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TERMINOLOGY A "glider" is an unpowered Aircraft . The most common types of glider are today used for sporting purposes. The design of these types enables them to climb using rising air and then to glide for long distances before finding the next source of lift. This has created the sport of '' Gliding '', or soaring. The term "sailplane" is sometimes used for these types, implying a glider with a high soaring performance. In addition to high-performance sailplanes, the term 'glider' also encompasses '' Hang Gliders '' and '' Paragliders ''. Like sailplanes these can use upwardly moving air to soar but differ in not having a fuselage, control surfaces or a control column. Although many gliders do not have engines, there are some that use engines occasionally (see '' Motor Glider ''). The manufacturers of high-performance gliders now often list an optional engine and a retractable propeller that can be used to sustain flight if required; these are known as 'self-sustaining' gliders. Some can even launch themselves and are known as 'self-launching' gliders. There are also 'touring motor gliders', which can switch off their engines in flight though without retracting their propellers. The term "pure glider" (or equivalently, but less commonly "pure sailplane") may be used to distinguish a totally unpowered glider from a motorized glider, without implying any differential in gliding or soaring performance. HISTORY In '' ( 659 ) and '' Zizhi Tongjian '' ( 1084 ) that Yuan Huangtou in Ye made a successful glide, taking off from a tower in 559 . Beishi 19 and Zizhi Tongjian 167: . Abbas was seriously injured in the resulting crash.David Tschanz (2003). ''Flights of Fancy on Manmade Wings''. Daniel Poore (1952). ''A History of Early Flight''. New York: Alfred Knopf.Smithsonian Institution (1990). ''Manned Flight''. Pamphlet. in flight]] The first heavier-than-air (i.e. non-balloon) aircraft to be flown in Europe was Sir George Cayley 's series of gliders which achieved brief wing-borne hops from around 1804 . Santos Dumont , Otto Lilienthal , Percy Pilcher , John J. Montgomery , and the Wright Brothers are other pioneers who built gliders to develop Aviation . After the First World War gliders were built for sporting purposes 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 Glider s were then developed by a number of countries, particularly during World War II , for landing troops. A glider was even built secretly by POWs as a potential escape method at Oflag IV-C near the end of the war in 1944 . The Orbiter vehicles or " Space Shuttle s" do not use their engines after re-entry at the end of each Spaceflight , and so land as gliders. LAUNCH METHODS See Also: Gliding 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 (about 200 ft) long. The glider's pilot releases the rope after reaching the desired altitude, but the rope can also be released by the towplane in an emergency. Winch launching uses a powerful stationary engine located on the ground at the far end of the launch area. The glider is attached to one end of 800-1200 metres (about 2,500-4,000 ft) of wire cable and the winch then rapidly winds it in. More rarely, automobiles are used to pull gliders into the air or gliders are launched from sloping ground or cliffs. STAYING ALOFT WITHOUT AN ENGINE See Also: Gliding Glider pilots can stay airborne for hours. This is possible because they seek out rising air masses (lift) from the following sources: Thermals The most commonly used source of lift is created by the sun's energy heating the ground which in turn heats the air above it. This warm air rises in columns known as clouds, cloud streets, dust devils and haze domes. Also, nearly every glider contains an instrument known as a Variometer (a very sensitive vertical speed indicator) which shows visually (and often audibly) the presence of lift and sink. Having located a thermal, a glider pilot will circle within the area of rising air to gain height. In the case of a cloud street thermals can line up with the wind creating rows of thermals and sinking air. A pilot can use a cloud street to fly long straightline distances by remaining in the row of rising air. Ridge lift Another form of lift occurs when the wind meets a mountain, cliff or hill. The air is deflected up the Windward face of the mountain forming lift. Gliders can climb in this rising air by flying along the feature. This is 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 name for flying with ridge lift is Slope Soaring . Mountain wave The third main type of lift used by glider pilots are the Lee Waves that occur near mountains. The obstruction to the airflow can generate Standing Wave s with alternating areas of lift and sink. The top of each wave peak is often marked by Lenticular Cloud formations. Convergence Another form of lift results from the Convergence of air masses, as with a Sea-breeze Front . More exotic forms of lift are the polar vortices which the has also been used by glider pilots in Australia. A Guide to the Morning Glory at www.dropbears.com MOVING FORWARD just before landing]] After climbing in lift, gliders move on to find the next source of lift, or to land. As the glider descends, the air moving over the wings generates Lift . The lift force acts slightly forward of vertical because it is created at right angles to the airflow which comes from slightly below as the glider descends, see Angle Of Attack . This horizontal component of lift is enough to balance Drag and allows the glider to move forward.''Glider Flying Handbook'', FAA Publication 8083-13, Page 3-2 GLIDER 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 Glider s" 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 gliders to soar more effectively than primary gliders, the designs minimized Drag . Gliders now have very smooth, narrow Fuselage s 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 FS-24 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. Drag has also been minimized by more aerodynamic shapes and retractable undercarriages. Flaps are fitted on some gliders so that the optimal Lift of the wing is available at all speeds. With each generation of materials and with the improvements in aerodynamics, the performance of gliders has increased. One measure of performance is the with a glide ratio of 3:1 NASA's web site for Space Shuttle Glider at www.nasaexplores.com. Due to the critical role that aerodynamic efficiency plays in the performance of a glider, gliders often have state of the art aerodynamic features seldom found in other aircraft. The wings of a modern racing glider have a specially designed low-drag Laminar Flow Airfoil . After the wings' surfaces have been shaped by a mold to great accuracy, they are then highly polished. Vertical Winglets at the ends of the wings are computer-designed to decrease drag and improve handling performance. Special aerodynamic seals are used at the Aileron s, Rudder and Elevator to prevent the flow of air through control surface gaps. Turbulator devices in the form of a zig-zag tape or multiple blow holes positioned in a span-wise line along the wing are used to trip laminar flow air into turbulent flow at a desired location on the wing. This flow control prevents the formation of laminar flow bubbles and ensures the absolute minimum drag. Bug-wipers may be installed to wipe the wings while in flight and remove insects that are disturbing the smooth flow of air over the wing. Modern competition gliders are also designed to carry jettisonable water ballast (in the wings and sometimes in the vertical stabiliser). The extra weight provided by the water ballast is advantageous if the lift is likely to be strong, and may also be used to adjust the glider's Center Of Mass . Although heavier gliders have a slight disadvantage when climbing in rising air, they achieve a higher speed at any given glide angle. 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 in weaker thermal conditions. To avoid undue stress on the airframe, gliders must jettison any water ballast before landing. Pilots can land accurately by controlling their rate of descent using Spoilers , also known as air brakes. These are metal devices which extend from either the upper-wing surface or from both upper and lower surfaces, thereby destroying some lift and creating additional Drag . A wheel-brake also enables a glider to be stopped after touchdown, which is particularly important in a short field. CLASSES OF GLIDER of the Two Seater Class]] For competitions several Classes of glider have been defined by the FAI . They are:
MAJOR MANUFACTURERS OF GLIDERS
See also the full Gliders And Manufacturers list, past and present. INSTRUMENTATION AND OTHER TECHNICAL AIDS -C in flight, showing instrument panel equipped for "cloud flying," configured in the Basic-T , with Airspeed , Attitude and Altitude display across the top row; below a GPS -driven computer, with wind and glide information, drives two electronic Variometer displays to the right. The Yaw String and Compass are above the glare shield]] Gliders must be equipped with an Altimeter , Compass , and an Airspeed Indicator in most countries, and are often equipped with a Variometer , Turn And Bank Indicator and an Airband radio ( Transceiver ), each of which may be required in some countries. An Emergency Position-Indicating Radio Beacon ( ELT ) may also be fitted into the glider to reduce Search And Rescue time in case of an accident. Much more than in other types of aviation, glider pilots depend on the Variometer , which is a very sensitive Vertical Speed Indicator , to measure the climb or sink rate of the plane. This enables the pilot to detect minute changes caused when the glider enters rising or sinking air masses. Both mechanical and electronic 'varios' are usually fitted to a glider. The electronic variometers produce a modulated sound of varying amplitude and frequency depending on the strength of the lift or sink, so that the pilot can concentrate on centering a thermal, watching for other traffic, on navigation, and weather conditions. Rising air is announced to the pilot as a rising tone, with increasing pitch as the lift increases. Maximizing time in the best lift areas in an otherwise invisible air mass can therefore be realized. Conversely, descending air is announced with a lowering tone, which advises the pilot to escape the sink area as soon as possible. (Refer to the '' Variometer '' article for more information). |
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