Glider
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Gliders are un-powered heavier-than-air aircraft.
They can be divided into two broad categories, pure gliders and sailplanes.
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Pure gliders
Pure gliders are designed for descent only. See also gliding for more complete information about the sport. See sailplanes for a description of soaring gliders.
Manned gliders were flown in China from at least 559 AD, and giant 'man sized' kites were used for military reconnaissance for many centuries before that. The very first glider seems to have been designed in 500BC by Lu Pan a contemporary of Confucius, although this was more of a toy than a genuine aircraft.
The first heavier-than-air (i.e. non balloon) aircraft to be flown in Europe, Sir George Cayley's Coachman Carrier (1853), was a pure glider. Otto Lilienthal is another significant contributor to the development of this type of aviation.
Other examples were the military gliders used during WWII to support paratroop operations. These craft were used for a single flight only. The troops landing by glider were referred to as airlanding as opposed to paratroops. A typical cargo plane could carry 8 to 10 soldiers, but that same plane could tow a glider with 20 men in it. Furthermore the glider could be released at some distance from the actual target, making it more difficult for the enemy to guess their intentions. Larger gliders were also used to land heavy equipment like anti-tank guns and jeeps, which was a major improvement in the power available to the otherwise lightly-armed paratroop forces. One of the most well known stories involving military gliders was in the taking of the Pegasus Bridge during the D-Day invasion of Normandy in the early hours of 6th June 1944 - the troops were flown to within 50 metres of the site in Horsa gliders.
A glider was even built secretly by POWs as a potential escape method at Colditz Castle near the end of the war in 1944.
The Orbiter vehicles or "space shuttles", which glide to earth at the end of each spaceflight, are also pure gliders.
Sailplanes
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Sailplanes are specifically intended for the sport of gliding. Their design enables them to use energy from the atmosphere to "soar"; they can climb as well as descend. For more about soaring, please see the gliding, the hang gliding and paragliding articles.
Launch Methods
The two most common methods of launching gliders are by aerotow and by winch. When aerotowed the glider is towed behind a powered aircraft using a rope about 60 meters long. The release is performed by the sailplane after reaching the required altitude, but can be released by the towplane in an emergency. Winch launching uses a powerful static engine to wind in rapidly about 800-1200 metres of cable. For more about these and other methods (see gliding). All methods of launching gliders (apart from self-launching motor- gliders) require assistance from other people and so sailplane pilots band together within clubs to share an airfield and launch equipment and to maintain high standards of safety. Because help is also needed to rig and retrieve gliders as well as to train new pilots, there is an important social aspect to the sport.
Staying aloft without an engine
Five hour (and much longer) flights over great distances are not at all uncommon. Sailplanes remain aloft by using rising air masses (lift) created by one or more of several naturally occurring weather phenomena. The primary source of lift are thermals created by the sun's energy heating the ground which in turn heats air. The warm air rises in columns (known as thermals. Soaring pilots quickly become aware of visual indicators of this type of lift such as; cumulus clouds, dust devils and haze domes. Another form of lift is formed when the wind meets a mountain, cliff or hill. The air mass is deflected up the windward face of the mountain forming lift and sailplanes can climb in this rising air. This is commonly referred to as "ridge running" and has been used to set record distance flights along the Appalachians in the USA and the Andes Mountains in South America. Another type of lift may occur downwind of the mountains because the airflow can generate standing waves with alternating lift and sink. More exotic still are the polar vortexes which may or have been used by the Perlan Project (http://perlanproject.com) to soar to incredible altitudes. A rare phenomenon known as Morning Glory (http://www.cloudappreciationsociety.org/3content/glory/glory1.html) has also been used by sailplane pilots in Australia.
Sailplane design
Early gliders had no cockpit and the pilot sat on a small seat located just ahead of the wing. These were known as "primary gliders" and they were usually launched from the tops of hills, though they are also capable of short hops across the ground while being towed behind a vehicle. To enable sailplanes to soar more effectively than primary gliders, the designs minimised drag. Sailplanes now have very smooth, narrow fuselages and very long, narrow wings with a high aspect ratio.
The early gliders were made mainly of wood with metal fastenings, stays and control cables. Later fuselages made of fabric-covered steel tube were married to wood and fabric wings for lightness and strength. New materials such as carbon-fiber, glass-fiber and Kevlar have since been used with computer-aided design to increase performance. The first glider to use glass-fiber extensively was the Akaflieg Stuttgart Phönix which first flew in 1957. This material is still used because of its high strength to weight ratio and its ability to give a smooth exterior finish to reduce drag.
With each generation of materials, the performance of gliders has increased. One measure of performance is the glide ratio. A ratio of 17:1 means that in smooth air the sailplane can horizontally travel 17 meters while losing 1 meter of altitude. Comparing some typical gliders that might be found in the fleet of a gliding club - the Grunau Baby from the 1930s had a glide ratio of just 17:1, the glass-fiber Libelle of the 1960s increased that to 39:1, and nowadays flapped 15 meter gliders such as the ASG29 have a glide ratio of over 50:1. The latest open-class sailplanes with spans of 26 meters can exceed ratios of 60:1 and maintain this efficiency over a wide range of air-speeds.
Gliding Competitions
In modern cross-country gliding competitions, the winner is the pilot who is the fastest completing the task set for the day. A task is a series of turnpoints selected from a pre- announced list by the contest director based on the day's weather condition and the advice of experienced competition pilots. Competing pilots are grouped together based on skill levels, glider quality and other factors. If the lift available is likely to be strong, gliders will often carry jettisonable water ballast. Heavier planes have a slight disadvantage climbing in rising air, but the extra wing load shifts the glider's performance curve into higher velocities, so that the plane can achieve the same glide ratio at a higher velocity. While this is an advantage in strong conditions when the gliders spend only little time climbing in thermals, the pilot can jettison the water ballast before it becomes a disadvantage when the thermal conditions weaken in the evening.
Much more than in other types of aviation, glider pilots use an instrument know as a variometer (a very sensitive vertical climb indicator), which measures the climb or sink rate of the plane. Electronic variometers produce a beeping noise of variable amplitude and frequency depending on the strength of the lift, so that the pilot can concentrate on watching for other traffic, on navigating and on the weather. For more about this, please see the variometer article. Thus lift is announced to the pilot as a rising tone which the pilot will react to, hopefully banking the sailplane into lift. Alternately sink is announced with a lowering tone and the pilot will typically accelerate to get away from the sink in the shortest time possible.
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Soaring flight computers, in combination with PDAs and specialize soaring software, have been specifically designed for sailplane use. Using GPS technology this tool set is able to...
- Provide the glider's position in 3 dimensions by a moving map display
- Alert the pilot to nearby airspace restrictions
- Indicate contest task position along with managing required course direction and distance
- Show airports within gliding distance (ignoring sink/lift)
- Calculate and display information to help in remaining aloft
- Determine wind direction and speed at current altitude
- Show historical lift information
- Create a secure GPS log of the flight, required for contest flying
...and a host of other soaring related data.
The flight computer's GPS log may be replayed on specialized computer software to analyze past flights, including watching one or more gliders fly together in a two or three dimension 3-D view. The 3-D representation is shown here with a typical topographical background showing map details such as roads, cities and airports. The glider ("CD") has just executed a series of tight thermalling turns in the Austrian Alps. Other backgrounds might be a satellite image or an FAA sectional map.
Aerobatic gliders
Another - less widespread - form of gliding is aerobatics. In this type of competition, the pilot fly a program of maneuvers (such as inverted flight, loop, roll, and various combinations). Each maneuver has a rating called the "K-Factor." This number of points is given if the maneuver is flown perfectly, otherwise a number of points is subtracted. The winner is the pilot with the highest sum of points in each skill based category.
Motor gliders
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Some sailplanes ("self-launching motor gliders") are equipped with propellers that retract into the fuselage. The motor is powerful enough to allow these gliders to launch independently. Recently electric self-launchers such as the Antares (http://www.lange-flugzeugbau.de/english/english.html) have been developed. Others ("self-sustaining motor gliders," also referred to as "turbo" or "sustainer" gliders) are equipped with motors just powerful enough to allow the glider to climb slowly but they must be launched like unpowered gliders. A third type, termed touring motorglider, has a conventional layout with a motor and propellor on the front of the aircraft.
The most important point in favor of powered gliders (retractable engine high-performance types) is that it helps pilots to avoid outlandings. Outlandings, while they are not necessarily dangerous, can be an expensive and time-consuming nuisance for competitive pilots who need to be back home at a set time. Another consideration is that a retrieve crew is needed on stand-by. However the sense of achievement in completing a difficult cross-country is lessened if an engine has been available.
Some people argue that an engine makes the aircraft safer, because the pilot can avoid storms, and can go on to an airstrip to land. An opposing view is that motor gliders are against the spirit of the sport, and, more importantly, that they sometimes give pilots a false sense of invulnerability. Even in a motor glider, it is important never to be out of gliding range of a 'landable' area.
More recently, pilot licensing terms have changed in Europe. Powered gliders are now categorized into gliders with retractable propellers/engines, which can be flown with an ordinary glider pilot license (GPL), and touring motor gliders (TMG), which require a specific license extension to the standard GPL. In the United Kingdom, where gliding is regulated by the British Gliding Association (http://www.gliding.co.uk), pilots of self-sustaining gliders, like those of pure gliders, do not have to be licensed with the United Kingdom Civil Aviation Authority.
In the United States, a U.S. private glider pilot certificate allows the pilot to fly unpowered gliders, self-launching motor gliders and sustainer motor gliders. An instructor must provide instruction and sign the logbook of the pilot to authorize the launch method, which may be by airplane towing, ground launch (winches, bungee, auto tow, etc.) or, in the case of a suitable motor glider, by self-launching.
Other meanings
- In Conway's Game of Life a glider is a certain small structure that moves indefinitely in a direction. In cellular automata in general, such features are known as spaceships
- A comfortable swinging padded seat with a back, usable by more than one person, and typically used on a porch or veranda, is also called a glider.
- Glider PRO by Casady & Greene, a game for the Apple Macintosh.
See also
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External links
- For more information on gliders and learning to glide, see article on gliding and contact your national gliding federation
- Links to all national gliding federations (http://start.fai.org/gliding-federations.asp)
- Information about all types of glider:
- Sailplane Directory (http://www.sailplanedirectory.com/ndxtype.htm) - An enthusiast's web-site that lists manufacturers and models of sailplanes, past and present.
- Web-sites of the major modern sailplane manufacturers:
- Alexander Schleicher (AS) (http://www.alexander-schleicher.de/)
- DG Flugzeugbau (DG) (http://www.dg-flugzeugbau.de/index-e.html)
- Schempp-Hirth (http://www.schempp-hirth.com/en/)
- Stemme (http://www.stemme.de/daten/e/)
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