Water Ballast
It may seem counter-intuitive, but pilots put water ballast into compartments in the wings to make their planes heavier. Modern gliders can take large quantities of water (a Nimbus-3 can hold 272 kg). The objective is to increase the gliding speed, while maintaining the same gliding angle. The downside is that the glider will climb more slowly in thermals. However in the right conditions, the time lost in climbing more slowly is more than recouped by the increased speed to the next thermal.
The benefits depend on three factors: the aerodynamic performance of the type of glider at various speeds and weights, the strength of the thermals on the day and the width of the thermals on the day. The increased sink rate will have a small percentage effect on the climb rate in strong thermals. The extra weight of ballast requires the pilot to bank more to stay in narrow thermals and this also increases the sink rate.
Competition pilots usually launch with ballast. If the thermals are weaker and/or smaller, it may be better to continue the flight without ballast and so they may dump it soon after the start or part way round the course. However it is possible that conditions may strengthen and so sometimes keeping the ballast throughout the task may be advantageous.
The airframe of a glider is not designed to withstand the stresses of a hard landing while the glider is loaded with water. Consequently, pilots start emptying the ballast tanks shortly before the gliders cross the finish line so they are empty when they land. This results in spectacular images when competition pilots cross the finish line at low altitude. Recent rules changes are making this practice less desirable for safety reasons.
Read more about this topic: Gliding Competitions
Famous quotes containing the word water:
“Communism, my friend, is more than Marxism, just as Catholicism ... is more than the Roman Curia. There is a mystique as well as a politique.... Catholics and Communists have committed great crimes, but at least they have not stood aside, like an established society, and been indifferent. I would rather have blood on my hands than water like Pilate.”
—Graham Greene (1904–1991)