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Parachutes and Skydiving
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A canopy device usually made of silk, rayon or nylon, a parachute, naturally inflated by air, slows the descent of a man or object through the air. Parachutes are standard equipment in aircraft, for use in cases of emergency and to drop cargo in isolated areas. They have proved to be useful in the deployment of aerial infantry, known as paratroops, and in reducing the landing speeds of aircraft on short runways. They are also used in aerial sports such as sky-diving.
The parachute consists of a canopy, suspension lines and a harness. The canopy and lines are folded inside a small pack, which is strapped to the back or chest and can be opened manually during free fall or by a static line attatched to the aircraft. In some cases a pilot parachute opens first, dragging with it the larger main canopy.
A ribbon parachute, slotted with vents through which wind resistance is lessened, reduces the initial shock of an inflating canopy. The vortex-ring chute, made of four rotating sections, is designed to allow the parachutist to be in full control during descent.
For supersonic aircraft and space vehicles, where bailing out is impossible, parachutes have successfully been fixed to ejectable cockpits. Parachutes are constructed in different shapes and sizes according to the weight and type of object carried; following World War II a greater understanding of aerodynamics influenced these differences.
Parachutes used for escape from disabled aircraft usually measure 8.5 m in diameter; those bearing fully equipped soldiers measure 10.6 m; cargo parachutes can measure up to 30.5 m.
Sky-diving originated in the exhibition jumps of the 1920s and rapidly became popular as an organised sport. By 1957 the Parachute Club of America was administering the sport and arranging national contests. In target-jumping the parachutist must jump from a height of 1000 or 1500 m and maximum points are awarded for landing within a target area of 100 m.
In 1514 Renaissance inventor Leonardo da Vinci outlined the theory of a rigid, pyramid-shaped parachute, which remained untested until 1783, when Louis Sebastien Lenormand jumped from a high tower. Frangois Blanchard dropped a dog by parachute from a balloon in 1785 and was reported to have broken a leg in testing the jump himself in 1793. Four years later Andre Garnin of France made a successful descent from 610 m; he improved the parachute's design and in 1802 jumped from 2439 m.
Parachutes were not widely used until the developments made by Captain Albert Barry of the United States and Kaethe Paulus of Germany in the years before World War I came into effect. The German air force was the first to use parachutes as emergency equipment. By 1920 fixed parachutes were also standard in the British Royal Flying Corps. In 1922 the first free parachutes, operated manually from a backpack, were in use by the US air force. In 1939 the Soviet Union used the first airborne infantry in its military campaign against Finland. In the following year the German invasion of Norway was achieved by deploying paratroopers, a trend followed by all armies by the end of the war.
Operation of a Parachute
A parachute is released from its pack by a rip cord, which may be pulled either by hand or by a static line connected to the aircraft. A pack that is opened by hand is called a free-fall pack.
When the rip cord is pulled, pins holding the pack cover in place are removed and the cover springs open, releasing the parachute. Some parachutes are equipped with a small pilot parachute that is connected to the top of the main canopy. The pilot parachute opens immediately and helps draw the main canopy out of the pack more quickly.
When released, the canopy fills with air. The large surface thus formed slows the parachute's fall by resisting the air through which it falls. The average speed of a falling parachute is about 12.5 miles (20 km) per hour, although it may be as slow as 8 miles (13 km) per hour or as fast as 17 miles (27 km) per hour, depending on the type of parachute and on the atmospheric conditions. On landing, therefore, the parachutist is still falling at a fast speed and needs considerable skill to avoid injury.
A parachute can be maneuvered by pulling on the risers. The position of the canopy can thus be changed to suit the wind motion or to guide the parachute in landing.