Tuesday, January 22, 2013

Types of parajumping.

Tandem skydiving

Tandem skydiving or tandem parachuting refers to a type of skydiving where a student skydiver is connected to a harness attached to a tandem instructor. The instructor guides the student through the whole jump from exit through freefall, piloting the canopy, and landing. The student needs only minimal instruction before making a tandem jump with the instructor.

static line

A static line is a fixed cord attached to a large, stable object. It is used for safety in construction and to open parachutes automatically for paratroopers and novice parachutists.

Instructor-assisted deployment (IAD)

Instructor-assisted deployment (IAD) is a parachute deployment program most adequately similar to static line. The main difference is that instead of being deployed by a static line, the student's jumpmaster (who is in the plane with them) deploys the student's parachute by throwing the pilot chute downward and clear of the door as the student exits.
Among the benefits to IAD is the ability to use the same parachute equipment as the students will use when they progress to deploying their parachutes on their own, and the decreased chance of an inconvenience called "line twists".

 Accelerated freefall (AFF)

Accelerated freefall (AFF) (known in Canada as progressive freefall) is a method of skydiving training. This method of skydiving training is called "accelerated" because the progression is the fastest way to experience solo freefall, normally from 10,000 to 15,000 feet "Above Ground Level" (AGL). In static line progression, many more jumps are required to experience solo freefall, but the jumps are less expensive for the student as one instructor can dispatch multiple students per load, whereas under accelerated freefall, one or sometimes two instructors are dedicated just to one student.
  

Types of jumping as per geography ?

BASE jumping

BASE jumping, also sometimes written as B.A.S.E. jumping, is an activity where participants jump from fixed objects and use a parachute to break their fall. "BASE" is an acronym that stands for four categories of fixed objects from which one can jump: buildings, antennas, spans (bridges), and earth (cliffs).

BASE Jumping Basics

Before we get into any discussions on the techniques and equipment used in BASE jumping, we need to make something very clear: BASE jumping is extremely dangerous. There is no margin for error. A slight mistake, or a little bad luck, and death is the result. BASE jumpers generally have about 100 regular skydiving jumps under their belt before they ever attempt a BASE jump, and they usually have an experienced BASE jumper who mentors them on the skills necessary to jump safely. No one should attempt BASE jumping without a lot of thought, training, experience and a good life insurance policy.

BASE jumping is essentially a variation on skydiving. For a good explanation of skydiving and the equipment used, check out How Skydiving Works. BASE jumpers use modern ram-air parachutes (the jumpers injured on El Capitan in 1966 were using older round parachutes, which contributed to their problems). Ram-air chutes are rectangular to give the jumper greater control over direction and speed once it has been deployed. There are some key differences between skydiving gear and BASE jumping gear, however, so BASE jumpers need special equipment and techniques. A parachute made especially for BASE jumping costs between $1,200 and $1,500.

BASE jumpers have to overcome two major obstacles: low altitude and the proximity of the BASE object. Skydivers typically open their chutes at around 2,000 feet. This gives them time to deploy the parachutes gradually (reducing line tangles and a sudden jerk on the diver) using a device called a slider [ref]. It also gives them a little breathing room. If there is a problem with the main parachute, they can still deploy their back-up chute.

But many BASE jumps start out well below 2,000 feet. While jump sites such as El Capitan and Angel Falls in Venezuela are around 3,000 feet, they are the exception. Skyscrapers and antenna towers are usually 1,000 to 1,500 feet tall. As a result, jumpers have to deploy their parachutes quickly.

A few alterations in basic skydiving equipment help to accomplish this. For example, some BASE jumpers use a larger pilot chute. This is the small parachute that drags open the main chute. Larger pilot chutes catch more air, create more drag and open main chutes more quickly. They are also helpful because low altitude jumps force jumpers to open their chutes at a lower velocity -- they haven't been falling long enough to achieve a freefalling human's terminal velocity (around 120 mph). Lower speeds mean reduced air pressure in the chute, so a larger chute is more effective. Because many BASE jumps are so low that only about five seconds of freefall are possible before impact, some BASE jumpers don't bother packing back-up chutes. If the main chute fails to deploy, or deploys incorrectly, there isn't the time to cut away a malfunctioning chute and deploy the back-up.

Instead of a ripcord, BASE jumpers release their pilot chute manually. For higher jumps, the pilot chute is stowed in an easily accessible pocket or flap, and the jumper pulls it free to release it at the right moment. This leaves both hands free during the brief freefall. If the jump is shorter, the jumper usually just holds the pilot chute in his or her hand [ref].

For jumps 300 feet or lower, BASE jumpers have almost no time at all to freefall and deploy a chute. They use a static line to deploy the chute automatically. This line runs from the jumper's pack to the object. During the jump, this line pulls the main chute open, and then separates from the pack.

Skydivers don't have to worry about object proximity. They have to worry about hitting the ground, not the side of a building or cliff. But most BASE jumping fatalities are due to object impacts, rather than freefalling to the ground. The need for fast parachute deployments compounds the problem -- these deployments can send the jumper off into an unintended direction, such as straight into a granite wall. Jumpers call this an "off-heading opening."

Jumpers try to compensate by using a smaller ram-air parachute, one with seven air cells instead of nine. Modern parachutes designed specifically for BASE jumping have started to incorporate modified sliders that ease the suddenness of deployment, making it easier to avoid an off-heading opening.

Body position at the jump and deployment are key factors in determining the success of a jump. Jumping head first and rotating forward is incorrect. Keeping the body oriented so that the jumper is facing down, with the chute deploying behind him, is vital. On jumps with a few seconds of freefall, jumpers use tracking to direct the body away from the object. This means that the jumper "flies" away from the object using the aerodynamic shape of the body, instead of just falling straight down.

Canopy skills are vital as well. Once a ram-air parachute has deployed, the jumper may be carrying a great deal of forward velocity. Being able to steer properly and avoid slamming into the object could literally be the difference between life and death.




Skydiving

skydiving, is the action sport of exiting an aircraft and returning to earth with the aid of gravity while using a parachute to slow down during the final part of the descent. It may or may not involve a certain amount of free-fall, a time during which the parachute has not been deployed and the body gradually accelerates to terminal velocity. The history of skydiving starts with Andre-Jacques Garnerin who made successful descents using a canvas canopy and small basket, tethered beneath a hot-air balloon.

Para sailing

Para sailing, also known as parascending, or "parakiting" is a recreational kiting activity where a person is towed behind a vehicle (usually a boat) while attached to a specially designed canopy wing that reminds one of a parachute, known as a parasail wing. On land or over water the manned kite's moving anchor may be a car, truck, or boat; parasailing just by kiting in heavy winds is highly discouraged. The boat then drives off, carrying the parascender or wing and person into the air. If the boat is powerful enough, two or three people can parasail behind it at the same time. The parascender has little or no control over the parachute. 

Bungee jumping

Bungee jumping is an activity that involves jumping from a tall structure while connected to a large elastic cord. The tall structure is usually a fixed object, such as a building, bridge or crane; but it is also possible to jump from a movable object, such as a hot-air-balloon or helicopter, that has the ability to hover above the ground. The thrill comes from the free-falling and the rebound.[3] When the person jumps, the cord stretches and the jumper flies upwards again as the cord recoils, and continues to oscillate up and down until all the energy is dissipated.  

 

Wednesday, January 9, 2013

What is parachute ?

A parachute is a device used to slow the motion of an object through an atmosphere by creating drag, or in the case of ram-air parachutes, aerodynamic lift. Parachutes are usually made out of light, strong cloth, originally silk, now most commonly nylon. Parachutes must slow an object's terminal vertical speed by a minimum 75% in order to be classified as such. Depending on the situation, parachutes are used with a variety of loads, including people, food, equipment, space capsules, and bombs.
Drogue chutes are used to aid horizontal deceleration of a vehicle (a fixed-wing aircraft, or a drag racer), or to provide stability (tandem free-fall, or a space shuttle after a touchdown).


The word "parachute" comes from the French prefix paracete, originally from the Greek, meaning to protect against, and chute, the French word for "fall", and it was originally coined, as a hybrid word which meant literally "that which protects against a fall", by the French aeronaut François Blanchard (1753–1809) in 1785.


                                                           

History

Early Renaissance Forms

The earliest evidence for the parachute dates back to the Renaissance period.[1] The oldest parachute design appears in an anonymous manuscript from 1470s Renaissance Italy (British Museum Add. MSS 34,113, fol. 200v), showing a free-hanging man clutching a cross bar frame attached to a conical canopy.[2] As a safety measure, four straps run from the ends of the rods to a waist belt. The design is a marked improvement over another folio (189v) which depicts a man trying to break the force of his fall by the means of two long cloth streamers fastened to two bars which he grips with his hands.[3] Although the surface area of the parachute design appears to be too small to offer effective resistance to the friction of the air and the wooden base-frame is superfluous and potentially harming, the revolutionary character of the new concept is obvious.[3]
Only slightly later, a more sophisticated parachute was sketched by the polymath Leonardo da Vinci in his Codex Atlanticus (fol. 381v) dated to ca. 1485.[2] Here, the scale of the parachute is in a more favorable proportion to the weight of the jumper. Leonardo's canopy was held open by a square wooden frame, which alters the shape of the parachute from conical to pyramidal.[3] It is not known whether the Italian inventor was influenced by the earlier design, but he may have learnt about the idea through the intensive oral communication among artist-engineers of the time.[4] The feasibility of Leonardo's pyramidal design was successfully tested in 2000 by the British Adrian Nicholas and again in 2008 by another skydiver.[5] According to the historian of technology Lynn White, these conical and pyramidal designs, much more elaborate than early artistic jumps with rigid parasols in Asia, mark the origin of "the parachute as we know it".[1]
The Venetian inventor Fausto Veranzio (1551–1617) examined da Vinci's parachute sketch, and set out to implement one of his own. He kept the square frame, but replaced the canopy with a bulging sail-like piece of cloth which he came to realize decelerates the fall more effectively.[3] A now-famous depiction of a parachute that he dubbed Homo Volans (Flying Man) appeared in his book on mechanics, Machinae Novae (1615 or 1616), alongside a number of other devices and technical concepts. It is widely believed that in 1617, Veranzio implemented his design and tested the parachute by jumping from St Mark's Campanile in Venice and that the event was documented some thirty years later by John Wilkins, founder and secretary of the Royal Society in London in his book Mathematical Magick or, the Wonders that may be Performed by Mechanical Geometry, published in London in 1648. However, in this book, John Wilkins wrote about flying, not about parachutes. He neither mentions Fausto Veranzio nor a parachute jump nor any event in 1617. Furthermore, the story does not explain how Veranzio could have managed to get the wooden frame out of the tower and into a horizontal position with himself underneath without the device tilting and collapsing. No evidence has been found that anyone ever tested Veranzio's parachute.[6]

Modern parachutes

18th and 19th centuries

The modern parachute was invented in the late 18th century by Louis-Sébastien Lenormand in France, who made the first recorded public jump in 1783. Lenormand also sketched his device beforehand.
Two years later, in 1785, Lenormand coined the word "parachute" by hybridizing the prefix para-, for "defense against," and chute, the French word for "fall," to describe the device's function, the word literally meaning "that which protects against a fall."
Also in 1785, 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 claimed to have had the opportunity to try it himself in 1793 when his hot air balloon ruptured and he used a parachute to descend (this event was not witnessed by others).
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 descent using such a parachute. Garnerin also invented the vented parachute, which improved the stability of the fall.


Eve of World War I

In 1911 a successful test was done with a dummy at the Eiffel tower in Paris. The puppet's weight was 75 kg; the parachute's weight was 21 kg. The cables between puppet and the parachute were 9 m long.[7] The following year Franz Reichelt fell to his death from the tower during initial testing of his wearable parachute.
Also in 1911, Grant Morton made the first parachute jump from an airplane, 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 where he held the chute in his arms as he left the aircraft. In the same year, a Russian inventor Gleb Kotelnikov invented the first knapsack parachute,[8] although Hermann Lattemann and his wife Käthe Paulus had been jumping with bagged parachutes in the last decade of the 19th century.
In 1912, on a road near Tsarskoye Selo, years before it became part of St. Petersburg, Kotelnikov successfully demonstrated the braking effects of parachute by accelerating a Russo-Balt automobile to the top speed, and then opening a parachute attached to the back seat, thus inventing also the drogue parachute.[8]
On 1 March 1912, U.S. Army Captain Albert Leo Stevens made the first (attached-type) parachute jump in the United States from a fixed-wing aircraft, a Benoist pusher, while flying above Jefferson Barracks, St. Louis, Mo. The jump utilized a 'pack' style chute with the 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 1914.[9] On 21 June 1913, Georgia Broadwick became the first woman to parachute jump from a moving aircraft, doing so over Los Angeles.[10]



World War I

The first military use for the parachute was for use by artillery detectors on tethered observation balloons in World War I. These were tempting targets for enemy fighter aircraft, though difficult to destroy, due to their heavy anti-aircraft 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. The main part of the parachute was in a bag suspended from the balloon with the pilot wearing only a simple waist harness which was attached to the main parachute. When the balloon crew jumped the main part of the parachute was pulled from the bag by the crew's waist harness, first the shroud lines, followed by the main canopy. This type of parachute was first adopted on a large scale by the Germans for their observation balloon crews, and then later by the British and French for their observation balloon crews. While this type of unit worked well from balloons it had mixed results when used on fixed wing aircraft by the Germans where the bag was stored in a compartment directly behind the pilot. In many instances where it did not work the shroud lines became entangled with the spinning aircraft. Although a number of famous German fighter pilots were saved by this type of parachute including Hermann Göring,[11] no parachutes were issued to Allied "heavier-than-air" aircrew, since it was thought at the time that if a pilot had a parachute he would jump from the plane when hit rather than trying to save the aircraft.[12] Airplane cockpits at that time also were not large enough to accommodate a pilot and a parachute, since a seat that would fit a pilot wearing a parachute would be too large for a pilot not wearing one. This is why the German type was stowed on the fuselage, rather than being of the "backpack" type. Weight was also a consideration, since planes had limited load capacity. Carrying a parachute served to lessen performance and reduced the useful offensive and fuel load.
In the U.K., Everard Calthrop, a railway engineer, and breeder of Arab horses, invented and marketed through his Aerial Patents Company a "British Parachute." Thomas Orde-Lees, known as the "Mad Major," demonstrated that parachutes could be used successfully from a low height (he jumped from Tower Bridge in London) which led to their being used by the Royal Flying Corps.
In 1911, Solomon Lee Van Meter, Jr. of Lexington Kentucky, submitted for and in 1916 received a patent for a backpack style parachute - the Aviatory Life Buoy, Patent # 1192479, July 25, 1916.[13] His self-contained device featured a revolutionary quick-release mechanism—the ripcord—that allowed a falling aviator to expand the canopy only when safely away from the disabled aircraft.[14]
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) after being accidentally rammed by another German aircraft) and Fritz Rumey who tested it in 1918, only to have it fail at a little over 3,000 ft (910 m).

Post-World War I

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.[15]
An early brochure of the Irvin Air Chute Company credits William O'Connor as having become, on 24 August 1920 at McCook Field near Dayton, Ohio, the first person to be saved by an Irvin parachute.[16] Another life-saving jump was made at McCook Field by test pilot Lt. Harold H. Harris on 20 October 1922. Shortly after Harris' jump, two Dayton newspaper reporters suggested the creation of the Caterpillar Club for successful parachute jumps from disabled aircraft.
In 1924 Gleb Kotelnikov became the first parachutist to apply the soft packing of a parachute instead of a hard casing.[17]
Beginning with Italy in 1927, several countries experimented with using parachutes to drop soldiers behind enemy lines. The regular Soviet Airborne Troops were established as early as 1931 after a number of experimental military mass jumps starting from the August 2, 1930.[8] Earlier the same year, in 1930, the first Soviet mass jumps led to the development of the parachuting sport in the Soviet Union.[8] By the time of World War II, large airborne forces were trained and used in surprise attacks, as in the Battle for The Hague, the first large scale deployment of airborne troops in military history, by the Germans (whose operation failed totally)[18] and in 1941 Battle of Crete and in 1944 the Operation Market Garden, again in the Netherlands and again a complete failure but still the largest airborne military operation ever carried out.[19] Aircraft crew were routinely equipped with parachutes for emergencies as well.[citation needed]
In 1937, drag chutes were used in aviation for the first time, by the Soviet airplanes in the Arctic that were providing support for the famous polar expeditions of the era, such as the first manned drifting ice station North Pole-1. The drag chute allowed to land safely on the ice-floes of smaller size.[8]



 


 

Types of parachutes

Today's modern parachutes are classified into two categories: ascending and descending canopies. All ascending canopies refer to paragliders which are built specifically to ascend and stay aloft as long as possible. Other parachutes including ram-air non elliptical are classified as descending canopies by manufacturers.
Some modern parachutes are classified as semi-rigid wings, which are maneuverable and can make a controlled descent to break on impact with the ground.


Round types

 

Round parachutes are purely a drag device (that is, unlike the ram-air types, they provide no lift) and 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 of the resemblance. Modern sports parachutists rarely use this type.
The first round parachutes were simple, flat circulars. These early parachutes suffered from instability caused by oscillations. A hole in the apex helped to vent some air and reduce the oscillations. Many military applications adopted conical (i.e. cone-shaped) or parabolic (a flat circular canopy with an extended skirt) shapes, such as the US Army T-10 static-line parachute. A round parachute with no holes in it is more prone to oscillate, and is not considered to be steerable.
A large (3-8 mph) forward speed and steering can be achieved by cuts in various sections (gores) across the back, or by cutting 4 lines in the back thereby modifying the canopy to allow air to escape from the back of the canopy, providing limited forward speed. Modifications can skirt bow out.[clarification needed] Turning is accomplished by forming the edges of the modifications, giving the parachute more speed from one side of the modification than the other. This gives the jumpers the ability to steer the parachute, enabling them to avoid obstacles and to turn into the wind to minimize horizontal speed at jumping.



Technical or Specification
Approximate Parachute Sizes for a Rocket Weighing 120 kilograms:
Descent
Rate
Diameter
3 mps
19.37 m
4 mps
14.27 m
                                    5 mps
                                  11.42 m

6 mps
 9.51 m











The above sizes are estimates based on a parachute with a drag coefficient of 0.75.
You may use the form below to calculate the parachute size for another rocket.


Minimum height for jump: 400feet/122m above ground level
 








Ram-air (square) types

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. The first Ram-air test jump was made by Navy test jumper Joe Crotwell.




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 (risers are strips of webbing joining the harness and the rigging lines of a parachute). 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. Reducing the amount of fabric decreases the air resistance. This can be done by making the slider smaller, inserting a mesh panel, or cutting a hole in the slider.



Technical or Specification
Size Sq. m.
Length
In ft
Length in meter
Breadth in
ft
Breadth in meter
Maximum Exit Weight Recommended in kg
Aspect Ratio
17.52
21.8
6.64
8.7
2.64
85.73
2.5
19.40
22.9
6.98
9.1
2.78
94.80
2.5
22.18
24.5
7.47
9.7
2.97
108.41
2.5
24.04
25.5
7.78
10.1
3.09
117.48
2.5
25.90
26.5
8.07
10.5
3.21
126.55
2.5
27.72
27.4
8.35
10.9
3.32
135.62
2.5

SPECIFICATIONS
Max Speed
150 keas / 278 kph
Max Altitude
20000ft / 6096m A.S.L
Max Weight
250 lbs / 114 kg
Glide Ratio
3.0:1
Minimum Height for jump
800ft/243.84m
SIZE
In sq ft/m
LENGTH
Ft/m
BREADTH
Ft/m
ASPECT
VOLUME
MAX. WEIGHT
170 /15.6
19.8 /6.0
8.6 /2.6
2.3
473
    86 kg’s / 50 kg’s Student
185 /16.74
20.6 /6.2
8.9 /2.7
2.3
482
    93 kg’s / 55 kg’s Student
200 /18.54
21.45/6.53
9.33 /2.84
2.3
516
  100 kg’s / 60 kg’s Student
230 /21.28
23 /7.0
10 /3.04
2.3
580
  105 kg’s / 70 kg’s Student
260 /23.99
24.4 /7.43
10.6 /3.23
2.3
600
  109 kg’s
290 /26.91
27.6 /8.41
10.5 /3.2
2.6
627
  114 kg’s (250 Lbs)
 


                                                           

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 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 3+ 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 5-foot (1.5 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.