Category FLIGHT and M ОТІOIM

A classic collection of stories from medieval times is One Thousand and One Nights. These tales from Southwest Asia relate the adventures of kings and councillors, fishermen and merchants, soldiers and slaves. In this world of magic and mys­tery, some stories involve that age-old dream of humans flying.

О By the 1800s and 1900s, science fiction had replaced ancient myths and legends about flight. Author Jules Verne described a journey to the Moon and back in From the Earth to the Moon (1865). The launch of Verne’s fictional craft (illustrated here) took place in Florida, which later became the real launch site for the U. S. space program.

MODERN MYTHS

Myths from many different cultures tell of gods who come down to Earth to meet with humans. Some people claim that these stories reveal vis­its from space travelers in ancient times and that some ancient drawings show gods in spaceships or wearing helmets. Scientists dis­miss these claims, however. Today, stories about aliens from other planets focus on unidentified flying objects, or UFOs. Since UFO sightings in Washington and Idaho gained great media attention in 1947, sightings of UFOs have increased dramatically. By the 1950s, some people were beginning to connect UFOs with religious and supernatural beliefs. Claims of UFO sightings are most common in the United States. The kinds of UFOs people report most frequently are flying saucers or moving lights.

О A photograph from the files of the Central Intelligence Agency (CIA) shows what the photographer claimed was a UFO over New Jersey in 1952.

Many UFO images appeared in the period, and there was much doubt about the authen­ticity of the images.

Even a handkerchief will act as a para­chute if strings are tied from each corner to a small weight. The idea may have struck someone far back in history. The Chinese invented the umbrella, and they may have adapted the umbrella shape to try parachuting 1,000 years ago. In around 1485, Italian artist and inventor Leonardo da Vinci drew a cone-shaped

parachute, but it is not known whether his device was ever tested.

The first parachute jumps recorded in Europe were made in 1783 by Sebastien Lenormand of France, who dropped weights and animals from a tower using a parachute that looked rather like a lampshade. In 1797, Andre Jacques Garnerin made a circular parachute of cotton cloth, from which hung a basket for a passenger. On October 22, 1797, he and his parachute were carried aloft by a balloon. Garnerin descended safely from about 2,000 feet (610 meters) above the city of Paris.

In the nineteenth century, parachute jumping from balloons became a popu­lar form of entertainment. Balloon jumper Charles Broadwick invented the first body-pack parachute in 1905. The parachute pack was fastened to the balloon by a line. As the jumper fell, the line tightened and pulled the para­chute canopy open. In 1912, Captain Albert Berry made the first parachute jump from an airplane, at a height of 1,500 feet (460 meters) above St. Louis, Missouri. Georgie Thompson, a teenager who jumped with Broadwick, was the first woman to jump from an airplane and land using a parachute, in 1913.

During World War I (1914-1918) few pilots had parachutes. Generals (and many pilots) argued that parachutes were too cumbersome. Military person­nel who went up in observation balloons did have parachutes, however, so they could leap out if their balloons were hit by enemy gunfire.

HOW A PARACHUTE WORKS

When a parachute opens, air pushes up to fill the canopy. The air acts against the force of gravity and slows the fall of the object to which it is attached. A parachute increases air resistance because it offers a large surface area that produces friction with the air. At first, friction is greater than gravity, so the parachutist slows down. When the friction decreases to the point at which it is equal to the force of gravity, the parachutist descends at a constant speed. In cer­tain weather conditions, the upward force of air may push the parachutist upward for a short time.

Pressure is the pressing effect of a force acting on a surface. Scientifically expressed, pressure is the force per unit area acting on a surface. Pressure (P) is defined as the force applied (F) divided by the area (A) of application. The equation for pressure is: P=F/A.

When a force acts on a material (solid, liquid, or gas), the result is pres­sure. The causes of pressure are as var­ied as the causes of forces. The force of a party balloon squeezing the air inside it produces pressure. The weight of a book pressing down onto a table pro­duces pressure. Oil forced through the pipes of an aircraft’s hydraulic system produces pressure. Gravity pulling air against Earth’s surface produces atmospheric pressure.

Atmospheric Pressure

Atmospheric pressure, or air pressure, can be measured in various ways. The weight of air pressing down on the Earth’s surface produces an air pressure at sea level of 14.7 pounds per square inch (psi), or about 100 kilopascals (100,000 pascals). Meteorologists (weath­er scientists) measure pressure in bars. The air pressure at sea level is about 1 bar, or 1,000 millibars. This pressure also is known as “1 atmosphere.”

Air pressure in the atmosphere falls with increasing height. Gravity pulls air against Earth’s surface. Air at Earth’s surface has the weight of all the rest of

THE BAROMETER

Atmospheric pressure is measured with an instrument called a barome­ter. The first barometer was made in 1643 by an Italian scientist named Evangelista Torricelli (1608-1647). He filled a long glass tube with mer­cury. Then he turned the tube upside down with its open mouth in a bowl of mercury. Some of the mercury ran down into the bowl, but not all of it. A column of mercury about 30 inches (76 centimeters) high stayed in the tube. Its weight was balanced by air pressure acting on the mercury in the bowl. Torricelli realized that changes in the column’s level were due to changes in atmospheric pressure. Mercury barometers work in this way.

An aneroid barometer works in a different way. It is a sealed can with some air taken out. Atmospheric pressure squashes the can. The amount of squashing changes when the air pressure changes. These small movements are linked to a needle pointing at a press scale. Because they do not need a tall tube of mercury, aneroid barome­ters are much smaller than mer­cury barometers.

the air above it bearing down on it, so the pressure is greatest here. Air higher in the atmosphere has less air from above pressing down on it, so the air pressure higher above the ground is lower. This is an important factor to consider for a person flying high in the atmosphere or going into space.

One-fifth of air, or about 20 percent, is oxygen. The thin, low-pressure air at the top of a high mountain contains the same percentage of oxygen as air near the ground, but because there is less air at high altitude, there is also less oxy­gen. The human body is very sensitive to sudden, even small, changes in pressure. Going up a tall building in a fast eleva­tor can make someone’s ears pop. The shortage of oxygen in low-pressure air at high altitudes can cause more severe effects. When people go higher in the atmosphere, they may experience a vari­ety of problems due to low air pressure.

Mountain climbers can suffer headaches, nausea, and dizziness when at altitude.

Controlled spaceflight needs a rocket in which the power can be varied and turned on and off. Liquid-fuel rockets can be controlled in this way. Liquid-fuel rockets are more complicated than solid rockets, because piping, valves, and pumping systems are needed to move the liquid propellants from their storage tanks to the engines. A type of kerosene called RP-1 (Refined Petroleum-1) is a commonly used liquid rocket fuel.

Unlike RP-1, some liquid propellants have to be kept very cold. Hydrogen and oxygen are common rocket propellants. They are normally gases, but they can be packed into very small tanks by chang­ing them into liquids. Hydrogen becomes liquid below a temperature of -423°F (-253°C). Oxygen becomes liquid
below -298°F (-183°C). Liquid oxygen also is called LOX. Propellants that have to be kept super-cold are known as cryo­genic propellants. They are not suitable for most military rockets and missiles because it is difficult to keep them sufficiently cold for long periods, and military equipment always must be kept ready to use. Instead, cryogenic propel­lants are used for civilian spaceflight, such as the Space Shuttle missions, because they are highly efficient, yield­ing a lot of power per gallon.

Some small rockets use propellants that ignite as soon as they meet. These are called hypergolic propellants. Rocket engines that use hypergolic pro­pellants can be very simple and reliable, because they do not need complicated ignition systems. Small rockets called thrusters use hypergolic propellants.

Strange materials have been used as rocket propellants. The Mythbusters tele­vision program, which aims to prove or disprove myths, built a working rocket fueled by a salami. SpaceShipOne, the first privately funded manned space

plane and winner of the Ansari X-Prize, burns rubber as its fuel. The rubber is solid, and the oxidizer, nitrous oxide, is liquid. A rocket like this, with a mixture of solid and liquid (or gas) propellants, is called a hybrid rocket.

Sikorsky struggled during his first few years in the United States. In 1923, with the assistance of several other Russian exiles, he formed Sikorsky Aero Engineering Company to build airplanes.

Within a few years, Sikorsky was build­ing successful aircraft again. His S-29 carried fourteen passengers. With two engines, it could reach a speed of 115 miles per hour (185 kilometers per hour). Sikorsky gave it an all-metal body.

Sikorsky’s company also produced the S-38, a ten-seater that could land on water. Pan American Airways bought several of these planes as the airline began to build its network, providing an air service to South America. Sikorsky based his company at Stratford, Connecticut. He became an U. S. citizen when he was naturalized in 1928.

Sikorsky ran into problems in 1929. He had built and sold several expensive planes, called “flying yachts,” to wealthy businessmen. The planes were not all paid for when, in October 1929, the stock market in New York City crashed.

Most of Sikorsky’s customers lost their fortunes when the stocks they owned plunged in value. As a result, many of the buyers did not make their promised payments. Losing money, Sikorsky sold out to the United Aircraft Corporation. Sikorsky continued to produce planes for Sikorsky Aircraft, which has remained part of what is now United Technologies Corporation (UTC).

Sikorsky’s next achievement was one of his most impressive. In 1931, the company launched the S-40, or the American Clipper. This large flying boat carried four engines. Pan American bought the planes and, by the late 1930s, was using Clippers to provide air service across both the Pacific and Atlantic oceans.

erodynamics is a branch of sci­ence that deals with the behavior of moving gases and how they affect objects passing through them. Designers use their knowledge of aero­dynamics to make aircraft and rockets the right shape.

The word aerodynamics comes from two Greek words. The first word, aer, means “air.” The second, dunamis, means “force.” Aerodynamics, therefore, means “force from air.”

Aerodynamic Force

When an object moves through air, it generates aerodynamic force. The size and direction of the force depend on the size, shape, and speed of the object.

The level of force also depends on the physical properties of the air, such as its pressure and temperature.

It does not matter whether it is the object that is moving or the air that is moving. Air flowing around a stationary object generates aerodynamic force, too.

A kite flies because of the force gen­erated by the wind blowing around it. The aerodynamic force that acts on a kite has two parts. These parts are called lift and drag. Lift takes the kite upward, and drag pulls it backward in the direc­tion that the wind is blowing. The kite does not fly away because these forces

О Two aerodynamic forces operate on a kite as it moves through the air. The movement creates lift, which raises the kite up, and drag, which pulls the kite back.

are balanced by the tension in the kite string. Kites often have a long tail. The tail has a purpose-it is there for aero­dynamic reasons. The drag it creates keeps the kite facing in the right direction.

Airplanes also generate lift and drag when they move through air. Lift oper­ates at right angles to a plane’s direction of flight. When the plane is flying straight and level, the lift generated by its wings acts straight upward. Drag operates in the opposite direction to a plane’s motion. When the plane is flying straight and level, therefore, drag pulls backward.

Two other forces act on every pow­ered airplane. First, thrust generated by its engines pushes the plane forward. Second, the plane’s weight pulls the plane downward. For an airplane flying straight and level at a steady speed, these forces are perfectly balanced.

A pilot begins a turn by operating the plane’s ailerons. The aileron panels work by tilting up and down. As the aileron in one of the wings tilts up, the aileron in the other wing tilts down. When an aileron is tilted up, it makes its wing lose
lift (the aerodynamic force that pulls it upward), and the wing tips down. In the other wing, the aileron that is tilted down creates more lift, and so the wing rises. The aircraft banks (rolls over to one side) like a bicycle leaning into a turn.

When an airplane flies straight and level, the lift produced by its wings acts straight upward. When an aircraft banks, the lift’s direction tilts with the plane. It acts upward and also to one side. It is this sideways part of the force that pulls the airplane around into a turn.

Using the ailerons alone, however, is not enough to make a smooth turn. The rudder has to be used, too.

Before takeoff a pilot completes a flight plan. This shows the flight as stages, or sectors. It lists details of aircraft type and registration, speed in knots (nautical miles per hour), height, wind speed, fuel consumption (in hours and minutes), number of passengers, and estimated
time for the flight. It indicates whether the pilot will be using visual flight rules (VFR) or instrument flight rules (IFR). The plan always allows for an aircraft to have some fuel in reserve, and it

includes details of alternate landing fields in case of emergency.

This flight plan goes to control cen­ters along the planned route. Flight plans are usually required for all flights using IFR. For VFR flights, they are optional (although recommended) unless an airplane is crossing national borders. Air traffic controllers enter flight plans into the FAA computer, which generates a flight progress strip. The strip is passed from center to center along the route and contains all the data needed to track the aircraft.

After an aircraft has been given clearance to take off, it is directed away from the airfield onto an outgoing route, safely clear of all other planes. A transponder on board picks up radar sig­nals from the ground and relays back flight details, which appear alongside a “blip” on the controller’s radar screen. During the flight, an airplane’s progress
is followed by a minimum of two traffic controllers in each sector of ARTCC air­space. Pilots and controllers exchange information during the flight, in case a change of plan is necessary to avoid bad weather, air turbulence, or possible congestion around an airport.

Most aircraft used by the U. S. military today are jet planes. There are super­fast spy planes-the Mach 3 SR-71A, for example-and enormous cargo planes designed to carry heavy loads, such as the C-5 Galaxy. Not all military aircraft need pilots. Drones, or unmanned air vehicles, are directed from the ground.

The main strike force of an air force is its bombers. The U. S. Air Force has the B-52, B-1B, and B-2 “stealth” bomber. Some planes designated as fighters, such as the F-117, are in fact ground attack aircraft that drop guided bombs and other weapons. Another effective air­craft is the A-10 Thunderbolt, which is heavily armed to support ground troops.

Electronic warfare planes can jam enemy communications and defense systems. Planes called Airborne Warning and Control Systems (AWACS) act as air­borne command centers.

The fastest planes now in service are multipurpose airplanes such as the F-15 Eagle, first flown in 1972 to combat the Soviet MiG-25. A recent version is the F-15E, which weighs 81,000 pounds (36,775 kilograms). The F-15 flies at 2.5 times the speed of sound and carries bombs, electronic jamming devices, guns, and guided missiles of various kinds.

Instead of weaving about the sky in dogfights like a World War II pilot, the modern pilot fights at long range. A mil­itary airplane is flown with the aid of computers. A visual display gives pilots a virtual reality image of the sky or battlefield and helps them detect and aim missiles at a target many miles away.

Most airplanes leave a radar trace, especially at very high speed. To evade radar, warplanes can fly at low levels to slip under the radar screen. Some high-tech aircraft, known as stealth planes, are designed to have a reduced radar profile, making them almost invis­ible to a hostile radar tracking system.

When their flight is announced, passen­gers make their way to one of the num­bered boarding gates. From the gate, most passengers walk directly to the air­plane doors along an enclosed bridge. At small airports, they may walk across the apron and climb steps to enter the cabin.

After all the passengers are seated on board, the pilot waits for air traffic control to give the signal for takeoff. When told to move into position, the pilot uses lanes called taxiways to move the plane from the airport terminal onto the runway.

As one aircraft takes off, another is usually preparing to land. Once a plane has landed, it moves off the runway onto the loading apron to unload its passengers and cargo. Passengers collect their bags from a baggage reclaim area, where the bags from each flight are delivered on conveyor belts.

Before leaving the airport, passengers who enter a country on an international flight must go through the additional step of being cleared through immigra­tion and customs. These government departments control the movement of people and goods into their countries.

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SEE ALSO:

• Air Traffic Control • Aircraft,

Commercial • Pilot

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