Category FLIGHT and M ОТІOIM

Date of birth: December 29, 1879.

Place of birth: Nice, France.

Died: February 19, 1936.

Major contributions: Led U. S. air forces in World War I; promoted the use of military aircraft.

Awards: Distinguished Service Cross; Distinguished Service Medal;

Congressional Medal of Honor.

he son of a U. S. senator from Wisconsin, Billy Mitchell was 18 years old and still at college when the Spanish-American war began in 1898. He immediately volunteered for the army, entering as a private. His father used his influence to gain Mitchell a commission as an officer. Mitchell was assigned to the Signal Corps, the group that sent messages from one military unit to another. In combat, the young officer showed brav­ery and quick thinking.

World War I

Mitchell remained in the army after the Spanish-American war ended. As early as 1906-just three years after the Wright brothers took the first airplane into the sky-Mitchell predicted that future wars would be fought in the air. In 1912, by then a captain, Mitchell joined the Army General Staff as the youngest officer in that prestigious unit. While in Washington, D. C., Mitchell began his lifelong mission of urging the military to develop air power.

In his spare time, Mitchell learned to fly and gained his pilot’s license. In 1915, he was assigned to the arm of the Signal Corps that was charged with developing a small air force. When the United States entered World War I in 1917, Mitchell was sent to France. He began talking to leading military figures from other nations allied with the United States who were interested in military aircraft. One of them was British gener­al Hugh “Boom” Trenchard. The general argued strongly that air power should play an important role in allied opera­tions. He is credited with advancing the

THE U. S. AIR SERVICE IN WORLD WAR I

When the United States entered World War I, its military air service was very small. The group numbered only 131 officers and about 1,000 enlisted men. It had fewer than 250 aircraft. The only manufacturing company in the country that could produce large quantities of planes belonged to Glenn Curtiss. He pro­duced many of his famous "Jenny" training planes, and they helped the war effort. However, the United States did not produce a single com­bat airplane during the war.

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role of military aircraft and in building Britain’s Royal Air Force.

Mitchell agreed with Trenchard’s ideas, and he went to work to create a U. S. air service. He began building air­fields near places where American troops were stationed. Other officers often found Mitchell’s personality to be brash and annoying, but he was deter­mined to carry out his plan.

Mitchell was put in charge of all Allied aircraft during the Battle of St. Mihiel in September 1918. Mitchell com­manded almost 1,500 planes-at the time, the largest air force ever assem­bled. In another battle later that fall, he sent massed forces of planes to carry out bombing missions.

NASA has achieved an impres­sive record of exploring the Solar System and beyond with unmanned probes, satellites, and space telescopes. In the 1970s, Pioneer 10 and 11 flew past Jupiter and Saturn. They were followed by Voyager 1 and 2, record-breaking probes that made a tour of the outer planets before eventually leav­ing the solar system. In 1976,

NASA landed two Viking spacecraft on the surface of Mars, and these landers sent the first pictures from the surface of the red planet back to Earth.

Not even NASA’s highly trained and experienced engineers are infallible, however. Sometimes spacecraft disap­pear. In 1993, the Mars Observer space­craft disappeared from tracking screens just three days before it was scheduled to go into orbit around Mars. A succes­sor spacecraft, Mars Global Surveyor, made it into orbit safely in 1998.

NASA often has proved itself adapt­able to challenges. After the Hubble Space Telescope was launched in 1990,
scientists discovered that it had a faulty mirror. NASA designed a rescue package to deal with the unexpected problem in such a costly piece of space hardware. The agency sent Shuttle astronauts to correct the fault, which they did, and Hubble began to provide Earth-based astronomers with their clearest view yet of the heavens.

As the airline industry grew in the 1920s and 1930s, barnstormers and air racers often became commercial pilots. Some of them entered the military. During World War II (1939-1945), many mili­tary pilots learned to fly straight out of college and were often pitched into combat after only a few weeks of train­ing. Fighter pilots in particular earned hero status. Most combat pilots were men, while female pilots delivered air­planes from factories and transported soldiers. After the war, test pilots broke new ground flying the jet – and rocket – powered planes of the supersonic era. Most of the first astronauts selected in the 1960s for the U. S. space program were ex-test pilots.

By the 1970s, with air traffic growing rapidly, the job of the commercial pilot became more demanding. Men still dominated the cockpit, but a few women started flying airliners. Ruth Nichols flew commercial planes as early as 1932. The first regular woman pilot for a U. S. scheduled airline was Emily Warner, who piloted Boeing 737s for Frontier Airlines in 1973. By the end of the twen­tieth century, military forces had women stationed alongside men in combat. The first American woman pilot to drop bombs in combat was Lieutenant Kendra Williams of the U. S. Navy, during Operation Desert Fox in Iraq (1998).

A few planes were built with one pro­peller at the front and another propeller at the back. They were called push-pull aircraft. The German Dornier Do-335 of the 1940s was a push-pull fighter. With one engine and propeller at the front and another at the back, it was very fast. The push-pull layout has been used in experimental aircraft, too. Voyager, the first plane to fly around the world with­out landing anywhere or refueling on the way, was a push-pull plane. It had an engine and propeller in its nose and another set in its tail. Its 25,000-mile (about 40,250-kilometer) flight took nine days in 1986.

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SEE ALSO:

• Engine • Helicopter • Thrust

Satellites vary in size from a few pounds to many tons. Some remain in orbit for only a few weeks, while others have an expected lifetime of hundreds of years. They are packed with scientific instru­ments, usually miniaturized to save weight and space. Manufacturing is closely monitored and takes place in germ-free conditions. All systems are thoroughly tested-once launched, satel­lites must continue to work under remote control for long periods of time.

SATELLITE LAUNCHERS

A satellite can be carried into space in the cargo bay of a Space Shuttle, or it may be blasted into space on top of a multistage rocket or launch vehicle. An expendable launch vehicle, or ELV, is used only once. An ELV has two or more booster stages; each stage falls away when its engine burn is completed. The final stage sends the pay­load (the satellite) into orbit.

The launch vehicle Pegasus is itself launched from beneath a converted Lockheed L-1011 aircraft. The launcher can place a satellite weighing up to 970 pounds (440 kilograms) into near-Earth orbit. Pegasus launched the Solar Radiation and Climate Explorer and the Galaxy Evolution Explorer satellites in 2003.

A larger satellite, or a satellite intended for high orbit, requires a more powerful launcher, such as a ground-launched Athena or Delta rocket. Delta rockets have launched many satel­lites since the 1960s, including TIROS, Nimbus, ITOS, and Landsat satellites. The big Delta IV can launch a payload of 50,800 pounds (23,070 kilo­grams) into low-Earth orbit.

O A huge Delta IV rocket stands at Cape Canaveral, ready to carry an observation satellite

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Most satellites are fitted with panels of solar cells that convert energy from sunlight into electricity. They use solar energy to power instruments and the communication systems that send data, such as video images, back to Earth.

A satellite is directed by remote con­trol from mission centers on the ground,
where scientists monitor its orbit, send instructions, and receive data from the satellite’s instruments. Under command from Earth, a satellite can be shifted in orbit by firing small thruster rockets.

A satellite may be in constant com­munication with mission control. If it is in a low orbit, it may be contacted only

when it passes overhead. Each pass may last just 10 minutes, but the satellite may fly by ten or twelve times a day, depend­ing on its orbit. Some satellites are visi­ble at night as they pass overhead.

A satellite that has malfunctioned, or has come to the end of its operational life, is normally shut down and then allowed to burn up as it reenters the atmosphere. Some defective satellites, however, have been picked up by Space Shuttle astronauts for repair.

Skydivers usually jump from an air­plane, although they also may leap from helicopters and balloons at various heights. A typical jump height is between 10,000 and 13,000 feet (3,050 and 3,960 meters). On August 16, 1960, Captain Joseph Kittinger of the U. S. Air Force stepped out of a balloon over New Mexico at a height of 102,200 feet (31,150 meters). He experienced a record-breaking free fall, skydiving for 4 minutes and 38 seconds before he opened his parachute at 17,500 feet (5,330 meters).

In free fall, a skydiver does not feel a falling sensation, even though speed through the air may reach 120 miles per hour (193 kilometers per hour). Skydivers do not experience the discom­fort of acceleration. During the descent, they may perform such maneuvers as turns, front and back loops, barrel rolls, and joining up with other skydivers in formations. There is a deceleration sensation when the parachute opens,

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О Members of a women’s skydiving team descend after opening their parafoils. Use of the parafoil has increased distance and maneuvering ability for skydivers.

slowing the descent to about 12 miles per hour (19 kilometers per hour).

The Parachutes

To end a dive, the skydiver first pulls out a pilot parachute. Measuring about 3 feet (0.9 meters), the pilot parachute is stored in a pocket on the harness, or rig. As this small parachute inflates in the wind, a cord known as the bridle operates the release mechanism for the main parachute and its lines. A rectan­gle of fabric (the slider) separates the

THE PARAFOIL

The invention in the 1960s of the wing parachute, or parafoil, revolutionized sports parachuting. The modern para­chute, known as a ram air wing, flies almost like a paraglider. The canopy contains seven to nine panels, or cells, open at the front so that air can enter.

The parachutist can alter the amount of air inside the canopy by twisting a handgrip. By tugging on the steering lines, the parachutist can make turns and steer toward a landing site.

parachute lines into four groups and works its way down until the canopy is fully open and the slider is just above the skydiver’s head.

A skydiver carries two full-size para­chutes, one of which is kept in reserve. The minimum safe height for opening a parachute is around 2,000 feet (610 meters). This height gives sufficient time for the skydiver to open the reserve parachute if the main parachute fails to function. Many skydivers carry an automatic activation device (AAD), which opens the reserve parachute at a safe altitude if the skydiver fails to open the main parachute. Skydivers always carry an altimeter so they know at what height to open the parachute. If the main parachute malfunctions after it has been opened, the skydiver uses one handle to discard it and pulls another

handle (on the parachutist’s chest) to open the reserve parachute.

Rectangular canopies are better than traditional round canopies for competition jumping as they are much easier to steer. A rectangular canopy will not collapse should another parachutist fly beneath it and take its air. Using these modern canopies, skydivers can fly in stacks, one above the other. An experienced skydiver with a modern parachute can fly cross-country for as much as 10 miles (16 kilometers), reach­ing speeds of up to 30 miles per hour (48 kilometers per hour) over the ground. He or she can perform dramatic maneuvers such as the swoop: a fast, downward approach before leveling off just above the ground.

eronautics is the science of building and flying aircraft. The term covers scientific study, design, and technology. It also includes the manufacture and operation of all types of aircraft, both lighter than air (such as airships) and heavier than air (such as airplanes).

Aeronautics involves a great variety of scientific and engineering disciplines. Aerodynamics and propulsion are important in aeronautics. So are materi­als, structures, control systems, and computing.

Energy from the Sun passes through the atmosphere’s layers to warm Earth’s sur­face. The surface then warms the atmos­phere. The warm air rises and draws in more air underneath to replace it. These air currents caused by the Sun and also by the spinning motion of Earth are responsible for the weather.

Some gases in the atmosphere are very good at soaking up warmth instead of letting it escape into space. These gases make the atmosphere warmer overall. The rise in temperature caused by these gases trapping heat is called the greenhouse effect, and the gases that trap the heat are known as greenhouse gases. Water vapor, carbon dioxide, and methane trap the most heat.

Without the greenhouse effect, the world would be about 60°F (33°C) cold­er than it is now. The world is gradually warming up, however, in a process called global warming. Many scientists believe this is happening because of the increase in greenhouse gases produced
by human activities. When fossil fuels such as coal and oil are burned, they release carbon dioxide, which traps heat.

Depending on how much the atmos­phere warms up, global warming could cause droughts in some parts of the world, floods in other parts, and more

BLUE SKIES AND RED SUNSETS

Air is colorless, so why is a clear sky blue? Sunlight contains all the colors of the rainbow mixed together. As sunlight streams through the atmosphere, it hits air molecules. The molecules scatter the light in all directions, but the blue part of the light is scattered more than the other colors, because its wavelengths are shorter. The sky, therefore, looks blue in every direction.

Brilliant red sunsets are also caused by light scattering. When the Sun is low in the sky just before it sets, sunlight travels more than thirty times farther through the atmosphere to reach the eyes of an observer than it does when the Sun is high in the sky. Most of the blue part of the sunlight is scattered out, leaving the red and orange parts of the light (with their longer wavelengths) to give the sunset those colors.

violent storms everywhere. If a warmer atmosphere melts the polar ice caps, the sea level could rise enough to flood coastal cities. Crops could fail in some places as the climate changes. Many people believe the effects of global warming are already being seen.

The introduction of jet planes brought about a revolution in passenger flying. The De Havilland Comet first flew in 1949 and went into service in 1952. It was followed by the Boeing 707, which could fly at 580 miles per hour (933 kilometers per hour) at 40,000 feet (12,190 meters). When the 707 entered service in 1958, critics argued that no airline would be able to fill its 130 seats. By 1969, however, the Boeing 747 was offering seats for 350 passengers.

Turboprop airliners, such as the Vickers Viscount and Lockheed Electra, proved briefly popular. Turboprop planes have gas turbine engines that turn propellers. They were slower than jets, but they were quiet and efficient. These aircraft were soon replaced, how­ever, by new medium-size jets.

The commercial aerospace industry of the late twentieth century had to

PRESSURIZED CABINS

The air is very thin at high altitudes, and early pilots flying above 10,000 feet (3,050 meters) would have needed oxy­gen tanks to breathe. A better system, introduced during World War II, was the pressurized cabin. Pressurized cabins were first used commercially in 1940, in the Boeing 307. After the war, pressur­ized cabins became standard on aircraft carrying passengers.

Commercial aircraft fly between 30,000 and 40,000 feet (9,150 meters to 12,200 meters). Whatever the temper­ature and altitude may be outside, the compressed air inside a pressurized cabin allows people to function as they would at lower altitudes. The pressurized air gives passengers enough oxygen to breathe comfortably. The introduced air system also maintains a comfortable temperature.

The pressurized air, which comes from compressors in the aircraft engines, flows through the wings to air condi­tioning units under the floor of the cabin.

It is mixed with filtered air already in the cabin (the filters trap any microbes) and is circulated in a continuous flow that dilutes odors and regulates temperature.

The air in the cabin changes every two to three minutes. In spite of the general belief that airplane air is full of recycled germs, airline passengers breathe cleaner air than most office workers.

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anticipate public demand for the future. Did passengers want cheaper fares in bigger aircraft, like the Boeing 747 and Airbus 380? Or would they pay more for the high-speed flights offered by the supersonic Concorde? The 747 won the commercial battle easily. Boeing 747s are still being built, while Concorde was retired in 2003. Only sixteen Concorde planes were ever flown commercially.

By 2000 Boeing aircraft had come to dominate the global market in com­mercial aviation. Boeing’s main rival is the European consortium Airbus Industries, a group of aerospace compa­nies that makes the Airbus family of commercial jets.

very part of an aircraft has been carefully designed by one or more aircraft designers. The materials used and the shapes of aircraft have changed over the years, but the impor­tance of design remains the same.

Four Aspects of Aircraft Design

There are four main subjects an aircraft designer must understand before an air­craft can be designed: aerodynamics, propulsion, materials and structures, and stability and control.

Aerodynamics is the scientific study of how air flows around an airplane. Propulsion is all about engines, which provide the thrust to move an airplane through the air. Materials and structures
cover what an airplane is made from and how it is built. Stability and control are concerned with how an aircraft flies and how its flight is controlled.

The shape and size of an aircraft depend on what it is designed to do. In other words, form follows function. Airliners have to be big enough to carry a certain number of passengers and their luggage. Fighter planes have to be small, highly maneuverable, and well armed. Cargo planes have to be large and pow­erful enough to carry huge weights of cargo, and they need big doors for load­ing and unloading their cargo easily.