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Gliding

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For other uses, see the aerial sport of gliding.

Gliding (or soaring) is a recreational activity and competitive sport where pilots fly un-powered aircraft known as gliders or sailplanes. Properly, the term gliding refers to descending flight of a heavier-than-air craft, whereas soaring is the correct term to use when the craft gains altitude or speed from rising air.[1]

File:LS40075.jpg
A modern glider crossing the finish line of a competition at high speed. It is jettisoning water that has been used as ballast.

The most common methods of launching gliders are by winch or by being towed by powered aircraft. The pilots then search for rising air to gain height. If conditions are good enough, experienced pilots can fly many hundreds, or even thousands, of kilometres before returning to their home airfields — although if the weather deteriorates, they must land elsewhere.

While all recreational glider pilots enjoy the freedom, the scenic views and the sense of achievement, some also compete by flying as quickly as possible round a pre-defined course and back to the starting point. These competitions test the pilots' abilities to make best use of local weather conditions as well as their flying skills. Local and national competitions are organised in many countries and there are also biennial World Gliding Championships.[2]

All methods of launching gliders (apart from self-launching motor-gliders) require assistance from other participants and so gliding clubs have been established to share airfields and equipment, to train new pilots and to maintain high safety standards.

History

The development of heavier-than-air flight between 1853 (Sir George Cayley's coachman) and 1903 (Wright brothers) mainly 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.[3] This 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 it had become an international event. In 1931 Gunther Grönhoff flew on 272 km (169 statute miles) from Munich to Czechoslovakia radically changing what was thought achievable. [4]

In the 1930s gliding spread to many other countries. In the 1936 Summer Olympics in Berlin gliding was a demonstration sport and was scheduled to be a full Olympic sport in the 1940 games. A glider, the Olympia, was developed in Germany for the event but the Second World War intervened. By 1939 the major gliding records were held by Russians, including a distance record of 748 km (465 statute miles).

During the war, civilian gliding in Europe was largely suspended. Although some military operations in WWII involved military gliders, they did not soar and so are unrelated to the sport of gliding. However several German aces, such as Erich Hartmann, had begun their flight training on gliders.

After the war there was a shortage of gliders and a disagreement whether a single type of competition glider would hinder development of new types. [5] As a result gliding did not feature in the 1948 Summer Olympics and subsequent games. The re-introduction of air sports such as gliding to the Olympics has been occasionally proposed by the world governing body, the FAI, but this has been rejected on the grounds of lack of public interest. [6]

In the 1950s in many countries there were a large number of trained pilots, many were also aeronautical engineers, who wanted to continue to fly. These pilots developed many of the clubs which still provide the basis of today's gliding movement. This gave considerable impetus to the development of gliding and gliders. For example, the Soaring Society of America grew from 1,000 members in the 1950s to its present total of 16,000. The increased numbers of pilots and improving technology helped set new records so that the pre-war altitude record was doubled by 1950, and the first 1,000 km (621 statute miles) flight was done in 1964. [7] New materials such as glass fibre and carbon fiber, advances in wing-shapes, electronic instruments, GPS and improved weather forecasting have since allowed many pilots to make flights that were once extraordinary. (Almost 500 pilots now have made flights over 1,000 km.)

In place of Olympic competition there are the World Gliding Championships. The first event was held at the Wasserkuppe in 1937 and since the war, every two years. There are now six competition classes open to both sexes, plus three classes for women and two junior classes. Germany remains the world centre of gliding, and the three major glider manufacturers are still based there. However the sport has been taken up in many countries and there are now over 116,000 active glider pilots,[8] plus military cadets. Each year many other people experience their first glider flight. It does not matter whether the countries are flat or mountainous, hot or temperate, because gliders can soar in most places.

Good gliding weather. Well formed cumulus humilis, with darker bases, suggests active thermals and light winds.

Soaring

Glider pilots can stay airborne for hours by flying through air that is ascending as fast or faster than the glider is descending, thus gaining potential energy.[9] The most commonly used rising masses of 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 m (2,000 ft) above the terrain; thermals, depending on the climate and terrain, can allow climbs in excess of 3,000 m (10,000 ft) in flat country and much higher above mountains; [10] wave lift has allowed a glider to reach an altitude of 15,447 m (50,671 ft). [11] In a few countries gliders can continue to climb into the clouds in uncontrolled airspace but in many countries the pilot must stop climbing before reaching cloud-base (see Visual Flight Rules).

Thermals

Thermals are streams of rising air that are formed on the ground through the warming of the surface by sunlight. If the air contains enough moisture, the water will condense from the rising air and form cumulus clouds (the fluffy, cotton-wool type of cloud) with sharply defined flat bases. Once a thermal is encountered, the pilot flies in circles to keep the glider within the thermal and so can gain altitude before flying off to the next thermal towards the destination. This is known as 'thermalling'. Climb rates depend on conditions, but several metres per second is common. Thermals can also be formed in an 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. [12] Thermals do not always create cumulus clouds. This can happen when the air has little moisture or when an inversion stops the thermal from rising high enough for the moisture to condense. Without clouds or dust devils to mark the thermals, the pilot must use his skill and luck to find them using a sensitive vertical speed indicator called a variometer that quickly indicates climbs or descents. Typical locations to find thermals are over towns, freshly ploughed fields and asphalt roads, but thermals are often hard to associate with any feature on the ground. Occasionally thermals are caused by the exhaust gases from power stations or by fires.

As it requires rising heated air, thermalling is only effective in mid-latitudes from spring through into late summer. During winter the solar heat can only create weak thermals, but ridge and wave lift can still be used.

Ridge lift

A pilot who is ridge soaring uses air that is being lifted as it flows up the sides of hills. It can also be augmented by thermals when the slopes also face the sun. [13] In places where a steady wind blows, a ridge may allow virtually unlimited time aloft, though records for duration are no longer recognised because of the danger of exhaustion.[14]

Wave lift

A lenticular cloud produced by a mountain wave

Mountain waves can produce powerful rising and sinking air, which allow gliders to climb, sometimes to great altitudes. [15] They were discovered by a glider pilot called Wolf Hirth in 1933. The lift is often marked by long, stationary lenticular (lens-shaped) clouds, perpendicular to the wind direction. Most altitude records for gliders have been set by using waves, though thunderstorms have also been used. Supplementary oxygen is used for high-altitude flights in gliders to avoid the risk of hypoxia. The current world distance record of 3,008 km (1,869 statute miles) by Klaus Ohlmann (set on 21 January 2003)[16] was also flown using mountain waves in South America.

A rare wave phenomenon is known as Morning Glory. Its roll cloud produces strong lift and near the Gulf of Carpentaria it is used by glider pilots in spring.

Other sources of lift

The boundaries where two air masses meet are known as a convergence zone. These can occur in sea breezes or in desert regions. 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.

On rare occasions glider pilots have been able to use a technique called "dynamic soaring", where a glider 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 gliders, so dynamic soaring is a technique only really useful to radio controlled model aircraft and to birds.

Launch methods

Gliders are launched into the air by one of several methods, the most common are 'aerotowing' and 'winching'.[17]

Aerotowing

File:AT0134.jpg
A Pawnee aerotowing a glider.

Aerotows normally use single-engined light aircraft, but motor gliders have also been permitted to tow gliders. The tow aircraft takes the glider to the desired height and place and the glider pilot releases the rope. At the tow plane end, a weak link is often fitted to the rope to ensure that any sudden loads do not damage the airframe of the tow plane.

During the aerotow, the glider pilot keeps the glider in one of two positions behind the tow plane.[18] This position can either be the "low tow" position, just below the slipstream from the tow-plane's propeller, or the "high tow" position just above the slipstream. In Australia the convention is to fly in low tow, whereas in the United States and Europe the high tow prevails. One aerotow variation is to attach two gliders to one tow plane, using a short rope for the high towed glider and the long rope for the low tow.

Winch-launching

A Ventus 2b being winch- launched at Lasham Airfield.

Gliders are often launched using a stationary ground-based winch mounted on a heavy vehicle. This method is widely used at many European clubs, often in addition to aerotowing. The engine is usually a large diesel, though hydraulic fluid engines and electrical motors are also used. The winch pulls in a 1,000 to 1,600 m (3,000 to 5,500 ft) long cable made of steel wire or a synthetic fibre which is attached to the glider. The glider releases the cable at a height of about 400 to 500 m (1,300 to 1,600 ft) after a short and steep ride. The main advantage of the winch launch is that it costs much less than an aerotow. One disadvantage of winch launching is that the launch height is usually lower than an aerotow, so that the flights are shorter unless the pilot can quickly make contact with a source of lift within a few minutes of releasing the cable. Although there is a risk of the cable breaking during this type of launch, this eventuality is frequently rehearsed.

Other methods of launching

A bungee launch at the Long Mynd by the Midland Gliding Club

In a few places gliders are launched from the top of a hill into a strong breeze using a rubber band, or "bungee". For this launch method, the glider's main wheel rests in a small concrete trough. The hook that is normally used for winch-launching is instead attached to the middle of the bungee. Each end of the bungee is then pulled by three or four people. One group runs slightly to the left, the other to the right of the glider. Once the tension in the bungee is high enough, the pilot releases the wheel brake and the glider's wheel pops out of the trough. The glider gains just enough energy to leave the ground and to fly away from the hill.

Another launch method, now uncommon, is the "autotow". This needs a long runway, a pick-up truck and a length of cable. After gently taking up slack in the cable, the driver accelerates hard and the glider rises like a kite to as much as 400 metres (1300 ft) if there is a good headwind and a runway of 1.5 km (1 mile) or more. A variation on this is the "reverse pulley" method in which the truck drives towards the glider that it is launching; the cable passing around a pulley at the far end of the airfield.

Glider licenses in some countries differentiate between aerotows and ground launch methods, due to the widely different techniques. Glider pilots who want to use both of these types of launch methods need to be proficient and in current practice in both.

Cross-country

File:Nimbus2.jpg
Glider on a cross-country flight in the Alps

Gliders can stay airborne for hours if the conditions are good. This enables gliders to fly long distances at high speeds. The record speed for 1,000 km is 169.7 km/h (621 statute miles at 105 miles/h). [19] Even in places with less favourable conditions (such as northern European countries) most good pilots have flights over 500 km (310 statute miles) every year. As the performance of gliders improved in the 1960s, the concept of flying as far away as possible became unpopular with the crews who had to retrieve the gliders. Pilots now aim to fly around a course (called a task) and back to the starting point.[20]

In addition to just trying to fly further, glider pilots also race each other in competitions. The winner is the fastest, or, if the weather conditions are poor, the furthest round the course. Tasks of up to 1000 km have been set[21] and speeds of 120 km/h are not unusual.

Originally proof of getting to the turn-points was gathered by observing the gliders from the ground. Later the pilots took photographs of the turn-points but nowadays gliders carry secure devices that record the position every few seconds from GPS satellites. National competitions generally last one week but international championships are normally over two weeks. The winner is the pilot who has amassed the greatest number of points over all the contest days. Because it would be unsafe for many gliders to cross a start line at the same time, pilots can choose their own start time. Furthermore, gliders are not visible to spectators for long periods during each day's contest and scoring is complex, so gliding competitions have been difficult to televise. This means that gliding is a sport in which the contestants are still amateurs.

In an attempt to widen the appeal of gliding contests, a new format contest, the Grand Prix, has been introduced.[22] Innovations introduced in the Grand Prix format include simultaneous starts for a small number of gliders, tasks consisting of multiple circuits, and simplified scoring. Also gaining popularity in recent years is an informal internet competition called the On-Line Contest [23] where pilots upload their GPS data files and are automatically scored based on distance flown. Nearly 9,000 pilots worldwide participate in this contest.

Maximising cross-country speed

Soaring pioneer Paul MacCready developed a mathematical theory for optimizing cross country soaring speeds.[24] His speed to fly theory allows the optimal cruising speed between thermals to be computed, using thermal strength, glider performance and other variables. The theory accounts for the fact that if a pilot flies faster between thermals, the next thermal is reached sooner. However at higher speeds the glider also sinks faster, requiring the pilot to spend more time circling to regain the altitude. The MacCready speed represents the optimal trade-off between cruising and circling. Most competition pilots make use of MacCready theory to optimize their flight speeds, and have the calculations programmed in their flight computers.

On cross-country flights where strong thermals are forecast, pilots fly with water ballast, which is stored in integral water tanks in the wings and in the tail fin. The ballast makes the glider fly faster, but it also makes the glider climb more slowly in thermals. However, if the thermals are strong, the disadvantage of slower climbs are outweighed by the higher cruising speeds between thermals. Thus, the pilot can improve the speed over the course by several percent. To prevent over-stressing the glider, the flight manuals of gliders require that the pilot should dump the water before landing.

Badges

Achievements in gliding have been marked by the awarding of badges since the 1920s. For the lower badges, such as the first solo flight, national glider federations set their own criteria. Typically a bronze badge shows preparation for cross-country flight, including precise landings and a pair of two hour flights. The higher badges follow the standards set down by the Federation Aeronautique Internationale (FAI). [25]

The FAI badges are defined in kilometers and meters. Earning the Silver Badge shows that a glider pilot has achieved an altitude gain of at least 1,000 m, made a five-hour duration flight, and has flown cross-country for a straight-line distance of at least 50 km: usually, but not invariably, in separate flights. The Sporting Code[26] defines the rules for observers and recording devices to validate the claims for badges. The Gold and Diamond Badges require pilots to fly higher and farther. A pilot with the three "Diamonds" has flown 300 km to a pre-defined goal, has flown 500 km in one flight (but not necessarily to a pre-defined goal) and gained 5,000 m in height. The FAI also issues a diploma for a flight of 1,000 km and further diplomas in increments of 250 km.

Landing out

File:OL0026.jpg
Pilot and crew about to de-rig a glider

If lift is not found during a cross-country flight, for example because of deteriorating weather, the pilot must choose a field and 'land out'. Although inconvenient and often mistaken for 'emergency landings', landing out is a routine event in cross-country gliding. From the air the pilot has to choose a field where it is safe to land and where the landing will not cause damage to the property. [27]

The glider and pilot can be retrieved by the pilot's ground crew using a purpose-built trailer which can be towed by a car. Alternatively, if the glider has landed in a suitable field, a tow plane can be summoned to re-launch the aircraft (with the permission of the field's owner). The pilot typically pays for the time the tow plane is in the air, both to and from the field, so this alternative can become expensive.

Use of engines

ASH25M - a self-launching two-seater glider

To avoid the inconvenience of landing out some gliders have a small engine and a retractable propeller, but these add to the weight and expense of a glider. 'Self-launching' gliders have engines that are powerful enough to launch the glider unaided. In 'self-sustaining' gliders' these engines are not powerful enough to launch the glider, but they can provide enough power to climb slowly and return to the home airfield. However, engines have to be started at a height that includes a margin that would still allow a safe outlanding to be made, if the engine were to fail to start. [28] Starting the engine is regarded as ending the flight in a competition. Gliders without an engine are lighter and, without needing a safety margin for starting the engine, they can safely thermal much lower. Consequently unpowered gliders may complete competition flights when the powered competitors cannot.

Touring motor gliders have a non-retractable propeller and the additional drag reduces the gliding performance. Although seldom used in competition, touring motor gliders can be particularly useful in training a pilot for cross-country flying. After take-off, the engine is switched off and the pupil pilot flies the aircraft as a glider, while also learning to navigate. Landings in unfamiliar fields can be practised while the motor is idling. If the pupil chooses and inappropriate field or misjudges the approach, the instructor can wait until the last moment before applying power and climbing away.

Aerobatics

File:SW0001.jpg
S-1 Swift - modern aerobatic glider

Aerobatic competitions are regular events.[29] In this type of competition, the pilots fly a program of maneuvers (such as inverted flight, loop, roll, and various combinations). Each maneuver has a rating called the "K-Factor". Efficient maneuvers also enable the program to be completed with the height available. This number of points is given if the maneuver is flown perfectly, otherwise a number of points is subtracted. The winner is the pilot with the highest sum of points.

Hazards

Although considered a relatively safe form of aviation, there are hazards in gliding. Gliders surround the pilot with a strong structure and the bi-monthly accident review in Sailplane & Gliding shows that most accidents cause no injuries. Training and safe procedures are central to the ethos of the sport. Nevertheless a small number of fatal accidents occur every year, almost all caused by pilot error. Causes include:

  • mid-air collisions: gliders pilots tend to fly to the same areas of lift and so there is a risk of collisions between gliders. To avoid other gliders and other general aviation traffic, pilots must comply with the rules of the air and keep a good look-out. They also usually wear parachutes. In Switzerland, Austria and Germany, the FLARM warning system is used to avoid mid-air collisions between gliders. Collisions with commercial aircraft are unlikely because gliders have greatly restricted access to the controlled airspace used by airliners
  • incorrect procedure during launch, especially when using a winch. A wing catching the ground, unlocked airbrakes, too rapid rotation into the full climb and too slow a speed during the launch can cause problems
  • incorrect landing procedures: a poorly trained pilot can undershoot or overshoot the landing area and so hit obstructions
  • low speeds while turning before landing, especially if excessive rudder is used, can cause a spin. The training of glider pilots emphasises spin avoidance and spin recovery
  • in-flight structural failures: these occur rarely because large safety margins are used when building gliders. High loads are needed to cause structural failures but they can arise during aerobatics or when incorrectly recovering from a loss of control. Annual inspections of gliders and training reduce the already minimal chances of structural problems
  • unconnected controls and other fittings: gliders are designed to be rigged each day. If the glider is not assembled properly, a pilot will not be able to control the glider. The controls of most of the gliders built in the last twenty years connect automatically
  • outlandings: there is some risk of striking power lines or other unseen objects on the ground when cross-country pilots have to make outlandings
  • contact with terrain: pilots who fly in mountainous terrain are especially wary of the risk of flying too close, especially in turbulent conditions
  • hypoxia: pilots who fly high should be aware of the need to use supplementary oxygen, incidents are therefore rare
  • failure to anticipate severe weather: storms may cause rapid and unpredictable changes in the wind when landing.
  • ground handling accidents: in high gusty winds, it is possible for an unsupervised glider to be blown over or even to take-off. If correct procedures are not followed, people nearby may be hurt by any unsecured gliders.

Challenges for the gliding movement

Gliding as a sport faces challenges in the years ahead. [30] These include:

  • Time pressures on participants: gliding typically takes whole days, which many people today find harder to devote. As a result the average age of glider pilots is getting older
  • Airspace: in many European countries the growth of civil aviation is reducing the amount of uncontrolled airspace
  • Competition from other activities: there is now a greater variety of similar sports such as hang gliding and paragliding that may attract potential glider pilots
  • Lack of publicity: without coverage by television, many people are unaware of the sport

Learning to glide

A Blanik L-23. A common training glider

Most clubs offer trial lessons to people interested in learning to glide and will accept bookings by phone. The national organisations given below will give the contact details for the nearest clubs. The pupil flies with an instructor in a two-seat glider fitted with dual controls. The instructor does the first launches and landings but otherwise the pupil uses the controls. Some clubs offer courses over several days, though, with a mixture of winch and aerotow launches, it often takes ab initios at least 50 training flights before they are allowed to fly solo. [31]

If winches are used, the cost of learning to glide is much less than that of learning to fly powered aircraft. If aerotowing is the only available method of launching, costs are higher than using winches even though fewer launches might be needed, perhaps as few as 30. Simulators are also beginning to be used for training, especially during poor weather.

Early solo flights are restricted to within gliding range of the airfield. Further training continues after the first solo until the pupil is judged capable of taking a glider cross-country. Some studying is required on topics such as the regulations, use of the radio, weather and navigation.

See also

Some national gliding associations

Notable glider pilots

Other pilots can be found at Category:Glider pilots.

Two minimalistic variations of the sport are hang gliding, where instead of a glider's full control surfaces and an enclosed cockpit, the craft has a fabric flying wing; and paragliding, where a sophisticated kind of parachute is flown. Another variation of the sport is radio-controlled gliding, where the operator of the aircraft flies the model glider from the ground via radio transmission.

References

  1. ^ "Frequently asked questions about gliding" (PDF). Retrieved 2006-08-24.
  2. ^ "Information about gliding competitions" (PDF). Retrieved 2006-08-24.
  3. ^ "History of gliding" (PDF). Retrieved 2006-08-24.
  4. ^ Welch, Ann (1980). The Story of Gliding 2nd edition. John Murray. ISBN 0-7195-3659-6.
  5. ^ Welch, Ann (1980). The Story of Gliding 2nd edition. John Murray. ISBN 0-7195-3659-6.
  6. ^ "FAI the Olympics". Retrieved 2006-08-24.
  7. ^ Welch, Ann (1980). The Story of Gliding 2nd edition. John Murray. ISBN 0-7195-3659-6.
  8. ^ "FAI membership summary". Retrieved 2006-08-24.
  9. ^ "Visual explanation of soaring". Retrieved 2006-08-24.
  10. ^ "Mountain flying". Retrieved 2006-09-14.
  11. ^ "Altitude record". Retrieved 2006-09-01.
  12. ^ "Diagram of thermals". Retrieved 2006-09-05.
  13. ^ "Diagram of ridge lift". Retrieved 2006-09-05.
  14. ^ "Duration record". Retrieved 2006-08-24.
  15. ^ "Diagram of wave lift". Retrieved 2006-09-05.
  16. ^ "Distance record". Retrieved 2006-08-24.
  17. ^ "Further information on launch methods". Retrieved 2006-09-03.
  18. ^ "Aerotowing explained". Retrieved 2006-09-03.
  19. ^ "FAI World records page". Retrieved 2006-09-06.
  20. ^ "On Line Contest". Retrieved 2006-08-24.
  21. ^ "Typical competition results". Retrieved 2006-08-24.
  22. ^ "Sailplane Grand Prix". Retrieved 2006-08-24.
  23. ^ "On Line Contest". Retrieved 2006-08-24.
  24. ^ "MacCready Theory". Retrieved 2006-08-24.
  25. ^ "FAI Badges page". Retrieved 2006-09-07.
  26. ^ "FAI Sporting Code". Retrieved 2006-08-24.
  27. ^ "Code of practice for field landings". Retrieved 2006-09-04.
  28. ^ "Information about self-sustaining gliders". Retrieved 2006-09-04.
  29. ^ "Information about gliding aerobatics". Retrieved 2006-08-24.
  30. ^ "Challenges facing gliding reported to FAI". Retrieved 2006-09-18.
  31. ^ "Information about learning to glide". Retrieved 2006-08-24.

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