Category FLIGHT and M ОТІOIM

A new aircraft must satisfy a particular need. Designers could produce all sorts of amazing designs for new aircraft, but if the aircraft are not needed, airlines or air forces will not buy the planes. The design for the Boeing 747 jumbo jet, for example, was produced when Pan American Airlines expressed a need for a new airliner that could carry up to 400 passengers.

In the early years of aviation, aircraft were built from very accurate drawings on paper. There was a drawing for every part of an aircraft and more drawings to show how they fit together. Every design goes through many changes before an airplane is built, and, before computers, every change needed new drawings. When the Boeing 747 was designed in the 1960s, 75,000 drawings were needed!

FLOATING AIRCRAFT

Some aircraft designs are very pop­ular for a while, and then they disappear. Between the 1920s and 1940s, there were a lot of seaplanes, or aircraft that can land on water. Many seaplanes land and rest on floats on the water. A flying boat is a seaplane with a watertight hull, like a boat. These aircraft were popular in the period when there were few runways, especially outside Europe and the United States.

The big flying boat airliners disappeared because they could not match the new generation of airliners that came along after World War II (1939-1945), such as the Lockheed Constellation. Small seaplanes are still used today in places such as northern Canada and Alaska. In these remote places, with a lot of water to land on and few runways, seaplanes still offer the best way of getting around.

О Researchers at NASA’s Langley Research Center in Hampton, Virginia, test the prototype X-48B aircraft in a full-scale wind tunnel in 2006.

to do some of the testing that actual models were used for in the past. Computer programs, for example, can simulate (or copy) the effect of air flowing around a plane. Computers cannot test everything, how­ever, so wind tunnel tests with models are still carried out. Sometimes a new design is so different from existing aircraft that the only way to find out if it really works is to build it and fly it. In the United States, a series of experimental planes, or X-planes, have been built to test new aircraft designs of all sorts. The X-1 was the first supersonic airplane. The X-plane series also includes the X – 15, a rocket-powered space plane, and the X-45, a plane without a pilot.

Eventually, a prototype is built for all new aircraft, experimental or not. Every new design for an aircraft must undergo a series of test flights before it is deliv­ered to the buyer. Designers have to make sure that the aircraft flies exactly as they intended. Flight tests for the Boeing 747 jumbo jet used five aircraft for ten months. They were in the air for more than 1,500 hours.

When an airplane is designed and manufacturing begins, the design process does not stop. The first Boeing 747, the 747-100, went into service in 1970. By that time, work had already begun on a new jumbo jet, the 747-200. This model could carry more fuel and fly farther. The revised model led to the 747-300, which could carry more passengers. Then the biggest and most powerful 747 of all, the 747-400, was developed. There were cargo-carrying versions of the 747, too. In total, fifteen designs of the 747 have been built.

Meanwhile, in 1913, the British news­paper the Daily Mail had offered a large cash prize to the first person or team to fly a plane across the Atlantic Ocean. Efforts to win the prize were interrupted by the war, but pilots became interested again when the war was over.

Alcock-now out of the service – hoped to win the prize. In 1919 he contacted Vickers, a British aircraft company, to enlist its support. Vickers officials agreed to supply an airplane. Soon after, Arthur Brown visited the Vickers offices looking for a job. He agreed to join the venture as Alcock’s copilot and navigator.

Vickers chose the Vimy aircraft for the flight, an airplane the company

had designed as a bomber for use in the war. Vickers gave Alcock and Brown the thirteenth Vimy it had made.

The Vimy was a biplane made most­ly of wood with fabric covering the wings and body. The airplane was about 55 feet (17 meters) long and had a wingspan of 68 feet (20.7 meters). The Vimy carried two engines, made by automaker Rolls-Royce, that could fly for about 100 hours without needing service. These highly reliable engines were one reason the Vimy was selected for the trip.

The team made three adjustments to the plane. All military equipment was taken off, and extra fuel tanks were
added. In addition, the cockpit was widened so Alcock and Brown could sit side by side.

After some test flights, the plane was partly taken apart to be shipped to Canada. There, it was reassembled and made ready to fly, but Alcock and Brown had to wait through a period of poor weather before beginning their journey. On June 14, 1919, after several days of rain and snow, the men finally took off. They left from an airfield near St. John’s, Newfoundland and carried

coffee, sandwiches, and candy for refreshment and toy cats as mascots.

The first living creature in space, the dog Laika, was put into Earth orbit in November 1957 by the Soviet Union. The Soviets then startled the world on April 12, 1961, by putting the first per­son into orbit. He was Yuri Gagarin, a pilot with the Soviet air force, and his spacecraft was Vostok 1. Although Gagarin made only one orbit, lasting 108 minutes, the mission’s impact was enormous. Gagarin was greeted as a hero after his historic flight, and the world became excited by the possibility of astronauts flying, not just around Earth, but to the Moon and even to other planets.

Gagarin started training in 1959, the same year in which seven Americans were chosen to become NASA’s first astronauts. The seven U. S. astronauts
were Donald Slayton, Virgil “Gus” Grissom, L. Gordon Cooper, M. Scott Carpenter, Walter Schirra, John Glenn, and Alan Shepard. They trained to fly the Mercury capsule, a cone-shaped spacecraft weighing about 3,000 pounds (1,360 kilo grams)-about one-third the weight of a ball-shaped Vostok capsule.

Shepard and Grissom were the first to test the Mercury craft, making fifteen – minute suborbital flights in May and July 1961. The U. S. astronaut chosen to fly into orbit was John Glenn, a former Korean War fighter pilot. His capsule was mounted on top of a U. S. Air Force Atlas rocket, which was more powerful than the Redstone rocket used for the first two Mercury flights. Glenn blasted off on February 20, 1962, and became
the first American to orbit Earth in his craft Friendship 7. Glenn’s three-orbit flight was followed by other manned flights by U. S. astronauts. They used Mercury spacecraft and then the larger Gemini two-man craft. These flights led to the Apollo program (1967-1972), which sent the first people to the Moon.

THE FIRST WOMAN IN SPACE

No women were among the first U. S. and Soviet astronauts. In the 1950s, there were few experienced female jet pilots, and some scientists believed women would be physically unable to withstand the stress of launch and reentry. In June 1963, however, the Soviet Union launched the spacecraft Vostok 6 that carried Valentina Tereshkova. The first woman in space was not a pilot but a former textile technologist in a cotton mill and an avid parachutist. Inspired by Yuri Gagarin’s flight, she had written to the Soviet govern­ment with a request to become a cosmonaut. Just over a year later, she was orbiting Earth. Tereshkova suf­fered no bad effects from her orbital mission. She later married and gave birth to a daughter. The normal birth showed that human reproduction was not affected by spaceflight.

Barnstorming

Barnstorming was a form of flying exhibition that was popular in the 1920s. Stunt pilots flew airplanes to entertain crowds in rural areas across the United States. The word barnstorming originally meant traveling around rural districts making political speeches or putting on theatrical shows in barns.

The Performance

To attract a crowd, the barnstormers would fly over a small town, usually at low level, to attract attention. Then they would land their planes in a farmer’s field or showground nearby. Local peo­ple would come running, and the pilots would distribute handbills and start sell­ing tickets for airplane rides for as little as $1 (about $10 today). Those who felt brave enough climbed in for a short flight. Others paid from 25 to 50 cents
($2.50 to $5 today) to stand and watch the aerobatics. Many people in the 1920s had never seen an airplane close-up, so they were thrilled to see the aircraft and the daring pilots.

Aerial barnstorming was exciting. Many youngsters who later grew up to become pilots or to work in the aviation industry got their first taste of flying at a barnstorming show.

Barnstormers performed aerobatics, such as dives, rolls, and loops. They flew upside down, and they zoomed down low over the crowd. They raced cars and trains. Wing walkers balanced on top of airplanes, and parachutists jumped out of them. Some performers climbed out of one plane into another in midair. Other pilots leapt down from a plane to a vehicle speeding beneath it or climbed out of a moving car into a low-flying aircraft. Another unbelievable stunt involved playing tennis on the wing!

When a bird takes off, it usually does so into the wind, like an airplane. To get airborne, it must produce enough for­ward momentum to generate lift. A small bird takes a short run or jumps into the air from a perch, such as a branch. A large, heavy bird needs a takeoff run, just like most airplanes. Water birds, such as ducks, often skitter across the surface of water, paddling with their feet to build up speed. Swifts have short legs and seldom walk on the

WING SPEEDS

Tiny hummingbirds flap their wings so fast-more than fifty times per second-that the wings are just a blur. The fastest wing beat of any bird is that of the horned sungem, a South American hummingbird species that beats its wings ninety times per second. A heron needs to flap its wings only two times per second, and condors can stay in the air for 50 miles (80 kilometers) or more, using air currents, without beating their wings once.

more than fifty times in a second.

ground. They just drop from their nests and open their wings.

To climb higher through the air, a bird tilts its wings to increase the angle of attack. This action pushes more air over the top of the wing. If the angle became too steep, turbulence in the airstream could cause the bird to stall—
it would stop climbing and could start falling. To prevent a stall, the bird uses a tuft of feathers (called the alula) on its “thumb.” This tuft can be spread forward to form a slot on the leading edge, or front of the wing. Air rushes through the slot, preventing turbulence and keeping a fast flow of air over the wing. In nor­mal flight, the tuft is folded back against the wing. This is similar to the slots and flaps used on the wings of airplanes.

A bird steers by tilting its body and wings and using its tail as a rudder. Birds can twist and turn sharply to avoid obstacles (such as tree branches) and to escape a pursuing predator. Tail shape does not seem to affect a bird’s control very much. A swift twists and turns when chasing flying insects, yet it has a short tail. Swallows fly very similarly, at high speeds, with long, forked tails. A partridge can turn sharply using its broad wings rather than its stubby tail.

When World War I began in 1914, planes carried bombs in bags slung from cords. Bombs were even stuffed into the pockets of the pilot, who dropped them over the side. In 1915 civilians were bombed for the first time when German Zeppelin airships attacked British cities.

Large bombing planes also took to the skies, such as the British Handley Page 0/400 (1916), which had two engines and a crew of three and carried sixteen 112-pound (51-kilogram) bombs. The German Gotha airplane, which bombed London in 1917, was the first bomber to attack at night.

Bombing raids alarmed civilian pop­ulations, and air defenses were hurriedly improvised. Fighter planes chased the intruders. Bombers were forced to fly as

high to avoid barrage balloons on long cables and the fire of anti-aircraft guns from the ground.

When peace returned in 1918, the military showed little interest in the new bombing planes. One person who did believe in the bomber was Billy Mitchell, a U. S. Army general who advo­cated for a separate air force. Mitchell believed that, in future warfare, aerial bombing could weaken the resistance of civilians and wreck the enemy’s commu­nications and industries. Tests showed that a dive bomber could even sink a battleship. Mitchell’s ideas about devel­oping a strong, independent air force went unheeded, however. Until 1946, all U. S. military airplanes were under the control of the U. S. Navy, U. S. Marine Corps, or U. S. Army.

A New Generation

Until the mid-1930s, most air fleets were equipped with biplane bombers, which were very slow. The future lay with fast, all-metal, monoplane bombers. In 1935 Boeing produced the four-engine Model 299 that then became the B-17 Flying Fortress. The B-17 could fly at 295 miles per hour (475 kilometers per hour), at a height of over 30,000 feet (9,144 meters). Equipped with the new Norden bombsight, a B-17 could, it was claimed, “drop a bomb into a pickle barrel.” During the 1930s, Nazi Germany built a fleet of bombing planes. These aircraft were mostly fast, twin-engine
types such as the Heinkel He-111 and Dornier Do-17. Germany also built the Junkers Ju-87 Stuke dive bomber, which swooped down in a vertical dive to drop its bombs.

The new German bombers were tested in combat during the Spanish Civil War of 1936-1939. Japan also used “terror bombing” in attacks on cities in China in the same period.

Voices on VHF radio sound clear and easy to understand, but HF radio has a lot of extra crackling and hissing noises called static. Static makes voices hard to hear. Hearing information correctly is important to air and space travel, so sys­tems have evolved to help with clarity. The international language of aviation is English. All pilots who fly interna­tionally and all air traffic controllers have to be able to communicate in English while engaged in aviation.

Some letters and words sound very similar over a noisy radio link, and pilots often use a spelling alphabet that can be heard more clearly. A word is used instead of each letter. The words are chosen so that they cannot be con­fused with each other. This alphabet is used to spell out important words.

THE INTERNATIONAL RADIOTELEPHONY SPELLING ALPHABET

The International Radiotelephony Spelling Alphabet (below) is used by many organizations, including the International Civil Aviation Organization (ICAO) and the Federal Aviation Administration (FAA).

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There has to be a way of identifying each aircraft so that pilots and air traffic controllers know exactly who is talking to whom. Each plane has its own code, or call sign, that the pilot spells out using the spelling alphabet. In general aviation, small planes use their registra­tion number as their call sign.

Airliners use a call sign for the airline, plus the flight number. The airline part of the call sign is often the airline’s name. American Airlines flight 142 would be identified in radio messages as American 142. Pilots of big aircraft, such as jumbo jets, add the word heavy to the call sign. This tells everyone that

this aircraft is big enough to cause tur­bulence (strong air currents) that may affect planes following it.

rone is a short name for a remotely piloted aircraft, also known as a remotely piloted vehicle (RPV). It is a small airplane that can be controlled by radio from the ground. A drone also can fly itself using data programmed into its com­puter system.

The main task of a drone is to fly reconnaissance missions, photographing enemy positions, but it also can be used as an attack weapon. The advantage of drones over manned aircraft is that they can operate over dangerous terri­tory without risk to a human pilot. Some drones have long endurance and can stay in the air for as long as two days.

Drone Development

A drone resembles a large model air­plane. Model enthusiasts build and fly radio-controlled airplanes, and the first drones were developed from this hobby. One of the first drones was the Hewitt- Sperry Automatic Airplane, which was developed during and after World War I (1914-1918).

During World War II (1939-1945), the U. S. Army used the Radioplane Target Drone, invented by Walter H. Righter and Reginald Denny. (Denny was at that time better known as a Hollywood actor.) The army used these miniature, unmanned airplanes as flying targets for pilots and antiaircraft gun­ners. Because they were meant to be destroyed by gunfire, the drone vehicles

VARIOUS ROLES

Modern drones have five main roles:

• As targets for gunnery practice by ground guns or pilots.

• For reconnaissance (obtaining information) over the battlefield.

• In combat, where there is high risk to human pilots.

• In research and development.

• In civilian use-for example, by police, or for geological surveys and environmental research.

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had to be cheap-the first Radioplanes cost $600 each in 1938 (which would be about $8,000 today).

Later models, such as the OQ-3 of 1943, could fly at 102 miles per hour (164 kilometers per hour). More than

9,0 OQ-3s were built, and all but six were destroyed during target practice.

Another kind of drone used in World War II was the German V-1 flying bomb. Its mission was offensive: It was basi­cally an unguided missile-a bomb with stubby wings and a pulse-jet motor (a kind of jet engine). The V-1 had a simple guidance system that determined how far it would fly before its engine cut out and it crashed to the ground, exploding on impact. The V-1 was fired from a launch ramp and flew at about 340 miles per hour (about 547 kilo­meters per hour). From June 1944, V-1s based in Nazi-occupied Europe were used to attack Britain. They were terrify­ing but relatively easy to shoot down because they flew in a straight line and had no way to alter their course after launch. The modern equivalent of the V-1 is the cruise missile.

Propellers did not work well when the tips of their blades reached the high speeds that airplane manufacturers wanted. Companies looked for a type of engine that did not use a propeller.

In the 1920s, an aircraft engineer called Frank Whittle had produced plans for a new type of aircraft engine. Instead of using a propeller, it produced a jet of gas. His first jet engine was working by 1937. One of his engines was fitted to an aircraft, which made its first flight on May 15, 1941.

Although Whittle had invented the jet engine, his was not the first jet plane to fly. In Germany, Hans von Ohain had

THE AEOLIPILE

A man named Hero of Alexandria made a very simple jet engine about

2,0 years ago. It was called the aeolipile, which means wind ball.

It was a hollow metal ball with small nozzles (pipes), one on each side. The two nozzles pointed in opposite directions. The ball was supported so that it was free to spin. When the ball was filled with water and heated over a fire, the water changed to steam. The steam jetted out of the nozzles and made the ball spin.

been working on jet engines separately from Whittle. One of his jet engines was fitted to a Heinkel He-178 aircraft, which made the world’s first jet-powered flight on August 27, 1939.

The jet engine belongs to a family of engines called gas turbines, or turbine engines. Today, all but the smallest air­planes and helicopters are powered by turbine engines, because they pack a lot of power into a small space.

The force that drives a jet plane forward is the thrust of its engine or engines. A jet engine produces forward thrust by accelerating gas backward. The forward thrust is a reaction to the backward force of the jet. Because of this, jet engines and rockets also are called reaction engines. A spinning propeller thrusts an airplane forward by accelerating the air backward.

Thrust is one of four forces that act on every powered aircraft. The other forces are drag, lift, and weight. Drag acts in the opposite direction to thrust. Weight is the force of gravity acting on the mass of the plane, pulling it down­ward. Lift is the upward force produced by a plane’s wings, a helicopter’s rotor blades, or the lifting gas of an airship.

Moving in a Circle

A force that acts in the same direction as an object’s movement can make it go

FORCE IN SPACE

Outside the atmosphere there is no air, so there is no lift or drag. Once a spacecraft is in space, it uses rockets to produce the thrust needed to change speed or direction. Without drag, a spacecraft does not have to keep firing its rockets to maintain its speed. Not all spacecraft travel completely outside the atmosphere. Spacecraft orbiting at a low altitude pass through the outer atmosphere.

The atmosphere causes drag, which slows spacecraft down, and they slowly lose altitude. To maintain orbit, they fire rockets to move back up to a higher orbit.

Spacecraft turn in space by firing small rockets or gas jets called thrusters. A spacecraft will continue to turn, even when a thruster stops firing, because there is nothing to stop it from doing so. A second thruster has to be fired in the oppo­site direction to stop it from turning.

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faster in a straight line. A force also can make something move in a circle. A turning force is also called torque or moment—the force applied by a wrench to tighten a nut, for example, is torque.

Earth’s surface and everything on it constantly moves in a circle. Spacecraft orbiting Earth are moving in a circle, too, or in an elongated circle shape

called an ellipse. An object can be made to move in a circle by a force directed toward the center of the circle. This sort of force is called centripetal force.

If a ball is whirled around at the end of a piece of string, the pull of the string provides the centripetal force that keeps the ball flying in a circle. The centripetal force that keeps everything on Earth’s surface and keeps orbiting spacecraft moving in a circle is gravity.

О The Moon stays in orbit around Earth because of Earth’s gravity, which is a centripetal force.