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Gliding

Gliding (or soaring) is a recreational activity and competitive sport where individuals fly un-powered aeroplanes known as gliders or sailplanes. Properly, the term gliding refers to descending flight of a heavier-than-air craft when its own weight is its sole motive force; soaring is the correct term to use when the craft gains altitude or speed from the atmosphere during the flight.

Recreation or sport?

History

Soaring

On rare occasions, glider pilots have been able to use a technique called "dynamic soaring", where a sailplane can be made to gain kinetic energy by repeatedly crossing the boundary between air masses of different horizontal velocity. However, such zones of high "wind gradient" are usually much too low to be used safely by aircraft, and dynamic soaring is a technique only really useful to birds, notably to the albatrosses who during long flights can be seen repeatedly pulling up, turning, and diving back down through the wind gradient close to the surface of the ocean.

In thermal flight, the glider pilot attempts to find streams of air that are moving upwards as a result of being heated by contact with sun-lit earth. Typical spots to find thermals are over freshly ploughed fields and asphalt roads, however most of the time thermals are hard to associate with any feature on the ground. As it requires rising heated air, thermalling is typically only effective in mid-latitudes from spring through into late summer, other latitudes tend to have vertical air temperatures-gradients suppressing thermal convection, and during winter there is too little solar heat to start thermals. Once a thermal is encountered, the pilot banks sharply to keep the plane turning in a small circle within the thermal. This way gliders can ride upward until the thermal either enters the clouds base (see Visual Flight Rules) or a warmer air layer called a Capping inversion stops it from rising any further.

Ridge running instead looks for air that is being mechanically lifted as it flows up the sides of hills or other vertical changes in the landscape (including buildings in some cases). Ridge running works in any climate or weather, but can only be used in certain locations. Often a combination of ridge and thermal gliding is used. Ridge lift can kick off strong thermals.

Mountain wave flying is a variation of ridge-running allowing the glider to climb much higher. Most sailplane altitude records were set by flying large scale mountain waves in the top flow of long mountain ranges all over the world. The current world distance record of 3008 km by Klaus Ohlmann (on 21 jan 2003) was also flown in the mountain wave in South America.

Glider pilots learn to spot the characteristic cloud formations that usually accompany zones of rising air or "lift". Well-formed cumulus clouds (the fluffy, cotton-wool type of cloud) with sharply defined flat bases often form at the tops of strong thermals, and long, stationary lenticular (lens-shaped) clouds, perpendicular to the wind direction, frequently mark the crests of atmospheric waves.

Launch methods

Sailplanes are normally launched by aero-tow with a single engine tow-plane. Lately, strong self-launching motor gliders and microlight planes have also been permitted to tow gliders. A very economical method for launching gliders is the use of a truck-mounted engine purpose-built winch. The engine is most often from a large car (Opel Diplomat, Oldsmobile) or a diesel truck (or even LPG). There are other engines in use, such as hydrolic fluid engines and electrical engines. Winch launch cost about EUR 3 per start. This is an order of magnitude less compared with an aero-tow. The winch pulls in a 1000-1600m long steel or synthetic fiber rope attached to the sailplane, which releases the rope in about 400-500m altitude after an amazingly short and steep ride comparable to a rocket lauch. This method is prevalent in gliding clubs all over Germany or the Netherlands.

Historically, gliders were also launched using a rubber band, or "bungee". For this launch method, the glider was fixed to its position with a tail hook, which could be released by the pilot. A hook on the nose of the glider was used to attach a rubber band which was pulled by two groups of people. One group ran slightly to the left, the other to the right of the glider. Once the tension in the cable was high enough, the pilot released the tailhook, and the glider would be launched. This method was most often used to launch a glider from a hill or dune, so it could attempt to do some ridge running.

Outlandings

Related sports

Two minimalistic variations of the sport are hang gliding, where instead of a fully-fledged plane with full control surfaces and an enclosed cockpit the craft used is basically a fabric flying wing, and paragliding, where a sophisticated kind of parachute is flown.

See also: glider

External links

• International Gliding Commission
• National Gliding Federations
• Gliding Magazine
• International Gliding Online Contest
• Soaring Society of America
• League of Silent Flight
• Danish Soaring Thermal-League Competition