Science Fair Project Encyclopedia
Gliders are un-powered heavier-than-air aircraft.
They can be divided into two broad categories, pure gliders and sailplanes.
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 Confucious, 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. A glider was even built secretly by POWs as a potential escape method at Colditz Castle near the end of the war in 1944.
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.
The most common method of launching gliders is being towed behind a powered aircraft via a long (approximately 60 meters) rope. The release is performed by the sailplane after reaching the required altitude, but can be released by the towplane in an emergency. There are several other methods (see gliding) which include winches and some older methods such as large bungee cords and launching off sloping hills and cliffs. It is very common for sailplane pilots to band together within clubs to secure flying field accommodations and launch equipment. This becomes a very important social aspect of the sport.
Five hour (and much longer) flights over great distances are not at all uncommon. Sailplanes remain aloft utilize 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 striking the ground which forms rising columns of air reaching cloud base (though thermals are strongest and most useable mid way up the column). 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 wind patterns strike a mountain, cliff or hill. The air mass is deflected up the windward face of the mountain forming lift and sailplanes can move perpendicular to this rising wind condition. This is commonly referred as "ridge running" and has been used to set record distance flights along the Andes Mountains in South America. Another type of lift condition may form downwind of the leeward face of the same mountain in which the airflow over the mountain peak can be visualized as waves with alternating lift and sink patterns. For that reason using this lift phenomena is known as soaring in "wave". More exotic still are the polar vortexes which may or have been used by the Perlan Project to soar to incredible altitudes.
To enable sailplanes to soar effectively, they are designed to minimise drag. They have very smooth, narrow fuselages and very long, narrow wings with a high aspect ratio. New materials such as carbon fiber plastic and computer-aided design have increased performance. While early gliders have had glide ratios below 20 to 1, the latest open-class competition models can exceed ratios of 60 to 1 and maintain this efficiency over a wide range of air-speeds. (The ratio of 60:1 means that in smooth air the sailplane can horizontally travel 60 meters while losing 1 meter of altitude).
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 (CD) 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. To adapt the glider to the thermals and lift available at the time, the competition rules sometimes allow gliders to 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 code their reading into an acoustic signal of variable amplitude and frequency, so that it can be used without drawing the pilot's attention away from watching the airspace and 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.
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 three dimensional positional information through a moving map display
- Indicate contest task position along with managing required course direction and distance
- Show airports within gliding distance (ignoring sink/lift)
- Calculate and display information conducive to 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 multiple gliders fly together in three dimensions.
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 after flying all programs of the competition.
Some sailplanes ("self-launching motor gliders") are equipped with motors, usually retractable into the fuselage, powerful enough to allow the gliders to launch independently. 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 under its own power after an assisted takeoff. A third type, termed touring motorglider, has a conventional layout with a motor and propellor on the front of the aircraft. Some people argue that an engine makes the aircraft safer, because the pilot can avoid storms, and can go 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. In gliding and in single-engine flying in general, it is important never to be out of gliding range of a safe landing site.
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.
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. This does not apply in the United Kingdom, where glider pilots are regulated by the British Gliding Association using a "badge" system, and do not have to be licensed with the 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.
- 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.
- Web-sites of the major modern sailplane manufacturers:
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