Gliding is very popular in the UK and elsewhere in the world. With approx 7000 members of gliding clubs in the UK it's a sport in which many people of all ages and sexes participate. You might wonder how do gliders fly if they do not have an engine. Donot worry, this question is asked by almost everyone. Read on to find out more about this amazing sport. If you still have any more questions please click here to go to the FAQ section.
For some people gliding is just a hobby that they do because they really enjoy the sensation of flight with no engine onboard. But others do it because they either have plans for an aviation career or love the competition elements of gliding, which take place all over the world with a chance to see the most beautiful sceneries.
So how do they fly?
Gliders stay up by using rising air currents. These rising air currents can be in the form of:
- Thermals (updrafts of warm rising air, which is warmer than the surrounding air);
- Ridge lift (Relatively strong wind, 15 knots or more, blowing towards the side of a hill causes the air to move up);
- Wave lift (Wind that blows over mountains, increasing in strength with height, can allow wave lift to form. ‘Wave’, if it were visible, would look similar to ocean waves. There are strong and smooth updrafts on the front (windward) side of wave.
This is how a thermal forms and the following diagrams show how gliders use thermals. Gliders can cover great distances using this type of lift as they occur in many places. The cumulus clouds start to appear at different times of the day, depending on what the ‘trigger’ temperature might be. If it's higher than usual then it might take a bit longer for them to start forming or it may never actually meet that temperature so the day might turn out to be 'blue' (that is, no visible clouds, to guide pilots to thermals). A day can be 'blue' for other reasons too.
This image shows how gliders use thermals to gain height in the most efficient way. Once a pilot is established in what is called the core, the climb rate will be at its peak. A glider pilot will usually carry on using this lift until reaching the bottom of the cloud, although strong lift will continue within the climb. The glider will need to be fitted with suitable instruments, and the pilot trained in their use, before cloud flying. Depending on many meteorological, and other factors, the strength of lift will vary from day to day. It can be ‘well formed’ with a constant rate of climb but it might be ‘broken’ which could mean that part of the turn could be in lift and another in ‘sink’.
Wave is a spectacular type of lift. It is very strong and smooth with high rates of climb that can help to set records. For wave to form several criteria have to be met. The air mass needs to be stable, which means little or no thermal activity must be present. If the air mass is too unstable it might not form. The wind profile needs to have a constant direction and increasing velocity with height.
As shown on the image, wave is triggered by meeting rising terrain. Often wave is marked by lenticular clouds high in the sky. A wave formation can extend for hundreds or even thousands of kilometres in some extreme cases. Many pilots make pilgrimages to the best locations such as Omarama in New Zealand (the Maori name for New Zealand, indeed, means ‘Land of the Long White Cloud’) to use wave to claim records. At Halesland, where Mendip Gliding Club is situated, wave generated over the Black Mountains of South Wales, forms less often but can sometimes be encountered. badge ‘legs’ or to set
Ridge Lift is the one form of lift from which our site benefits when the wind is blowing from the right direction(s). Because MGC is located on the Mendip Hills we have the access to a moderately sized ridge. When a wind is directed more or less perpendicularly to the face of the ridge at speeds of 15 knots or more, flights can be expected to be longer. Many pilots at the Club have used this source of lift for claiming their 5 hour duration flights (for ‘Silver C’ badges). Gliders use this rising air as indicated in the image.
All the diagrams are supplied by Steven Longland.