Gliding is a recreational activity and competitive air sport[1] in which pilots fly unpowered aircraft known as gliders or sailplanes using naturally occurring currents of rising air in the atmosphere to remain airborne. The word soaring is also used for the sport.[2]
 A Ventus 2 glider landing while jettisoning water that has been carried as ballast | |
| Highest governing body | Fédération Aéronautique Internationale |
|---|---|
| Characteristics | |
| Contact | No |
| Mixed gender | Yes |
| Type | Air sports |
| Presence | |
| Country or region | Worldwide |
| Olympic | No |
| World Games | 2017 (aerobatics) |
Gliding as a sport began in the 1920s. Initially the objective was to increase the duration of flights but soon pilots attempted cross-country flights away from the place of launch. Improvements in aerodynamics and in the understanding of weather phenomena have allowed greater distances at higher average speeds. Long distances are now flown using any of the main sources of rising air: ridge lift, thermals and lee waves. When conditions are favourable, experienced pilots can now fly hundreds of kilometres before returning to their home airfields; occasionally flights of more than 1,000 kilometres (621 mi) are achieved.[3]
Some competitive pilots fly in races around pre-defined courses. These gliding competitions test pilots' abilities to make best use of local weather conditions as well as their flying skills. Local and national competitions are organized in many countries, and there are biennial World Gliding Championships.[4][5] Techniques to maximize a glider's speed around the day's task in a competition have been developed, including the optimum speed to fly, navigation using GPS and the carrying of water ballast. If the weather deteriorates pilots are sometimes unable to complete a cross-country flight. Consequently, they may need to land elsewhere, perhaps in a field, but motorglider pilots can avoid this by starting an engine.
Powered-aircraft and winches are the two most common means of launching gliders. These and other launch methods require assistance and facilities such as airfields, tugs, and winches. These are usually provided by gliding clubs who also train new pilots and maintain high safety standards. Although in most countries the standards of safety of the pilots and the aircraft are the responsibility of governmental bodies, the clubs and sometimes national gliding associations often have delegated authority.
History
The development of heavier-than-air flight in the half century between Sir George Cayley's coachman in 1853 and the Wright brothers in 1903 mainly involved gliders (see History of aviation). However, the sport of gliding only emerged after the First World War, as a result of the Treaty of Versailles,[6] which imposed severe restrictions on the manufacture and use of single-seat powered aircraft in Germany's Weimar Republic. 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 aircraft, 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 farther and faster. With the active support of the German government, there were 50,000 glider pilots by 1937.[7] The first German gliding competition was held at the Wasserkuppe in 1920,[8][9]:51 organized by Oskar Ursinus. The best flight lasted two minutes and set a world distance record of 2 kilometres (1.2 mi).[9]:54 Within ten years, it had become an international event in which the achieved durations and distances had increased greatly. In 1931, Gunther Grönhoff flew 272 kilometres (169 mi) on the front of a storm from Munich to Kadaň (Kaaden in German) in Western Czechoslovakia, farther than had been thought possible.[9]:85
In the 1930s, gliding spread to many other countries. In the 1936 Summer Olympics in Berlin gliding was a demonstration sport, and it was scheduled to be a full Olympic sport in the 1940 Games.[9]:148 A glider, the Olympia, was developed in Germany for the event, but World War II intervened. By 1939 the major gliding records were held by Russians, including a distance record of 748 kilometres (465 mi).[9]:107 During the war, the sport of gliding in Europe was largely suspended, though several German fighter aces in the conflict, including Erich Hartmann, began their flight training in gliders.[10] :46
Gliding did not return to the Olympics after the war for two reasons: a shortage of gliders, and the failure to agree on a single model of competition glider. (Some in the community feared doing so would hinder development of new designs.)[9]:172 The re-introduction of air sports such as gliding to the Olympics has occasionally been proposed by the world governing body, the Fédération Aéronautique Internationale (FAI), but has been rejected on the grounds of lack of public interest.[11]
In many countries during the 1950s, a large number of trained pilots wanted to continue flying. Many were also aeronautical engineers who could design, build and maintain gliders. They started both clubs and manufacturers, many of which still exist. This stimulated the development of both gliding and gliders, for example the membership of the Soaring Society of America increased from 1,000 to 16,000 by 1980.[12] The increased numbers of pilots, greater knowledge and improving technology helped set new records, for example the pre-war altitude record was doubled by 1950,[9]:195 and the first 1,000-kilometre (620 mi) flight was achieved in 1964.[13] New materials such as glass fiber and carbon fiber, advances in wing shapes and airfoils, electronic instruments, the Global Positioning System and improved weather forecasting have since allowed many pilots to make flights that were once extraordinary. Today over 550 pilots have made flights over 1,000 kilometres (620 mi).[14] Although there is no Olympic competition, there are the World Gliding Championships. The first event was held at the Samedan in 1948.[9]:161 Since World War II it has been held every two years. There are now six classes open to both sexes, plus three classes for women and two junior classes. The latest worldwide statistics for 2011 indicate that Germany, the sport's birthplace, is still a center of the gliding world: it accounted for 27 percent of the world's glider pilots,[15] and the three major glider manufacturers are still based there. However the meteorological conditions that allow soaring are common and the sport has been taken up in many countries. At the last count, there were over 111,000 active civilian glider pilots and 32,920 gliders,[15] plus an unknown number of military cadets and aircraft. Clubs actively seek new members by giving trial flights, which are also a useful source of revenue for the clubs.[16]
Soaring
Glider pilots can stay airborne for hours by flying through air that is ascending as fast or faster than the glider itself is descending, thus gaining potential energy.[17] The most commonly used sources of rising air are
- thermals (updrafts of warm air);
- 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 600 metres (2,000 ft) above the terrain; thermals, depending on the climate and terrain, can allow climbs in excess of 3,000 metres (9,800 ft) in flat country and much higher above mountains;[17] wave lift has allowed a glider to reach an altitude of 23,202 metres (76,122 ft).[18] In a few countries such as the UK, gliders may continue to climb into the clouds in uncontrolled airspace,[19] but in many European countries the pilot must stop climbing before reaching the cloud base (see Visual Flight Rules).[20]
Thermals
Thermals begin as bubbles of rising air that are formed on the ground through the warming of the surface by sunlight.[17] If the air contains enough moisture, the water will condense from the rising air and form cumulus clouds.[21]:41 When the air has little moisture or when an inversion stops the warm air from rising high enough for the moisture to condense, thermals do not create cumulus clouds. Without clouds or dust devils to mark the thermals, thermals are not always associated with any feature on the ground. The pilot must then use both skill and luck to find them using a sensitive vertical speed indicator called a variometer that quickly indicates climbs and descents. Occasionally reliable thermals can be found in the exhaust gases from power stations or from fires.[22] :6[23]:72[24]:29
Once a thermal is encountered, the pilot can fly in tight circles to keep the glider within the thermal, thus gaining altitude before flying toward the destination or to the next thermal. This is known as "thermalling". Alternatively, glider pilots on cross-country flights may choose to 'dolphin'. This is when the pilot merely slows down in rising air, and then speeds up again in the non-rising air, thus following an undulating flight path. Dolphining allows the pilot to minimize the loss of height over great distances without spending time turning. Climb rates depend on conditions, but rates of several meters per second are common and can be maximized by gliders equipped with flaps. Thermals can also be formed in a line usually because of the wind or the terrain, creating cloud streets. These can allow the pilot to fly straight while climbing in continuous lift.[22]:61
As it requires rising heated air, thermalling is most effective in mid-latitudes from spring through late summer. During winter, the sun's heat can only create weak thermals, but ridge and wave lift can still be used during this period.[21]:108
Ridge lift
A ridge soaring pilot uses upward air movements caused when the wind blows on to the sides of hills. It can also be augmented by thermals when the slopes also face the sun.[6][24]:135 In places where a steady wind blows, a ridge may allow virtually unlimited time aloft, although records for duration are no longer recognized because of the danger of exhaustion.[25]
Wave lift
The powerfully rising and sinking air in mountain waves was discovered by glider pilot, Wolf Hirth, in 1933.[9]:100 Gliders can sometimes climb in these waves to great altitudes, although pilots must use supplementary oxygen to avoid hypoxia.[24]:149
This lift is often marked by long, stationary lenticular (lens-shaped) clouds lying perpendicular to the wind.[6] Wave lift was used to set the current altitude record (to be ratified) of 23,202 metres (76,122 ft) on 2 September 2018 over El Calafate, Argentina. The pilots, Jim Payne and Tim Gardner, wore pressure suits.[18] The current world distance record of 3,008 kilometres (1,869 mi) by Klaus Ohlmann (set on 21 January 2003)[26] was also flown using mountain waves in South America.
A rare wave phenomenon is known as Morning Glory, a roll cloud producing strong lift. Pilots near Australia's Gulf of Carpentaria make use of it in springtime.[27]
Other sources of lift
The boundaries where two air masses meet are known as convergence zones.[28]:100 These can occur in sea breezes or in desert regions. In a sea-breeze front, cold air from the sea meets the warmer air from the land and creates a boundary between two masses of air like a shallow cold front. Glider pilots can gain altitude by flying along the intersection as if it were a ridge of land. Convergence may occur over considerable distances and so may permit virtually straight flight while climbing.[24]:55
Glider pilots have occasionally been able to use a technique called "dynamic soaring"[22]:35 allowing a glider 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 too close to the ground to be used safely by gliders.[22]:35
Launch methods
Most gliders do not have engines or at least engines that would allow a take-off under their own power. Various methods are therefore used to get airborne. Each method requires specific training, therefore glider pilots must be in current practice for the type of launch being used. Licensing rules in some countries, such as the US, differentiate between aerotows and ground launch methods, due to the widely different techniques.[29][30]
Aerotowing
In an aerotow a powered aircraft is attached to a glider with a tow rope. Single-engined light aircraft or motor gliders are commonly used. The tow-plane takes the glider to the height and location requested by the pilot where the glider pilot releases the tow-rope.[31]:133 A weak link is often fitted to the rope to ensure that any sudden loads do not damage the airframe of the tow-plane or the glider. Under extreme loads the weak link will fail before any part of the glider or plane fails.[32] There is a remote chance that the weak link might break at low altitude, and so pilots plan for this eventuality before launching.
During the aerotow, the glider pilot keeps the glider behind the tow-plane in either the "low tow" position, just below the wake from the tow-plane, or the "high tow" position just above the wake.[33]:7–11 In Australia the convention is to fly in low tow, whereas in the United States and Europe the high tow prevails. One rare aerotow variation is attaching two gliders to one tow-plane, using a short rope for the high-towed glider and a long rope for the low tow. The current record is nine gliders in the same aerotow.[34]
Winch launching