Editing Parachute (section)

==== Varieties ====
[[File:Ram air square.jpg|thumb|upright|A [[United States Navy]] Parachute Team "Leap Frogs" jumper landing a "square" ram-air parachute.]]

Personal ram-air parachutes are loosely divided into two varieties – rectangular or tapered – commonly called "squares" or "ellipticals", respectively. Medium-performance canopies (reserve-, [[BASE jumping|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 on the leading edge (front), and sometimes in the trailing edge (tail).

Ellipticals are usually used only by sport parachutists. They 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.<ref>{{Cite journal |last=Dhiman, Chakraborty |date=June 2011 |title=Parachute: The aerodynamic lifting and deaccelerating device |url=https://www.researchgate.net/publication/298449819 |journal=Asian Textile Journal |issue=June 2011 |pages=65–75}}</ref>

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 lower [[glide ratio]].

Wing loading of parachutes is measured similarly to that of aircraft, comparing exit weight to area of parachute fabric. Typical wing loading for students, accuracy competitors, and BASE jumpers is less than 5&nbsp; kg per square meter – often 0.3 kilograms per square meter or less. Most student skydivers fly with wing loading below 5&nbsp; kg per square meter. Most sport jumpers fly with wing loading between 5 and 7&nbsp; kg per square meter, but many interested in performance landings exceed this wing loading. Professional canopy pilots compete with wing loading of 10 to over 15 kilograms per square meter. While ram-air parachutes with wing loading higher than 20 kilograms per square meter 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.{{Citation needed|date=March 2018}}

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 {{convert|1.5|m|ft|adj=on}} tall entry gate. Current world records exceed {{convert|180|m|ft}}.

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 a small tolerance, or "sweet spot", for timing the landing flare.

Because of their predictable opening characteristics, parachutes with a medium aspect ratio around 2.1 are widely used for reserves, BASE, and canopy formation competition.  Most medium aspect ratio parachutes have seven cells.

High aspect ratio parachutes have the flattest glide and the largest tolerance 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.