Paragliding

Takeoff from a ramp, Tegelberg, Schwangau, Germany

Paragliding over Jounieh Bay, Lebanon

Paragliding is the recreational and competitive adventure sport of flying paragliders: lightweight, free-flying, foot-launched glider aircraft with no rigid primary structure. The pilot sits in a harness suspended below a hollow fabric wing whose shape is formed by its suspension lines, the pressure of air entering vents in the front of the wing and the aerodynamic forces of the air flowing over the outside.

Despite not using an engine, paraglider flights can last many hours and cover many hundreds of kilometres, though flights of 1–2 hours and covering some tens of kilometres are more the norm. By skilful exploitation of sources of lift the pilot may gain height, often climbing to altitudes of a few thousand metres.

Paragliders are unique among soaring aircraft in being easily portable. The complete equipment packs into a rucksack and can be carried easily on the pilot's back, in a car, or on public transport. In comparison with other air sports this substantially simplifies travel to a suitable takeoff spot, the selection of a landing place and return travel.

Paragliding is related to the following activities:

• Hang gliding is a close cousin, and hang glider and paraglider launches are often found in proximity. Despite the considerable difference in equipment the two activities offer similar pleasures and some pilots are involved in both sports.

• Powered paragliding is the flying of paragliders with a small engine attached.

• Speed riding or speed flying is the separate sport of flying paragliders of reduced size. These wings have increased speed, though they are not normally capable of soaring flight. The sport involves taking off on skis or on foot and swooping rapidly down in close proximity to the slope, even periodically touching it if skis are used. These smaller wings are also sometimes used where wind speeds are too high for a full-sized paraglider, although this is invariably at coastal sites where the wind is laminar and not subject to as much mechanical turbulence as inland sites.

• Paragliding can be of local importance as a commercial activity. Paid accompanied tandem flights are available in many mountainous regions, both in the winter and in the summer. In addition there are many schools offering courses, and guides who lead groups of more experienced pilots exploring an area. Finally there are the manufacturers and the associated repair and after sales services.
• Paraglider-like wings also find other uses, for example in ship propulsion and wind energy exploitation, and are related to some forms of power kite.
• Kite skiing uses equipment similar to paragliding sails.

History

In 1952 Domina Jalbert advanced governable gliding parachutes with multi-cells and controls for lateral glide.

In 1954, Walter Neumark predicted (in an article in Flight magazine) a time when a glider pilot would be “able to launch himself by running over the edge of a cliff or down a slope ... whether on a rock-climbing holiday in Skye or ski-ing in the Alps”.

In 1961, the French engineer Pierre Lemoigne produced improved parachute designs which led to the Para-Commander. The ‘PC’ had cutouts at the rear and sides that enabled it to be towed into the air and steered – leading to parasailing/parascending.

Sometimes credited with the greatest development in parachutes since Leonardo da Vinci, the American Domina Jalbert invented the Parafoil which had sectioned cells in an aerofoil shape; an open leading edge and a closed trailing edge, inflated by passage through the air – the ram-air design. He filed US Patent 3131894 on January 10, 1963.

Land-based practice: Kiting

Meanwhile, David Barish was developing the Sail Wing (single-surface wing) for recovery of NASA space capsules – “slope soaring was a way of testing out ... the Sail Wing”. After tests on Hunter Mountain, New York in September 1965, he went on to promote ‘slope soaring’ as a summer activity for ski resorts (apparently without great success).

Author Walter Neumark wrote Operating Procedures for Ascending Parachutes, and he and a group of enthusiasts with a passion for tow-launching ‘PCs’ and ram-air parachutes eventually broke away from the British Parachute Association to form the British Association of Parascending Clubs (BAPC) in 1973. Authors Patrick Gilligan (Canada) and Bertrand Dubuis (Switzerland) wrote the first flight manual "The Paragliding Manual" in 1985, officially coining the word Paragliding.

These threads were pulled together in June 1978 by three friends Jean-Claude Bétemps, André Bohn and Gérard Bosson from Mieussy Haute-Savoie, France. After inspiration from an article on ‘slope soaring’ in the Parachute Manual magazine by parachutist & publisher Dan Poynter, they calculated that on a suitable slope, a ‘square’ ram-air parachute could be inflated by running down the slope; Bétemps launched from Pointe du Pertuiset, Mieussy, and flew 100 m. Bohn followed him and glided down to the football pitch in the valley 1000 metres below. ‘Parapente’ (pente being French for slope) was born.

From the 1980s equipment has continued to improve and the number of paragliding pilots and established sites has continued to increase. The first Paragliding World Championship was held in Kössen, Austria in 1989. Europe has seen the greatest growth in paragliding, with France alone currently registering over 25,000 active pilots.

Equipment

Wing

3d CAD drawing of a paraglider showing the upper surface in green, the lower surface in blue and the leading edge openings in pink. Only the left half of the suspension cone is shown.

Transverse cross section showing parts of a paraglider:
1) upper surface
2) lower surface
3) rib
4) diagonal rib
5) upper line cascade
6) middle line cascade
7) lower line cascade
8) risers

The paraglider wing or canopy is usually what is known in aeronautical engineering as a "ram-air airfoil". Such wings comprise two layers of fabric which are connected to internal supporting material in such a way as to form a row of cells. By leaving most of the cells open only at the leading edge, incoming air keeps the wing inflated, thus maintaining its shape. When inflated, the wing's cross-section has the typical teardrop aerofoil shape. Modern paraglider wings are made of high-performance non-porous materials such as ripstop polyester or nylon fabric.

In some modern paragliders (from the 1990s onwards), especially higher performance wings, some of the cells of the leading edge are closed to form a cleaner aerodynamic profile. Holes in the internal ribs allow a free flow of air from the open cells to these closed cells to inflate them, and also to the wingtips which are also closed.

The pilot is supported underneath the wing by a network of suspension lines. These start with two sets of risers made of short (40 cm) lengths of strong webbing. Each set is attached to the harness by a carabiner, one each side of the pilot, and each riser of a set is generally attached to lines from only one row of its side of wing. At the end of each riser of the set there is a small delta maillon with a number (2-5) of lines attached forming a fan. These are typically 4–5 metres long, with the end attached to 2-4 further lines of around 2m, which are again joined to a group of smaller, thinner lines. In some cases this is repeated for a fourth cascade.

The top of each line is attached to small fabric loops sewn in to the structure of the wing, which are generally arranged in rows running span-wise (i.e. side to side). The row of lines nearest the front are known as the A lines, the next row back the B lines and so on. A typical wing will have A, B, C and D lines, but recently there is a tendency to reduce the rows of lines to three, or even two (and experimentally to one), to reduce drag.

Paraglider lines are usually made from Dyneema/Spectra or Kevlar/Aramid. Although they look rather slender, these materials are immensely strong. For example, a single 0.66mm diameter line (about the thinnest used) can have a breaking strength of 56 kg.

Paraglider wings typically have an area of 20–35 square metres (220–380 sq ft) with a span of 8–12 metres (26–39 ft), and weigh 3–7 kilograms (6.6–15.4 lb). Combined weight of wing, harness, reserve, instruments, helmet, etc. is around 12–22 kilograms (26–49 lb).

The glide ratio of paragliders ranges from 8.8 for recreational wings, to about 11.0 for modern competition models. For comparison, a typical skydiving parachute will achieve about 3:1 glide. A hang glider ranges from 11.0 for recreational wings, to about 17.0 for modern competition models. An idling (gliding) Cessna 152 light aircraft will achieve 9:1. Some sailplanes can achieve a glide ratio of up to 72:1.

The speed range of paragliders is typically 20–75 kilometres per hour (12–47 mph), from stall speed to maximum speed. Beginner wings will be in the lower part of this range, high-performance wings in the upper part of the range.

For storage and carrying, the wing is usually folded into a stuffsack (bag), which can then be stowed in a large backpack along with the harness. For pilots who may not want the added weight or fuss of a backpack, some modern harnesses include the ability to turn the harness inside out such that it becomes a backpack.

Tandem paragliders, designed to carry the pilot and one passenger, are larger but otherwise similar. They usually fly faster with higher trim speeds, are more resistant to collapse, and have a slightly higher sink rate compared to solo paragliders.

Harness

Pilot with harness (light blue) performing a reverse launch

The pilot is loosely and comfortably buckled into a harness which offers support in both the standing and sitting positions. Most harnesses have foam or airbag protectors underneath the seat and behind the back to reduce the impact on failed launches or landings. Modern harnesses are designed to be as comfortable as a lounge chair in the sitting position. Many harnesses even have an adjustable 'lumbar support'. A reserve parachute is also typically connected to a paragliding harness.

Instruments

Most pilots use variometers, radios, and, increasingly, GPS units when flying.

Variometer

Vario-altimeter

Main article: Variometer

The main purpose of a variometer is in helping a pilot find and stay in the "core" of a thermal to maximise height gain and, conversely, to indicate when a pilot is in sinking air and needs to find rising air. Humans can sense the acceleration when they first hit a thermal, but cannot detect the difference between constant rising air and constant sinking air. Modern variometers are capable of detecting rates of climb or sink of 1 cm per second. A variometer indicates climb-rate (or sink-rate) with short audio signals (beeps, which increase in pitch and tempo during ascent, and a droning sound, which gets deeper as the rate of descent increases) and/or a visual display. It also shows altitude: either above takeoff, above sea level, or (at higher altitudes) "flight level".

Radio

Radio communications are used in training, to communicate with other pilots, and to report where and when they intend to land. These radios normally operate on a range of frequencies in different countries—some authorised, some illegal but tolerated locally. In rare cases, pilots use radios to talk to airport control towers or air traffic controllers. Many pilots carry a cell phone so they can call for pickup should they land away from their intended point of destination.

GPS

GPS (global positioning system) is a necessary accessory when flying competitions, where it has to be demonstrated that way-points have been correctly passed. The recorded GPS track of a flight can be used to analyze flying technique or shared with other pilots. GPS is also used to determine drift due to the prevailing wind when flying at altitude, providing position information to allow restricted airspace to be avoided, and identifying one’s location for retrieval teams after landing-out in unfamiliar territory. GPS is integrated with some models of variometer. This is not only more convenient, but also allows for a three dimensional record of the flight. The flight track can be used as proof for record claims, replacing the 'old' method of photo documentation.

Control

Speedbar mechanism

Brakes: Controls held in each of the pilot’s hands connect to the trailing edge of the left and right sides of the wing. These controls are called 'brakes' and provide the primary and most general means of control in a paraglider. The brakes are used to adjust speed, to steer (in addition to weight-shift), and flare (during landing).

Weight Shift: In addition to manipulating the brakes, a paraglider pilot must also lean in order to steer properly. Such 'weight-shifting' can also be used for more limited steering when brake use is unavailable, such as when under 'big ears' (see below). More advanced control techniques may also involve weight-shifting.

Speed Bar: A kind of foot control called the 'speed bar' (also 'accelerator') attaches to the paragliding harness and connects to the leading edge of the paraglider wing, usually through a system of at least two pulleys (see animation in margin). This control is used to increase speed, and does so by decreasing the wing's angle of attack. This control is necessary because the brakes can only slow the wing from what is called 'trim speed' (no brakes applied). The accelerator is needed to go faster than this.

More advanced means of control can be obtained by manipulating the paraglider's risers or lines directly:

• Most commonly, the lines connecting to the outermost points of the wing's leading edge can be used to induce the wingtips to fold under. The technique, known as 'big ears', is used to increase rate of descent (see picture and therefore description below).
• The risers connecting to the rear of the wing can also be manipulated for steering if the brakes have been severed or are otherwise unavailable.
• In a 'B-line stall' (see below for therefore description)

Fast descents

Problems with “getting down” can occur when the lift situation is very good or when the weather changes unexpectedly. There are three possibilities of rapidly reducing altitude in such situations, each of which has benefits and issues to be aware of:

• "Big ears" induces descent rates of 2 m/s or so. It is the most controllable of the techniques, and the easiest for beginners to learn.
• A B-line stall induces descent rates of 5 m/s or so. It increases loading on parts of the wing (the pilot's weight is mostly on the B-lines, instead of spread across all the lines). There is not a risk of the pilot becoming disoriented as a result of using this technique.
• A spiral dive offers the fastest rate of descent, at 10-15m/sec. It places greater loads on the wing than other techniques do, and requires the highest level of skill from the pilot to execute safely.

Big Ears

Paraglider in "Big Ears" maneouvre

Pulling on the outer A-lines folds the wing tips in drastically deteriorating the glide angle with only a small decrease in forward speed. When the lines are released the wing reinflates. As the effective wing area is reduced, the wing loading is increased and it becomes more stable. However the angle of attack is increased and the craft is closer to stall speed, but this can be ameliorated by applying the speed bar.

B-Line stall

In a 'B-line stall', the second set of risers from the leading-edge/front (the B-lines) are pulled down independently of the other risers; with the specific lines used to initiate the condition being responsible for its name. This puts a spanwise crease in the wing, thereby separating the airflow from the upper surface of the wing. This dramatically reduces the lift produced by the canopy and thus induces a higher rate of descent.

Spiral Dive

The spiral dive is the most rapid form of controlled fast descent; a sink rate of 15 m/s can be achieved.

However, spiral dives put strong G-forces on the wing and glider and must be done carefully and skilfully. The G-forces involved can induce blackouts, and the rotation can produce disorientation.

Flying

Launching

Paraglider reverse launch demonstration video

Paraglider towed launch, Mirosławice, Poland

Paraglider in Sopelana, Biscay, Basque Country

As with all aircraft, launching and landing are done into wind.

Forward launch

In low winds, the wing is inflated with a ‘forward launch’, where the pilot runs forward with the wing behind so that the air pressure generated by the forward movement inflates the wing.

Reverse launch

In higher winds a ‘reverse launch’ is used, with the pilot facing the wing to bring it up into a flying position, then turning around under the wing and running to complete the launch.

Reverse launches have a number of advantages over a forward launch. It is more straight forward to inspect the wing and check the lines are free as it leaves the ground. In the presence of wind, the pilot can be tugged toward the wing and facing the wing makes it easier to resist this force, and safer in case the pilot slips (as opposed to being dragged backwards). These launches are normally attempted with a reasonable wind speed making the ground speed required to pressurise the wing much lower – the pilot is initially launching while walking forwards as opposed to running backward.

Towed launch

Paraglider launching in Araxá, Brazil

In flatter countryside pilots can also be launched with a tow. Once at full height (towing can launch pilots up to 2500 feet altitude), the pilot pulls a release cord and the towline falls away. This requires separate training, as flying on a winch has quite different characteristics from free flying. There are two major ways to tow: Pay-in and pay-out towing. Pay-in towing involves a stationary winch that winds in the towline and thereby pulls the pilot in the air. The distance between winch and pilot at the start is around 500 meters or more. Pay-out towing involves a moving object, like a car or a boat, that pays out line slower than the speed of the object thereby pulling the pilot up in the air. In both cases it is very important to have a gauge indicating line tension to avoid pulling the pilot out of the air. There is one other form of towing; ‘static’ towing. This involves a moving object, like a car or a boat, attached to a paraglider or hanglider with a fixed length line. This is very dangerous because now the forces on the line have to be controlled by the moving object itself, which is almost impossible to do. With static line towing a lockout (moving to the side away from the tow direction or stalling) is very likely. Static line towing is forbidden in most countries, and should be avoided at all cost.

Landing

Paraglider along the beach

Landing involves lining up for an approach into wind, and just before touching down, ‘flaring’ the wing to minimise vertical and/or horizontal speed. This consist of gently going from 0% brake at around 2 meters to 100% brake when touching down on the ground.

In light winds, some minor running is common. In moderate to medium headwinds, the landings can be without forward speed. With strong winds even going backwards with respect to the ground, but this would usually mean that the conditions were too strong for that glider.

Additionally, at around 4 meters before touching ground, some momentary braking (50% for around 2 seconds) can be applied, then released thus using forward pendular momentum to gain speed for flaring more effectively and approach the ground with minimal vertical speed.

For strong winds during landing two techniques are common:

• 'flapping' the wing to make it lose performance and thus descend faster by alternatively braking and releasing (around once per second).
• Collapsing it immediately after touchdown to avoid being dragged by braking at maximum.

Soaring

Ridge soaring along the California coast

Ridge Soaring in Israel

Soaring flight is achieved by utilizing wind directed upwards by a fixed object such as a Dune or Ridge. In slope soaring, pilots fly along the length of a slope feature in the landscape, relying on the lift provided by the air which is forced up as it passes over the slope. Slope soaring is highly dependent on a steady wind within a defined range (the suitable range depends on the performance of the wing and the skill of the pilot). Too little wind, and insufficient lift is available to stay airborne (pilots end up scratching along the slope). With more wind, gliders can fly well above and forward of the slope, but too much wind, and there is a risk of being blown back over the slope.

Thermal flying

Paragliders in the air at Torrey Pines Gliderport

When the sun warms the ground, it will warm some features more than others (such as rock-faces or large buildings), and these set off thermals which rise through the air. Sometimes these may be a simple rising column of air; more often, they are blown sideways in the wind, and will break off from the source, with a new thermal forming later. Once a pilot finds a thermal, he or she begins to fly in a circle, trying to center the circle on the strongest part of the thermal (the "core"), where the air is rising the fastest. Most pilots use a vario-altimeter ("vario"), which indicates climb rate with beeps and/or a visual display, to help core-in on a thermal. Often there is strong sink surrounding thermals, and there is often also strong turbulence resulting in wing collapses as a pilot tries to enter a strong thermal. Good thermal flying is a skill which takes time to learn, but a good pilot can often core a thermal all the way to cloud base.

Cross-country flying

Once the skills of using thermals to gain altitude have been mastered, pilots can glide from one thermal to the next to go 'cross country'. Having gained altitude in a thermal, a pilot glides down to the next available thermal. Potential thermals can be identified by land features which typically generate thermals, or by cumulus clouds which mark the top of a rising column of warm, humid air as it reaches the dew point and condenses to form a cloud. In many flying areas, cross-country pilots also need an intimate familiarity with air law, flying regulations, aviation maps indicating restricted airspace, etc.

In-flight Wing Deflation (Collapse)

Since the shape of the wing (airfoil) is formed by the moving air entering and inflating the wing, in turbulent air, part or all of the wing (airfoil) can deflate (collapse). Piloting techniques referred to as "active flying" will greatly reduce the frequency and severity of deflations or collapses. On modern recreational wings, such deflations will normally recover without pilot intervention. In the event of a severe deflation, correct pilot input will speed recovery from a deflation, but incorrect pilot input may slow the return of the glider to normal flight, so pilot training and practice in correct response to deflations is necessary. For the rare occasions when it is not possible to recover from a deflation (or from other threatening situations such as a spin), most pilots carry a reserve (rescue, emergency) parachute. Most pilots never have cause to ‘throw’ their reserve. Should a wing deflation occur at low altitude, i.e., shortly after takeoff or just before landing, the wing (paraglider) may not recover its correct structure rapidly enough to prevent an accident, with the pilot often not having enough altitude remaining to successfully deploy a reserve parachute (with the minimum altitude for this being approximately 60 m (200 ft), but typical deployment to stabilization periods using up 120–180 m (400 – 600 ft) of altitude). Different packing methods of the reserve parachute affect its deploying time. It is also important to note that, should the wing collapse due to turbulence, this 'bad air' can cause the reserve parachute to take significantly longer to inflate and stabilize. In this case, it may be of greater benefit to the paraglider to purposefully lose altitude to 'clear' this turbulent air before deploying their reserve; should they have spare altitude to use on this process. Low altitude wing failure can result in serious injury or death due to the subsequent velocity of a ground impact where, paradoxically, a higher altitude failure may allow more time to regain some degree of control in the descent rate and, critically, deploy the reserve if needed. In-flight wing deflation and other hazards are minimized by flying a suitable glider and choosing appropriate weather conditions and locations for the pilot's skill and experience level.

Sports/competitive flying

Some pilots like to stretch themselves beyond recreational flying. For such pilots, there are multiple disciplines available:

• Cross Country Competitions – races around waypoints with typical distances of 50 to 150 kilometers
• National/international records – despite continually improving gliders, these become ever more difficult to achieve; aside from longest distance and highest altitude, examples include distance to declared goal, distance over triangular course, speed over 100 km triangular course, etc.
• "Acro" – aero-acrobatic manoeuvres and stunt flying; tricks such as "helicopters", wing-overs, synchro spirals, infinity tumbles, and so on.
• Cross-country leagues – annual regional, national and worldwide leagues scored based on accumulated best distance flights
• Accuracy – spot landing competitions where pilots land on targets with a 3 cm centre spot out to a full 10 meter circle.

Competitive flying is done on high performance wings which demand far more skill to fly than their recreational counterparts, but which are far more responsive and offer greater feedback to the pilot, as well as flying faster with better glide ratios.

The current FAI world champion is Charles Cazaux of France; he won the title in July 2011 in Piedrahita, Spain. His predecessor was Andy Aebi of Switzerland, and before him Bruce Goldsmith from the UK.

The current Paragliding World Cup (PWC) Champion is Aaron DUROGATI of Italy; he won the title in January 2013 in Roldanillo, Colombia.

See also: World Air Games

Safety

Paraglider launch video in Araxá, Brazil

Paragliding is a potentially dangerous recreational activity. In the United States for example, an average of slightly less than 1 in every 1,000 active paraglider pilots has been fatally injured every year since 1994. In France (with over 25,000 registered fliers), around 6 of every 1,000 pilots were seriously injured (more than 2 day hospital stay), while 2 of every 10,000 pilots were fatally injured in 2011.

The potential for injury can be significantly reduced by training and risk management. The use of proper equipment such as a wing designed for the pilot's size and skill level, as well as a helmet, reserve parachute, and a cushioned harness also minimize risk. The pilot's safety is influenced by their understanding of the site conditions such as air turbulence (rotors), strong thermals, gusty wind, and ground obstacles such as power lines. Sufficient pilot training in wing control and emergency maneuvers from competent instructors can minimize accidents. Many paragliding accidents are the result of a combination of pilot error, and poor flying conditions.

Learning to fly

Most popular paragliding regions have a number of schools, generally registered with and/or organized by national associations. Certification systems vary widely between countries, though around 10 days instruction to basic certification is standard.

Flying above Stubaital, Austria

Tandem Paragliding at Painan, Indonesia

There are several key components to a paragliding pilot certification instruction program. Initial training for beginning pilots usually begins with some amount of ground school to discuss the basics, including elementary theories of flight as well as basic structure and operation of the paraglider.

Students then learn how to control the glider on the ground, practicing take-offs and controlling the wing 'overhead'. Low, gentle hills are next where students get their first short flights, flying at very low altitudes, to get used to the handling of the wing over varied terrain. Special winches can be used to tow the glider to low altitude in areas that have no hills readily available.

As their skills progress, students move on to steeper/higher hills (or higher winch tows), making longer flights, and learning to turn the glider, control the glider's speed, then moving on to 360° turns, spot landings, ‘big ears’ (used to increase the rate of descent for the paraglider), and other more advanced techniques. Training instructions are often provided to the student via radio, particularly during the first flights.

A third key component to a complete paragliding instructional program provides substantial background in the key areas of meteorology, aviation law, and general flight area etiquette.

Tandem paraglider launch

To give prospective pilots a chance to determine if they would like to proceed with a full pilot training program, most schools offer tandem flights, in which an experienced instructor pilots the paraglider with the prospective pilot as a passenger. Schools often offer pilot's families and friends the opportunity to fly tandem, and sometimes sell tandem pleasure flights at holiday resorts.

Most recognised courses lead to a national licence and an internationally recognised International Pilot Proficiency Information/Identification card. The IPPI specifies five stages of paragliding proficiency, from the entry level ParaPro 1 to the most advanced stage 5. Attaining a level of ParaPro 3 typically allows the pilot to fly solo or without instructor supervision.

World records

FAI (Fédération Aéronautique Internationale) world records:

• Straight distance – 502.9 km: Nevil Hulett (South Africa); Copperton, South Africa – Lesotho; 14 December 2008. Flight record
• Previous Straight distance – 461.6 km: Frank Brown, Marcelo Prieto, Rafael Monteiro Saladini (Brazil); Quixadá – Duque, Brazil; 14 November 2007.
• Straight distance to declared goal – 411.3 km: Nevil Hulett (South Africa); Copperton, South Africa – Lesotho; 14 December 2008.
• Previous Straight distance to declared goal – 368.9 km: Aljaž Valič, Urban Valič (Slovenia); Vosburg – Jamestown (South Africa); 7 December 2006
• Gain of height – 4526 m: Robbie Whittall (UK); Brandvlei (South Africa); 6 January 1993

See also

• Foot-launched powered hang glider
• Glider (sailplane)∋* USHPA – US Hang Gliding & Paragliding Association

References

Notes

Citations

Bibliography

• Les visiteurs du ciel – Guide de l'air pour l'homme volant. Hubert Aupetit. ISBN :2000154018

External links

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