in the middle of the leaking bays of the back baffle.  Here I set the fuel tank on a blanket on the floor and then used the 5" hole saw you see sitting on the bench (top down view) to cut the holes.  Pretty simple process but the cuts definitely needed some cleaning up.
Once I had the tank open I was able to look inside with a mirror and see where the bead of sealant had not made contact with the back baffle.  This leaves a direct path for the air/fuel to flow out of the tank.  In this picture you can see two spots where the sealant did not make contact with the baffle (up in this photo).  It looks like little dark shaped lines just above the bead of sealant.

Another area that needed work.  Again look for the dark line on top of the bead of sealant toward the right side of the picture.

I used my Solidworks skills, limited as they are, to design the circular patch.  The circle is 6.375" in diameter with 24 holes evenly spaced around the inner perimeter.  In this picture you can see the CNC as it starts to cut the outer ring.  The holes are already punched in this picture.  I used .032 2024 alclad for this step which is the same material/thickness that the back baffle is made of.
Next up I had to fit the patch panel to the baffle.  You can see where I measured and marked the center of the holes so that I could use those lines to center the patch plate.  In this picture I had just drilled the first upper hole that I used as a starting point for aligning the patch panel.

  Once I had the panel aligned I drilled the bottom hole, cleco'd the panel in place, and finally I match drilled the remainder of the holes.

Here is the final result of the match drilling.  Next up was deburring all the holes, inside and out, followed by a thorough vacuuming and wipe down with lacquer thinner.

Once everything was clean and deburred I mixed up a batch of sealant and proceeded to create a nice bead of it along the leaking seam using my 10 cc syringe method.  This is a picture of one of those beads after I had used my finger as a squeegee to smooth the bead and work the sealant into the cracks.

Next up was to run two beads of sealant around the opening in the baffle; one bead between the rivet holes and the inner 5" hole and one bead outside of the rivet holes.  The sealant you see oozing out is from that outer ring of sealant.  Finally I put a cleco in each hole to help pull the patch panel down to the baffle.
And finally I used some AD-41H rivets to fasten the cover plates to the baffle.  The rivets are twirled in sealant, inserted and pulled, then I put a smear of sealant over the back of the rivet just in case there was a rupture in the sealed portion of the rivet.

A closeup of one of the covers after riveting and sealing.

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