Staying Aloft

Thermal Lift

The most common method of gaining height in a sailplane, is to use a thermal. These are columns of rising air, perhaps 80 to 300m in diameter, which expand with height.

They start by a patch of ground air warming up to such an extent that eventually it allows a bubble of hot air to break away and rise, much like hot air balloons do.

Often as the hot air rises and cools, the condensation will form a cumulus cloud - which will mark an area of rising air to the glider pilot. In summer, dust can be seen rising, another indication of lift.

Ridge Lift

Wind rushing against a hill-side has nowhere to go except upwards. This also provides useful lift for sailplanes, although not to great heights.

Often in winter clubs will hold camps at sites known to favour ridge lift, as it is still a novelty to many pilots. This was a common means of staying aloft in the early days of gliding, before thermals were discovered. It was probably the origin of the question: "What do you do when the wind stops?" asked of many glider pilots.

Wave Lift

When wind is blowing at near right angles to a mountain range, it can create a pattern of invisible waves with the air rising and falling, sometimes many miles down-wind from, and many times higher than the mountains.

This type of lift can carry sailplanes to great heights. Most world height records have been set in wave, to altitudes of just over 40,000ft, which is the maximum attainable using oxygen for breathing. In mountainous countries such as New Zealand, wave conditions are common, and can result in long distance flights carried out at altitudes of 15 to 25,000ft.

Wave is encountered in areas within most states of Australia, with on occasion climbs to perhaps 30,000ft or so. The presence of this type of lift is indicated by lenticular clouds.