Flying on hot air.

Have you ever wondered what keeps a glider in the air? Gliding does Seem to be a bit of a mystery. A glider has no engine to power it, yet it Can fly for long distances before landing. It can even climb through the Air.

The glider stays in the air, and climbs, because of air currents. At the Beginning of each flight, the glider has to be towed into the air. Once it Has been released, however, it can fly for as long as the pilot can find Rising air currents to keep it airborne.
The best pilots are highly skilled At finding these air currents. Cross-country flights of 300 km or more are Often carried out.

Below you can see a diagram of a glider's cross-country flight. You can See where the glider climbs, and where it loses height. Most of the rising air is in the form of thermals, currents of hot air rising because of convection. A thermal is produced whenever some air is heated more Than the air round about it. If a pilot finds a thermal. He will circle in it and gain height.