COMBAT AND COMPETITION.pdf - Lakes Gliding Club

HOW A GLIDER FLIES
A glider flies, like an aeroplane, when the speed of the airflow over the wings
produces lift. In an aeroplane this speed is provided by the engine. A glider
obtains its speed by following a descending path through the air, using gravity
as its motive power.
If the pilot can find and fly in an upcurrent, which is going up faster than the
rate at which the glider is descending, it will gain height and the flight will be
prolonged. This is soaring.
Traditionally a pilot soars across country by circling and gaining height in
rising currents of warm air, called thermals. Having used a thermal in this way
he then flies straight, and often quite fast, in the direction he wants to go.
During this phase height will be lost and the pilot will be looking for another
thermal in which to climb up again.
When the air is moist, the rising thermal upcurrent will produce a cumulus
cloud at its top. The pilot uses these cloud markers dotted about the sky on a
fine summer's day to seek out thermals. If the air is dry, cumulus clouds do not
appear and the thermals are said to be 'blue.' Thermals rise generally to some
three to five thousand feet in Britain during the summer. In the winter any
thermals that do develop are weak and mostly unusable.
Gliders have flat gliding angles and will travel a long way for little loss of
height. Modem high performance gliders, or sailplanes, may achieve or even
exceed 1:50 and thus can travel in excess of 50 miles from a height of a one
mile - 5,280 feet. In good weather conditions it is often possible for such
efficient soaring machines to fly for considerable distances without circling,
slowing down in thermals and speeding up between them. This is dolphin flying.
Gliders can also soar in the upcurrents created by wind blowing over a hill.
These upcurrents are known as slope or hill lift.
Giant atmospheric wave systems frequently develop over, around, and
particularly in the lee of hilly and mountainous regions. They can extend over
hundreds of square miles and may sometimes be identified by the lens shaped
'Zeppelin Clouds' well known to mountaineers - hard edged and high in the sky.
In moist conditions these 'Standing Waves' may reveal themselves in long
parallel gaps, lying across the wind, between adjacent areas of lower cloud.
Gliders can soar in the upward moving areas of these waves. Flights to heights
in excess of thirty to forty thousand feet and over distances of many hundred
miles are possible.
Acknowledgements to the British Gliding Association.
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