Figure 5-21.  Water ballast tank vented filler cap. It is important to check the drain valves for correct operation  prior to flight. Water ballast should drain from each wing  tank at the same rate. Unequal draining leads to a wing-heavy  condition that makes in-flight handling, as well as landings,  more difficult. If the wing-heavy condition is extreme, it is  possible the pilot will lose control of the glider. Ballast drains should also be checked to ensure that water  ballast drains properly into the airstream, rather than leaking  into the fuselage and pooling in the bottom of the fuselage.  Water that is trapped in the fuselage may flow through or  over bulkheads, causing dislocation of the CG of the glider.  This CG dislocation can lead to loss of control of the glider. The flight manual provides guidance regarding the length  of time it takes for the ballast tanks to drain completely. For  modern gliders, it takes about 3 to 5 minutes to drain a full  tank. When landing is imminent, dump ballast early enough  to give the ballast drains sufficient time to empty the tanks. Use of water ballast when ambient temperatures are low can  result in water freezing the drain valve. If the drain valve  freezes, dumping ballast is difficult or impossible. If water  in the wings is allowed to freeze, serious wing damage is  likely to occur. Damage occurs because the volume of water  expands during the freezing process. The resulting increased  volume can deform ribs and other wing structures or cause  glue bonds to delaminate. When weather or flight conditions  are very cold, do not use water ballast unless antifreeze has  been added to the water. Prior to using an antifreeze solution,  consult the GFM to ensure that antifreeze compounds are  approved for use in the glider. A glider carrying large amounts of water ballast has  noticeably different handling characteristics than the same  glider without water ballast. Water ballast: Water ballast is routinely dumped before landing to reduce  the weight of the glider. Dumping ballast: Figure 5-22.  Water ballast drain valve handles. •  Decreases stall speed. •  Decreases the optimum airspeed for the landing  approach. •  Shortens landing roll. •  Reduces the rate of acceleration of the glider at  the beginning of the launch due to the increased  glider weight. •  Increases the length of ground roll prior to glider liftoff. •  Increases stall speed. •  Reduces aileron control during the takeoff roll,  increasing the chance of uncontrolled wing drop and  resultant ground loop. •  Reduces rate of climb during climb-out. •  Reduces aileron response during free flight. The  addition of large amounts of water increases lateral  stability substantially. This makes quick banking  maneuvers difficult or impossible to perform. Drain valve closed Drain valve open 5-15