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 gravity (its own weight) is its sole motive force; soaring is the correct term to use when the craft gains altitude or speed from movements of the atmosphere during the flight.
Recreation or sport?
While recreational glider enthusiasts enjoy the freedom, scenic views and sheer enjoyment of controlling the planes, others concentrate on building their own craft, while still others fly in competitions where the goal is to complete a circuit around designated "turning-points" as quickly as possible. These competitions test the pilot's (and, in two-seat gliders,the co-pilot's) ability to recognise and make use of local weather conditions, their flying skills and navigational abilities. There are also glider aerobatics competitions.
History
Nearly all developments in heavier-than-air flight between 1853 (Sir George Cayley's coachman), and 1903 (Wright brothers) involved gliders (See History of Aviation). However, the sport of gliding only emerged after the First World War and the reason for its development can be traced to the Treaty of Versailles. The peace settlement imposed severe restrictions on the manufacture and use of single-seater powered aeroplanes in Germany. Thus, in the 1920s and 1930s, while aviators and aircraft makers in the rest of the world were working to improve the performance of powered aeroplanes, the Germans were designing, developing and flying ever more efficient gliders and discovering ways of using the natural forces in the atmosphere to make them fly further and faster. The first German gliding competition was held at the Wasserkuppe in 1920, organised by Oskar Ursinus, and ten years later had become an international event. The sport has since taken hold in many countries, not only those offering large areas of relatively flat land but also those where the terrain provides more challenging flying. Germany, however, remains the world centre of gliding, as evinced by the fact that all the major glider manufacturers are based in that country.
Good gliding weather. Well formed
cumulus humilis, with white bases, suggests active
thermals and light winds.
Soaring
Soaring is usually achieved by flying through a mass of air that is ascending as fast or faster than the sailplane is descending, and thus gaining potential energy. The most commonly exploited rising masses of air are thermals (updrafts of hot ground layer air caused by local differences in air temperature), ridge lift (found where the wind blows against the face of a hill and is forced to rise), and wave lift (standing waves in the atmosphere, analogous to the ripples on the surface of a stream). Ridge lift rarely allows pilots to climb much higher than about 2,000 ft (600 m); thermals, depending on the climate and terrain, can exceed 10,000 ft (3 000 m) in flat country and much higher in the mountains; wave lift has allowed gliders to achieve altitudes approaching 50,000 ft (15 000 m).
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.
Badges
A challenging aspect of soaring is the attainment of badges, pins which since the 1920s have been awarded for specific achievements. For the lower badges national glider federations set their own criteria. For example, in the United States an "A" badge is issued for the first solo, while "B" and "C" require longer flights and more training. A bronze badge shows preparation for cross-country work, including spot landings and a pair of two hour flights. The Soaring Society of America also issues badges for going above 25,000 feet and for enough cross-country flying to circle the world!
The higher badges follow the standards set down by the Federation Aeronautique Internationale. Earning a silver badge shows that a glider pilot has achieved an altitude gain of at least 1000 meters, made a five hour flight, and gone cross-country at least 50 kilometers. These can be done on separate flights, but observers and recording devices are needed to make the claims "legal," and a pilot should know the rules before starting. In the United States alone, over 6000 have been issued.
The gold and diamond badges require higher and longer flights. The ultimate challenge is to add a "2000 km" scroll for a single flight exceeding that distance. Only a few people have ever achieved it.
Launch methods
Gliders are initially launched into the air by one of several methods, most commonly "aerotowing" (being towed behind a powered aircraft by means of a detachable cable) or "winching" (using a stationary ground-based winch possibly mounted on a heavy vehicle). Other less common methods are "auto-towing" (towing behind a car or truck), "reverse auto-towing" (like auto-towing except the launch cable is threaded through a fixed pulley at one end of the airfield, so the truck is driving towards the aircraft),"bungee-launching" (propulsion from a steep hillside using an elastic rope) and "self-start" (a retractible engine is placed on the glider).
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
Outlandings are common in cross country gliding. These are often mistaken for 'emergency landings'. They are entirely normal, although a hassle. When this happens, either the pilot's ground crew is called in to retrieve the plane in a purpose-built trailer which can easily be towed by a car, or, if the sailplane has landed in a field where it can be safely towed out (with the field owner's permission of course), a tow plane is dispatched to relaunch the aircraft.
To avoid this time consuming hassle, some modern more expensive gliders have a very light retractable propeller/two-stroke engine, too light for self take off but enough to allow them to return to their home airfield.
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
- Links to all national gliding federations http://start.fai.org/gliding-federations.asp
- International Gliding Commission http://www.fai.org/gliding/
- Gliding Magazine http://www.glidingmagazine.com/
- International Gliding Online Contest http://www.onlinecontest.org/olcphp/olc-i.php?olc=olc-i
- League of Silent Flight http://www.silentflight.org/
- Danish Soaring Thermal-League Competition http://www.termik-ligaen.dk/
Last updated: 02-08-2005 12:35:10
Last updated: 05-03-2005 17:50:55
