Ballast Tank Removal and Repair

[Roger Helton]

One of our aircraft owners has had to make a repair to a leaking ballast tank. I want to share his procedure with everyone for future use if necessary. Julian Ruiz from SCODA provided the service instruction however, Patt had to improvise to make it happen:

The first comment I can make is that it is next to impossible to simply cut the adhesive with a razor knife. There is just to sufficient room working through the access hole in the nose. Prying the tank between the wheel well and the tank will break something, the Sikaflex adhesive holds to well so that bond has to be broken. The support plate is about 1.5 by 6 inches with adhesive covering 80% of the surface.

I tried many tools, long fishing knives, screw drivers, etc and came up with this:

Make 4 1×2 hardwood sticks and cut a very sharp long point on one end. Position the sharp end at the junction of the tank and tank support. The length is important as the dull end will be in the cockpit laying on the seat where you can easily hammer it in. I started the first on on the outside and drove 3 more in along the seam between the brake cylinders and brake lines each one getting closer to the center of the airplane. The last on did the trick and broke the seam.

Removal of the tank is straight forward once you remove rudder interconnect cable from the pulley and lay the pedals down.

What I found, there is a small hole that was either a defect or was caused by abrasion at the bottom most forward edge of the tank where it contacts the fuselage. This will be easy to glass over and repair and I believe it would be wise to glue some sheet rubber or dense foam strips along the bottom and edge of the seam.

Finally my problem solved.

I have attached photos to show the process and the leak.

Roger, if there is a way to post this in the owners forum I would really like to do it or have you do it. I know at some point someone else is going to have this issue. It would be great to post stuff like this and my missing gasket issues so that others might learn from them.

I also am a bit concerned that the issue here might be a bit bigger that just mine. The tank sits on a relatively small bearing plate put cantilevers out over the front with no apparant other means of support. Was my hole a defect in the tank or was it caused by vibration of the tank during water landings or even hull vibration perhaps.

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