Parachute

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This article is about the device.
The Apollo 15 capsule landed safely despite failure of one of the parachutes.
U.S. Army paratroopers training in a jump at Fort Bragg, North Carolina.

A parachute is a device used to slow the descent of a person or object falling through the atmosphere by creating drag. The atmosphere is usually that of Earth, but it could be that of another celestial body. The parachute slows its load sufficiently to prevent or minimize injury on impact with the ground.

Parachute design has changed considerably over the years, from roughly cut shapes to aerodynamic "ram-air" parafoils. Many modern parachutes are quite maneuverable and can facilitate controlled descent similar to that of a glider. In addition, smaller "drogue parachutes" are sometimes used to aid deceleration of a fast-moving vehicle such as a drag racer, a fixed-wing aircraft, or a spacecraft during reentry or after touchdown.

Folding a parachute requires a high degree of skill, as an improperly folded parachute may not deploy correctly, leading to deadly results. Malfunctions of parachutes range from minor difficulties that can be corrected during flight to major problems when the main parachute has to be cut away and the reserve needs to be deployed.

Contents

Etymology

The word "parachute" comes from a French word that may be translated as "that which protects against a fall." It is a combination of para, meaning "defense against" (from the Latin parare, meaning "to prepare") and chute, meaning "fall."[1]

History

Early forms

Faust Vrančić's design of one of the first parachutes, in 1595.

In the ninth-century region of Al-Andalus (on the Iberian peninsula), Abbas Ibn Firnas (Armen Firnas) developed a primitive form of parachute.[2][3][4][5] John H. Lienhard described it in The Engines of Our Ingenuity as "a huge winglike cloak to break his fall" when he "decided to fly off a tower in Cordova."[6]

Did you know?
An early parachute design was called "Homo Volans" (Flying Man)

A conical parachute appears for the first time in the 1470s in an Italian manuscript, slightly preceding Leonardo da Vinci's conical parachute designs.[7] It was intended as an escape device to allow people to jump from burning buildings, but there is no evidence that it was actually used. Leonardo da Vinci sketched a parachute while he was living in Milan around 1480-1483: a pyramid-shaped canopy held open by a square wooden frame.

In 1595 the Croatian inventor Faust Vrančić designed a parachute-like device which he called Homo Volans (Flying Man). A book by John Wilkins, who was secretary of the Royal Society in London, written in 1648 apparently described the testing of this design by jumping from a tower in Venice in 1617.[8]

Modern parachutes

The modern parachute was invented in the late eighteenth century by Louis-Sébastien Lenormand in France, who made the first recorded public jump in 1783. Lenormand also sketched it beforehand. Two years later, Jean-Pierre Blanchard demonstrated it as a means of safely disembarking from a hot air balloon. Blanchard's first parachute demonstrations were conducted with a dog as the passenger. Later, in 1793, he tried it himself when his hot air balloon ruptured and he used a parachute to escape.

Subsequent development of the parachute focused on making it more compact. Early parachutes had been made of linen stretched over a wooden frame, but in the late 1790s, Blanchard began making parachutes from folded silk, taking advantage of silk's strength and light weight. In 1797, André Garnerin made the first jump using such a parachute. Garnerin also invented the vented parachute, which improved the stability of the fall.

In San Francisco in 1885, Thomas Scott Baldwin was the first person in the United States to descend from a hot air balloon in a parachute of his own design, the first of many such descents made by Baldwin.[9][10] In 1911, Grant Morton made the first parachute jump from an airplane, in a Wright Model B, at Venice Beach, California. The pilot of the plane was Phil Parmalee. Morton's parachute was of the 'throw-out' type, which he held in his arms as he left the aircraft.

In 1911, Gleb Kotelnikov invented the first knapsack parachute, later popularized by Paul Letteman and Kathchen Paulus. On March 1, 1912, US Army Captain Albert Berry made the first parachute jump from a moving aircraft over Missouri using a 'pack' style chute. In this style, the chute was housed in a casing on the jumper's body. Štefan Banič from Slovakia invented the first actively used parachute, patenting it in 1913. On June 21, 1913, Georgia Broadwick became the first woman to parachute jump from a moving aircraft over Los Angeles.

The first military application of the parachute was for artillery spotters on tethered observation balloons in World War I. These were tempting targets for enemy fighter aircraft, though difficult to destroy due to heavy antiaircraft defenses. Because they were difficult to escape from, and dangerous when on fire due to their hydrogen inflation, observers would abandon them and descend by parachute as soon as enemy aircraft were seen. The ground crew would then attempt to retrieve and deflate the balloon as quickly as possible.

No parachutes were issued to Allied "heavier-than-air" aircrew.[11] As a result, a pilot's only options were to ride his machine into the ground, jump from several thousand feet, or commit suicide using a standard-issued revolver (though the last two options were used only by those who did not wish to die by burning).

In the UK, Everard Calthrop, a railway engineer and breeder of Arab horses, invented and marketed through his Aerial Patents Company a "British Parachute." The German air service, in 1918, became the world's first to introduce a standard parachute and the only one at the time. Despite Germany issuing their pilots with parachutes, their efficiency was relatively poor. As a result, many pilots died whilst using them, including aces such as Oberleutnant Erich Lowenhardt (who fell from 12,000 feet (3,700 m)) and Fritz Rumey (whose chute failed from a little over 3,000 feet during a test in 1918.)

Tethered parachutes were initially tried but caused problems when the aircraft was spinning. In 1919, Leslie Irvin invented and successfully tested a parachute that the pilot could deploy when clear of the aircraft. He became the first person to make a premeditated free-fall parachute jump from an airplane.[12]

An early brochure[13] of the Irvin Air Chute Company credits William O'Connor as the first person to be saved by an Irvin parachute, on August 24, 1920, at McCook Field near Dayton, Ohio. Another life-saving jump was made at McCook Field by test pilot Lt. Harold H. Harris on October 20, 1922. Shortly after Harris's jump, two Dayton newspaper reporters suggested the creation of the Caterpillar Club for successful parachute jumps from disabled aircraft.

Beginning with Italy in 1927, several countries experimented with using parachutes to drop soldiers behind enemy lines. By World War II, large airborne forces were trained and used in surprise attacks. Aircraft crew were routinely equipped with parachutes for emergencies as well.

Design and materials

A parachute is made from thin, lightweight fabric, support tapes, and suspension lines. The lines are usually gathered through cloth loops or metal connector links at the ends of several strong straps called risers. The risers in turn are attached to the harness containing the load. As the thin material inflates, it increases drag and in turn slows down the person or object it is carrying. The parachute slows its load sufficiently to prevent it from breaking on impact with the ground.

Parachutes were once made from silk, but recently they have been made from more durable woven nylon fabric, sometimes coated with silicone to improve performance and consistency over time. When square (also called ram-air) parachutes were introduced, manufacturers switched to low-stretch materials like Dacron, or zero-stretch materials like Spectra, Kevlar, Vectran, and high-modulus aramids.

Types of parachutes

Round types

An American paratrooper using an MC1-1C series 'round' parachute.

Round parachutes are purely "drag" devices—that is, unlike the ram-air types, they provide no lift). They are used in military, emergency, and cargo applications. They have large, dome-shaped canopies made from a single layer of triangular cloth gores. Some skydivers call them "jellyfish 'chutes" because they look like dome-shaped jellyfish. Modern sports parachutists rarely employ this style of parachute.

The first round parachutes were simple, flat circulars, but suffered from instability, so most military round parachutes are some sort of conical (cone-shaped) or parabolic (having a flat circular canopy with an extended skirt) US Army T-10 parachute used for static-line jumps.

Round parachutes are designed to be steerable or non-steerable. Steerable versions are not as maneuverable as ram-air parachutes. An example of a steerable round is provided in the picture (on the right) of the paratrooper's canopy; it is not ripped or torn but has a "T-U cut." This kind of cut allows air to escape from the back of the canopy, providing the parachute with limited forward speed. This gives the jumpers the ability to steer the parachute and to face into the wind to slow down the horizontal speed for the landing. The variables impact the way and the speed that the parachute falls, because it depends on the speed or the amount of force in the wind that might change the way in which a parachute falls.

Cruciform types

The unique design characteristics of cruciform parachutes reduces oscillations and violent turns(swinging back and forth) during descent. This technology will be used by the US Army as it replaces its current T-10 parachutes under a program called ATPS (Advanced Tactical Parachute System). The ATPS canopy is a highly modified version of a cross/cruciform platform and is square in appearance. The ATPS (T-11) system will reduce the rate of descent by 30 percent from 21 feet per second (6.4 m/s) to 15.75 feet per second (4.80 m/s). The T-11 is designed to have an average rate of descent 14 percent slower than the T-10D, thus resulting in lower landing injury rates for jumpers. The decline in rate of descent will reduce the impact energy by almost 25 percent, to lessen the potential for injury.

Annular and pull-down apex types

A variation on the round parachute is the pull-down apex parachute, invented by the Frenchman LeMogne. It is referred to as a Para-Commander-type canopy in some circles, after the first model of this type. It is a round parachute, but with suspension lines to the canopy apex that applies load there and pulls the apex closer to the load, distorting the round shape into a somewhat flattened or lenticular shape.

Often these designs have the fabric removed from the apex to open a hole through which air can exit, giving the canopy an annular geometry. They also have decreased horizontal drag due to their flatter shape, and when combined with rear-facing vents, can have considerable forward speed, of around 10 mph (15 km/h).

Ribbon and ring types

Ribbon and ring parachutes have similarities to annular designs. They are frequently designed to deploy at supersonic speeds. A conventional parachute would instantly burst upon opening at such speeds. Ribbon parachutes 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. These large leaks lower the stress on the parachute so it does not burst or shred when it opens. Ribbon parachutes made of kevlar are used with nuclear bombs, such as the B61 and B83.

Ram-air types

A paraglider demonstrates the use of a ram-air parachute.

Most modern parachutes are self-inflating "ram-air" airfoils, known as parafoils, that allow one to control speed and direction similar to paragliders. Paragliders have much greater lift and range, but the 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 airfoil-shaped fabric ribs to form "cells." The cells fill with high-pressure air from vents that face forward on the leading 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. This airfoil is sometimes maintained by use of fabric one-way valves called airlocks.

Personnel parachutes

A U.S. Navy display jumper lands with a 'square' ram-air parachute.

Deployment

Reserve parachutes usually have a ripcord deployment system, first designed by Theodore Moscicki, but most modern main parachutes used by sports parachutists use a form of hand-deployed pilot chute. A ripcord system pulls a closing pin (sometimes multiple pins), which releases a spring-loaded pilot chute, and opens the container. The pilot chute is propelled into the air stream by its spring, then uses the force generated by passing air to extract a deployment bag containing the parachute canopy, to which it is attached via a bridle. A hand-deployed pilot chute, once thrown into the air stream, pulls a closing pin on the pilot chute bridle to open the container, then the same force extracts the deployment bag. There are variations on hand-deployed pilot chutes, but the system described is the more common throw-out system.

Only the hand-deployed pilot chute may be collapsed automatically after deployment, by a kill line, reducing the in-flight drag of the pilot chute on the main canopy. Reserves, on the other hand, do not retain their pilot chutes after deployment. The reserve deployment bag and pilot chute are not connected to the canopy in a reserve system. This is known as a free-bag configuration, and the components are often lost during a reserve deployment.

Occasionally, a pilot chute does not generate enough force to pull the pin or extract the bag. This effect, known as "pilot chute hesitation," may be caused by any of several factors: the pilot chute may be caught in the turbulent wake of the jumper (the "burble"), the closing loop holding the pin may be too tight, or the pilot chute may not be generating sufficient force. If the problem does not clear, it can lead to a total malfunction, requiring reserve deployment.

Paratroopers' main parachutes are usually deployed by static lines that release the parachute, yet retain the deployment bag that contains the parachute—without relying on a pilot chute for deployment. In this configuration, the deployment bag is known as a direct-bag system, in which the deployment is rapid, consistent, and reliable. This type of deployment is also used by student skydivers going through a static line progression, a student program.

Varieties of personal ram-airs

Personal ram-air parachutes are loosely divided into two varieties: rectangular or tapered, commonly referred to as "squares" or "ellipticals" respectively. Medium-performance canopies (reserve-, BASE-, canopy formation-, and accuracy-type) are usually rectangular. High-performance, ram-air parachutes have a slightly tapered shape to their leading and/or trailing edges when viewed in planar form, and are known as ellipticals. Sometimes all the taper is in the leading edge (front), and sometimes in the trailing edge (tail).

Ellipticals are usually used only by sports parachutists. Ellipticals often have smaller, more numerous fabric cells and are shallower in profile. Their canopies can be anywhere from slightly elliptical to highly elliptical—indicating the amount of taper in the canopy design, which is often an indicator of the responsiveness of the canopy to control input for a given wing loading, and of the level of experience required to pilot the canopy safely.

The rectangular parachute designs tend to look like square, inflatable air mattresses with open front ends. They are generally safer to operate because they are less prone to dive rapidly with relatively small control inputs, they are usually flown with lower wing loadings per square foot of area, and they glide more slowly. They typically have a less-efficient glide ratio.

Wing loading of parachutes is measured similarly to that of aircraft: comparing the number of pounds (exit weight) to square footage of parachute fabric. Typical wing loadings for students, accuracy competitors, and BASE jumpers are less than one pound per square foot—often 0.7 pounds per square foot or less. Most student skydivers fly with wing loadings below one pound per square foot. Most sport jumpers fly with wing loadings between 1.0 and 1.4 pounds per square foot, but many interested in performance landings exceed this wing loading. Professional canopy pilots compete at wing loadings of 2 to 2.6 pounds per square foot. While ram-air parachutes with wing loadings higher than four pounds per square foot have been landed, this is strictly the realm of professional test jumpers.

Smaller parachutes tend to fly faster for the same load, and ellipticals respond faster to control input. Therefore, small, elliptical designs are often chosen by experienced canopy pilots for the thrilling flying they provide. Flying a fast elliptical requires much more skill and experience. Fast ellipticals are also considerably more dangerous to land. With high-performance elliptical canopies, nuisance malfunctions can be much more serious than with a square design, and may quickly escalate into emergencies. Flying highly loaded, elliptical canopies is a major contributing factor in many skydiving accidents, although advanced training programs are helping reduce this danger.

High-speed, cross-braced parachutes (such as the Velocity, VX, XAOS and Sensei) have given birth to a new branch of sport parachuting called "swooping." A race course is set up in the landing area for expert pilots to measure the distance they are able to fly past the 6-foot (1.8 m) tall entry gate. Current world records exceed 600 feet (180 m).

Aspect ratio is another way to measure ram-air parachutes. Aspect ratios of parachutes are measured the same way as aircraft wings, by comparing span with chord. Low aspect ratio parachutes (i.e. span 1.8 times the chord) are now limited to precision landing competitions. Popular precision landing parachutes include Jalbert (now NAA) Para-Foils and John Eiff's series of Challenger Classics. While low aspect ratio parachutes tend to be extremely stable—with gentle stall characteristics—they suffer from steep glide ratios and small "sweet spots" for timing the landing flare.

Medium aspect ratio (i.e. 2.1) parachutes are widely used for reserves, BASE, and canopy formation competition because of their predictable opening characteristics. Most medium aspect ratio parachutes have seven cells.

High aspect ratio parachutes have the flattest glide and the largest "sweet spots" (for timing the landing flare) but the least predictable openings. An aspect ratio of 2.7 is about the upper limit for parachutes. High aspect ratio canopies typically have nine or more cells. All reserve ram-air parachutes are of the square variety, because of the greater reliability, and the less-demanding handling characteristics.

General characteristics of ram-airs

Main parachutes used by skydivers today are designed to open softly. Overly 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. Four collections of lines go through the grommets 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. This reduces the speed at which the canopy can open and inflate.

At the same time, the overall design of a parachute still has a significant influence on the deployment speed. The deployment speeds of modern sport parachutes vary considerably. Most modern parachutes open comfortably, but individual skydivers may prefer harsher deployment.

The deployment process is inherently chaotic. Rapid deployments can occur even with well-behaved canopies. On rare occasions, deployment can be so rapid that the jumper suffers bruising, injury, or death.

Drogue parachutes

A B-52H Stratofortress from the 5 Bomb Wing deploys its drag chute for landing.

A drogue parachute is a small parachute designed to be deployed from a rapidly moving object. It is often used to gain control of very fast descents, including the descent of spacecraft during reentry, before deployment of the main parachute. A drogue parachute is more elongated and far thinner than a conventional parachute, and thus provides less drag. It cannot slow an object as much as a conventional parachute, but it can be deployed at speeds at which conventional parachutes would be torn apart.

Also, its simpler design allows for easier deployment. Whereas a conventional parachute could get caught in itself while unfolding and fail to inflate properly, the drogue parachute will inflate more easily and more reliably generate the expected amount of drag.

Drogue parachutes are sometimes used to deploy a main or reserve parachute by using the drag generated by the drogue to pull the main parachute out of its container. The most familiar drogue parachute is the one used for this purpose in parachuting. Such a drogue is referred to as a pilot chute when used in a single-user (sports) parachute system. The pilot chute is used only to deploy the main or reserve parachute; it is not used for slowing down or for stability.

Tandem systems are different. To reduce the terminal velocity of a pair of tandem jumpers, a drogue is deployed shortly after they exit the aircraft. It is later used to deploy the main parachute, as on sports systems.

Safety

A parachute is carefully "packed" (folded) to ensure that it will open reliably. If a parachute is not packed properly, the main parachute might fail to deploy correctly or fully, potentially resulting in a fatality. 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. Sport skydivers are 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 landed safely, to catastrophic malfunctions that require cutting away the main parachute (using a modern 3-ring release system) and deploying the reserve. Most skydivers also equip themselves with small, barometric computers (known as AADs or Automatic Activation Devices) that automatically activate the reserve parachute if the skydiver has not deployed a parachute to reduce his rate of descent by a preset altitude.

Exact numbers are difficult to estimate, but approximately one in a thousand sports main parachute openings malfunction, and must be cut away, although some skydivers have performed many hundreds of jumps and have never had to cut away.

Reserve parachutes are packed and deployed differently. They are also designed more conservatively and are built and tested to more exacting standards, making them more reliable than main parachutes. However, the primary safety advantage of a reserve chute comes from the probability of an unlikely main malfunction being 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 cut away 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.

As parachutes deteriorate, they need to be replaced. Failure to do so could result in loss of life.

Specific types of malfunctions

Some specific types of malfunctions of round parachutes are listed below.

A "Mae West" is a type of parachute malfunction in which the canopy becomes contorted by a suspension line going over its top, producing the appearance of an enormous brassiere. The shape reminded some of Mae West's large proportions.[14]

"Squidding" occurs when a parachute fails to inflate properly and its sides flutter like the fins of a squid swimming through water. This type of malfunction occurred during parachute testing for the Mars Exploration Rover.[15]

A "cigarette roll" occurs when a parachute deploys fully from the bag but fails to open. The parachute then appears as a vertical column of cloth (in the general shape of a cigarette), providing the jumper with very little drag. It is caused when one skirt of the canopy, instead of expanding outward, is blown against the opposite skirt. The column of nylon fabric, buffeted by the wind, rapidly heats from the friction of nylon rubbing against nylon and can melt the fabric and fuse it together, preventing the canopy from opening.

An "inversion" occurs when one skirt of the canopy blows between the suspension lines on the opposite side of the parachute and then catches air. That portion then forms a secondary lobe with the canopy inverted. The secondary lobe grows until the canopy turns completely inside out.

See also

Notes

  1. Parachute. Online Etymology Dictionary. Retrieved July 11, 2008.
  2. Daniel Poore, A History of Early Flight. (New York, NY: Alfred Knopf, 1952).
  3. Smithsonian Institution. Manned Flight. (Pamphlet 1990.)
  4. David W. Tschanz, Flights of Fancy on Manmade Wings. IslamOnline.net. Retrieved July 11, 2008.
  5. Principles of Aeronautics, Parachutes. Franklin Institute. Cislunar Aerospace, Inc. Retrieved July 11, 2008.
  6. John H. Lienhard, "Abbas Ibn Firnas" in The Engines of Our Ingenuity. NPR. KUHF-FM Houston. No. 1910 (2004). Retrieved July 11, 2008.
  7. Lynn White, "The Invention of the Parachute" Technology and Culture 9(3) (1968): 462-467.
  8. John Wilkins. Mathematical Magic of the Wonders that may be Performed by Mechanical Geometry, part I: Concerning Mechanical Powers Motion, part II, Deadloss or Mechanical Motions. (London, UK, 1648)
  9. National Aviation Hall of Fame, Thomas Scott Baldwin Retrieved May 1, 2012.
  10. Arlington National Cemetery Website, Thomas Scott Baldwin: Major, United States Army Retrieved May 1, 2012.
  11. Arthur Gould Lee, No parachute. (London, UK: Jarrolds, 1968, ISBN 0090865901).
  12. Milestones. Airborne Systems. Retrieved July 11, 2008.
  13. The Irvin Parachute & the Caterpillar Club. copied from Irvin Aerospace. Retrieved July 11, 2008.
  14. Mae West. Dictionary, encarta.msn.com. Retrieved July 11, 2008.
  15. Mars Exploration Rover Mission., August 26, 2004, NASA. Retrieved July 11, 2008.

References

  • Federal Aviation Administration. Powered Parachute Flying Handbook 2007: FAA-H-8083-29. (FAA Handbooks series.) Oklahoma City, OK: Federal Aviation, Administration, 2007. ISBN 1560276711.
  • Federal Aviation Administration. Sport Pilot Practical Test Standards for Airplane, Weight-Shift Control, Powered Parachute, and Flight Instructor: FAA-S-8081-29 and 31. Practical Test Standards series. Newcastle, WA: Aviation Supplies & Academics, 2008. ISBN 1560277254.
  • Lee, Arthur Gould. No parachute. London, UK: Jarrolds, 1968. ISBN 0090865901.
  • Poore, Daniel. A History of Early Flight. New York, NY: Alfred Knopf, 1952.
  • Poynter, Dan. The Parachute Manual: A Technical Treatise on Aerodynamic Decelerators. Santa Barbara, CA: Para Pub, 1984. ISBN 0915516357.
  • White, Lynn, The Invention of the Parachute. Technology and Culture 9(3) (1968): 462-467.

External links

All links retrieved May 1, 2012

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