Category FLIGHT and M ОТІOIM

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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There are plans to build new supersonic passenger aircraft, but most of them are for small business jets. Any future supersonic transport will have to fly passengers farther, less noisily, and more efficiently than earlier aircraft.

Designers believe that they already know how to deal with the problems of engine efficiency, engine noise, and sonic booms. There are designs for more efficient engines that behave like ordi­nary, quieter jet engines for takeoff and climbing. At high altitude, these engines fly supersonically. This type of engine is called a variable cycle engine.

In 2003, an experimental aircraft car­ried out test flights called the Shaped Sonic Boom Demonstration. Using a Northrop F-5E fighter, scientists showed
that it is possible to make a sonic boom quieter by changing the shape of an air­craft’s nose. In the Shaped Sonic Boom Demonstration the intensity of the sonic boom was reduced by about half. Researchers are working toward build­ing an experimental aircraft incorporat­ing every known technique for reducing the intensity of sonic booms to see how quiet a supersonic aircraft can be.

SEE ALSO:

• Bell X-1 • Concorde • Future of

Aviation • Shock Wave

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The masters of vertical flight are the common housefly and the humming­bird. Both of them have remarkable flight control and are able to take off vertically and hover motionless in the air.

Most insects have two pairs of wings, but the housefly has only one pair—its hind wings have withered away to form two little stumps called halteres. The housefly flaps its wings about 200 times every second. Instead of flapping up and down, they make a figure-eight shape in the air. This directs air downward for takeoff. As the insect flies, the halteres vibrate. If the fly changes direction, the halteres’ vibration is disturbed, instantly giving the fly information about how it is moving. This helps the fly to control its flight with great precision.

Hummingbirds are the helicopters of the natural world. Most birds’ wings generate all of their lift on the down – stroke, but a hummingbird’s wings gen­erate lift on the upstroke, too. The bird’s body is tipped up so that its wings beat back and forth parallel to the ground. About three-fourths of the lift comes from the forward downstroke and the rest from the backward upstroke. To generate enough lift, the wings flap at up to eighty times a second.

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Hinged panels called spoilers on top of a wing serve the opposite purpose from flaps and slats. When a spoiler is raised, it spoils the wing’s aerodynamic shape, increases drag, and cuts the amount of lift. Spoilers are used to cut lift after an airplane has landed. They may be used to help a big, heavy plane turn. The spoilers on one wing are raised to help the ailerons.

Ailerons are panels in the trailing edge of an airplane’s wings that are used for turning the plane. One aileron tilts up, and the other tilts down. One wing produces more lift than the other and rises. The wing that produces less lift falls, and the plane rolls into a turn.

Big airliners often have two sets of ailerons. The ailerons closest to the wingtips have more leverage for rolling the plane at low speeds. At high speed, the ailerons closest to the fuselage have enough leverage to turn the plane.

At sea, the aircraft carrier proved a deci­sive weapon. In the Pacific, both sides deployed naval strike forces headed by aircraft carriers flying four main types of combat airplanes: fighters, dive – bombers, high-level bombers, and torpe­do bombers.

The first sea battle to be won by naval aircraft rather than battleships was the Battle of the Coral Sea (May 1942). At the Battle of Midway (June 1942), dive-bombers from U. S. Navy carriers destroyed four of the Japanese

Navy’s carriers. The biggest naval air battle of the war was Leyte Gulf, yet another U. S. victory in October 1944.

During the island-hopping Pacific battles, U. S. Navy and U. S. Marine Corps pilots flew hundreds of miles across the ocean to attack Japanese ships and island bases, using the speed and power of strike planes such as the P-38 and F6F to great effect. At sea, flying boats such as the Catalina proved effective. As well as attacking enemy ships and sub­marines, they located and picked up Allied pilots shot down in the water and tracked enemy battle fleets. Equally valuable were land-based reconnais­sance and submarine-hunting aircraft, such as the B-24.

The Development of Jets

Until 1944, all combat planes had piston engines driving propellers. The Germans had flown the world’s first jet airplane, the He-178, in 1939. The Me-262, the work of designer Willy Messerschmitt (1898-1978), became the first jet fighter in 1944. Two other German jets, the Heinkel He-162 and the Arado Ar-234 jet bomber, were hurried into service before German’s surrender in May 1945.

No Japanese jet plane fought in the war, although several were under devel­opment when peace came in August 1945. The U. S. Bell Airacomet and Lockheed XP-80 Shooting Star jets did not see combat, but the British Meteor jet flew its first operational missions in the summer of 1944, chasing German V-1 flying bombs.

paceflight means traveling in space. Manned spacecraft of dif­ferent kinds, from the space cap­sules of the 1960s and 1970s to the Space Shuttle, have carried people on spaceflights. Spacecraft called satellites are in flight as they orbit Earth. Space probes have visited planets such as Mars, Venus, and Jupiter, and they have even flown beyond the solar system.

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WHERE DOES SPACE START?

There are several definitions for where space begins. The atmosphere, a blanket of air around Earth, gradu­ally thins as altitude (distance from Earth’s surface) increases. Earth’s atmosphere fades away almost completely at the top of the thermo­sphere, which is about 400 miles (640 kilometers) from Earth’s surface. In terms of spaceflight, however, people define space as beginning much closer to home, either 50 miles (80 kilometers) or 62 miles (100 kilo­meters) above Earth’s surface. Space scientists and engineers refer to "entry interface" as being just over 75 miles (120 kilometers) above Earth’s surface. This is the point at which the air becomes thick enough to begin heating up a spacecraft as it returns from space.