Gliding
Overview
 
Gliding is a recreational activity and competitive air sport
Air sports
The term Air sports covers a range of aerial activities such as:* Aerobatics* Ballooning* General aviation including Air racing* Gliding* Hang gliding* Human powered aircraft* Model aircraft* Parachuting* Paragliding...

 in which pilots fly unpowered aircraft
Glider aircraft
Glider aircraft are heavier-than-air craft that are supported in flight by the dynamic reaction of the air against their lifting surfaces, and whose free flight does not depend on an engine. Mostly these types of aircraft are intended for routine operation without engines, though engine failure can...

 known as gliders
Glider (sailplane)
A glider or sailplane is a type of glider aircraft used in the sport of gliding. Some gliders, known as motor gliders are used for gliding and soaring as well, but have engines which can, in some cases, be used for take-off or for extending a flight...

 or sailplanes using naturally occurring currents of rising air in the atmosphere to remain airborne. The word soaring is also used for the sport.

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.
Discussions
Encyclopedia
Gliding is a recreational activity and competitive air sport
Air sports
The term Air sports covers a range of aerial activities such as:* Aerobatics* Ballooning* General aviation including Air racing* Gliding* Hang gliding* Human powered aircraft* Model aircraft* Parachuting* Paragliding...

 in which pilots fly unpowered aircraft
Glider aircraft
Glider aircraft are heavier-than-air craft that are supported in flight by the dynamic reaction of the air against their lifting surfaces, and whose free flight does not depend on an engine. Mostly these types of aircraft are intended for routine operation without engines, though engine failure can...

 known as gliders
Glider (sailplane)
A glider or sailplane is a type of glider aircraft used in the sport of gliding. Some gliders, known as motor gliders are used for gliding and soaring as well, but have engines which can, in some cases, be used for take-off or for extending a flight...

 or sailplanes using naturally occurring currents of rising air in the atmosphere to remain airborne. The word soaring is also used for the sport.

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
Ridge lift
Ridge lift is created when a wind strikes an obstacle, usually a mountain ridge or cliff, that is large and steep enough to deflect the wind upward....

, thermal
Thermal
A thermal column is a column of rising air in the lower altitudes of the Earth's atmosphere. Thermals are created by the uneven heating of the Earth's surface from solar radiation, and are an example of convection. The sun warms the ground, which in turn warms the air directly above it...

s and lee waves
Lee waves
In meteorology, lee waves are atmospheric standing waves. The most common form is mountain waves, which are atmospheric internal gravity waves...

. When conditions are favorable, experienced pilots can now fly hundreds of kilometres before returning to their home airfields; occasionally flights of more than 1000 kilometres (621 mi) are achieved.

Some competitive pilots fly in races around pre-defined courses. These gliding competitions
Gliding competitions
Some of the pilots in the sport of gliding take part in gliding competitions. These are usually racing competitions, but there are also aerobatic contests and on-line league tables.-History of 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
World Gliding Championships
The World Gliding Championships is a gliding competition held every two years or so by the FAI Gliding Commission. The dates are not always exactly two years apart, often because the contests are sometimes held in the summer in the Southern Hemisphere....

.
Techniques to maximize a glider's speed around the day's task in a competition have been developed, including the optimum speed to fly
Speed to fly
Speed to fly is a principle used by soaring pilots when flying between sources of lift, usually thermals, ridge lift and wave. The aim is to maximize the average cross-country speed by optimizing the airspeed in both rising and sinking air...

, navigation using GPS
Global Positioning System
The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...

 and the carrying of water ballast
Sailing ballast
Ballast is used in sailboats to provide moment to resist the lateral forces on the sail. Insufficiently ballasted boats will tend to tip, or heel, excessively in high winds. Too much heel may result in the boat capsizing. If a sailing vessel should need to voyage without cargo then ballast of...

. 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
National gliding associations
The sport of gliding is managed in each country by national gliding associations, subject to governmental aviation authorities to varying degrees...

 often have delegated authority.

The sport is facing challenges to maintain its popularity. Many factors have put pressure on the movement such as the increasing demands on people's time, cost of insurance and fuel, competition from other air sports and the growing requirement for land and controlled airspace.

History

The development of heavier-than-air flight in the half century between Sir George Cayley's coachman in 1853 and the Wright brothers
Wright brothers
The Wright brothers, Orville and Wilbur , were two Americans credited with inventing and building the world's first successful airplane and making the first controlled, powered and sustained heavier-than-air human flight, on December 17, 1903...

 mainly involved gliders (see Aviation history
Aviation history
The history of aviation has extended over more than two thousand years from the earliest attempts in kites and gliders to powered heavier-than-air, supersonic and hypersonic flight.The first form of man-made flying objects were kites...

). However, the sport of gliding only emerged after the First World War, as a result of the Treaty of Versailles
Treaty of Versailles
The Treaty of Versailles was one of the peace treaties at the end of World War I. It ended the state of war between Germany and the Allied Powers. It was signed on 28 June 1919, exactly five years after the assassination of Archduke Franz Ferdinand. The other Central Powers on the German side of...

, which imposed severe restrictions on the manufacture and use of single-seat powered aircraft in Germany's Weimar Republic
Weimar Republic
The Weimar Republic is the name given by historians to the parliamentary republic established in 1919 in Germany to replace the imperial form of government...

. 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.
The first German gliding competition was held at the Wasserkuppe
Wasserkuppe
The Wasserkuppe is a high plateau , the highest peak in the Rhön Mountains within the German state of Hessen. Between the first and second World Wars, during the era of the so-called Golden Age of Aviation, great advances in sailplane development were made there.Remark: The German wording takes its...

 in 1920, organized by Oskar Ursinus
Oskar Ursinus
Carl Oskar Ursinus was a pioneer of German aviation and is remembered mainly for his contributions to sailplane designs and the sport of gliding...

. The best flight lasted two minutes and set a world distance record of 2 kilometres (1.2 mi). 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
Munich
Munich The city's motto is "" . Before 2006, it was "Weltstadt mit Herz" . Its native name, , is derived from the Old High German Munichen, meaning "by the monks' place". The city's name derives from the monks of the Benedictine order who founded the city; hence the monk depicted on the city's coat...

 to Kadaň
Kadan
Kadaň , is a city in the Ústí nad Labem Region of the Czech Republic.The city lies on the banks of the river Ohře. Although it is situated in an industrial part of the Czech Republic there is no major industry within the city and people usually work in offices or have to commute. There are two...

 (Kaaden in German) in Western Czechoslovakia
Czechoslovakia
Czechoslovakia or Czecho-Slovakia was a sovereign state in Central Europe which existed from October 1918, when it declared its independence from the Austro-Hungarian Empire, until 1992...

, further than had been thought possible.

In the 1930s, gliding spread to many other countries. In the 1936 Summer Olympics
Gliding at the 1936 Summer Olympics
Gliding at the 1936 Summer Olympics was a demonstration sport. The sport of gliding had been developed in Germany in the 1920s but had spread widely by 1936, allowing an international demonstration to the International Olympic Committee ....

 in Berlin gliding was a demonstration sport
Demonstration sport
A demonstration sport is a sport which is played to promote itself, most commonly during the Olympic Games, but also at other sporting events.Demonstration sports were officially introduced in 1912 Summer Olympics, when Sweden decided to include glima, traditional Icelandic wrestling, in the...

, and it was scheduled to be a full Olympic sport in the 1940 Games
1940 Summer Olympics
The anticipated 1940 Summer Olympics, officially known as the Games of the XII Olympiad and originally scheduled to be held from September 21 to October 6, 1940, in Tokyo, Japan, were cancelled due to the outbreak of World War II...

. A glider, the Olympia
DFS Olympia Meise
|-General characteristics:*Crew: one, pilot*Length: 7.27 m *Wingspan: 15.00 m *Height: m *Wing area: 15 m² *Aspect ratio: 15:1*Empty: 205 kg...

, 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 (464.8 mi). During the war, the sport of gliding in Europe was largely suspended, though several German fighter aces
Flying ace
A flying ace or fighter ace is a military aviator credited with shooting down several enemy aircraft during aerial combat. The actual number of aerial victories required to officially qualify as an "ace" has varied, but is usually considered to be five or more...

 in the conflict, including Erich Hartmann
Erich Hartmann
Erich Alfred Hartmann , nicknamed "Bubi" by his comrades and "The Black Devil" by his Soviet enemies, was a German World War II fighter pilot and is the highest-scoring fighter ace in the history of aerial warfare...

, began their flight training in gliders.

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.) 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
Fédération Aéronautique Internationale
The Fédération Aéronautique Internationale is the world governing body for air sports and aeronautics and astronautics world records. Its head office is in Lausanne, Switzerland. This includes man-carrying aerospace vehicles from balloons to spacecraft, and unmanned aerial vehicles...

 (FAI), but has been rejected on the grounds of lack of public interest.

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
Soaring Society of America
The Soaring Society of America was founded at the instigation of Warren E. Eaton to promote the sport of soaring in the USA and internationally. The first meeting was held in New York City in the McGraw-Hill building on February 20, 1932. Its first objective was to hold a national soaring...

 increased from 1,000 to 16,000 by 1980. 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, and the first 1000 kilometres (621.4 mi) flight was achieved in 1964.
New materials such as glass fiber and carbon fiber
Carbon fiber
Carbon fiber, alternatively graphite fiber, carbon graphite or CF, is a material consisting of fibers about 5–10 μm in diameter and composed mostly of carbon atoms. The carbon atoms are bonded together in crystals that are more or less aligned parallel to the long axis of the fiber...

, advances in wing
Wing
A wing is an appendage with a surface that produces lift for flight or propulsion through the atmosphere, or through another gaseous or liquid fluid...

 shapes and airfoils, electronic instruments, the Global Positioning System
Global Positioning System
The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...

 and improved weather forecasting have since allowed many pilots to make flights that were once extraordinary. Today over 550 pilots have made flights over 1000 kilometres (621.4 mi).
Although there is no Olympic competition, there are the World Gliding Championships. The first event was held at the Samedan in 1948. Since World War II it has been held every two years. There are now six classes
Glider Competition Classes
Competition classes in gliding, as in other sports, mainly exist to ensure fairness in competition. However the classes have not been targeted at fostering technological development as in other sports...

 open to both sexes, plus three classes for women and two junior classes. The latest worldwide statistics in 2004 indicate that Germany, the sport's birthplace, is still a center of the gliding world: it accounted for 30 percent of the world's glider pilots, 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 116,000 active glider pilots, plus an unknown number of military cadets. Clubs actively seek new members by giving trial flights, which are also a useful source of revenue for them.

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
Potential energy
In physics, potential energy is the energy stored in a body or in a system due to its position in a force field or due to its configuration. The SI unit of measure for energy and work is the Joule...

.
The most commonly used sources of rising air are
  • thermal
    Thermal
    A thermal column is a column of rising air in the lower altitudes of the Earth's atmosphere. Thermals are created by the uneven heating of the Earth's surface from solar radiation, and are an example of convection. The sun warms the ground, which in turn warms the air directly above it...

    s (updrafts of warm air);
  • ridge lift
    Ridge lift
    Ridge lift is created when a wind strikes an obstacle, usually a mountain ridge or cliff, that is large and steep enough to deflect the wind upward....

     (found where the wind blows against the face of a hill and is forced to rise); and
  • wave lift
    Lee waves
    In meteorology, lee waves are atmospheric standing waves. The most common form is mountain waves, which are atmospheric internal gravity waves...

     (standing wave
    Standing wave
    In physics, a standing wave – also known as a stationary wave – is a wave that remains in a constant position.This phenomenon can occur because the medium is moving in the opposite direction to the wave, or it can arise in a stationary medium as a result of interference between two waves traveling...

    s in the atmosphere
    Earth's atmosphere
    The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...

    , analogous to the ripples on the surface of a stream).


Ridge lift rarely allows pilots to climb much higher than about 600 metres (1,968.5 ft) above the terrain; thermals, depending on the climate and terrain, can allow climbs in excess of 3000 metres (9,842.5 ft) in flat country and much higher above mountains; wave lift has allowed a glider to reach an altitude of 15447 metres (50,679.1 ft).
In a few countries such as the UK, gliders may continue to climb into the clouds in uncontrolled airspace,
but in many European countries the pilot must stop climbing before reaching the cloud base (see Visual Flight Rules
Visual flight rules
Visual flight rules are a set of regulations which allow a pilot to operate an aircraft in weather conditions generally clear enough to allow the pilot to see where the aircraft is going. Specifically, the weather must be better than basic VFR weather minimums, as specified in the rules of the...

).

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.
When the air has little moisture or when an inversion
Inversion (meteorology)
In meteorology, an inversion is a deviation from the normal change of an atmospheric property with altitude. It almost always refers to a temperature inversion, i.e...

 stops the warm air from rising high enough for the moisture to condense, thermals do not create cumulus clouds. Without clouds or dust devil
Dust devil
A dust devil is a strong, well-formed, and relatively long-lived whirlwind, ranging from small to large . The primary vertical motion is upward...

s 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
Variometer
The term variometer also refers to a type of variable transformer or an instrument for measuring the magnitude and direction of a Magnetic field....

 that quickly indicates climbs and descents. Occasionally reliable thermals can be found in the exhaust gases from power station
Power station
A power station is an industrial facility for the generation of electric energy....

s or from fires.

Once a thermal is encountered, the pilot can fly in tight circles to keep the glider within the thermal, so gaining altitude before flying towards the destination or to the next thermal. This is known as "thermalling". Alternatively, glider pilots on cross-country flights
Cross-country flying
Cross-Country flying is a type of distance flying which is performed in a powered aircraft on legs over a given distance and in operations between two points using navigational techniques; and an unpowered aircraft by using upcurrents to gain altitude for extended flying time...

 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
Flap (aircraft)
Flaps are normally hinged surfaces mounted on the trailing edges of the wings of a fixed-wing aircraft to reduce the speed an aircraft can be safely flown at and to increase the angle of descent for landing without increasing air speed. They shorten takeoff and landing distances as well as...

. 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.
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.

Ridge lift

A ridge soaring
Ridge lift
Ridge lift is created when a wind strikes an obstacle, usually a mountain ridge or cliff, that is large and steep enough to deflect the wind upward....

 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. 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.

Wave lift

The powerfully rising and sinking air in mountain waves was discovered by glider pilot, Wolf Hirth
Wolf Hirth
Wolfram Kurt Erhard Hirth was a German gliding pioneer and sailplane designer. He was a co-founder of Schempp-Hirth, still a renowned glider manufacturer....

, in 1933. Gliders can sometimes climb in these waves to great altitudes, although pilots must use supplementary oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 to avoid hypoxia
Hypoxia (medical)
Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...

.

This lift is often marked by long, stationary lenticular
Lenticular cloud
Lenticular clouds are stationary lens-shaped clouds that form at high altitudes, normally aligned perpendicular to the wind direction. Lenticular clouds can be separated into altocumulus standing lenticularis , stratocumulus standing lenticular , and cirrocumulus standing lenticular...

 (lens-shaped) clouds lying perpendicular to the wind. Mountain wave was used to set the current altitude record of 15453 metres (50,698.8 ft) on 29 August 2006 over El Calafate
El Calafate
- Population :In the last census 6,143 permanent residents were counted . This represents a 20.1% increase compared with the 1991 census. However, due to the expansion of tourism, the population was estimated at 8,000 people in 2005.- Wildlife :...

, Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...

. The pilots, Steve Fossett
Steve Fossett
James Stephen Fossett was an American commodities trader, businessman, and adventurer. Fossett is the first person to fly solo nonstop around the world in a balloon...

 and Einar Enevoldson, wore pressure suits. The current world distance record of 3008 kilometres (1,869.1 mi) by Klaus Ohlmann
Klaus Ohlmann
Klaus Ohlmann, born 1952 in Neustadt, Germany is a German glider pilot who has established 36 world records approved by FAI. Among these is the record for a free distance flight with up to 3 turn-points by flying 3,009 km from Chapelco Airport at San Martín de los Andes in a Schempp-Hirth Nimbus 4...

 (set on 21 January 2003) was also flown using mountain waves in South America.

A rare wave phenomenon is known as Morning Glory
Morning glory cloud
The Morning Glory cloud is a rare meteorological phenomenon occasionally observed in different locations around the world. The southern part of Northern Australia's Gulf of Carpentaria is the only known location where it can be predicted and observed on a more or less regular basis. The settlement...

, a roll cloud producing strong lift. Pilots near Australia's Gulf of Carpentaria
Gulf of Carpentaria
The Gulf of Carpentaria is a large, shallow sea enclosed on three sides by northern Australia and bounded on the north by the Arafura Sea...

 make use of it in springtime
Spring (season)
Spring is one of the four temperate seasons, the transition period between winter and summer. Spring and "springtime" refer to the season, and broadly to ideas of rebirth, renewal and regrowth. The specific definition of the exact timing of "spring" varies according to local climate, cultures and...

.

Other sources of lift

The boundaries where two air masses meet are known as convergence zone
Convergence zone
Convergence zone usually refers to a region in the atmosphere where two prevailing flows meet and interact, usually resulting in distinctive weather conditions....

s.
These can occur in sea breeze
Sea breeze
A sea-breeze is a wind from the sea that develops over land near coasts. It is formed by increasing temperature differences between the land and water; these create a pressure minimum over the land due to its relative warmth, and forces higher pressure, cooler air from the sea to move inland...

s 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
Cold front
A cold front is defined as the leading edge of a cooler mass of air, replacing a warmer mass of air.-Development of cold front:The cooler and denser air wedges under the less-dense warmer air, lifting it...

. 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.

Glider pilots have occasionally been able to use a technique called "dynamic soaring
Dynamic soaring
Dynamic soaring is a flying technique used to gain energy by repeatedly crossing the boundary between air masses of significantly different velocity...

" allowing a glider to gain kinetic energy
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...

 by repeatedly crossing the boundary between air masses of different horizontal velocity. However, such zones of high "wind gradient
Wind gradient
In common usage, wind gradient, more specifically wind speed gradientor wind velocity gradient,or alternatively shear wind,...

" are usually too close to the ground to be used safely by gliders.

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
Glider pilot license
In most countries one is required to obtain a glider pilot license or certificate before acting as pilot of a glider. The requirements vary from country to country....

 rules in some countries, such as the USA, differentiate between aerotows and ground launch methods, due to the widely different techniques.

Aerotowing

In an aerotow a powered plane is attached to the glider with a tow rope. Single-engined light aircraft or motor gliders are used. The tow-plane takes the glider to the height and location requested by the pilot where the glider pilot releases the tow-rope. A weak link is often fitted to the rope to ensure that any sudden loads do not damage the airframe
Airframe
The airframe of an aircraft is its mechanical structure. It is typically considered to include fuselage, wings and undercarriage and exclude the propulsion system...

 of the tow-plane or the glider. Under extreme loads the weak link will fail before any part of the glider or plane fails. 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
Wake turbulence
Wake turbulence is turbulence that forms behind an aircraft as it passes through the air. This turbulence includes various components, the most important of which are wing vorticies and jetwash. Jetwash refers simply to the rapidly moving gases expelled from a jet engine; it is extremely turbulent,...

 from the tow-plane, or the "high tow" position just above the wake. 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 the long rope for the low tow. The current record is nine gliders in the same aerotow.

Winch launching

Gliders are often launched using a stationary ground-based winch
Winch
A winch is a mechanical device that is used to pull in or let out or otherwise adjust the "tension" of a rope or wire rope . In its simplest form it consists of a spool and attached hand crank. In larger forms, winches stand at the heart of machines as diverse as tow trucks, steam shovels and...

 mounted on a heavy vehicle. This method is widely used at many European clubs, often in addition to an aerotow service. The engine is usually a large diesel
Diesel engine
A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...

, though hydraulic fluid
Hydraulic fluid
Hydraulic fluids, also called hydraulic liquids, are the medium by which power is transferred in hydraulic machinery. Common hydraulic fluids are based on mineral oil or water...

 engines and electrical motors are also used. The winch pulls in a 1,000 to 1,600-metre (3,000 to 5,500 ft) cable, made of high-tensile steel wire or a synthetic fiber, attached to the glider. The cable is released at a height of about 400 to 700 metres (1,300 to 2,200 ft) after a short, steep ride.
Winch launches are cheaper than aerotows and have the advantage that many members of a club can be taught to operate the equipment. A winch may also be used at sites where an aerotow could not operate, because of the shape of the field or because of noise restrictions. The height gained from a winch is usually less than from an aerotow so pilots need to find a source of lift soon after releasing from the cable, otherwise the flight will be short. A break in the cable of the weak link during a winch launch is a possibility for which pilots are trained.

Auto-tow

Another method of launching, the "autotow", is rarer nowadays. The direct autotow requires a hard surface and a powerful vehicle that is attached to the glider by a long steel cable. After gently taking up slack in the cable, the driver accelerates
Acceleration
In physics, acceleration is the rate of change of velocity with time. In one dimension, acceleration is the rate at which something speeds up or slows down. However, since velocity is a vector, acceleration describes the rate of change of both the magnitude and the direction of velocity. ...

 hard and as a result the glider rises rapidly to about 400 metres (1,300 ft), especially if there is a good headwind and a runway
Runway
According to ICAO a runway is a "defined rectangular area on a land aerodrome prepared for the landing and take-off of aircraft." Runways may be a man-made surface or a natural surface .- Orientation and dimensions :Runways are named by a number between 01 and 36, which is generally one tenth...

 of 1.5 kilometre (0.93205910497471 mi) or more. This method has also been used on desert dry lake
Dry lake
Dry lakes are ephemeral lakebeds, or a remnant of an endorheic lake. Such flats consist of fine-grained sediments infused with alkali salts. Dry lakes are also referred to as alkali flats, sabkhas, playas or mud flats...

s.

A variation on the direct autotow is known as the "reverse pulley" method. In this method, the truck drives towards the glider being launched. The cable passes around a pulley at the far end of the airfield, resulting in an effect similar to that of a winch launch.

Bungee launch

Bungee launching was widely used in the early days of gliding, and occasionally gliders are still launched from the top of a gently sloping hill into a strong breeze using a substantial multi-stranded rubber band, or "bungee
Bungee cord
A bungee cord , also known as a shock cord, is an elastic cord composed of one or more elastic strands forming a core, usually covered in a woven cotton or polypropylene sheath...

". For this launch method, the glider's main wheel rests in a small concrete trough. The hook normally used for winch-launching is instead attached to the middle of the bungee. Each end is then pulled by three or four people. One group runs slightly to the left, the other to the right. 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 fly away from the hill.

Cross-country

One of the measures of a glider's performance is the distance that it can fly for each meter it descends, known as its lift-to-drag ratio
Lift-to-drag ratio
In aerodynamics, the lift-to-drag ratio, or L/D ratio, is the amount of lift generated by a wing or vehicle, divided by the drag it creates by moving through the air...

 (L/D). Depending on the class, this can range in modern designs from 44:1 in the Standard Class up to 70:1 for the largest aircraft. A good gliding performance combined with regular sources of rising air enables modern gliders to fly long distances at high speeds. The weather is a major factor in determining cross-country speeds. The record average speed for 1000 kilometres (621.4 mi) is 203.1 kilometres per hour (126.2 mph). required unusually good conditions, but even in places with less favorable conditions (such as Northern Europe
Northern Europe
Northern Europe is the northern part or region of Europe. Northern Europe typically refers to the seven countries in the northern part of the European subcontinent which includes Denmark, Estonia, Latvia, Lithuania, Norway, Finland and Sweden...

) a skilled pilot could expect to complete flights over 500 kilometres (310.7 mi) 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 usually plan to fly around a course (called a task) via turn-points
Waypoint
A waypoint is a reference point in physical space used for purposes of navigation.-Concept:Waypoints are sets of coordinates that identify a point in physical space. Coordinates used can vary depending on the application. For terrestrial navigation these coordinates can include longitude and...

, returning to the starting point.

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 1,000 km have been set and average speeds of 120 km/h are not unusual.

Initially, ground observers confirmed that pilots had rounded the turn-points. Later, the glider pilots photographed these places and submitted the film for verification. Today, gliders carry secure GNSS Flight Recorders that record the position every few seconds from GPS
Global Positioning System
The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...

 satellites. These recording devices now provide the proof that the turn-points have been reached.

National competitions generally last one week, with international championships running over two. The winner is the pilot who has amassed the greatest number of points over all the contest days. However, these competitions have as yet failed to draw much interest outside the gliding community for several reasons. 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 the spectators for long periods during each day's contest and the scoring is complex, so traditional gliding competitions are difficult to televise. In an attempt to widen the sport's appeal, a new format, the Grand Prix
Grand Prix gliding
FAI World Grand Prix Gliding Championships are gliding competitions promoted by the Fédération Aéronautique Internationale for gliders that are both more spectacular and more easily understood by the public than conventional gliding competitions....

, has been introduced. Innovations introduced in the Grand Prix format include simultaneous starts for a small number of gliders, cockpit mounted cameras, telemetry giving the positions of the gliders, tasks consisting of multiple circuits, and simplified scoring.

There is a decentralized Internet-based competition called the Online Contest
Online Contest
The aerokurier Online Contest , a worldwide decentralized soaring competition for glider, hang glider, and paraglider pilots. The OLC is operated by Segelflugszene Gemeinnützige GmbH, a German not-for-profit founded in 2000...

, in which pilots upload their GPS data files and are automatically scored based on distance flown. Worldwide, 6,703 pilots registered for this contest in 2010.

Maximizing average speed

Soaring pioneer Paul MacCready
Paul MacCready
Paul B. MacCready, Jr. was an American aeronautical engineer. He was the founder of AeroVironment and the designer of the human-powered aircraft that won the Kremer prize...

 is usually credited with developing mathematical principles for optimizing the speed at which to fly when cross-country soaring, although it was first described by Wolfgang Späte in 1938. The speed to fly
Speed to fly
Speed to fly is a principle used by soaring pilots when flying between sources of lift, usually thermals, ridge lift and wave. The aim is to maximize the average cross-country speed by optimizing the airspeed in both rising and sinking air...

 theory allows the optimal cruising speed between thermals to be computed, using thermal strength, glider performance and other variables. It 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 use MacCready theory to optimize their average speeds, and have the calculations programmed in their flight computers, or use a "McCready ring", a rotatable bezel on the glider's variometer to indicate the best speed to fly. The greatest factor in maximizing average speed, however, remains the ability of the pilot to find the strongest lift.

On cross-country flights on days when strong lift is forecast, pilots fly with water ballast stored in tanks or bags in the wings and fin. The fin tank is used to reduce trim drag by optimizing the center of gravity
Center of gravity
In physics, a center of gravity of a material body is a point that may be used for a summary description of gravitational interactions. In a uniform gravitational field, the center of mass serves as the center of gravity...

, which typically would shift forward if water is stored only in the wings ahead of the spar. Ballast enables a sailplane to attain its best L/D at higher speeds but slows its climb rate in thermals, in part because a sailplane with a heavier wing loading cannot circle within a thermal as tightly as one with a lower, unballasted wing loading. But if lift is strong, typically either from thermals or wave, the disadvantage of slower climbs is outweighed by the higher cruising speeds between lift areas. Thus, the pilot can improve the average speed over a course by several percent or achieve longer distances in a given time. If lift is weaker than expected, or if an off-field landing is imminent, the pilot can jettison the water ballast by opening the dump valves.

On days with particularly strong and widespread lift pilots can attain high average speeds by alternating periods of fast flight with pull-ups, merely slowing down in areas of lift without deviating from the course. This 'dolphining' technique can result in high average speeds because the height lost can be minimised until particularly strong lift is encountered when circling would be most effective.

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 gliding federations set their own criteria. Typically, a bronze badge shows preparation for cross-country flight, including precise landings and witnessed soaring flights. Higher badges follow the standards set down by the Gliding Commission
FAI Gliding Commission
The International Gliding Commission is a leading international governing body for the sport of gliding.It is one of several Air Sport Commissions of the Fédération Aéronautique Internationale , or "World Air Sports Federation"...

 of the Fédération Aéronautique Internationale (FAI).

The FAI's Sporting Code defines the rules for observers and recording devices to validate the claims for badges that are defined by kilometers of distance and meters of altitude gained.
The Silver-C badge was introduced in 1930. Earning the Silver Badge shows that a glider pilot has achieved an altitude gain of at least 1000 metres (3,281 ft), made a five-hour duration flight, and has flown cross-country for a straight-line distance of at least 50 kilometres (31 mi): these three attainments are usually, but not invariably, achieved in separate flights. The Gold and Diamond Badges require pilots to fly higher and further. A pilot who has completed the three parts of the Diamond Badge has flown 300 kilometres (186 mi) to a pre-defined goal, has flown 500 kilometres (311 mi) in one flight (but not necessarily to a pre-defined goal) and gained 5000 metres (16,404.2 ft) in height. The FAI also issues a diploma for a flight of 1000 kilometres (621 mi) and further diplomas for increments of 250 kilometres (155 mi).

Landing out

If lift is not found during a cross-country flight, for example because of deteriorating weather, the pilot must choose a location to "land out". Although inconvenient and often mistaken for "emergency landing
Emergency landing
An emergency landing is a landing made by an aircraft in response to a crisis which either interferes with the operation of the aircraft or involves sudden medical emergencies necessitating diversion to the nearest airport.-Types of emergency landings:...

s", landing out (or "outlanding") is a routine event in cross-country gliding. The pilot has to choose a location where the glider can be landed safely, without damaging the plane, the pilot, or property such as crops or livestock. The glider and the pilot(s) can then be retrieved by road from the outlanding location using a purpose-built trailer. In some instances, a tow-plane can be summoned to re-launch the aircraft.

Use of engines or motors

Although adding to the weight and expense, some gliders are fitted with small power units and are known as motor glider
Motor glider
A motor glider is a fixed-wing aircraft that can be flown with or without engine power. The FAI Gliding Commission Sporting Code definition is: A fixed wing aerodyne equipped with a means of propulsion ,...

s. This avoids the inconvenience of landing out. The power units can be internal combustion engines, electrical motors , or retractable jet engine
Jet engine
A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...

s. Retractable propellers are fitted to high performance sailplanes, though in another category, called touring motor gliders, non-retractable propellers are used. Some powered gliders are "self launching", which makes the glider independent of a tow plane. However some gliders have "sustainer" engines that can prolong flight but are not powerful enough for launching. All power units have to be started at a height that includes a margin that would still allow a safe landing out to be made, if there were a failure to start.

In a competition, using the engine ends the soaring flight. Unpowered gliders are lighter and, as they do not need a safety margin for starting the engine, they can safely thermal at lower altitudes in weaker conditions. Consequently, pilots in unpowered gliders may complete competition flights when some powered competitors cannot. Conversely, motor glider pilots can start the engine if conditions will no longer support soaring flight, while unpowered gliders will have to land out, away from the home airfield, requiring retrieval by road using the glider's trailer.

Aerobatic competitions

World and European
European Gliding Championships
The European Gliding Championships is a gliding competition held every two years or so.Gliding is a competitive sport and was even a demonstration sport at the 1936 Summer Olympics. It was due to become an official Olympic sport in the Helsinki Games in 1940. However since the war, gliding has not...

 Aerobatic competitions are held regularly. In this type of competition
Competition aerobatics
Competition aerobatics is an air sport in which judges rate the skill of pilots performing aerobatic flying. It is practiced in both piston-powered single-engine airplanes and gliders....

, the pilots fly a program of maneuvers
Aerobatic maneuver
Aerobatic maneuvers are flight paths putting aircraft in unusual attitudes, in air shows, dog fights or competition aerobatics. Aerobatics can be performed by a single aircraft or in formation with several others...

 (such as inverted flight, loop, roll, and various combinations). Each maneuver has a rating called the "K-Factor". Maximum points are given for the maneuver if it is flown perfectly; otherwise, points are deducted. Efficient maneuvers also enable the whole program to be completed with the height available. The winner is the pilot with the most points.

Hazards

Unlike hang gliders and paragliders
Paragliding
Paragliding is the recreational and competitive adventure sport of flying paragliders: lightweight, free-flying, foot-launched glider aircraft with no rigid primary structure...

, gliders surround the pilots with strong structures and have undercarriages to absorb impacts when landing. These features prevent injuries from otherwise minor incidents,
but there are some hazards. Although training and safe procedures are central to the ethos of the sport, a few fatal accidents occur every year, almost all caused by pilot error. In particular there is a risk of mid-air collisions between gliders, because two pilots might choose to fly to the same area of lift and so might collide. Because of this risk, pilots usually wear parachute
Parachute
A parachute is a device used to slow the motion of an object through an atmosphere by creating drag, or in the case of ram-air parachutes, aerodynamic lift. Parachutes are usually made out of light, strong cloth, originally silk, now most commonly nylon...

s. To avoid other gliders and general aviation
General aviation
General aviation is one of the two categories of civil aviation. It refers to all flights other than military and scheduled airline and regular cargo flights, both private and commercial. General aviation flights range from gliders and powered parachutes to large, non-scheduled cargo jet flights...

 traffic, pilots must comply with the Rules of the Air and keep a good lookout. In several European countries and Australia, the FLARM
FLARM
FLARM is an electronic device to selectively alert pilots to potential collisions between aircraft. It is not formally an implementation of ADS-B, as it is optimised for the specific needs of small aircraft such as gliders, not for long-range communication or ATC interaction.FLARM obtains its...

 warning system is used to help avoid mid-air collisions between gliders. A few modern gliders have a ballistic emergency parachute to stabilize the aircraft after a collision.

Training and regulation

In addition to national laws controlling aviation, the sport in many countries is regulated though national gliding associations and then through local gliding clubs. Much of the regulation concerns safety and training.

Many clubs provide training for new pilots. The student flies with an instructor in a two-seat glider fitted with dual controls. The instructor performs the first launches and landings, typically from the back seat, but otherwise the student manages the controls until the student is deemed to have the skill and the airmanship
Airmanship
Airmanship is skill and knowledge applied to aerial navigation, similar to seamanship in maritime navigation. Airmanship covers a broad range of desirable behaviors and abilities in an aviator...

 necessary to fly solo. Simulators
Flight simulator
A flight simulator is a device that artificially re-creates aircraft flight and various aspects of the flight environment. This includes the equations that govern how aircraft fly, how they react to applications of their controls and other aircraft systems, and how they react to the external...

 are also beginning to be used in training, especially during poor weather.

After the first solo flights glider pilots are required to stay within gliding range of their home airfield. In addition to solo flying, further flights are made with an instructor until the student is capable of taking a glider cross-country and of handling more difficult weather. Cross-country flights are allowed when they have sufficient experience to find sources of lift away from their home airfield, to navigate, and to select and land in a field if necessary. In most countries pilots must take a written examination on the regulations, navigation, use of the radio, weather, principles of flight and human factors. Proposals are being made to standardise the training requirements across European countries.

In addition to the regulation of pilots, gliders are inspected annually and after exceeding predetermined flight times. Maximum and minimum payloads are also defined for each glider. Because most gliders are designed to the same specifications of safety, the upper weight limit for a pilot, after allowing for a parachute, is usually 103 kilograms (227.1 lb). There is also a limit, 193 centimetres (6 ft 4 in), on the tallest pilots who can safely fit into a typical glider's cockpit.

Challenges for the gliding movement

According to the FAI President, gliding as a sport faces challenges in the years ahead. These include:
  • Time pressures on participants: gliding typically takes whole days that many people today find harder to devote. As a result the average age of glider pilots is increasing.
  • In some countries, the need for more land for housing is threatening small airfields. These airfields may also be used for other general aviation activities, and the addition of gliding may be difficult to accommodate. This can limit the number of available airfields and so it can require longer drives to reach them.
  • Airspace
    Airspace
    Airspace means the portion of the atmosphere controlled by a country above its territory, including its territorial waters or, more generally, any specific three-dimensional portion of the atmosphere....

    : in many European countries, the growth of civil aviation
    Civil aviation
    Civil aviation is one of two major categories of flying, representing all non-military aviation, both private and commercial. Most of the countries in the world are members of the International Civil Aviation Organization and work together to establish common standards and recommended practices...

     is reducing the amount of uncontrolled airspace
    Uncontrolled airspace
    Uncontrolled airspace is airspace where an Air Traffic Control service is not deemed necessary or cannot be provided for practical reasons. According to the airspace classes set by ICAO both class F and class G airspace are uncontrolled...

    . In the U.S. new security requirements, and the growth of controlled airspace around cities, has also had some impact on where to fly.
  • Competition from other activities: there is now a greater variety of similar sports such as hang gliding
    Hang gliding
    Hang gliding is an air sport in which a pilot flies a light and unmotorized foot-launchable aircraft called a hang glider ....

     and paragliding that may attract potential glider pilots.
  • Lack of publicity: without coverage by television or popular publications, many people are unaware that gliding is even a sport. Without this knowledge the public may have a poor understanding of how flying without an engine is possible and safe.
  • Increasing costs: due to higher costs of fuel and insurance, and due to greater regulation requiring equipment such as new radio
    Radio
    Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...

    s, or in some cases transponder
    Transponder
    In telecommunication, the term transponder has the following meanings:...

    s, gliding costs have increased, although without the continuous use of engines and fuel, they are still considerably lower than traditional power flying.

Related air sports

The two air sports that are most closely related to gliding are hang gliding and paragliding. Although all three sports rely on rising air, there are significant differences which are listed in detail in a comparison of sailplanes hang gliders and paragliders. The main difference is that both hang gliders and paragliders are simpler, less sophisticated and cheaper aircraft that use the pilot's feet as the undercarriage. All paragliders and most hang gliders have no protective structure around the pilot. However, the dividing line between basic gliders and sophisticated hang-gliders is becoming less distinct. For example hang gliders typically use fabric wings, shaped over a framework, but hang gliders with rigid wings and three-axis controls are also available. The lower air speeds and lower glide ratios of typical hang gliders means that shorter cross-country distances are flown than in modern gliders. Paragliders are more basic craft. They are also foot-launched, but their wings usually have no frames and their shape is created by the flow and pressure of air. The airspeeds and glide ratios of paragliders are generally lower still than the typical hang gliders, and so their cross-country flights are even shorter. Radio-controlled gliding
Radio-controlled glider
A radio-controlled glider is a type of radio-controlled aircraft that normally does not have any form of propulsion. They are able to sustain continuous flight by exploiting the lift produced by slopes and thermals, controlled remotely from the ground with a transmitter...

 uses scale-models of gliders mainly for ridge soaring; however thermic aeromodelling craft are also used.

See also

  • Wingsuit flying
    Wingsuit flying
    Wingsuit flying is the sport of flying the human body through the air using a special jumpsuit, called a wingsuit, which adds surface area to the human body to enable a significant increase in lift. Modern wingsuits, first developed in the late 1990s, create the surface area with fabric between the...

  • Powered hang glider
    Powered Hang Glider
    A foot-launched powered hang glider , also called powered harness, nanolight, or hangmotor, is a powered hang glider harness with a motor and propeller in pusher configuration...

  • List of notable glider pilots
  • Flying and gliding animals
    Flying and gliding animals
    A number of animals have evolved aerial locomotion, either by powered flight or by gliding. Flying and gliding animals have evolved separately many times, without any single ancestor. Flight has evolved at least four times, in the insects, pterosaurs, birds, and bats. Gliding has evolved on many...

  • Paper glider

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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