Category FLIGHT and M ОТІOIM

aterials and structures are gen­eral terms used in flight. They refer to the selection of materi­als used in aircraft and spacecraft and the science of constructing the craft for endurance and safety. Together and sep­arately, the two fields are vital to aero­space engineering.

Wood and Canvas

The first aircraft were made from wood because it was light, fairly strong, avail­able, easily shaped, and easy to repair.

The Wright brothers’ Flyer airplane of 1903 was made mainly from spruce and bamboo covered with canvas.

To save weight, wings were not solid wood. Instead, they had a skeleton-like wooden frame. Long timbers called spars ran the length of the wings. Shorter pieces of wood, called ribs, ran from front to back. Fabric stretched over the ribs gave the wings their shape. Rib­and-spar construction is still used today.

About 170,000 aircraft were built during World War I (1914-1918), and nearly all of them were wooden. Most early planes had biplane wings-one wing above the other-although the first powered monoplane had flown a short distance in 1906. Some were triplanes, with three wings stacked on top of each other. The wings were connected by wooden struts and tight bracing wires that formed a strong structure.

New Materials

Aircraft engines quickly became too large, heavy, and powerful for wooden aircraft. Manufacturers looked for a stronger material that also was light and easy to shape. The first material they chose was aluminum. Aluminum is a lightweight metal that is rustproof, but it is fairly soft and weak.

In the early 1900s, a substance called duralumin was made. It was an alloy, or

О Work begins on the frame of an airship built in the 1930s. The metal ring-frames that give the nose of the giant aircraft its shape are clearly visible.

a metal mixed with other substances. Duralumin was made from aluminum with tiny amounts of copper, man­ganese, and magnesium added. When heated and quickly cooled again, it was soft and easy to bend and shape into parts for aircraft. After being shaped, the duralumin slowly hardened and strengthened over the next few days, becoming much harder and stronger than pure aluminum. This process is called age hardening, and it made dura­lumin an ideal material for aircraft. Duralumin was used to make the metal frames that gave airships their shape.

Duralumin was not perfect, however. Although pure aluminum did not corrode, duralumin did. Corrosion is a chemical reaction that eats away at

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ALLOYS

The properties of a metal can be changed by mixing other substances with it to create an alloy. Brass is an alloy of most­ly copper and zinc, while bronze is made up of copper and tin. Steel is an alloy of iron and carbon, and stainless steel com­prises iron, carbon, and chromium.

Aluminum is alloyed with other met­als to make it stronger. Today, there are dozens of different aluminum alloys for building aircraft and spacecraft. Instead of a name, such as duralumin, each alloy now has a code number that shows what it is made of and what its properties are.

For example, aluminum alloys with num­bers beginning with 2 contain copper.

If the number begins with 7, the alloy contains zinc and magnesium. Other numbers indicate different ingredients.

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a metal. The most familiar example of corrosion is iron turning to rust in damp conditions. A new material called Alclad was invented to deal with the problem of corrosion in duralumin. It was made by coating duralumin with pure aluminum. The pure metal protected the alloy.

Mitchell was promoted to the rank of brigadier general for his service in World War I. After the war, he returned to the United States as second in command of the air service. Mitchell urged research into better bombing sights, more power­ful aircraft engines, and torpedoes that could be dropped by plane. He wanted to build planes that could carry troops and to form a separate air force with an inde­pendent command. He also managed to form an aerial force to fight forest fires.

Mitchell made sure that aviation stayed in the news and in the minds of Americans. He sent his pilots on speed and endurance flights to build publicity. In 1922, Lieutenant James Doolittle became the first person to fly across the United States in less than a day. The next year, Lieutenants John Macready and Oakley Kelly made headlines by fly­ing across the country nonstop. In 1924, Mitchell sent eight airmen in four planes to fly around the world. Two of the planes crashed along the way, but two arrived back in Seattle, Washington State (their departure point), six months and 26,345 miles (42,389 kilometers) after taking off.

NASA today has ten major centers around the nation. The Kennedy Space Center at Cape Canaveral, Florida, is probably the best known. The others are:

Ames Research Center, Dryden Flight Research Center, Glenn Research Center, Goddard Space Flight Center, the Jet Propulsion Laboratory, Johnson Space Center, Langley Research Center, Marshall Space Flight Center, and Stennis Space Center. All NASA activi­ties rely on teamwork, not only among personnel at the various centers, but also between NASA and its partners in indus­try and the academic world.

Today, space is a business. The NASA launch services program based at the Kennedy Space Center offers commercial launch services from a number of launch sites. The sites include Cape Canaveral Air Force Station in Florida; Vandenberg Air Force Base in California; Wallops Island in Virginia; Kwajalain Atoll in the

О Personnel from NASA’s Jet Propulsion Laboratory prepare Mars Global Surveyor for transfer to the launch pad. NASA’s success in exploring the solar system has greatly increased human knowledge of space.

Republic of the Marshall Islands; and Kodiak Island, Alaska. To provide a range of launch options, NASA buys expendable launch vehicle (ELV) services from commercial providers—for example, Atlas rockets are built by Lockheed Martin and Deltas are built by Boeing. NASA also works closely with international partners. The Cassini spacecraft, for example, was developed by the Jet Propulsion Laboratory in association with the Italian space agency. Launched in 1997, Cassini arrived at Saturn in 2004.

NASA also carries out research into supersonic flight within the atmosphere, following up on the pioneer work done by NACA. In the 1960s, the record­breaking X-15 rocket plane soared so high and so fast that it almost became a spacecraft. Its flights provided valuable data and pilot experience for the manned space program. NASA contin­ues to research high-speed flight in the atmosphere. In 2004, the X-43A scram – jet set a new world speed record for an aircraft with an air-breathing engine, flying at ten times the speed of sound.

NASA’s long-term ambitions for the twenty-first century include sending astronauts back to the Moon and designing a mission to explore Mars. The program will involve construction

One of the more unusual facilities used by NASA is located 62 feet (19 meters) underwater. To train astronauts for NASA Extreme Environment Mission Operations (NEEMO), NASA sends them to Aquarius, off Key Largo, Florida. Aquarius is an underwater laboratory belonging to the National Oceanic and Atmospheric Administration (NOAA). Here, humans can experience life in an artificial habitat similar in many respects to being in space. NASA crews have stayed in Aquarius for between two and three weeks to train for missions to the Moon. They test techniques for commu­nication, navigation, geological sample retrieval, construction, and using remote-controlled robots. Facing these challenges in Aquarius helps NASA’s designers and engineers improve designs of habitats, robots, and spacesuits for future lunar projects.

of a new generation of spacecraft, including the Orion manned spacecraft. In addition, NASA will continue its ambitious scientific program of explor­ing the universe.

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SEE ALSO:

• Apollo Program • Astronaut

• Cape Canaveral • Kennedy Space Center • Satellite • Spaceflight

• Space Race

Many flying students start with a short introductory lesson at a flying school.

No pilot certificate or medical certificate is needed for a trial flight, but these are required if a student continues and wants to fly solo. To be certified fit to fly, a student must consult an aviation medical examiner approved by the Federal Aviation Administration (FAA). There are three classes of medical certifi­cate: class 1 for airline pilots, class 2 for other commercial pilots (anyone paid to fly), and class 3 for recreational pilots.

At first, the beginner student flies with an instructor in a two-seat plane, but does most of the actual handling of controls. The trainee pilot must obtain a student pilot certificate, issued by the FAA. Only sports pilots (flying micro­lights or similar airplanes) in the United States can fly on the basis of a motor vehicle driver license. The student pilot must pass a written test and learn to perform certain maneuvers—including takeoff and landing—before being allowed to fly solo. To gain a private pilot certificate, a person must be at least seventeen years old.

Pilots in the United States may not carry passengers unless they have a recreational pilot certificate or a private pilot certificate. Obtaining these certifi­cates can cost several thousand dollars. Flight training is usually charged by the hour, and most students need 40 to 60 hours for private pilot training. It takes less time to obtain a recreational pilot certificate, but this restricts pilots in cer­tain ways (for example, they cannot fly where communications with air traffic control are required).

Students also must pass a written exam on a computer. The FAA provides information needed to gain a certificate. Study materials include information on weather, airplane flying, glider flying, balloon flying, and rotorcraft flying. The final flight exam, or check ride, is done with an examiner and includes a ques – tion-and-answer session and a flight test lasting up to 1/2 hours.

adar is a system that uses radio waves to detect and locate objects and movement. It has become a vital tool for safety and other purposes in aviation and spaceflight.

Air traffic control systems use radar to monitor aircraft movements and guide pilots safely. They use two types of radar. Primary radar locates an air­craft. Secondary radar transmits a signal that is received by a transponder (trans­mitter responder) in the plane. The transponder responds by sending back information about the aircraft, such as its call sign and current altitude.

Airliners and other aircraft are equipped with their own weather radar. The nose of an airliner contains a small
radar antenna that scans the sky ahead of the aircraft and detects storms. Then the crew can change course as needed.

A satellite’s orbit depends on the task for which it is designed. Most satellites are launched in the same direction as Earth is spinning, and this is called a prograde orbit. To launch in the opposite direction, like throwing a ball into the wind, requires more booster power and fuel.

О A polar-orbiting satellite is prepared for launch in 2000. The satellite joined the polar – orbiting operational environmental satellite (POES) program, which provides data about the global climate and weather.

Scientists choose various orbits for their satellites, depending on the loca­tion of the launch site and the task of the satellite. Orbits fall into three types: high geostationary orbit, Sun – synchronous polar orbit, and low orbit.

A high geostationary orbit keeps a satellite always in the same position with respect to Earth. The satellite makes one orbit in the same period of time as Earth makes one rotation (23 hours, 56 minutes, 4.09 seconds). To do this, it must orbit at a height of about 22,300 miles (about 35,900 kilometers) above Earth’s surface. By orbiting in tandem with Earth, the satellite appears station­ary, or synchronous (in time), with respect to the rotation of the planet.

A Sun-synchronous polar-orbiting satellite travels above the North and South poles. It flies at a height of about 540 miles (about 870 kilometers) and passes the Equator and each of Earth’s latitudes at the same time each day. Being Sun-synchronous means the satellite passes overhead at the same solar time through the year, so it can transmit data (on weather, for example) at consistent times. Its data can be com­pared year by year.

Low-orbiting satellites fly at a height of 200-300 miles (320-485 kilometers). A low orbit requires the least rocket

power and is often chosen for observa­tory satellites, such as the Hubble Telescope. Hubble orbits Earth at a height of about 375 miles (600 kilome­ters), making one orbit every 97 minutes.

Some orbits are circular, while others are elliptical (egg-shaped). The length of time a satellite takes to make one orbit is called its orbital period.

A satellite’s initial velocity is high enough to counter the force of gravity and keep it in orbit, but friction (from Earth’s atmosphere and from the Sun’s energy) gradually slows the satellite’s speed. Its orbit begins to decay. Eventually, as the satellite descends into the thicker layers of the atmosphere, it burns up or breaks up.

Military Satellites

Military satellites include spy or reconnaissance satellites. These satellites are fitted with scanning devices and cameras that can detect objects on the ground. Some of these objects may be as small as a truck hundreds of miles below the spacecraft. Spy satellites also can detect missiles being fired. The first military satellite able to detect missile launches was Midas 2, launched by the United States in 1960. Early spy satel­lites took photographs on film that were returned to Earth in small capsules that landed by parachute. Modern spy satel­lites are equipped with digital imaging systems, and they relay their images directly from space.

A number of countries have military satellites. Military navigation satellites are used by aircraft, submarines, surface ships, and land vehicles. Anti-satellite weapons, known as “killer” or “suicide” satellites, are designed to track, locate, and destroy other satellites or orbital weapons systems.

Free-fall parachuting is best taught by an experienced instructor. After ground instruction, the first jumps are often made in tandem (instructor and student together). The tandem jump also offers a way for elderly or physically disabled people to skydive.

Most people experience fear when beginning to skydive. Training helps the beginner develop confidence before going on to practice advanced tech­niques with fellow skydivers. The U. S. Air Force Academy, for example, trains cadets for more than 33 hours on the ground before their first jump. Advanced training consists of more than 150 free fall jumps, progressing from a large (and therefore slow) canopy to a high-

performance display parachute with a vertical descent speed of 2 to 16 feet per second (0.6 to 5 meters per second). Top students may go on to jump with the Wings of Blue display team.

The history of aeronautics began long before people understood the principles of flight. The Italian explorer Marco Polo (1254-1324) was one of the first Europeans known to have gone to China. When he returned to Europe in 1295, he told stories of people who flew using giant kites. Kites may have been built in China as long ago as 1000 b. c.e. They are the world’s first aerial vehicles.

Even before Marco Polo, there were people who believed they would fly if they strapped a pair of wings to their arms and flapped like a bird. They tested their ideas by jumping from towers and mountains. Without any real understanding of lift, gravity, or the properties of air, they fell to the ground much faster than expected. Injuries and death were common.

О Samuel Perkins tested man-lifting kites for observational uses by the U. S. Army during World War I. This 1910 photograph shows five Perkins kites holding a man aloft at Harvard Aviation Field in Atlantic, Massachusetts.

One of the most famous of these early “jumpers” was Abbas Ibn Fimas (810-887 c. e.). He lived in Andalusia, now part of Spain. Firnas was an inven­tor who studied chemistry, astronomy, and physics. In 875, when he was sixty – five years old, Firnas built a glider. He made a successful flight, which was seen by a large number of people, but he was injured when the glider hit the ground. This happened about 1,000 years before modern aeronautical pioneers started making successful glider flights.

In the year 1010, an English monk named Eilmer tried to fly from the top of a tower with wings fastened to his arms and feet. Eilmer managed to glide for about 650 feet (200 meters), but he landed badly and broke his legs.

Many of the wings used by early fliers copied the wing shape or flapping action of birds’ wings. Even the great Italian artist and inventor Leonardo da Vinci (1452-1519), who drew designs for flying machines more than 500 years ago, thought the first successful flying machine would have flapping wings.

The atmosphere does not have a defined top, like the surface of land or ocean. Air becomes thinner with altitude until it is too thin to measure. Scientists chose an altitude within the atmosphere where they consider space begins. The most widely used definition for the beginning of space is 62 miles (100 kilometers) above sea level, in the thermosphere. In the United States, however, a person is defined as an astronaut when traveling above 50 miles (80.45 kilometers).

Space scientists and engineers defined the beginning of space at a dif­ferent altitude in the thermosphere. They chose an altitude of 400,000 feet (121,920 meters), or about 76 miles (122 kilometers), and they call it the entry interface. This is the altitude where the air is thick enough to begin heating up a spacecraft as it returns from space.

The air doesn’t stop suddenly at this altitude. There is still some air higher up, where spacecraft orbit Earth. In fact, there is enough air at those levels to slow down a spacecraft.

Commercial aircraft are built for strength and safety rather than speed, although many can travel at just below the speed of sound. A modern airliner can fly nonstop from San Francisco to Sydney, Australia; from Washington, D. C., to Rome, Italy; or from New York

City to Tokyo, Japan. It can cruise high above the clouds at over 600 miles per hour (965 kilometers per hour).

Most airliners have turbofan engines, powerful enough to lift a payload of 400 tons (363 metric tons) or more. Each engine of a Boeing 747, for example, generates about 50,000 pounds (22,700 kilograms) of thrust-about the same as the two engines of an F-15 fighter. Four engines provide insurance against engine failure, but modern engines are so powerful and reliable that many modern airliners, such as the Boeing 777, make do with two.

Commercial airplanes with piston or turboprop engines are still used, too. Propeller planes, although slower than jet planes, are quieter and cheaper to run. They can also take off and land from small airports.

Private airplane owners fly light air­planes, carrying between two and ten people, for business and pleasure. U. S. manufacturers, such as Beech, Cessna, and Piper, have built many of the world’s most successful light aircraft. Modern business planes, with jet engines, carry five to ten passengers, and they cruise at much the same speeds as jet airliners.