Lift (soaring)
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Not to be confused with lift (force).
Lift, or more precisely "static lift" is rising air used by soaring birds and by humans in gliding, hang gliding and paragliding to make extended soaring flights. There are four principal types of lift:[1]
- Orographic lift
- Rising air on the windward side of a slope that permits slope soaring known as hill or ridge lift. With winds of 20 to 25 knots (46 km/h), it is possible to soar at an altitude up to two times the height of the obstacle.
- Thermal
- Rising bubbles or columns of unstable air from a relatively warm surface, especially when heated by the sun. The top of the thermal will be marked with a cumulus cloud if the air is moist enough. This is the type of lift most commonly used in modern soaring.
- Mountain wave
- Atmospheric waves which can carry gliders into the stratosphere. With a wind of 25 knots (46 km/h) blowing over an obstruction, and winds increasing with altitude, it is possible to reach heights of 10 times the obstacle height or more in the waves downwind.
- Convergence zone
- The boundary where winds flowing from different air masses meet along a shear line. This creates a narrow band of soarable lift with winds as light as 10 knots (19 km/h).
Although thermal lift was known to the Wright Brothers in 1901, it was not exploited by humans until 1921 by William Leusch at the Wasserkuppe in Germany.[2] It was not until about 1930 that the use of thermals for soaring in gliders became commonplace.[1]
[edit] References
- ^ a b Welch, John (1999). Van Sickle's Modern Airmanship. City: McGraw-Hill Professional, pp. 856-858. ISBN 0070696330. “There are five kinds of lift which the soaring pilot may use....”
- ^ Irving, Frank (1998). The Paths of Soaring Flight. City: World Scientific Publishing Company, p. 53. ISBN 1860940552. “Thermals were known to the Wright Brothers in 1901, but were first really discovered in 1921 by one William Leusch at the Wasserkuppe...”
