How The Glider 'Soars'

Once they have left the tow plane, gliders are always descending through the air. Whilst we are aware of winds blowing horizontally, there are also vertical movements of the air, up or down. If a glider encounters rising air, or 'lift' the glider descends slower or rises and a skill which pilots develop is how to locate and use lift. The diagrams below illustrates the three sources of lift, all of which are exploited at our club.

When the wind blows against an obstruction, such as a hill or mountain range, the air is forced over the top, creating a band of rising air in front of and above the face of the hill. Provided that the glider is flown within this band, the pilot can stay aloft for many hours. The maximum height achieved in hill lift is normally about double the hill height. The hills of the College Valley including Cheviot, the hills from Yeavering Bell, at the mouth of the College Valley, to Humbleton, near Wooler and the lower hills at Milfield and Doddington are all used for hill soaring locally.

Dark areas of ground heat up more rapidly from the Sun's rays than lighter areas. The warm ground, in turn, heats the air directly above it. This invisible, heated air expands, becoming lighter, causing it to rise in a column or bubble which can rise thousands of feet. This is a 'thermal' and is often marked by fluffy white 'cauliflower' or cumulus clouds. By circling in these thermals gliders gain height which can then be used to fly across country to another thermal. In this way gliders can cover considerable distances, our club record is over 300km but the UK record is more than 1000 km ! (640 miles)

When the wind blows over a hill or mountain range it can, under certain conditions, cascade down the downwind or leeward side of the hill before rebounding in a series of 'waves'. (A similar phenomena can be seen downstream of a rock in a river) These waves can extend for several cycles downwind of the hill or mountain and to considerable height. Waves are often marked by smooth lens shaped, or Lenticular, clouds. Despite often forming in strong winds, these clouds form across the wind and appear stationary with respect to the ground. As can be seen from the diagram above, the air alternately rises and descends. By flying in the rising part of the wave gliders can reach impressive heights. As a rule of thumb the maximum height the wave reaches is around 10 times the height of the obstruction. Our club record is approximately 28,000' achieved in the lee of Cheviot (2682'), the World record is approximately 50,000' ! A bottled oxygen supply is needed for pilots to fly above 10,000'.