The length of a flight depends on both the weather and the pilot’s ability to get the most out of it. Glider pilots can fly for many hours by finding areas of rising air, called ‘lift’. They climb in one area of lift and then glide to the next area, while trying to avoid areas of swiftly descending air.
Thermals
Thermals are the most common form of lift used in Australia, so it’s just as well we have the best thermal flying conditions in the world. Thermals are giant columns of hot air, set off when one area on the ground is hotter than its surroundings. During the summer, they will frequently reach heights of 12,000 feet above ground (almost 4km!) and move upwards at speeds of up to 10 knots, or 5 meters per second.
Pilots find thermals by learning to recognise air currents and the sometimes subtle effects they have on the movement of a glider. All gliders are equipped with an instrument called a variometer, or vario for short, that gives an indication of the energy a glider is gaining or losing. The vario can help a pilot to find the best part of a thermal. However, the read outs are a few seconds behind reality, so it is essential to learn feel of the air.
Ridge
When the wind blows straight towards a mountain ridge, sometimes there’s nowhere for it to go but up! Gliders can soar in this area of lift, flying back and forth along the hillside.
This type of lift does not go very high, but if the hillside also faces the sun then thermals my be generated, allowing the pilot to climb away from the ridge and explore elsewhere.
In theory, ridge lift is purely mechanical. It’s just the wind with the hillside acting as a barrier. In reality, it gets a lot more complicated than this. It is influenced by the angle of the wind to the ridge, whether the sun is heating the ridge as well, if the ridge surface is trees, grass, dirt or something else and the shape and size of the hill.
When the wind is strong, ridge lift can be quite good and a pilot can enjoy flying at high speeds without losing any height!
Wave
When winds blows over hills and mountains, it will often ‘bounce’ off the ground and create one of more standing ‘waves’ downwind of the mountain.
These waves often go much higher than the hill or mountains which created it, so by flying back and forth along this wave a pilot can often reach heights of 20,000 feet or more. The altitude record for a glider was achieved in wave, when a pilot managed to climb to just over 50,000 feet (over 15km). That’s higher than a jet airliners’ cruising altitude!
The world record for the longest flight in a glider is just over 3000km and was achieved in wave in the South American Andies.
For more information about wave soaring, check out the website of the Perlan Project. Its aim is to get a glider to 90,000 feet – the edge of space – using wave lift! If this is achieved, it will break altitude records set by both the SR-71 and U2 planes.