for: glider (disambiguation)
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for: glider (disambiguation)
The type of aircraft that are most commonly known as gliders, sometimes as sailplanes, are used in the sport of gliding.Definition of gliders used for sporting purposes in FAI Sporting Code Some gliders, known as motor gliders are also used for gliding and soar well, but have engines which can in some cases be used for take-off or for extending a flight. Foot-launched aircraft (such as hang gliders and paragliders) are described in separate articles. Gliders have also been used for purposes other than recreation, for example for military purposes and for research.
Use of engines
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 before retracting their propellers and are known as 'self-launching' gliders. There are also 'touring motor gliders', which can also launch themselves and can switch off their engines in flight, though without retracting their propellers.
History
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 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 gliders to soar more effectively than primary gliders, the designs minimized drag. Gliders now have very smooth, narrow fuselages and very long, narrow wings with a high aspect ratio and winglets.
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 glide ratio. A ratio of 30:1 means that in smooth air a glider can travel forward 30 meters while only 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 18 meter gliders such as the ASG29 have a glide ratio of over 50:1. The largest open-class glider, the eta, has a span of 30.9 meters and has a glide ratio over 70:1. Compare this to the infamous Gimli Glider, a Boeing 767 which ran out of fuel mid-flight and was found to have a glide ratio of only 12:1, or to the Space Shuttle with a glide ratio of 4.5.
