Category FLIGHT and M ОТІOIM

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.

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.

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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When researchers found it difficult to accelerate experimental aircraft through the sound barrier, they looked at the shape of the airplane’s wings. As a normal wing nears the speed of sound, a high-pressure shock wave forms on top

of it. This causes drag, which makes it difficult for an aircraft to go faster with­out using a lot more engine power. It also makes an aircraft harder to control.

Simply by changing the shape of the airfoil, the shock waves can be made smaller. Airfoils changed in this way are called supercritical wings. In a supercrit­ical wing, the upper surface is flattened

The high-pressure air below a wing tries to flow around the wingtip into the low – pressure air above the wing. This makes the air spin off the wingtips and trail behind the plane. The spinning trails are called vortices. The vortices behind a big airliner are powerful enough to flip over a small plane flying behind it. Wingtip vortices also cause extra drag. Some air­planes have wingtips that are specially shaped to reduce the drag caused by vor­tices. Many aircraft use turned-up wingtips called winglets for this purpose.

A few planes have been built with wings that sweep forward to increase maneuver­ability. The first forward-swept wing airplanes were built in the 1940s, but their metal wings could not be made stiff enough, and so they bent. When new materials such as carbon fiber were developed, designers looked at forward-swept wings again. An experimental jet-powered aircraft with forward-swept wings, the Grumman X-29, was built in the 1980s. In Russia, the manufacturer Sukhoi has produced an experi­mental forward-swept wing supersonic fighter, the Su-47 Golden Eagle.

The Wright brothers solved the problem of how to steer a plane by making its wingtips bend, which is called wing warping. By twisting the wingtips on one side of the plane in one direction and the wingtips on the other side in the opposite direc­tion, more lift was produced on one side and less on the other side, so the plane rolled into a turn. Since then, most airplanes have used ailerons instead of wing warping.

Today’s designers are still working on flexible wings, however. They now are called aeroelastic wings. The X-53 is an experimental plane with flexible wings. When wings bend, the result is usually more drag, which is not wanted. The X-53’s wings and the positions of its flaps and ailerons have been designed so that when the wings bend, the result is more lift. One advantage of flexible wings is that they can be up to one – fifth lighter than stiff wings. Flexible wings may enable future aircraft to burn less fuel, carry heavier cargo, or fly farther.

and the curve at the trailing edge is increased. Planes with supercritical wings can go faster with less engine power. Although supercritical wings were developed for supersonic aircraft, they also can produce a lot of lift at low speeds, so they are used by cargo aircraft. The extra lift is good for getting heavy loads off the ground at low speeds.

The V-1 was one of several innovative weapons developed by the Germans. These included the V-2 ballistic missile, anti-aircraft missiles, guided bombs, and the rocket-powered Me-163 interceptor, capable of speeds of 620 miles per hour (1,000 kilometers per hour). The Dornier Do-335 Pfeil “Arrow” was a twin-engine fighter, with one propeller in its nose and another in its tail. This unique air­plane was almost as fast as a jet, but only a handful reached the Luftwaffe before the war ended.

The Germans were the first to use remote-guided rockets, in 1943, firing HS-293 missiles against British ships

KAMIKAZE MISSIONS

As the war swung against Japan, the nation resorted to kamikaze attacks, which started in October 1944. The word kamikaze means "divine wind." Volunteer pilots crash-dived their planes packed with explosives onto U. S. Navy ships, killing themselves and creating as much destruction as possible. Japan even built a rocket-powered suicide plane, the Ohka, which was launched from a carrier plane. An estimated 3,000-4,000 pilots flew kamikaze missions for Japan, sink­ing between thirty and eighty U. S. ships and damaging many more.

in the Atlantic Ocean. Similar radio – controlled missiles, air-launched from Dornier 217 bombers, sank the Italian battleship Roma following Italy’s surren­der to the Allies in 1943.

The Japanese proved resourceful in building robust fighting airplanes, such as the Mitsubishi Zero. The Japanese, like the Germans, had no long-range heavy bombers, but in 1944 they did attack the West Coast of the United States by flying balloons carrying small bombs across the Pacific. About 9,000 balloons were launched; around 1,000 reached the United States, causing 285 recorded incidents and six deaths.