Water Ballast Issues
Leak Proofing Integral Tanks
A caution about using water in ships with integral tanks rather than bags:
Before each season, the tanks should be checked for leaks by
pressurizing with air to about 5 in water pressure and
checking that the pressure is held for several minutes. If
there is a leak detected, it can usually be fixed by
"sloshing" some latex-based sealant (1) around the tank and
allowing it to dry. (The wings will need to be removed from
the glider for this) Make sure the breather tube from the
outboard end of the tank is not blocked by blowing through
it after the "sloshing" to clear any sealant which has run
into the tube. (The breather exits in the aileron recess at
the inboard end) Flying with a leaky tank can allow water to seep into the
wing structure, and it will creep along glass fibres,
weakening the bond with the resin, and so lower the strength
of the wing. The tank is right against the main spar !!
The [pressure] test is done most easily when the wing is separated from
the fuse, so you can get to the tube which connects with the
dump system in the fuselage.
I use rubber stoppers which you can get at rubber supply
shops or laboratory suppliers. A large stopper closes the
above mentioned tube, another goes in the filler hole and a
very small one goes in the breather hole, which on my ship
comes out in the inboard edge of the aileron cut-out in the
wing, not along the hinge line, but in the short piece of
rib at the end of the cut-out.
Fit a piece of tubing through one of the large stoppers to
allow air to be blown into the tank and a water-filled
U-tube for measuring the pressure connected.
The attached file is a jpeg version of a sketch of the test
I find the easiest way to pressurize the tank is to blow
into the tube with your mouth while watching the U-tube so
that no more than 5 in water pressure is applied.
Have some means of sealing off the pipe you blow into to
maintain the pressure However, your breath is warm, so
initially the pressure will go down slowly as the air in the
tank cools to the tank temperature. Allow some time for
this to occur, then start checking for leaks by watching for
continued drop in pressure over a half hour or so.
DON'T USE AN AIR COMPRESSOR. You can easily apply far too
much pressure and burst the wing :-(
Be careful what you use for a sealant! Materials that dry to a hard surface may pull the wing skin, causing shrinkage.
This can create depressions along the ballast tank region, severely affecting performance.