How does a glider fly?

A glider has a wing with a special cross-section/profile. Similar to powered aircraft. The weight of the glider in the air is counteracted by the ‘lift’ generated by air flowing over and under the wing. Like any other aircraft the wing must be moving quite quickly through the air to generate lift. Powered aircraft achieve this using an engine to pull (or push) the aircraft forward. A glider must use gravity to help it ‘slide’ forwards through the air to generate the flow over the wing. So the glider is always descending relative to the air.

However, as the air in our atmosphere is constantly, moving gliders prolong flight using various forms of rising air, which we refer to as “lift”. Once launched to height by a tow plane or a winch, gliders seek out and fly in this ‘lift’. If the air is going up faster than the descent rate of the glider then the glider will climb higher.

There are several things that generate this ‘lift’. Often, it’s because large areas of air near the ground has been warmed by the sun, and warm air rises. This ‘warming’ can result in huge ‘bubbles’ or ‘columns’ of rising air. We call these ‘thermals’. As the warm and often moist air rises through the cooling atmosphere it reaches a level where the moisture in the air condenses, forming fluffy cumulus clouds.

There are other forms of lift. Mountain ridges form a barrier to the wind, the air is forced to move up and over the rising ground. Gliders can use this reliable form of lift to stay airborne and fly for long periods upwind of the high ground. 

Glider pilot fly their aircraft for long periods and often covering hundreds of miles. They are able to soar to cloud-base and even higher. And in certain conditions to 30,000ft and higher.