Parachute

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This article refers to the aerodynamic deceleration device. For the hot air ]], see Parachute music festival. For the album by the band Coldplay, see Parachutes

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 within an atmosphere. Drogue 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 "fall protection". Most modern parachutes are classified as semi-rigid wings, are quite maneuverable, and can be flown as a glider.

Parachutes were once made from silk but these days are almost always constructed from more durable woven nylon fabric, sometimes coated with a - silicone - zero porosity coating to improve performance and consistency over time. Originally silk was used for parachute suspension lines, but was replaced by nylon during the Second World War. When square (aka ram-air) parachutes were introduced, manufacturers switched to low-stretch materials like Dacron or zero-stretch materials like Spectra, Kevlar, Vectran or high modulous aramids. Kevlar is rarely seen except on reserve canopies.

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 the 9th century, another Muslim (Abbas Ibn Firnas) attempted a similar feat. 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 1480-1483. 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 Sébastien 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, André Garnerin made the first jump using such a parachute. Garnerin also invented the vented parachute, which improved the stability of the fall. Gleb Kotelnikov invented the first knapsack parachute, later popularized by Paul Letteman and Kathchen Paulus.

At San Francisco in 1885, Thomas Scott Baldwin was the first person in the United States to descend from a balloon in a 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 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 airplane over Los Angeles.

The first military use for the parachute was for use by artillery spotters on tethered observation balloons in World War I. These were tempting targets for enemy fighter aircraft, though difficult to destroy, due to their 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. Aircraft crews, however, were forbidden from carrying their own parachutes. It was believed to encourage a lack of nerve in action. As well, early parachutes were very heavy, and fighters lacked the performance to carry the additional load through most of WW1. Only in 1918 did the German air service become the world's first to introduce a standard parachute.

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.

An early brochure [link] of the Irvin Air Chute Company credits William O'Connor 24 August 1920 at McCook Field near Dayton, Ohio as the first person to be saved by an Irvin parachute. Another life-saving jump was made at McCook Field by test pilot Lt. Harold H. Harris on Oct 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.

Uses

The first use of the parachute was as an escape device for obersvers manning observation balloons in the First World War.

Between the world wars, several nations adopted the parachute as an escape device for military pilots, and examined its use as a means of tactically deploying infantrymen to combat zones. The word Paratrooper was adopted in English (collectively, paratroopers were grouped into airborne forces) to describe soldiers who arrive in enemy territory by parachute. Airborne forces were widely used in the Second World War, initially by the Germans. Ironically, shortly after Germany stopped using mass parachute drops due to heavy losses in the Battle of Crete, the Allies were inspired to adopt the tactic themselves.

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. Early reconnaissance satellites ejected a film pack that came to earth and was recovered from under its parachute by specially-equipped aircraft.

Some bombs are equipped with a parachute, such as the World War Two "parafrag" (an 11kg (25 pound) fragmentation bomb), the Vietnam-era daisy cutters, and the bomblets of some modern cluster bombs. Parachutes slow the bomb's descent, thus giving the dropping aircraft time to get to a safe distance from the explosion. (This is especially important with airburst nuclear weapons.)

Food aid packages are sometimes delivered by parachute, and military forces routinely drop cargo on pallets under parachutes. Heavy loads have used a special system which uses a braking rocket.

Parachutes (commonly called "drag 'chutes") 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. Drag racers use a related technique.

The drag chute deployed by the Space Shuttle shortly after it touchs down is designed primarily to stabilise the craft during the roll out and not, as is commonly believed, for braking.

Jet fighter ejector seats are equipped with automatically deployed parachutes.

Aircraft flight testing has also used parachutes on aircraft to provide additional safety. A recent development led to a method able to safely bring down an entire general aviation aircraft (with passengers), the Ballistic Recovery System.

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

A paraglider with a motor and possibly wheels is called a powered parachute or, sometimes, a paraplane.

Also in rocket engineering parachutes were in some (why only rare ) cases used for descending burned-out rocket stages. Professionel rockets equipped with parachutes were

• Cirrus and Kumulus - rocket
• Rockets of Berthold Seliger
• Space Shuttle Boosters

Parachutes can be also used for soft landings on other celestial bodies. However they do not work on celestial bodies without atmosphere as the moon. For a soft landing on Mars a parachute alone does not reduce the sinking speed in the necessary intensity and there are always brake rockets or airbags necessary for a soft landing. Soft landings on Venus do not require a parachute, because the extremely dense atmosphere of Venus breaks the descent enormously, even without the use of a parachute. Because of the high temperatures and the limited cooling possibilities of probes, the last part of the descent to Venus is done without a parachute.

Landings on Saturn's moon, Titan, are possible using only a parachute.

Parachutes can be also used for reducing the descent velocity of atmospheric probes in the atmosphere of gaseous planets.

Parachutes are also used in model construction. Applications there are model rocketry (some advanced users use multiple redundancies and multi stage deployments)and the ejection of small things from telecontrolled planes. However there are also telecontroled model paragliders.

Design

General

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.

Deployment systems

Freefall deployed parachutes are pulled out of their containers by a smaller parachute called a pilot chute.

A way of deploying a parachute directly after leaving the aircraft is the static line. One end of the static line is attached to the airplane, and the other to the deployment system of the parachute container.

Types of parachutes

Round parachutes

Round parachutes, which are pure drag devices (i.e., they provide no lift like the ram-air types), are used in military, emergency and cargo applications. 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. Rounds are rarely used by skydivers these days. The first round parachutes were simple, flat circulars, but suffered from instability, so most modern round parachutes are some sort of concial (i.e Strong 26 foot diameter Mid-Lite found in pilot emergency parachutes) or parabolic (picture a flat circular canopy with an extended skirt) US Army T-10 static-line.

Some round parachutes are steerable, but not to the extent of the ram-air parachutes. An example of a steerable round is provided in the picture of the paratroopers 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.

Annular & pull down apex parachutes

A variation on the round parachute is the pull down apex parachute - invented by a Frenchman named LeMoigne - often referred to as a ParaCommander-type canopy, named after the first model of the type. It is essentially 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. At first glance, para-sailing canopies resemble Para-Commanders, but have fewer vents. Para-sailing canopies are normally towed aloft behind cars or boats.

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 around 10 mph (15 km/h). Para-Commanders usually have large stabilizers hanging down the sides.

Ribbon and ring parachutes

Ribbon and ring parachutes have similarities to annular designs, they 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.

Ram-air parachutes

Most modern parachutes are self-inflating "ram-air" airfoils known as a parafoil that provide control of speed and direction similar to 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 airfoil-shaped fabric ribs. The space between the two fabric layers fills 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.

Personnel parachutes

Reserves

Paratroopers and sports parachutists carry two parachutes. The primary parachute is called a main parachute, the second, a reserve parachute. The jumper uses the reserve if the main parachute fails to operate correctly.

Reserve parachutes were introduced in World War II by the US Army paratroopers, and are now almost universal. For human jumpers only emergency bail-out rigs have a single parachute and these tend to be of round design on older designs while modern PEPs (i.e P124A/Aviator) contain large, docile ram-air parachutes.

Deployment

Reserve parachutes usually have a ripcord deployment system, 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 is 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 either pull the pin or extract the bag, causes may be that the pilot chute is caught in the turbulent wake of the jumper (the burble), the closing loop holding the pin is too tight or the pilot chute is generating insufficient force, this effect is known as pilot chute hesitation and if it does not clear in can lead to a total malfunction requiring reserve deployment.

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

Varieties of personal ram-airs

Personal ram-air parachutes are loosely divided into two varieties: rectangular or tapered. Medium-performance canopies (reserves, BASE, canopy formation and accuracy) are usually rectangular. 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. Sometimes all the taper is in the leading edge (front). Sometimes all the taper is in the trailing edge (tail) (i.e Aerodyne's Diablo). These are usually only used by sports parachutists. Ellipticals usually have smaller, more numerous fabric cells and are shallower in profile.

Lower performance parachutes look like square inflatable air-mattresses with open front ends. They are generally safer to operate. They usually have lower wing loadings per square foot of area, and glide more slowly. They may have a less-efficient glide ratio.

Wing-loading of parachutes is measured the same way as airplanes: 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 (i.e. 0.7 pounds per square foot). Most recreational skydivers prefer wing-loadings between one pound per square foot and two pounds per square foot. Professional pond swoopers compete at wing-loadings of 2 to 2.2 pounds per square foot. While professionals have landed ram-air parachutes loaded as high as four pounds per square foot, this is strictly the realm of professional rest 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.

Aspect ratio is anothe way to measure ram-air parachutes. Aspect ratios of parachutes are measured the same way as airplane wings,by comparing span with chord. Low aspect ratio parachutes (i.e. span 1.8 times the chord) are now limited to precision landig competitions. Popular precision landing parachutes in clude 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. 2.7 is about the upper limit for parachute aspect ratios. 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 less-demanding handling characteristics.

General characteristics of ram-airs

Main 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. 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.

The overall design of a parachute still has a significant influence on the deployment speed. Modern sport parachutes' deployment speeds vary considerably. Most modern parachutes open comfortably, but individual skydivers prefer different deployment speeds.

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

Emergency and reserve parachutes by design tend to deploy more rapidly than sports main canopies. They still have sliders, but the sliders descend rapidly, and are constructed with less air-resistance than a sports canopy's slider. For example, one method of reducing the air-resistance of a reserve's slider is to make it of open-mesh fabric.^{[[Citing sourcescitations needed]]}

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 the reserve 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 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 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 skydiving 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.

External links

• [Parachute History] Parachute History
• [History of parachute]
• [FAI] The Federation Aeronautique Internationale -- The international governing body for all airborne sports.
• [USPA] The United States Parachute Association -- The governing body for sport skydiving in the U.S.
• [CSPA] The Canadian Sport Parachuting Association -- The governing body for sport skydiving in Canada.
• [Dropzone.com] Skydiving, dropzones and modern parachuting
• [Parachute]

 

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