Parachute is a device that uses air resistance to slow the movement of a person or object, usually in a fall from a flying aircraft or any other great height. Two forces act on any falling object—gravity and air resistance. Gravity pulls the object toward the ground. But air resists the movement. Large surfaces offer the greatest resistance to the air. A parachute provides a large, resistant surface, slowing an object’s fall. In general, the larger the parachute’s surface, the more air resistance it meets and the more slowly the object falls. A parachute can also slow an object moving along the ground.
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Uses of parachutes.
One of the early uses of parachutes was to allow descent from gas-filled balloons. Since the development of airplanes, parachutes have been used for emergency jumps from damaged aircraft. They have also been used to deliver cargo. Airplanes drop food and medicine by parachute to places that cannot be reached easily by other means. Special military uses for parachutes were developed during the 1930’s. Both the Allies and the Axis powers used parachute troops, or paratroops, during World War II (1939-1945). Some landing airplanes use parachutes as brakes, as do some high-speed race cars. Parachutes are also used to recover reusable booster rockets that separate from spacecraft in the atmosphere. Today, most parachutes are used for sport jumping, called skydiving.
Parts of a parachute.
The part of the parachute that catches the air is called the canopy. For many years, parachutes had a round canopy that looked somewhat like an umbrella. Today, most canopies have a more rectangular shape. They generally measure two to three times as wide as they are deep, with a total area of around 100 to 400 square feet (9 to 37 square meters). Round parachutes, used mainly for cargo, may measure about 100 feet (30 meters) across.
The canopy is designed according to principles of aerodynamics—a branch of physics that deals with forces acting on an object as it moves through air. Internal structures called ribs give the canopy its shape. Openings allow air to flow into the canopy, inflating it.
Parachute canopies were once made of silk. But nylon, which is stronger and cheaper, has been used since the early 1940’s, when World War II interrupted the flow of silk from Japan.
The canopy is packed in a container made of heavy cloth, usually nylon. Special pins hold the container shut. The container is attached to the parachutist’s body by a harness that fits around the shoulders and legs. Straps called risers connect the harness to suspension lines, which attach to the canopy. Skydivers wear a main parachute and a reserve parachute for emergencies. The reserve parachute is usually mounted just above the main parachute.
How parachutes work.
Skydivers generally open their parachutes at about 2,500 feet (750 meters), leaving time to open the reserve parachute if the main parachute fails. The parachutist pulls a handle on the bottom of the container to bring out a pilot parachute. This parachute, which measures about 3 feet (0.9 meter) across, quickly inflates and pulls out the canopy.
A typical descent to the ground takes from one to three minutes. The parachute moves forward at about 20 miles (32 kilometers) per hour but can be made to move faster. The parachutist can pull on the right steering line to turn right and on the left steering line to turn left.
Rectangular parachutes have a greater forward speed than round parachutes and so are not easily blown backward in the wind. At landing, the parachutist uses the steering controls to pull down the back edge of the rectangular canopy. Done properly, this slows the parachute’s motion and permits a gradual, soft landing.
History.
As early as the 1100’s, the Chinese may have experimented with parachutes by jumping from high structures with rigid, umbrellalike devices. The first known parachute jump was made from a tower in 1783 by the French physicist Sebastian Lenormand. The first parachute jump from a balloon was made in 1797, and the first free-fall parachute jump from a damaged airplane in 1922.
See also Airborne troops ; Skydiving .
