Category FLIGHT and M ОТІOIM

Such attacks highlighted a new threat to air travel and the need for tighter securi­ty at airports. The Hague Convention of 1970, an international agreement signed by more than 130 nations, was drawn up to combat skyjacking and stop terrorists from escaping to “friendly” countries.

From 1973, the Federal Aviation Administration in the United States has required all airlines to screen passengers and their baggage to prevent people from carrying weapons-or objects that might be used as weapons-onto flights. Airports tightened security procedures, especially at check-in and during bag­gage handling. Armed guards, called sky marshals, traveled on some flights.

When an airplane is hijacked, mili­tary craft may escort it to a landing field
agreed to by the authorities. After it has landed, troops and police will surround the hijacked aircraft while skilled nego­tiators try to talk the skyjackers into releasing the hostages and surrendering. Armed assault also may be used. In 1976, following the hijacking of an Air France flight, Israeli commandos flew in to attack the Palestinian hijackers, who were holed up at Entebbe Airport in Uganda, Africa. The commandos rescued more than 100 hostages. In most hijack­ing situations, however, airport and law enforcement agencies usually try to avoid a gun battle, which risks injuring or even killing innocent hostages.

Skyjacking incidents decreased in the United States during the 1980s and 1990s, but violent terrorist incidents continued to take place in other parts of the world. Some of these skyjackings resulted in airplanes crashing. In 1996, a stolen Ethiopian airliner crashed into the Indian Ocean. About fifty passengers

managed to survive, but the crash killed 125 of the people onboard.

NASA provides up-to-date information on its current space probe missions through its Web sites. The Jet Propulsion Laboratory provides updates on missions in progress and on future missions. NASA’s Web sites also display the latest photos taken by space probes.

Robot probes will continue to play an important part in twenty-first-century

space exploration. Some already have set out on their long journeys. The Messenger probe left Earth in 2004 and will arrive at Mercury in 2011. The New Horizons probe, launched in 2006, should reach Pluto in 2015.

Space probes continue their journeys into infinity, long after they have ceased to communicate with Earth. Scientists calculate that by the year 34,593, Pioneer 10 will have reached a star called Ross 248, 10.3 light years distant from Earth.

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The Soviets had been developing power­ful rocket motors for some time, and they originally had hoped to launch a large satellite packed with scientific instruments. They scaled down their plan when they learned how small Vanguard was (the U. S. satellite weighed only 3.5 pounds, or 1.5 kilograms).

To ensure success, the Soviets opted to start by launching Sputnik 1, an “artificial moon” simpler and smaller than their science satellite, but still much bigger and heavier than its U. S. rival. Soviet space scientists were confi­
dent of putting this small satellite into orbit, even if its scientific value would be limited.

Sputnik 1 was designed and built in conditions of great secrecy by a team of Soviet scientists and engineers led by Sergey Korolev (1907-1966), chief designer of the Soviet space bureau. Korolev had helped design the long – range ballistic missiles from which the R-7 satellite launcher rocket was devel­oped. After successful R-7 test flights in the summer of 1957, a modified version of the R-7 was prepared to launch Sputnik 1 .

It is easy to tell if a plane is flying faster than sound because a supersonic plane makes a telltale boom as it flies past. The sound of an aircraft travels away from it in all directions through the air. Sound
travels faster than a subsonic plane, so a plane such as a jumbo jet can be heard coming before it passes overhead. A supersonic plane flies faster than its own sound, so it passes silently overhead before its sound arrives.

Supersonic aircraft compress, or squash, the air ahead of them, producing a high-pressure wave called a shock wave. Several shock waves form on var­ious parts of the aircraft. As a plane nears the speed of sound, a shock wave forms in the middle of each wing. The shock wave forms over the wing first because the air flowing over the top of the wing speeds up. The speed of the wing relative to the air is therefore high­er than the speed of other parts of the
aircraft relative to the air. So even when a plane is flying just below the speed of sound, the tops of its wings may be supersonic relative to the air, and that is where the first shock waves appear.

The biggest shock wave forms on an aircraft’s nose. It makes a cone shape, with the aircraft’s nose at the cone’s tip. This shock wave spreads out into the surrounding air and travels all the way down to the ground. As it sweeps across the ground, the sudden change in air pressure it causes sounds like a boom to anyone below the shock wave.

The intensity of this sonic boom depends on an aircraft’s altitude. The higher it is, the more time the shock wave has to spread out into the sur­rounding air, reducing its intensity. A supersonic plane flying at an altitude of more than 35,000 feet (10,700 meters) makes a loud, thunderlike sonic boom. The same plane flying at the same speed, but at an altitude of less than 10,000 feet (3,050 meters), produces a sonic boom powerful enough to shatter windows. For this reason, Concorde was only allowed to fly at supersonic speeds when at high altitude and over water.

When something falls through the air toward the ground, the force of gravity makes it accelerate. As it accelerates, the drag (air resistance) it experiences increases. If it falls for long enough, its weight is exactly balanced by drag, and it stops accelerating. This velocity is called its terminal velocity.

A large but very light object, such as a feather, reaches its terminal velocity very quickly. A heavier object of the same size has a higher terminal velocity, because a higher speed is needed to cre­ate enough drag to balance its weight.

In the usual skydiving position­falling with arms and legs held out-a skydiver’s terminal velocity is about 120 miles per hour (195 kilometers per hour). With arms and legs pulled in, however, there is less drag, and the skydiver accelerates. Terminal velocity increases to about 200 miles per hour (320 kilo­meters per hour) before weight and drag are once again balanced.

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SEE ALSO:

• Gravity • Laws of Motion

• Relativity, Theory of • Skydiving

• Speed

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Awing, or airfoil, is a surface that produces a lifting force when it moves through air. A flat surface creates lift if it moves through air at the correct angle, like a kite. A curved sur­face produces more lift and less drag.

Wing Shapes

Most aircraft wings are curved on top and flatter underneath. Fixed-wing air­craft generally have one of four types of wing: straight, swept, delta, or swing. Small, slow airplanes usually have wings that stick straight out from the sides of the plane’s body, or fuselage. Straight wings are not suitable for high­speed flight, because they create too much drag. Wings that are angled back­ward, called swept wings, are better for high-speed aircraft, such as jet airliners. A delta wing is a triangular wing that
is very efficient for supersonic flight. It produces little lift at low speeds, how­ever, so delta-wing aircraft have to take off and land faster than other aircraft, and they are not very maneuverable. One solution is to fit the plane’s nose with small, movable wings called canards. The canards create more lift and swiveling them makes the plane react faster during maneuvers.

A few planes have swing wings, which are straight at low speeds and swept back at high speeds. Their wings actually move, swinging backward as a plane accelerates. This is called variable geometry, or swing-wing technology. These planes are rarely built, however, because the swing-wing mechanism is heavy and complicated.

In September 1940, the German Luftwaffe switched its attention to bombing British cities, beginning the Blitz. The British retaliated by bombing the German capital of Berlin. These offensives were the start of a strategic bombing war.

The Germans did not have a heavy bomber. Lacking a first-class bombsight to help them bomb from high altitudes, German designers had been told to give all bombers a dive-bombing capability so they could dive low over their targets for accuracy.

Dive bombers attacked in a steep dive; the pilot released his bomb above the target and zoomed away to avoid the explosion. Dive bombers were good at attacking ground targets, such as airfields, and enemy ships; the German Ju-87 Stuka was widely used for this.

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This bomber’s weakness was its relative­ly slow speed, which made it vulnerable to fighters.

The British and the Americans were building four-engine heavy bombers, such as the Lancaster, Halifax, B-17, and B-24. From the time the United States joined the war (after the attack on Pearl Harbor in December 1941), these bombers played an important role in Allied offensive strategies.

The worst skyjacking in history hap­pened in the United States in 2001. On the morning of September 11, nineteen terrorists hijacked four U. S. airliners: American Airlines Flights 11 and 77 and United Airlines Flights 93 and 175. Flights 11 and 175 had taken off from Boston, Massachusetts; Flight 77 left from Dulles Airport in Washington, D. C.; and Flight 93 departed from Newark, New Jersey. The first three airplanes were on early-morning flights to Los Angeles, California; the fourth was heading for San Francisco, California.

Two of the hijacked planes (Flight 11 and Flight 175) were deliberately flown into the twin towers of the World Trade Center in New York City. Flight 11 hit the North Tower just before 8:45 a. m. Flight 175 hit the South Tower at 9:03 a. m. Both 110-story structures became fiery infernos, pouring black smoke into a blue sky, before collapsing to the ground. At 9:40 a. m., Flight 77 was flown into the side of the Pentagon in Washington, D. C.

On Flight 93, the hijackers-who had smuggled knives onboard-had locked themselves in the cockpit and headed the plane toward Washington, D. C. Flight 93’s passengers learned from cell

О Terrorists flew an airplane into the Pentagon building in Washington, D. C., as part of their skyjacking operation on September 11, 2001.

phone calls to friends and relatives what had happened to the other three planes. They decided to attack the hijackers. The plane went out of control and crashed near Shanksville, Pennsylvania.

Every person onboard the four hijacked airplanes, including the hijack­ers, was killed. Furthermore, many more people were killed on the ground in New York City and Washington, D. C. The total death count was 2,752 at the World Trade Center, 189 at the Pentagon, and 44 in Pennsylvania.

he space race was a period of rivalry between the United States and the Soviet Union during which the two nations competed in the exploration of space. The race was at its height in the 1950s and 1960s.

The Cold War

The space race had its origins in the Cold War, a time of mutual suspicion between the United States and the Soviet Union that began after World War II (1939-1945). The hostility resulted from the deep divide between two political systems: Soviet communism and U. S. capitalism, or free enterprise. The two nations became the world’s military super-powers, each building up huge stocks of weapons, including rockets.

In 1945, after Germany’s defeat in World War II, both the United States and the Soviet Union acquired German rock­et technology. The German V-2 rocket could fly faster than sound and reach a height of 60 miles (96 kilometers). German scientists were taken to the Soviet Union and the United States, where they worked on more advanced rockets for their adopted countries.

On October 4, 1957, the rocket carrying “Elementary Satellite 1,” or Sputnik 1, took off from the desert near Tyura-Tam, in what is now the Kazakh Republic. All went well, and the first radio signals from space told the waiting Soviet sci­entists that Sputnik 1 was in orbit. They announced their success to the world, and almost every newspaper, radio, and television network carried the story. Sputnik 1 was headline news. Astronomers trained radio telescopes on the tiny satellite. Amateur radio enthu­siasts in many countries picked up the satellite’s “beep beep” radio signals as it passed overhead.

Sputnik 1 had a brief working life, but its historic flight proved that a human-made craft could survive launch and fly in orbit. The scientific data gath­ered from the flight was limited, but Sputnik 1 did help to identify the density of the layers in the upper atmos­phere and provided useful information on how radio signals from space were received on Earth.

Scientists had feared that space dust or meteoroid impact might damage the spacecraft. Even a minute hole in the satellite would have caused a detectable drop in pressure and temperature. However, Sputnik 1 continued to orbit Earth undamaged. The spacecraft’s radio batteries ran out before the end of October, after which no more signals were received. The satellite stayed in orbit until January 1958, when it burned up as it reentered Earth’s atmosphere, having traveled about 37 million miles (60 million kilometers).