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Parachute

A parachute is a wind resistance or lift creating device made of fabric. They can be used to slow aircraft, motor vehicle or spacecraft. They are also used to allow its wearer to jump, or skydive, from an aircraft or fixed object and land safely.

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Parachute History

Parachutes have long been used by military and space programs around the world. The first parachute jumps were from hot air balloons in the early 1800s. The very first parachute was linen, but silk was soon adopted because of its strength and light weight. On March 1, 1912 Albert Berry[?] made the first parachute jump from a moving airplane.

Parachute Uses

Paratroopers are soldiers who arrive by parachute in this way in enemy territory.

Most space vehicles descend to Earth using several parachutes. The pair of reusable solid-fuel rocket boosters (SRB) of the Space Shuttle have parachutes; after falling in the ocean they are recovered.

Some bombs are equipped with a parachute, for example some daisy cutters and the bomblets of some cluster bombs.

Food aid packages are sometimes delivered by parachute.

Parachutes can also be deployed from a jet aircraft horizontally from the tail cone at the point of touchdown or shortly afterwards to shorten its landing run, for example if landing on an aircraft carrier or with a tailwind, or on a relatively short runway. The parachute will normally be jettisoned after the aircraft has slowed to taxiing speed and then retrieved by ground crew. This technique reduces the chance of it becoming entangled with the airframe once it has ceased to be deployed in its functional, hemispherical shape. A similar parachute is used to slow drag racers.

Jet fighter[?] ejection seats are equipped with automatically deployed parachutes.

Parachuting is a hobby and sport based on human parachute jumps. Paragliding instead uses a parachute as a form of glider.

Parachute Design

A parachute is made from thin, lightweight fabric and ropes. The fabric is called the "canopy" or (on gliding parachutes) the "wing" and the ropes are called "lines." The lines are usually gathered through loops or rings at several strong straps called "risers." The risers directly strap the item or person being supported, called the "load." Parachutes are pulled out of their packages by a smaller parachute called a "pilot 'chute." Pilot chutes usually have a large spring that pushes them into the air-stream, or forces them open. The pilot 'chute is released by a cable called a "rip cord." Usually the rip cord pulls a metal pin that releases fabric flaps that hold the pilot 'chute in a compact package. Pilot 'chutes may be released by a "static line." The static line is a length of string clipped to the airplane. After it pulls the ripcord, the static line breaks. In most sport parachutes and some emergency parachutes, the rip cord is a manual device (a "T" (pronounced "tee") handle attached to the chest straps. Emergency parachutes have the "T" handle when the designer cannot know when to release the parachute. Cargo parachutes are always released by static lines. Paratroop chutes are also usually released by static lines.

Paratroopers and sport skydivers carry two parachutes. The primary parachute is larger, with a lower landing speed or a gliding parasail. The second, "reserve parachute" is smaller, and quicker-opening with a manual rip cord. The jumper uses the emergency chute if the primary parachute fails to open. Reserve parachutes were introduced in World War II by the US Airborne Unit, and are now universal.

There are several types of parachutes in common use. Ribbon and ring parachutes can be designed to open at speeds as high as Mach 2 (two times the speed of sound). These have a ring-shaped canopy, often with a large hole in the center to release the pressure. Sometimes the ring is broken into ribbons connected by ropes to leak air even more. The large leaks lower the stress on the parachute so it does not burst when it opens.

Often a high speed parachute slows a load down and then pulls out a lower speed parachute. The mechanism to sequence the parachutes is called a "delayed release" or "pressure detent release" depending on whether it releases based on time, or the reduction in pressure as the load slows down.

Emergency parachutes and cargo parachutes designed to go straight down are pure drag devices. These have large dome-shaped canopies made froma single layer of cloth. Some skydivers call them "jellyfish 'chutes" because they look by dome-shaped jellyfish. Some dome parachutes can be steered by flaps. They usually have a small hole the center of the dome to spill air, so that the parachute does not have to swing to spill air from its edges.

Parasails are parachutes that are like inflatable wings. They have two layers of fabric, connected by shaped fabric gores. The space between the two fabric layers fills with low pressure air from vents that face forward. The gores are cut in the cross-section of a wing, so that they pull the ballooning fabric into an inflated wing-shape.

Parasails divide into two further types. High speed parasails are shaped like an ellipse. Usually their vents are small tringular scoops on the underside, pulled open by lines. Low-speed parasails look much like square inflatable air-mattresses with open front ends. Ellipticals move faster, but this is not always an advantage, because it makes the parachute harder to fly, and more dangerous to land. In the early days, some ellipticals opened and inflated less reliably than low-speed parasails, but reliable makes of parachute have resolved these problems.

Sport parachutes used by skydivers often have a delayed opening device. This is a sleeve or strap that slides on the canopy from about 2/3 of the way down to the top as the canopy opens. This slows the opening of the canopy, and makes the opening shock more comfortable. Modern sport parachutes rarely create strap bruises from the opening shock. Emergency parachutes almost always do.

Parachute Safety

A parachute is carefully folded, or "packed" to assure that it will open reliably. In the U.S. and many developed countries, emergency parachutes are packed by "riggers" who must be trained and certified according to legal standards. Paratroops and sport skydivers are always trained to pack their own primary parachutes.

When a parachute fails to open, it is usually a "streamer." In most streamers, the lines are twisted, and the canopy cannot open enough to catch the air. Jumpers usually try to open a streamer by shaking the lines. If this fails, they open their emergency parachute (usually called the "reserve 'chute").

About one in a hundred primary parachute openings is a streamer. Emergency parachutes have a better ratio, with between one in three hundred, and one in five hundred parachute openings failing. Most skydivers believe that they can pack their primary parachutes as carefully as a professional rigger. Thus, a typical jumper can expect to die when both parachutes fail, between once in 30,000 and once in 250,000 dives, depending on the care taken in packing the parachutes. Most skydivers retire from age and infirmity before they reach 10,000 jumps.

This is why jumpers should never pack their parachutes when hurried, sleepy, drunk or on drugs.



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