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Gliding

2007 Schools Wikipedia Selection. Related subjects: Recreation; Sports


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

   Gliding (or soaring) is a recreational activity and competitive sport
   in which 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.

   After launching, glider pilots search for rising air to gain height. If
   conditions are good enough, experienced pilots can fly many hundreds,
   and in some cases thousands, of kilometres before returning to their
   home airfields. However, if the weather deteriorates they must often
   land elsewhere, but some can avoid this by using engines.

   While many glider pilots merely enjoy the sense of achievement, some
   competitive pilots fly in races around pre-defined courses. 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 organized in many countries and there are also
   biennial World Gliding Championships.

   Powered aircraft and winches are the two most common means of launching
   gliders. These and other methods (apart from self-launching
   motor-gliders) require assistance from other participants. Gliding
   clubs have thus been established to share airfields and equipment,
   train new pilots and maintain high safety standards.

History

   The development of heavier-than-air flight in the half-century between
   Sir George Cayley's coachman in 1853 and the Wright brothers mainly
   involved gliders (see aviation history). However, the sport of gliding
   only emerged after the First World War as a result of the Treaty of
   Versailles, which imposed severe restrictions on the manufacture and
   use of single-seat powered aircraft 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 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.

   The first German gliding competition was held at the Wasserkuppe in
   1920, organized by Oskar Ursinus. The best flight lasted two minutes
   and set a world distance record of 2 km. 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 km
   (169 miles) from Munich to Czechoslovakia, further than had been
   thought possible.
   The "gull wing" Göppingen Gö 3 Minimoa produced in Germany starting in
   1936.
   Enlarge
   The "gull wing" Göppingen Gö 3 Minimoa produced in Germany starting in
   1936.

   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. 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 km (465 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.
   Nonetheless, several German fighter aces in the conflict, including
   Erich Hartmann, began their flight training in gliders.

   Gliding did not return to the Olympics after the war, for two reasons:
   first, the shortage of gliders following the war; and second, 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 been
   occasionally proposed by the world governing body, the FAI, but this
   has been rejected on the grounds of lack of public interest.

   Still, in many countries during the 1950s there were a large number of
   trained pilots who wanted to continue flying. Many were also
   aeronautical engineers. They started both clubs and manufacturers, many
   of which still exist. This stimulated the development of both gliding
   and gliders; for example, the Soaring Society of America grew from
   1,000 members then to its present total of 16,000. The increased
   numbers of pilots, greater knowledge 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. New materials such as glass fibre and carbon fibre, advances in
   wing shapes, electronic instruments, GPS and improved weather
   forecasting have since allowed many pilots to make flights that were
   once extraordinary. Today almost 500 pilots have made flights over
   1,000 km.

   Instead of Olympic competition there are the World Gliding
   Championships. The first event was held at the Wasserkuppe in 1937.
   Since WWII 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. Germany, the sport's birthplace, is still a centre of the
   gliding world: it accounts for 30% of the world's glider pilots, 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, plus an unknown number of 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.

Soaring

   Duo Discus T flying over the ridges of Pennsylvania USA.
   Enlarge
   Duo Discus T flying over the ridges of Pennsylvania USA.

   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. 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 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; wave lift has allowed a glider
   to reach an altitude of 15,447 m (50,671 ft). 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).
   Good gliding weather: Well-formed cumulus humilis, with darker bases,
   suggests active thermals and light winds.
   Enlarge
   Good gliding weather: Well-formed cumulus humilis, with darker bases,
   suggests active thermals and light winds.
   A lenticular cloud produced by a mountain wave
   Enlarge
   A lenticular cloud produced by a mountain wave

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. Once a thermal is encountered, the pilot usually flies
   in circles to keep the glider within the thermal, so gaining altitude
   before flying off to the next thermal and towards the destination. This
   is known as 'thermalling'. Climb rates depend on conditions, but rates
   of several meters per second are common. 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.

   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, 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 during this period.
   A Scimitar glider ridge soaring in Lock Haven, Pennsylvania USA
   Enlarge
   A Scimitar glider ridge soaring in Lock Haven, Pennsylvania USA

Ridge lift

   A ridge soaring pilot uses air lifted up 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, though 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 a glider pilot, Wolf Hirth, in 1933. Gliders can sometimes climb in
   these waves to great altitudes, if pilots use supplementary oxygen to
   avoid hypoxia. This lift is often marked by long, stationary lenticular
   (lens-shaped) clouds lying perpendicular to the wind. Most altitude
   records for gliders have been set this way, though thunderstorms have
   also accounted for a share. The current world distance record of
   3,008 km (1,869 statute miles) by Klaus Ohlmann (set on 21 January
   2003) was 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.

Launch methods

   A Pawnee aerotowing a glider
   Enlarge
   A Pawnee aerotowing a glider

Aerotowing

   Aerotows normally use single-engined light aircraft, although motor
   gliders have also been permitted to tow gliders. The tow-plane takes
   the glider to the desired height and place and the glider pilot
   releases the rope. 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. This position can either be the "low
   tow" position, just below the wake 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 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.
   A Ventus 2b being winch-launched at Lasham Airfield
   Enlarge
   A Ventus 2b being winch-launched at Lasham Airfield

Winch-launching

   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-foot)
   cable, made of steel wire or a synthetic fibre, attached to the glider.
   The cable is released at a height of about 400 to 500 m (1,300 to 1,600
   feet) after a short and steep ride.

   The main advantage of a winch launch is its lower cost. However, the
   launch height is usually lower than an aerotow, so 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, pilots are trained to deal
   with this.
   A bungee launch at the Long Mynd by the Midland Gliding Club
   Enlarge
   A bungee launch at the Long Mynd by the Midland Gliding Club

Other methods of launching

   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 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.

   Another launch method, the "autotow", was used more frequently in the
   past. It requires a long runway, a pick-up truck and the 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 m (1300 feet) if there
   is a good headwind and a runway of 1.5 km (1 mile) or more. This method
   has been employed upon various desert dry lakes. A variation on this is
   the "reverse pulley" method in which the truck drives towards the
   glider that it is launching with the cable passing around a pulley at
   the far end of the airfield. A third method uses a pulley on the
   vehicle, with one end of the cable fixed - a dangerous method since the
   glider will be pulled twice as fast as the vehicle travels, and so
   requiring an experienced and cautious driver.

   Glider pilots who want to use the different types of launch methods
   must be in current practice in each. Licensing rules in some countries
   differentiate between aerotows and ground launch methods, due to the
   widely different techniques.

Cross-country

   Glider on a cross-country flight in the Alps
   Enlarge
   Glider on a cross-country flight in the Alps

   The distance that a glider can fly for each meter it descends is
   expressed as its lift-to-drag ratio. Depending on the class, this can
   be between 44:1 and 70:1 in modern designs. This performance combined
   with regular sources of rising air 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). Even in places with less favorable
   conditions (such as Northern Europe) most skilled pilots complete
   flights over 500 km (310 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 usually plan to fly around a course
   (called a task) via turn-points, returning to the starting point.

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

   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 speeds of 120 km/h are not unusual.

   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 gliding competitions have been difficult to televise.

   In an attempt to widen the sport's appeal, a new format, the Grand
   Prix, has been introduced. Innovations introduced in the Grand Prix
   format include simultaneous starts for a small number of gliders, tasks
   consisting of multiple circuits, and simplified scoring. There is
   decentralized Internet based competition called the Online Contest
   where pilots upload their GPS data files and are automatically scored
   based on distance flown. 7,800 pilots worldwide participated in this
   contest in 2006.

Maximizing speed

   Soaring pioneer Paul MacCready is usually credited with developing a
   mathematical theory for optimizing the speed to fly when cross-country
   soaring, though it was first described by Wolfgang Späte (who later
   became famous for flying Messerschmitt Me 163 Komet rocket fighters
   with the Luftwaffe late in World War II) in 1938. The speed to fly
   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 flight speeds, and have
   the calculations programmed in their flight computers. The greatest
   factor in maximizing speed, however, remains the ability of the pilot
   to find the strongest lift.

   On cross-country flights where strong thermals are forecast, pilots fly
   with water ballast, which is stored in tanks in the wings. Ballast
   makes the glider fly faster, but slows its climb rate in thermals.
   However, if the thermals are strong, the disadvantage of slower climbs
   are outweighed by the higher cruising speeds between them. 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 pilots dump their 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 gliding 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. Higher badges follow
   the standards set down by the Federation Aeronautique Internationale
   (FAI). The FAI's Sporting Code defines the rules for observers and
   recording devices to validate the claims for badges, which 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 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 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 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 for increments of 250 km.

Landing out

   Pilot and crew about to de-rig a glider
   Enlarge
   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 (or "outlanding") is a routine event in cross-country
   gliding. The pilot has to choose a field where the glider can be landed
   safely, without damaging property such as crops or livestock.

   The glider and the pilot(s) can be retrieved from the field using a
   purpose-built trailer. Alternatively, if the glider has landed in a
   suitable field, a tow-plane can be summoned to re-launch the aircraft
   (as long as the property owner gives permission). The glider 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
   Enlarge
   ASH25M - a self-launching two-seater glider

   To avoid the inconvenience of landing out, some gliders are motor
   gliders, optionally fitted with a small engine and a retractable
   propeller, adding both weight and expense. "Self-launching" motor
   gliders have engines that are powerful enough to launch the glider
   unaided. In "self-sustaining" motor gliders these engines are not
   powerful enough for launch, but 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 landing-out to be made, if the engine were to fail to start.

   In a competition, starting the engine ends the soaring flight. Gliders
   without an engine are lighter and, as they do not need a safety margin
   for an engine-start, they can safely thermal at lower altitudes in
   weaker conditions. So, 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.

   Touring motor gliders have a non-retractable propeller. Since the
   additional drag reduces their performance, they are seldom used in
   competition. They can, however, be useful in training for cross-country
   flights. After take-off, the engine is switched off, and the trainee
   flies the aircraft as a glider. Landings in unfamiliar fields can be
   practiced while the motor idles. If the trainee chooses an
   inappropriate field, or misjudges the approach, the instructor can
   apply power and climb away safely, after pointing out the error.

Aerobatics

   S-1 Swift - modern aerobatic glider
   Enlarge
   S-1 Swift - modern aerobatic glider

   Aerobatic competitions are held regularly. 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". 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

   Gliders, unlike hang-gliders and paragliders, surround the pilot with a
   strong structure, so most accidents cause no injuries, but there are
   some hazards. Even though training and safe procedures are central to
   the ethos of the sport, a small number of fatal accidents occurs every
   year, almost all caused by pilot error. In particular there is a risk
   of mid-air collisions between gliders because the pilots tend to fly to
   the same areas of lift. To avoid other gliders and general aviation
   traffic, pilots must comply with the rules of the air and keep a good
   lookout. They also usually wear parachutes. In Switzerland, Austria,
   Germany, and Australia, the FLARM warning system is used to avoid
   mid-air collisions between gliders.

Challenges for the gliding movement

   Gliding as a sport faces challenges in the years ahead. 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 increasing
     * 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 competitive gliding.
     * Increasing bureaucracy.

Learning to glide

   The Blanik L-23, a common training glider
   Enlarge
   The Blanik L-23, a common training glider

   Most clubs offer trial lessons to people interested in learning to
   glide. National gliding associations have contact details for their
   member 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.

   If winches are used, the cost of learning to glide is much less than
   that of learning to fly powered aircraft. Training using aerotow costs
   more than using winches, even though fewer launches (as few as 30)
   might be needed. Simulators are also beginning to be used in 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. Pilots must
   also familiarize themselves with the regulations, use of the radio,
   weather and navigation.

Related air sports

   Hang-gliding uses simpler and cheaper aircraft in which pilots exercise
   control by shifting body weight, whereas glider-pilots use conventional
   flight controls. Hang-gliders typically use fabric wings, shaped over a
   rigid framework. The lower aerodynamic efficiency of these wings means
   that shorter cross-country distances are flown than in gliders. Unlike
   the hang-gliders' wings, paragliders' wings have no frames and their
   shape is entirely formed by the pressure of the air. The aerodynamic
   efficiency of paragliders is lower still and so cross-country flights
   are even shorter. Radio-controlled gliding uses scale-models of gliders
   mainly for ridge soaring.

   Retrieved from " http://en.wikipedia.org/wiki/Gliding"
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