Category FLIGHT and M ОТІOIM

Responsibility for the attacks was lev­eled at al-Qaeda, a secretive Islamist ter­rorist organization led by Osama bin Laden. U. S. President George W. Bush announced a “war on terror,” and U. S. warplanes were ordered to shoot down any hijacked airliner that might pose a danger. No-fly zones were enforced.

Some of the 9/11 terrorists had been living in the United States and had even taken flying lessons there. The 9/11 attacks led to a review of the nation’s security. Stricter antihijacking regula­tions were introduced to prevent explo­sives or weapons from being taken onto airplanes. Air marshals disguised as pas­sengers traveled on flights, ready to dis­arm potential skyjackers. Within a few weeks, President Bush had signed a new law, the Anti-Terrorism Act, giving the U. S. government increased powers.

Other suicide attacks were foiled. Later in 2001, for example, law enforce­ment agents seized al-Qaeda terrorist

Richard Reid (a British citizen), who had been planning to blow up a U. S. airliner with a bomb hidden in his shoe.

Today, passenger and baggage screening systems are provided by the Transportation Security Administration (TSA), part of the Department of Homeland Security. Under new secure flight arrangements, airlines and securi­ty services exchange information to identify all persons buying airline tick­ets, checking identities against those of known terrorists. Counterterrorist intelli­gence in the United States is spearhead­ed by the National Counterterrorism Center, which took over the State Department’s responsibility in that area.

SEE ALSO:

• Airport • Pilot

In the 1940s, some scientists believed that rockets held the key to exploring space. Much postwar space research involved testing missiles to carry nuclear weapons, and this research was carried out in secret. Although little was known about the Soviet program, American scientists suspected that Soviet rockets were bigger than those being tested in the United States, which included the Viking and WAC Corporal. In 1949, however, the United States fired the world’s first two-stage rocket, using a V-2 as the first stage and a Corporal for the second stage. This two-stage rocket was capable of reaching space.

July 1957 to December 1958 was designated International Geophysical Year. As part of this worldwide science program, the United States planned to launch the first artificial satellites into orbit around Earth. With the Cold War still at its height, there was little exchange of information between the United States and the Soviet Union. Apart from releasing some information about radio communications for con­trolling a satellite, the Soviets gave no hint of what was to come.

Finally, on October 4, 1957, Moscow announced that Soviet scientists had launched Sputnik 1, the world’s first space satellite. With Sputnik 1 bleeping its radio signals from orbit, the Soviets had grabbed the lead in the space race.

With the successful orbit of Sputnik 1, the space race between the United States and Soviet Union had begun. President Dwight D. Eisenhower sent congratula­tions to the Soviet leadership, but the success of the Sputnik program caused surprise-and dismay-in the United States, especially among space scientists.

О Sputnik missions were launched from Tyura – Tam in the Soviet Union. The launch of Sputnik 2, shown here, took place in November 1957. The spacecraft carried a dog named Laika into space.

Many scientists had attended a science symposium in Washington, D. C., the week before the launch, at which Soviet space scientists had been present. Not a hint had been given that a satellite launch was pending.

The Sputnik program was a blow to U. S. scientific prestige. Sputnik 1 was over fifty times heavier than Vanguard. Its weight, the Americans knew, must have required a powerful launch vehicle and suggested a dangerous technology gap. The Soviets were taking the lead with more powerful space rockets and, presum­ably, bigger bomb-carrying missiles.

The National Aeronautics and Space Administration (NASA) was created in 1958 to oversee a new program of U. S. space flights. Explorer and Vanguard satellites were successfully launched in 1958, showing that the United States also had a space capability, and further success soon followed.

When anything flies through air very fast, it heats up due to the increased fric­tion with the air. The higher the speed, the higher the temperature climbs. Concorde cruised at a speed of 1,345 miles per hour (2,160 kilometers per hour), or Mach 2.04. At this speed, its body and wings heated up to more than 195°F (91°C). The tip of its nose reached 260°F (127°C)-hotter than boiling water. Planes designed to fly faster than this must be made from materials that can withstand such high temperatures.

The Space Shuttle returns from space at a speed of about Mach 25. As it descends into the atmosphere, it heats up. The hottest parts of the spacecraft are the nose and the leading edges of the wings, which reach 2,750°F (1,510°C). Heat-resistant tiles and other materials are vital to protecting the Space Shuttle’s aluminum structure.

Some jet planes are able to take off and land verti­cally by swiveling their engine nozzles downward. This is called vectored thrust. Fighter planes increasingly use vectored thrust for steering. VTOL aircraft use it to generate lift. The Harrier Jump Jet uses this method.

The jet of gas from the Harrier’s engine comes out through four nozzles instead of just one. There are two noz­zles at the front of the aircraft and two more at the back. The pilot can rotate all of the nozzles together by moving one control in the cockpit. The nozzles are pointed downward for vertical takeoff, landing, and hovering, and turned back­ward for normal forward flight. They even can swivel forward a little, so the Harrier can fly backward.

When a jet plane is taking off verti­cally, hovering, or flying slowly, air does not flow around it fast enough for its control surfaces (the rudder, elevators, and ailerons) to work. The plane has to control its attitude, or position in rela­tion to the horizon, in a different way. A small amount of air from the engine is piped to small nozzles in the aircraft’s nose, tail, and wingtips. Blowing air out of these nozzles can turn the aircraft about all three axes-up and down, rolling side to side, and turning to the left or to the right.

An airplane needs big wings to produce large amounts of lift when it is flying slowly during takeoff and landing. Big wings that produce a lot of lift, howev­er, also produce a lot of drag. Excessive
drag makes the wings inefficient when the plane is cruising at high speed, because the engines have to burn more fuel to overcome it.

Designers solve this problem by cre­ating the best wings for high-speed cruising but changing their size and shape for takeoff and landing. As an air­liner prepares for takeoff or landing, flaps slide out from the trailing edges of its wings, and strips called slats slide out from the leading edges. Flaps and slats are called high-lift devices because they produce extra lift. Flaps produce more lift by making a wing bigger and more curved. When slats are extended, they make the leading edge of a wing more curved. This shape enables the wing to be tilted to a greater angle of attack without stalling. The higher angle of attack produces extra lift.

The simplest flaps hinge downward from the wing’s trailing edge. Fowler flaps slide backward and then tilt down.

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THE ANATOMY OF AN AIRPLANE WING

The front edge of a wing also is called its leading edge, and the back edge is the trail­ing edge. The measurement from the leading edge straight back to the trailing edge is the wing’s chord. The length from one wingtip to the other is the wingspan. The curvature of the top and bottom of a wing is called its camber. The part of a wing where it joins a plane’s fuselage is the wing root. A wing’s aspect ratio is a measure of how long and slender it is. A wing that has a high aspect ratio (long and slender) causes less drag, so it is good for gliding. Wings usually tilt up from an airplane’s body toward the wingtips, forming a shallow V shape. The angle of this tilt is called the dihedral, and the wing’s dihedral makes an airplane more stable.

They increase the size and curve, or camber, of a wing. Flaps are nearly always on a wing’s trailing edge, but Krueger flaps are on the leading edge.

The increased curve in the wing shape produced by flaps may cause a wing to stall and lose lift if the smooth airflow over the wing breaks away from the drooping flaps.

When a slotted flap slides out, a gap opens up between the flap and the rest of the wing. Air from below the wing comes up through the slot and flows over the top of the flap. This extra air­flow helps to stop the wing from stalling. There are also slotted slats. Air coming up through the slot from below flows over the top of the wing and

enables the wing to work safely at a higher angle of attack without stalling. A blown flap is a device that blows air from the engine over the flaps. The extra airflow produces more lift and delays stalling even more.

In May 1942, RAF Bomber Command launched its first “1,000-bomber” raid, targeting the German city of Cologne. Bombs were unguided, but aim was more accurate, thanks to the U. S.-

designed Norden bombsight. This device had a gyroscopically stabilized telescope for the bombardier to sight the target during the bombing run. The bombsight computer automatically made course corrections to ensure that the bombs were released over their targets.

The weight of bombs increased. In 1943, the first 12,000-pound (5,440- kilogram) bomb was used. The first 22,000-pound (9,990-kilogram) “grand slam” bomb followed in 1944. The size of airplanes also grew. The B-29 of 1944 was twice as heavy as the earlier British Lancaster. The B-29 could cruise at

30,0 feet (9,140 meters) during a mis­sion that might last 15 hours, driving off enemy fighters with thirteen defensive guns controlled by a computer system.

The most destructive weapons in history were the two atomic bombs dropped by B-29s on the Japanese cities of Hiroshima and Nagasaki (August 1945). The bombs destroyed the cities and killed an estimated 200,000 people.

ound is a form of energy that travels through the air as a series of pressure waves. The waves’ effect on the ear produces the sensation of hearing.

Anything that vibrates produces sound waves that spread out through the air. When something vibrates, it pushes against the air next to it and squashes the air. This pressure creates a pulse

MEASURING SOUND

The frequency of a sound is meas­ured in hertz (abbreviated as Hz).

One hertz is equal to one compres­sion per second. The human ear can hear sounds ranging in frequency from about 20 hertz to 20,000 hertz. Sounds below 20 hertz are called infrasound, and sounds above 20,000 hertz are called ultrasound.

Sound intensity is measured in units called decibels (abbreviated as dB). The quietest sound that can be heard has an intensity of 0 decibels.

A sound ten times more intense is 10 decibels. A sound 100 times more intense is 20 decibels. A sound 1,000 times more intense is 30 decibels. A whisper is about 20 decibels, while a jet engine 100 feet (30 meters) away is about 150 decibels.

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that travels away through the air. After pushing against the air, the object pulls back again before the next push. When it pulls back, it creates a region of low pressure in the air. These high – pressure pulses are called compressions, and the low-pressure regions between them are known as rarefactions. The sound waves they create are called longitudinal waves.

The distance between one compression and the next is a sound wavelength. The number of compressions that pass any point in a second is the sound’s frequency. A high-pitched whistling sound has a high frequency, or a lot of pulses per second. A deep rumbling sound has a low frequency. Frequency and wavelength are linked. As frequency increases, wavelengths get smaller.

Sound needs something to travel through. It can travel through liquids and solid materials as well as air and other gases, but it cannot travel through space without air. The speed of sound in air depends on how fast vibrations spread from molecule to molecule, and this depends on the temperature of the air. Sound travels faster in warm air than in cold air. On an average day, with an air temperature of about 59°F (15°C), the speed of sound in air is about 760 miles per hour (1,220 kilometers per hour).

Vibrations produce sound, but sound itself also can make things vibrate. We hear because sound waves enter our ears and make our eardrums vibrate. Every machine, and every part of a machine, has a resonant frequency at which it

Tympanic membrane (eardrum)

■ Sound waves

in liquid

vibrates very strongly. Engineers try to ensure that aircraft and their engines do not vibrate at their resonant frequency. This is because strong vibrations can cause damage, shake things loose, and make an aircraft very noisy.

Vibrating rotors and propellers can cause a lot of noise inside helicopters and propeller planes. The noise makes it difficult for pilots to hear messages in their radio headsets. To counteract this, pilots can wear headsets that remove unwanted sound by making more sound. The system listens to the background noise and instantly makes a copy of it with the compressions and rarefactions reversed. The compressions of one sound fill up the rarefactions of the other sound, and thus the two sounds cancel each other out.

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SEE ALSO:

• Air and Atmosphere • Communi­cation • Energy • Pressure

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Sputnik 1 weighed 183 pounds (83 kilograms), compared with the tiny U. S. satellite weighing 3.5 pounds (1.5 kilo­grams) that still awaited launch by a U. S. Navy Vanguard rocket. Soviet leader Nikita Khrushchev promised an even bigger surprise. This came on November 3, 1957, when the Russians

О The space race was a competition between two nations. When the Soviet Union sent the first person into space in 1961, the United States raced to catch up.

sent up Sputnik 2, carrying a dog named Laika. In January 1958, the United States responded by launching its first satellite, Explorer 1.

The success of the Soviet space pro­gram caused a reaction in the United States. To counter the Soviet lead in space exploration and rocketry, the U. S. government established the National Aeronautics and Space Administration (NASA) in October 1958.

The Soviets, however, continued to chalk up firsts. In 1959 their Luna 2 probe made a crash landing on the Moon. Then another Luna probe pho­tographed the far side of the Moon for the first time. Soviet cosmonauts and American astronauts were already in training for manned missions. Soviet plans remained shrouded in secrecy, however, while NASA introduced its seven Mercury astronauts to the media.

In 1961, the Soviet Union made more headlines when Yuri Gagarin became the first person in space. His Vostok space­craft was three times heavier than the U. S. Mercury capsule, in which John Glenn became the first American to orbit Earth in 1962.

Sputnik 1 was crude by modern stan­dards, but the Soviets launched the much larger Sputnik 2 on November 3, 1957. Inside that spacecraft was the first animal to orbit Earth, a dog named Laika. Sputnik 2 was not designed to reenter the atmosphere and land, so Laika died in space.

By the end of 1957 the Soviet Union was clearly the winner of the first lap of the space race. Sputnik was a political triumph, trumpeted by the Soviet Union and its supporters as a brilliant example of Communist achievement.

SPUTNIK REPLICAS

A model of Sputnik 1 was presented to the United Nations and is on dis­play at its building in New York City. There is also a replica at the National Aerospace Museum in Washington,

D. C. In 1997, to mark the fortieth anniversary of the launch of Sputnik 1, a scale model of the satellite – made by students at one-third of the original size-was launched from the Mir space station.

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Altogether there were ten Sputnik missions. Sputnik 3 (May 1958) was the Soviets’ original large science satellite. On August 19, 1960, Sputnik 5 carried into orbit two dogs (named Belka and Strelka), forty mice, two rats, and an assortment of plants. The following day, the spacecraft landed successfully with its animal and plant passengers alive and well. Sputnik 10 was the last Sputnik, in March 1961, and it also carried a dog, Zvezdochka. This final mission was flown in preparation for the first manned spaceflight by Yuri Gagarin in April 1961.

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SEE ALSO:

• Gagarin, Yuri • NASA • Satellite

• Space Race

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