Wednesday, September 26, 2007
A parachute is usually a soft fabric device used to slow the motion of an object through an atmosphere by creating drag. Parachutes are normally 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 (a fixed-wing aircraft, or a drag racer), or to provide stability (tandem freefall, or space shuttle after touchdown). The word parachute comes from the French words para, protect or shield, and chute, the fall. Therefore parachute actually means "fall protection". Many modern parachutes are classified as semi-rigid wings, are quite maneuverable, and can facilitate a controlled descent similar to that of a glider. Although skydiving can have its thrills and excitements, it can be very dangerous too. Folding a parachute requires a high degree of skill, and an improperly folded parachute will not deploy, causing you to fall freely to the ground.
Parachutes were once made from silk but now they are almost always constructed 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. Kevlar is rarely seen except on reserve canopies.
In the 9th century, a muslim arab daredevil named Armen Firman jumped from a tower in Córdoba using a loose cloak stiffened with wooden struts to arrest his fall with only minor injuries. According to Joseph Needham there were working parachutes in China as early as the 12th 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 successful test of such a parachute was made in 1617 in Venice by the Dalmatian inventor Fausto Veranzio which he named Homo Volans (Flying Man).
The modern parachute was 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 in 1793 when 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. In 1911 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. 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 whereas he held the chute in his arms as he left the aircraft. 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. This is the style of chute that became en reg with the actual chute being stored or 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 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. Allied 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 WWI. As a result, a pilot's only options were to ride their machine into the ground, jump from several thousand feet, or commit suicide using a standard-issued revolver. In the UK, Everard Richard 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.
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 freefall parachute jump from an airplane .
An early brochure  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. Beginning with Italy in 1927, several countries experimented with using parachutes to drop soldiers behind enemy lines, and 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,
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.
Types of parachutes
Round parachutes, which are purely drag devices (that is, unlike the ram-air types, they provide no lift ), are used in military, emergency and cargo applications. These 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. Rounds are rarely used by skydivers these days.
The first round parachutes were simple, flat circulars, but suffered from instability, so most military round parachutes are some sort of conical (i.e. cone-shaped) or parabolic (picture 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 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 how a parachute falls.
The unique design characteristics of cruciform parachutes reduces oscillations (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 25 percent from 21 feet per second to an incredible rate of 18 feet per second. The T-11 is designed to have an average rate of decent 14% 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% to lessen the potential for death.
Cruciform (Square) parachutes
A variation on the round parachute is the pull down apex parachute—invented by a Frenchman named LeMogne—referred to as a Para-Commander-type canopy in some circles, after the first model of the 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 around 10 mph (15 km/h).
Annular and pull down apex parachutes
Ribbon and ring parachutes have similarities to annular designs. They are frequently designed to deploy at supersonic speeds eg Mach 2 ie speeds at which a conventional parachute would instantly burst upon opening. 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 on nuclear bombs such as the B61 and B83.
Ribbon and ring 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 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.
Paratroopers and parachutists carry two parachutes. The primary parachute is called a main parachute, the secondary is called a reserve parachute. The jumper uses the reserve if the main parachute fails to deploy or operate correctly.
Reserve parachutes were introduced in World War II by the US Army paratroopers, and are now almost universal. For civilian jumpers, the only exceptions are BASE jumping parachutes and emergency bail-out rigs, which both have a single parachute. These emergency parachutes tended to be of round design in the past, while modern PEPs (e.g., P124A/Aviator) contain the large, docile ram-air type.
Personnel 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 plan 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 to 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 tall entry gate. Current world records exceed 600 feet.
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.
Varieties of personnel 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. Modern sport parachutes' deployment speeds vary considerably. Most modern parachutes open comfortably, but individual skydivers may prefer harsher deployment.
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.
For example, one method of reducing the air-resistance of a reserve's slider is to make it of open-mesh fabric.
The below list malfunctions specific to round-parachutes. For malfunctions specific to square parachutes, see Malfunction (parachuting).
A "Mae West" is a type of round parachute malfunction which contorts the shape of the canopy into the appearance of a brassiere, presumably one suitable for a woman of Mae West's proportions. 
"Squidding" occurs when a parachute fails to inflate properly and its sides are forced inside the canopy. This kind of malfunction occurred during parachute testing for the Mars Exploration Rover. 
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 the nylon rubbing against nylon and can melt the fabric and fuse it together, preventing any hope of the canopy 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.
Posted by allenwoow at 8:34 AM