Vertical draft

A lift is a localized, vertical air movement. In large-scale effects, such as on a front that says you " sliding up ". Counterpart to the updraft are downdraft, downdraft, downburst, colloquially called " air hole".

• 2.1 thermals in Glider
• 2.2 updrafts of gliders and hang-gliders

Formation

Thermal updraft

Thermal updrafts ( thermals ) caused by temperature differences between the air masses. So heated solar radiation, the Earth's surface and in consequence of the overlying air. Since warm air is lighter and less dense than cold air, climb onto the heated air packages like soap bubbles. They will soar on until they find themselves in similar dense air or cooled to the ambient temperature. Climbers feel him often during the afternoon descent as warm headwind from the valley. In their environment less warm air masses sink down again and provide for an exchange of air.

The intensity of the thermals depends on the insolation, the temperature profile of the atmosphere, the characteristics of the surface, the humidity and the irradiation angle. A dry cereal field can dissipate more heat than a wet meadow, a tilted towards the sun mountain flank is more heated than the lowlands. These updrafts are usually limited to some 10 to some 100 meters. Tight updrafts is called in gliding thermals or "beard".

Large-scale updrafts occur mostly under clouds, in particular under cumulus clouds, the usual fair-weather or " fleecy cloud." Clouds are indicators of rising air, the moisture carried cools with increasing altitude and condense when it reaches the dew point. The liberated heat of condensation can in favorable conditions lead to a further upgrade of the air parcels. The cloud then begins from himself, to suck more air and provide further impetus.

At low humidity, or lack of condensation nuclei, cloud formation may also not occur, then one speaks of blue thermals. The thermal updrafts can be located at most by mitaufsteigende pollen or dust.

Hang updraft

Slope updrafts caused by contrast, orographic forced rising of the air when the wind against a mountain side sweeps and windward upslope distracted. On the lee side of the Berggrats the air flows as downdraft down again. In certain situations may arise in Lee updrafts, the so-called lee waves.

Slope updrafts are large-scale and stable by the continuing flow of air as the thermals and allow gliders and paragliders in suitable terrain, ie at a cliff or a cut bank in the valley wind, often quiet, for hours and miles wide soaring.

Lee waves updraft

Mountain waves are caused by a wind weather phenomenon which can on the leeward side ( Lee) created by the mountains. The air flow unit when passing over a mountain range in vibration. The shaft consists of an ascending part ( updraft ) and a downdraft. It may also be horizontal vortex of air rotors. As worn smooth Lenticular these waves can be seen.

These updrafts are a way to rise to great heights for gliders. For other aircraft lee waves are due to the associated high wind speeds can not be used or set by the turbulence rather represents a danger

Convergence

Flowing air masses each other, without being able to move laterally, for example in mountain valleys, then they rise. In the mountains convergences occur, for example, in the vicinity of passports when different valley winds collide. They are sometimes identified by a solitary cloud over the central valley, while others are clouds above mountain peaks.

In the evening, when cooled air on both sides of a valley flows down from the mountain slopes, forms over the valley also a convergence, known in aviation circles as " evening thermals " and popular.

In the free atmosphere convergences occur in connection with fronts and often bring deteriorating weather (clouds, precipitation).

Use

Updrafts in gliding

A glider sets at medium flight speed of 120 km / h is about 33 m / s back. With 1:40 glide ratio which means a decrease of 0.83 m / s Therefore, it is s already slightly rise in an updraft of 1 m / s. The circles in narrow thermals however caused by the skew additional height loss. The " minimum sink " (maximum height loss per unit time) is achieved at a lower speed than the " best glide " (maximum height loss per unit distance traveled ). One good is it, especially when circling in thermals where it does not depend on replacement of track, but in the best possible utilization of the thermal. As zero lift is called a weak thermal sufficient to keep a glider on the height.

For gliding records in long-haul flight or delta flight stable slope winds are more favorable than thermals, because often long distances can be flown without circles on the upswing. The record lengths are already more than 2000 km, on 21 January 2003 flew the pilot Klaus Ohlmann with his co-pilot in Argentina a distance of 3009 km.

Updrafts of gliders and hang-gliders

For paragliders the glide ratio is about 1:9, with hang-gliders at about 1:20. Thus, to be covered as gliders these aircraft not such long distances. But you can fly closer orbits because of their lower speed and exploit climbing in thermals beards better. Dynamic updrafts are of limited use because of the limited maximum speed of this aircraft.

Nevertheless, the track record for gliders is over 500 km.