Parachute
A parachute is a soft fabric device used to slow the motion of an object through an atmosphere by creating drag. Parachutes are generally used to slow the descent of a person or object to Earth or another celestial body with an atmosphere. Parachutes are also sometimes used to aid horizontal deceleration of a vehicle (an airplane or space shuttle after touchdown, or a drag racer). The word parachute comes from the French words para, protect or shield, and chute, to fall. Therefore parachute actually means to protect from a fall. Many types of modern parachute are quite maneuverable, and can be flown like gliders.
Parachutes were once made from silk but these days are almost always constructed from more durable woven nylon fabrics, sometimes coated with a zero porosity coating to improve performance and consistency over time.
History
A few medieval documents record the use of parachute-like devices to allow a person to fall (somewhat) safely from a height. In 852, an Andalusian daredevil named Armen Firman jumped from a tower in Cordoba using a loose cloak stiffened with wooden struts to arrest his fall, sustaining only minor injuries. In 1178, another Muslim attempted a similar feat in Constantinople, but he broke several bones and later died of his injuries. According to Joseph Needham there were working parachutes in China as early as the twelfth century.
Leonardo da Vinci sketched a parachute while he was living in Milan around 1485. However, the idea of the parachute may not have originated with him: the historian Lynn White has discovered an anonymous Italian manuscript from about 1470 that depicts two designs for a parachute, one of which is very similar to da Vinci's. The first known test of such a parachute was made in 1617 in Venice by the Croatian inventor Faust Vrančić. A 1595 sketch of Vrančić's parachute is at left.
The parachute was re-invented in 1783 by Sebastien Lenormand in France. Lenormand also coined the name parachute. Two years later, Jean-Pierre Blanchard demonstrated it as a means of safely disembarking from a hot air balloon. While Blanchard's first parachute demonstrations were conducted with a dog as the passenger, he later had the opportunity to try it himself when in 1793 his hot air balloon ruptured and he used a parachute to escape.
Subsequent development of the parachute focused on it becoming more compact. While the early parachutes were made of linen stretched over a wooden frame, in the late 1790s, Blanchard began making parachutes from folded silk, taking advantage of silk's strength and light weight. In 1797, Andrew Garnerin made the first jump using such a parachute. Garnerin also invented the vented parachute, which improved the stability of the fall. In 1890, Paul Letteman and Kathchen Paulus made the first knapsack parachute.
On March 1, 1912, US Army Captain Albert Berry made the first parachute jump from a moving airplane over Missouri. Štefan Banič from Slovakia registered the first modern parachute patent in 1913.
Uses
Paratroopers are soldiers who arrive in enemy territory by parachutes.
Smokejumpers are firefighters who parachute into remote areas to build firebreaks.
Most space vehicles descend to Earth using several parachutes. The pair of reusable solid-fuel rocket boosters (SRB) of the Space Shuttle have parachutes; they are recovered after falling to the ocean. Some exploration rovers (such as NASA's Spirit and ESA's Beagle 2) descend to their target destination with parachutes.
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 called a drogue parachute is used to slow drag racers, and the Space Shuttle after its runway touchdown.
Jet fighter ejector 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.
A paraglider with a motor and possibly wheels is called a powered parachute or, sometimes, a paraplane.
Design
A parachute is made from thin, lightweight fabric, support tapes and suspension 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. Reserve pilot chutes usually have a large spring that pushes them into the air-stream, but most modern main parachutes use a form of hand deployed pilot chute with no spring. Hand deployed pilot chutes are usually pulled from a pouch located on the parachute container and they in turn pull a pin opening the main parachute container. Spring loaded pilot chutes are released 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 and canopy a compact package. Pilot chutes and containers may be released by a "static line." The static line is a length of bridle attached to an airplane or platform. In most sport reserve and emergency parachutes the rip cord is a manually operated by pulling a "D" (pronounced "dee") handle attached to the harness although there are many variations. Cargo parachutes are always released by static lines. Paratroop parachutes are also usually deployed by static lines which release the parachute yet retain the bag which contains the parachute without relying on a pilot chute for deployment, making their deployment rapid, consistent and reliable.
Paratroopers and sport skydivers carry two parachutes. The primary parachute is called a main parachute, the second, a reserve parachute. The reserve is quicker-opening with a manual rip cord but other secondary deployment systems are usually used. The jumper uses the emergency chute if the primary parachute fails to operate correctly. 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 from a single layer of cloth. Some skydivers call them "jellyfish 'chutes" because they look like 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.
Most modern parachutes are self-inflating "ram-air" airfoils known as a parafoil that provide control of speed and direction similar to the related paragliders. Paragliders have much greater lift and range, but parachutes are designed to handle, spread and mitigate the stresses of deployment at terminal velocity. All ram-air parafoils have two layers of fabric; top and bottom, connected by shaped fabric I-beams and/or gores. The space between the two fabric layers fills with high pressure air from vents that face forward on the leding edge of the airfoil. The fabric is shaped and the parachute lines trimmed under load such that the ballooning fabric inflates into an airfoil shape.
Ram-air parachutes loosely divided into two varieties. High performance ram-air parachutes have a slightly elliptical shape to their leading and trailing edges when viewed in plan form and are known as ellipticals. Usually their vents are smaller they have more numerous, smaller fabric cells and are shallower in profile. Lower performance parachutes look more like square inflatable air-mattresses with open front ends. Smaller parachutes tend to fly faster for the same load and ellipticals respond faster to control input, small eliptical designs are therefore often chosen by experienced canopy pilots for the thrill of the flying they provide. This requires much more skill and experience to pilot and is considerably more dangerous to land. With high performance elliptical canopy designs nuisance malfunctions can be much more serious than with a square design and may quickly escalate into emergencies. All reserve ram-air parachutes are of the square variety because of the reliability and handling characteristics.
Sport parachutes used by skydivers today are designed to open softly, rapid deployment was an early problem with ram-air designs. The primary innovation that slows the deployment of a ram-air canopy is the slider; a small rectangular piece of fabric with a grommet near each corner through which four collections of lines are routed to the risers. During deployment the slider slides down from the canopy to just above the risers, the slider is slowed by air resistance as it descends and reduces the rate at which the lines can spread and therefore the speed at which the canopy can open and inflate. The overall design of a parachute still has a significant influence on the deployment speed. Modern sport parachutes deployment speed varies considerably between designs but most modern parachutes open comfortably with individual skydivers preferring different deployment speeds. The deployment process is inherently a chaotic one and rapid deployments can still occur even with well behaved canopies, on rare occasions deployment can even be so rapid that the jumper suffers bruising or even injury. Emergency and reserve parachutes by design tend to deploy more rapidly than sports main canopies, they still have sliders but the sliders are designed to descend rapidly with for example a partial mesh construction to catch less air resistance than a fully fabric slider design.
Safety
A parachute is carefully folded, or "packed" to ensure that it will open reliably. In the U.S. and many developed countries, emergency and reserve 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 "main" parachutes.
Parachutes can malfunction in several ways. Malfunctions can range from minor problems that can be corrected in-flight and still be landed to catastrophic malfunctions that require the main parachute to be cut away using a modern 3-ring release system and a second parachute called a reserve to be deployed. Most skydivers are also equipped with small barometric computers (known as an AAD or Automatic Activation Device like Cypres, FXC or Vigil) that will automatically deploy the reserve parachute if the skydiver himself has not done so at a preset altitude and decent rate.
Exact numbers are difficult to estimate but approximately one in several hundred sports main parachute openings malfunction and must be cut away, although some skydivers have many thousands of jumps and never cut away, (either they pack their mains more carefully than average or they are just lucky). Reserve parachutes are packed and deployed differently, they are also designed more conservatively and built & tested to more exacting standards so they are more reliable than main parachutes, but the real safety advantage comes from the probability of an unlikely main malfunction multiplied by the even less likely probability of a reserve malfunction. This yields an even smaller probability of a double malfunction although the possibility of a main malfunction that cannot be cutaway causing a reserve malfunction is a very real risk. In the U.S., the average fatality rate is considered to be about 1 in 80,000 jumps. Most injuries and fatalities in sport skydivng occur under a fully functional main parachute because the skydiver performed unsafe maneuvers or made an error in judgement while flying their canopy typically resulting in a high speed impact with the ground or other hazards on the ground.
The average skydiver in the U.S. makes about 150 jumps per year and will leave the sport before the 5th year.
Powered Parachute Flight
Powered parafoils are a form of ultralight aircraft. A go-cart like frame or other rigid harness is used to mount the engine, creating a stable flying platform that is very easy to fly in calm weather conditions.
See also
- Parachuting
- Paraglider
- Hang glider
- Ultralight aviation
- Smokejumping
- Paratrooper
- Freefall (accidents of failed or missing parachute)
External links
- USPA The United States Parachute Association -- The governing body for sport skydiving in the U.S.
- Dropzone.com the Premier web resource for information on Skydiving, Dropzones and modern parachuting
- National Parachute Test Center - Part of NAF El Centro located near El Centro,California.
- Parachute