Large, umbrella-like devices attached to people or other objects by ropes called shrouds and used to slow down falls to the ground from aircraft or any other great height.
A parachute is a very light, flexible device which is intended to retard the passage of an object through Earth’s atmosphere to the ground. Parachutes resemble huge umbrellas. They are most frequently used to slow the fall of a human or of other valuable objects from high-flying aircraft or from any other great height, most often ensuring a safe landing. The term “parachute” derives from a French term which means to protect one from a fall or a bad tumble.
The theory of the parachute is credited to the fifteenth century Italian genius Leonardo da Vinci. However, the first practical application of a parachute occurred in the late eighteenth century. At that time, parachutes were used for exhibition purposes in France to allow aeronauts quick descent from gas-filled balloons. By the beginning of World War I, this use had evolved into the application of parachutes as life-saving devices for emergency jumps from damaged aircraft. By the 1920’s, parachutes had become familiar devices with widespread military uses, including the dropping of airborne troops (paratroopers), weapons, vehicles, and supplies. Parachutes have developed many additional uses related to peacetime aircraft recovery and to spaceflight.
Parachute operation is based upon several simple principles of physics. Two forces act on falling objects. These are gravity (or Earth’s gravitational force) and air resistance. Gravity pulls any object initially suspended in the atmosphere downward, toward Earth’s surface. Air resistance, due to particles of matter in the air, slows a falling object’s movement. The pull of gravity is so much stronger than air resistance that the downward speed of a falling object, whether a rock or a human, is only slowed very slightly.
With two objects of the same weight, air resistance is much greater for the one which has the larger surface area. This is because objects of the same weight with large, flat surfaces, such as clay saucers, offer greater areas of resistance to the air than those with small surfaces, such as a clay brick of the same weight as the saucer. Therefore, when an object is shaped like a saucer, it falls more slowly than a sphere of the same weight.
Parachutes designed for human use are all oblate hemispheres 2 to 3 feet across when open, and of weights ranging between 22 and 30 pounds. Parachutes used to drop cargo are often 100 feet across or larger, and heavier. Parachutes used to decelerate aircraft or spacecraft for landing and recovery are even larger than this. They are also most often used in assembled groups of three or more parachutes. The most common parachute used by humans is the seat pack model associated with a seat in an aircraft. The other kinds of parachutes attach directly to the chest or the back of a wearer.
All parachutes are worn on harnesses. Each parachute harness is made up of a group of straps fitting around the shoulders and the legs of a parachutist. The parachute harness straps connect parachute and parachutist, also supporting the parachutist during descent to the ground. Straps called risers are attached to the shoulder portions of the parachute harnesses to hold the lines, called shrouds, that attach to the parachute canopy. The canopy is the umbrella-like part of the parachute. A rip cord is also attached to a harness strap, usually on the parachutist’s left side. It terminates in a ring that the parachutist pulls soon after jumping. Pulling a rip cord causes the parachute canopy and its shrouds to leave their enclosing pack. This process is accomplished by the ejection of a small parachute from the pack. The small chute opens and pulls the larger one out after it. As each canopy leaves the pack, air enters it and causes it to open. All parachutes are carefully folded before insertion into their carry packs. This careful treatment makes sure that the parachute will open properly when the rip cord is pulled by a parachutist.
The initial opening of the canopy can slow down the descent through the air so quickly that the parachutist is jerked sharply upward in “opening shock.” To reduce the extent of this opening shock and to stabilize the parachutist’s descent, manufacturers use several canopy modifications that lead to a planned canopy air porosity. Often, ribbon canopy material, having planned holes (slots), is used. These slots allow enough airflow through the canopy to reduce air resistance and minimize opening shock. They also help to minimize parachutist sway and maximize comfort during the descent. Another type, the vortex-ring parachute, is composed of four sections that rotate during the descent, functioning like a helicopter rotor to produce maximum parachute stability.
A parachute is most often made of one type of material, usually nylon, silk, cotton, rayon, or a plastic film, although mixed materials are used in some cases. The fiber is turned into cloth for canopies, cord for shrouds, and webbing for harnesses. The most important parachute construction factors include proper air porosity, adequate material strength, good aerodynamic behavior, the lightest weight possible, and easy operation. The materials experimented with and used increase as new fabrication techniques, new artificial polymers, and new fabrics develop.
Parachutes are decelerators (or air brakes) that allow parachutists to descend toward Earth at rates of 9 to 11 miles per hour, depending on the parachutist’s weight and the canopy’s diameter. All parachute jumps made from under 500 feet above ground level are very dangerous because this height does not allow enough distance and time for complete parachute opening. Even safe jumps can lead to parachutists landing with great force, due to the excessive rate of their decelerated fall, and spraining their ankles or breaking bones. This is most often true of jumps over rough terrain. Winds also add to landing dangers, because they engender sideways parachute motion through the air. The addition of this motion to air-braked fall speed causes some landings to seem like jumps from fast-moving automobiles and can cause similar injuries. It is therefore crucial that the parachutist be well trained in how to control a parachute. The other skills needed include a well-honed ability to judge the current wind speed, the altitude, the direction of sideways motion, and potential ground speed. Parachute jumping, or skydiving, nonetheless has become a popular sport that has a great many enthusiasts in Europe and America.
In skydiving, a slow-moving aircraft, cruising at a 2-mile altitude, is used as a jumping platform and skydivers often perform stunts while falling. Sport parachutes are unlike those used for simple descent. Many safety features are removed for ease in maneuvering. Also, the sport parachutes are often designed to be rotated by a control that regulates the direction of air passing through the canopy. In addition, skydivers do not pull their rip cords quickly after leaving the plane. Rather, they use an altimeter, which notes the rate of descent and indicates the last instant when the parachute can be opened safely.
In addition to the classical application of parachutes as devices to carry humans, parachutes are used to deploy paratroops in military assaults; to distribute supplies from aircraft; to slow, as needed, the rates of descent of bombs or flares; to decelerate jet airplanes during their landing; and to recover space vehicles and weather or flight recorders.
Fechet, James E., Joe Crane, and Glenn H. Smith. Parachutes. New York: National Aeronautics Council, 1942. A solid exposition of parachutes, their composition, and their uses. Hearn, Peter. The Sky People: A History of Parachuting. Shrewsbury, England: Airlife, 1990. Contains a great deal of information on parachutes, their uses, and their evolution from the early days. Lanza, Joseph. Gravity. London: Quartet, 1997. An excellent work on gravity and gravitation that also covers topics relating to parachuting. Lucas, John. The Big Umbrella. New York: Drake, 1975. A fine, brief book holding much information on parachutes, their uses, and parachuting. Poynter, Dan. The Parachute Manual: A Technical Treatise on Aerodynamic Decelerators. 4th ed. Santa Barbara, Calif.: Parachuting Publications, 1992. A useful parachuter’s manual, discussing parachutes and their aerodynamic properties. _______. Parachuting: The Skydivers’s Handbook. 8th ed. Santa Barbara, Calif.: Parachuting Publications, 2000. An interesting book on parachutes, parachuting, and sport parachuting or skydiving. U.S. Department of the Army. Organizational and DS Manual for General Maintenance of Parachutes and Other Airdrop Equipment. Washington, D.C.: Headquarters, Department of the Army, 1996. Part of an ongoing series of manuals, with clear information on parachute and other airdrop maintenance and repair.
Forces of flight