PARACHUTES AND PARAFOILS
Parachutes are used as emergency lifesaving devices, to transport and
deploy supplies, equipment and people and to assist in slowing
down an object for landing. Food and medical supplies are
dropped by parachute to disaster struck areas. Parachutes are used
to drop very heavy equipment onto land and life rafts and
other survival equipment in air-sea rescue operations. Some
high speed airplanes use parachutes to slow down during landing.
During the early years of the space program, parachutes were
used to slow returning space capsules after reentering the Earth's
atmosphere. The X-38, the new escape vehicle
for the International Space Station, also uses a parachute to
assist in its reentry. Parachuting is also a sport!
Parachutes are used as emergency lifesaving devices, to transport and deploy supplies, equipment and people and to assist in slowing down an object for landing. Food and medical supplies are dropped by parachute to disaster struck areas. Parachutes are used to drop very heavy equipment onto land and life rafts and other survival equipment in air-sea rescue operations. Some high speed airplanes use parachutes to slow down during landing. During the early years of the space program, parachutes were used to slow returning space capsules after reentering the Earth's atmosphere. The X-38, the new escape vehicle for the International Space Station, also uses a parachute to assist in its reentry. Parachuting is also a sport!
You may think of a parachute as a type of flying machine, but parachutes really do not fly. Parachutes are considered "deceleration" devices. Deceleration means "to slow down". A parachute allows for a much slower and safer landing.
The first record of a parachute design was found in the notes of the famous artist and inventor, Leonardo Da Vinci. Dated 1495, Da Vinci, wrote "if a man have a tent of closely woven linen without any apertures, twelve braccia across and twelve in depth, he can throw himself down from any great height without injury." The word "braccia" comes from the Italian word for arm; so experts believe that "braccia" refers to an "arms length". Da Vinci sketched a diagram of a person floating down attached to a pyramid shaped parachute. (A pyramid has a polygon as a base and its faces are triangles - in Da Vinci"s diagram the parachute had a square base.) Even though Da Vinci's design was never built, many experts believe his parachute would have worked.
Although several individuals claimed to be the first parachutists, in 1797 thousands of people witnessed balloonist Andre Jacques Garnerin parachute from his balloon over Paris. Garnerin's silk parachute looked like a giant umbrella and was "unvented" (there were no openings or as Da Vinci advised "without any apertures"). Unfortunately, Garnerin's parachute erratically swung back and forth (oscillated) as air first spilled out of one side of the parachute and then the other. To prevent this from happening, other early parachute designers added a vent or hole at the top center of the parachute. The vent allowed some of the air to escape and reduced most of the oscillations. This made the parachute more stable (helped keep the parachute along the same path).
Parachutes were first used in balloon exhibitions. Parachutists would draw and excite crowds of people by performing stunts from an aerial balloon and then float down. At that time, people did not think of parachutes as an emergency life-saving device. The first parachute used in an emergency was in 1808 over Warsaw, Poland, when Jodaki Kuparento escaped from his burning balloon. Even with the airplane's invention in 1903 and rapid advances made in aviation before World War I (WWI), parachutes were still considered a stunt person's tool.
During World War I, balloons and aircraft were used to observe and spot artillery and troop movement of the opposite side. Early aviators from both sides were known to wave and greet one another. Unfortunately, this comradery did not last. Although balloonists who were shot down used parachutes, pilots believed that their flying machines were far superior to a parachute. It was even considered "dishonorable" to abandon an aircraft and use a parachute. Pilots were shot down and could not escaped because there were no parachutes.
Towards the end of the war, several Austrian pilots used parachutes to bail out of aircraft and were saved. Subsequently, both the Austrian and German pilots used parachutes and later the United States adopted the practice for pilots.
After the war, the United States government supported the development of the parachute. As aviation grew and planes were surplused after the war, air shows became popular as did parachuting exhibitions.
Different parachute designs were developed. As in most of engineering, these designs were used to solve a variety of problems parachutists experienced and to address different needs. These new designs made parachuting safer, strengthened the different parts of the parachute, minimized the violent oscillations parachutists experienced and allowed the parachute to open slower and reduce the sudden jerk felt by the parachutist. There were also different designs for different uses: high altitude, high speed, cargo, supplies, sport jumping. Slots and holes were added to traditional round canopies. These openings allowed air to escape through the parachute and provided more control.
One of the most important improvements was the development of the parafoil in the 1970's. You can see how different the parafoil looks. Air inflates the parafoil which acts like an airplane wing and creates lift. Even the language changed: while you "jump" with a parachute, parafoils are "flown".
Why do we need parachutes? You know that when you drop an object it falls down (towards the earth) until it hits another object in its path or reaches the ground. Have you ever dropped and broken a raw egg? Does the egg always break? If you drop an egg 1/4 inch from the kitchen counter, it probably will not break. The egg will probably not break if you drop the egg 1/2 inch from the counter. What do you think will happen if you drop the egg from 1 foot (12 inches) onto the counter or from a much taller height? The egg will break. Why does the egg break in this case and not when it is close to the counter? What's the difference?
The difference is the force or more specifically terminal velocity (the final speed) the egg has. Newton's Second Law states that:
What is mass? Mass is the amount of material an object has. In general the mass of an object does not change. What is acceleration? Acceleration is the rate of change of velocity. What exactly does that mean? Here's an example. Look at a car's speedometer. If someone is driving steadily at 30 miles/hour then they are not accelerating (speeding up) or decelerating (slowing down). If you start to speed the car up to 50 miles/hour, then you are changing the velocity and you are accelerating; if you apply the brakes to slow down, then you are decelerating. Believe it or not gravity is not really a force, it is an acceleration and on Earth it is about 32 feet/sec2.
This same science principle applies in decelerating devices like parachutes and parafoils. The parachute decelerates or slows down the fall of the object. The speed as it reaches the ground is slow enough so that the parachutists (or cargo) is not hurt or damaged.
In aeronautical engineering, different forces act on different types of air vehicles and devices. The forces of lift, drag, weight, and thrust act on an airplane in flight. These different forces all act on the airplane at the same time. Lift created by the wings keeps the airplane aloft. The thrust of the engine pushes the airplane forward. The drag caused by the air resistance tries to hold the airplane back; drag acts in a direction opposite to the flight path. The weight of the airplane pulls it towards the ground.
Because parachutes do not have an engine, there is no thrust. Also parachutes (unlike parafoils) do not create lift. Parachutes have two forces acting on them: drag and weight. The weight pushes the parachutist down, while the drag acts opposite the direction of flight (up). So even though gravity acts on an object at a rate of 32 ft/sec2, if you do not account for the drag acting in the opposite direction, you will not calculate the forces acting on the parachute correctly.
It turns out that in a free fall stable position, a parachutist reaches a terminal velocity of about 174 ft/sec or about 118 miles/hour. (This is before the parachute is opened.) This terminal velocity is reached within 12 seconds of jumping and the parachutists does not fall any faster. Once the parachute is opened, the parachutist begins slowing down. Although it will vary, ideally, the parachutist will land at about 14 miles/hour.
The main part of the parachute is the canopy - the fabric which inflates. Strong lines attach the canopy to the harness which the parachutist wears.