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Glider aircraft
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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 force other types of aircraft to glide.
There are a wide variety of types differing in the construction of their wings, aerodynamic efficiency, location of the pilot and controls.
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Encyclopedia
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 force other types of aircraft to glide.
There are a wide variety of types differing in the construction of their wings, aerodynamic efficiency, location of the pilot and controls. Some may have power-plants to take off and/or extend flight. Some are designed simply to descend, but the most common varieties exploit meteorological phenomena to maintain or even gain height. These types are principally used for the air sports of gliding, hang gliding and paragliding. Perhaps the most familiar type is the paper aeroplane.
History of gliders
Early attempts
Early accounts of flight are often sketchy and it is unclear whether each craft was a kite, parachute or a truly controllable aircraft. In China, kites rather than gliders were used for military reconnaissance. However the Extensive Records of the Taiping Era (978) suggests that something similar to a glider was designed in the 5th century BC by Lu Ban, a contemporary of Confucius. There is also a report from the History of Northern Dynasties (659) and Zizhi Tongjian (1084) that Yuan Huangtou in Ye made a successful glide, taking off from a tower in 559. Abbas Ibn Firnas invented and piloted the first manned ornithopter in 875. Abbas was seriously injured in the resulting crash. In circa 1630-1632 Ottoman Turkey, Hezârfen Ahmed Çelebi reputedly flew from the Galata Tower by glider, across the Bosporus, landed in Dogancilar square in Üsküdar -and was rewarded by Murad Khan with him a sack of golden coins and exile to Algeria.
19th century
Although models were built by The first heavier-than-air (i.e. non-balloon) man-carrying aircraft that were based on published scientific principles were Sir George Cayley's series of gliders which achieved brief wing-borne hops from around 1849. Thereafter gliders were built by pioneers such as Jean Marie Le Bris, John J. Montgomery, Otto Lilienthal, Percy Pilcher, Octave Chanute and Augustus Moore Herring to develop aviation. Of these Lilienthal was the first to make repeated successful flights, achieving over 2,000 and was the first to use rising air to prolong the flight. The Wright Brothers developed a series of three manned gliders after preliminary tests with a kite as they worked towards achieving powered flight. They returned to glider testing in 1911 by removing the motor from one of their later designs.
Development of gliders
After World War I recreational gliders were built in Germany (see link to Rhön-Rossitten Gesellschaft) and in the United States (Schweizer brothers). The sporting use of gliders rapidly evolved in the 1930s and is now the main application. As their performance improved gliders began to be used to fly cross-country and now regularly fly hundreds or even thousands of kilometers in a day, if the weather is suitable.
Military gliders were developed during World War II by a number of countries for landing troops. A glider - the Colditz Cock - was even built secretly by POWs as a potential escape method at Oflag IV-C near the end of the war in 1944.
Development of flexible-wing hang gliders
Foot-launched aircraft had been flown by Lilienthal and at the meetings at Wasserkuppe in the 1920s. However the innovation that led to modern hang gliders was in 1951 when Francis Rogallo and Gertrude Rogallo applied for a patent for a fully flexible wing with a stiffening structure. The American space agency NASA began testing in various flexible and semi-rigid configurations of this Rogallo wing in 1957 in order to use it as a recovery system for the Gemini space capsules. Charles Richards and Paul Bikle developed the concept producing a wing that was simple to build which was capable of slow flight and as gentle landing. Between 1960-1962 Barry Hill Palmer used this concept to make foot-launched hang gliders, followed in 1963 by Mike Burns who built a kite-hang glider called Skiplane. In 1963, John W. Dickenson began commercial production.
Development of paragliders
January 10, 1963 American Domina Jalbert filed a patent on 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. David Barish developed the Sail Wing further for recovery of NASA space capsules by using ridge lift. 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). NASA originated the term ‘paraglider’ in the early 1960’s, and ‘paragliding’ was first used in the early 1970’s to describe foot-launching of gliding parachutes.
Recreational types
The main application today of glider aircraft is sport and recreation.
Glider (sailplane)
Gliders were developed from the 1920s for recreational purposes. As pilots began to understand how to use rising air, gliders were developed with a high lift-to-drag ratio. These allowed longer glides to the next source of 'lift', and so increase their chances of flying long distances. This gave rise to the popular sport known as gliding although the term can also be used to refer to merely descending flight.
Gliders were mainly built of wood and metal but the majority now have composite materials using glass, carbon fibre and aramid fibres. To minimise drag, these types have a fuselage and long narrow wings, ie a high aspect ratio. Both single-seat and two-seat gliders are available.
Initially training was done by short 'hops' in primary gliders which are very basic aircraft with no cockpit and minimal instruments. Since shortly after World War 2 training has always been done in two-seat dual control gliders, but high performance two-seaters are also used to share the workload and the enjoyment of long flights. Originally skids were used for landing, but the majority now land on wheels, often retractable. Some gliders, known as motor gliders, are designed for unpowered flight, but can deploy piston, rotary, jet or electric engines.
Gliders are classified by in the FAI for competitions into glider competition classes mainly on the basis of span and flaps. However a new class of ultralight sailplanes, known as microlift gliders has been defined by the FAI based on a maximum weight.
Hang gliders
Hang gliders are foot-launched aircraft. In the original and still most common designs, the pilot is suspended from the center of the wing and controls the aircraft by shifting his/her weight. Since their invention, other types have been developed, so that there are now three classes of hang glider:
- The flexible wing hang glider, having flight controlled by a wing whose shape changes by virtue of the shifted weight of the pilot.
- The rigid wing hang glider, having flight controlled by spoilers, typically on top of the wing. In both flexible and rigid wings the pilot hangs below the wing without any additional fairing.
- Class 2 (designated by the FAI as Sub-Class O-2) where the pilot is integrated into the wing by means of a fairing. These offer the best performance and are the most expensive.
In a hang glider the shape of the wing is determined by a structure, and it is this that distinguishes them from the other main type of foot-launched aircraft, paragliders. Some hang gliders have engines- powered hang gliders. Due to their commonality of parts, construction and design, they are usually considered by aviation authorities to be hang gliders, even though they may use the engine for the entire flight.
Paragliders
A paraglider is a free-flying, foot-launched aircraft. The pilot sits in a harness suspended below a fabric wing. Unlike a hang glider whose wings have frames, shape of a paraglider's wing is formed by its suspension lines and the pressure of air entering vents in the front of the wing. The concept of ram-air inflated wings has been refined so that the best of these have a glide ratio of 10 at 45 km/h. Like sailplanes and hang gliders, paragliders use rising air to gain height and this process is the basis for most recreational flights and competitions, though aerobatics and 'spot landing competitions' also occur. Launching is often by stepping from a slope, but winch launches are also used. Paramotors are attached to some types which are known as powered paragliders. These in turn have spawned paraplanes, which are wheeled and motorized but which still use ram-air wings.
Military gliders
Military gliders were used mainly during the Second World War for carrying troops and heavy equipment (see Glider infantry) to a combat zone. These aircraft were towed into the air and most of the way to their target by military transport planes, eg C-47 Dakota, or by bombers that had been relegated to secondary activities, eg Short Stirling. Once released from the tow near the target, they landed on as close to target as possible. The advantage over paratroopers were that heavy equipment could be landed and that the troops were quickly assembled rather than being dispersed over a drop zone. The gliders were treated as disposable leading to construction from common and inexpensive materials such as wood, though a few were retrieved and re-used. By the time of the Korean War, transport aircraft had also become larger so that that even light tanks could be dropped by parachute, and so gliders were not used.
Research aircraft and rocket gliders
Even after the development of powered aircraft, gliders have been built for research such as flying wings, flexible wings and lifting bodies. Examples are the Horten flying wing gliders, Armstrong Whitworth A.W.52G, the Baynes Bat, the NASA Parasev Rogallo flexible wing and the X-26 Frigate. The lifting body uses the fuselage itself to produce lift. The objective is to minimize the drag and structure of a wing for very high supersonic or hypersonic flight or spacecraft re-entry. An example of type is the Northrop HL-10.
Rocket powered aircraft consume their fuel quickly and so most must land unpowered, unless there is another type of engine. The first was the Lippisch Ente. Later examples include the Messerschmitt Me 163 and the American series of research aircraft starting with the Bell X-1. that spent more time unpowered than flying under power. The Space Shuttle orbiters and the Russian Buran are the culmination of these types and are by far the fastest type of gliders to date. Unlike most of these rocket aircraft SpaceshipOne is a private development intended for sub-orbital flight.
Rotary wing
Most unpowered rotary-wing aircraft are kites rather than gliders, ie they are usually towed behind a car or boat rather than being capable of free flight. These are known as rotor kites. However rotary-winged gliders, 'gyrogliders', were investigated that could descend like an autogyro or helicopter, using the lift from rotors to reduce the vertical speed. These were evaluated as a method of dropping people or equipment from other aircraft.
Unmanned gliders
Model gliders
A 'radio-controlled glider' is a type of radio-controlled airplane that normally does not have any form of propulsion. Like piloted gliders they can remain airborne for extended periods by using the lift produced by slopes and thermals. They are controlled remotely from the ground with a transmitter. A paper aeroplane, also known as a 'paper plane' or 'paper dart', is another example of a model glider.
Flying bombs
Glide bombs are bombs with aerodynamic surfaces to allow a gliding flightpath rather than a ballistic one. This increases the protection of the carrying aircraft that is attacking a heavily defended target. Remote control systems allow the carrying aircraft to direct the bomb to the target. These were developed in Germany from as early as 1915. In World War Two they were most successful as anti-shipping weapons. Some air forces today are equipped with gliding devices that can remotely attack airbases with a cluster bomb warhead.
See also
- Flight
- Unpowered aircraft
- Underwater glider
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