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 setup.

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 :-(

Cheers,
John Giddy
Australia

(1) Warning: 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.