Category FLIGHT and M ОТІOIM

Some aircraft, especially fast military aircraft, cannot be made from aluminum alloys. Airplanes heat up as they fly faster because they both compress the air they fly through and create friction as they rub against it. Planes flying faster than about two-and-a-half times the speed of sound heat up so much that an aluminum body would become danger­ously soft and weak. Aluminum melts at a temperature of about 1220°F (660°C).

О A worker at the Douglas Aircraft Company in California during World War II fastens the frame of an A-20 bomber with thousands of rivets.

An aircraft that flies faster than three times the speed of sound reaches nearly 1000°F (538°C). These planes are built from a metal called tita­nium. The Lockheed SR-71 Blackbird spy plane was the first to be built from titanium in the 1960s. It could fly at three-and-a-half times the speed of sound.

The first manned space capsules used in the Mercury and Gemini space proj­ects also were made from titanium. The Apollo command module was made of a lightweight aluminum honeycomb sand­wiched between aluminum sheets. It had a heat shield to protect it from the high temperatures of reentry. The Space Shuttle is made of aluminum protected by insulation material.

omentum is a property of all moving objects, including both aircraft and spacecraft. An object’s momentum is calculated by multiplying its mass by its velocity. Velocity is a vector-it has direction as well as size. Momentum, therefore, is also a vector.

A ball rolling down a hill gathers momentum as it goes faster and faster. A skydiver jumping out of a plane gath­ers momentum as gravity accelerates his or her rate of motion toward the ground.

Momentum depends on mass as well as speed, so a massive aircraft, such as a jumbo jet, has a lot more momentum

than a smaller, lighter plane flying at the same speed. If an aircraft speeds up, its momentum increases. If it slows down, its momentum decreases. When it lands and comes to a stop, its momen­tum falls to zero.

Until electronic navigation systems were developed, pilots also navigated during long flights by using the positions of the Sun, Moon, and stars as explorers on

land and sea had done for centuries. Navigation of this kind is called celestial navigation. Using a device called a sex­tant, the positions of the Sun, Moon, or certain known stars can be measured to pinpoint an aircraft’s location. Each sighting enables the navigator of an air­craft to draw a line on a map. After sev­eral sightings, the point at which the lines cross show the airplane’s position.

Celestial navigation involves making repeated sightings, doing many calcula­tions, and plotting maps. For this reason, the crews of long-range airliners and bombers using this system included a specially trained navigator.

Electronic Systems

A variety of electronic navigation aids have since been developed to help pilots navigate more accurately. The most basic are beacons, or radio transmitters,

The magnetic compass was devel­oped in about the twelfth century in both China and Europe. People noticed that a type of rock called lodestone, when placed on a piece of wood floating in water, caused the wood to turn. It always turned so that one end pointed north. When a magnetic needle is used instead, the needle turns in the same way to line up with the Earth’s magnetic field.

In a simple magnetic compass, the needle is on a dial marked with points of the compass-north, south, east, and west. Because the needle always turns to point north, a person holding a compass can figure out which way to head if, for instance, he or she wants to go west.

A normal magnetic compass does not work well in an aircraft. It swings wildly when the aircraft turns, and it is inaccurate near Earth’s poles. A different type of compass, called a gyrocompass, does not use magnetism. Instead, it uses a spinning wheel called a gyroscope that keeps pointing in the same direction. A gyrocompass installed in an aircraft keeps pointing north, whatever way the plane moves or turns, so it can be used as a reliable compass.

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on the ground. Their positions are marked on navigation maps. A radio in an aircraft picks up radio signals from the nearest beacons and figures out their bearings (the direction of the beacons in relation to the plane). Knowing this helps a pilot to determine an airplane’s position and to steer an accurate course. A variety of systems use radio beacons, including NDB (non-directional bea­cons), VOR (VHF omnidirectional radio range) and LORAN (long-range naviga­tion). There also is a more accurate ver­sion of VOR called TACAN (tactical air navigation) for military aircraft.

When computers became small enough and reliable enough to be car­ried by aircraft, much more advanced navigation systems became possible. One of these is the inertial navigation

system (INS) or inertial guidance system (IGS). The location of an aircraft is programmed into the system at the beginning of a flight. As the plane flies along, the system detects its movements by using devices called accelerometers. Knowing how much the aircraft has moved, and in which direction, enables its computer to determine the aircraft’s position and to keep track of its progress.

An inertial navigation system can navigate a plane automatically. The sys­tem is programmed with the locations during a flight where the plane has to turn. These places are called waypoints. During the flight, the inertial navigation system controls the plane’s autopilot and flies the plane along the planned route from one waypoint to the next.

A modern airliner is equipped with several navigation systems so that if one should fail, another can take over. If everything fails, an air traffic controller
on the ground can guide the pilot or pilots of an aircraft over the radio.

Every airplane is slightly different to fly, so pilots have to qualify in every kind of plane they have not flown previously. Initial training for pilots joining an
airline takes about ten weeks, during which they learn the specific procedures of the airline and get used to the aircraft. Training is often done in pairs and includes simulator training and practice in all maneuvers. After pilots pass this training course, they receive their initial operating experience in the air alongside an instructor pilot. They take a final flight test or “line check” and are then cleared to fly scheduled passenger flights.

Statistically, flying is very safe. According to the FAA, a well-built, well-maintained aircraft flown by a competent and prudent pilot is as safe as any other form of transportation.

STEVE FOSSETT’S RECORD FLIGHTS

American pilot Steve Fossett set remarkable records piloting balloons and specialized airplanes. In 1995, he made the first solo flight across the Pacific Ocean in a balloon. In 2002, he made the first solo, nonstop, round-the-world balloon flight (in 14 days and 19 hours). In 2005, Fossett piloted the Virgin Atlantic Globalflyer on the first nonstop, solo, round-the – world airplane flight, a trip that took 67 hours and covered 22,878 miles (36,811 kilometers). In February 2006 Fossett then set a record for the world’s longest flight, when he flew Globalflyer for 26,389 miles (42,460 kilometers) in a journey lasting nearly 77 hours. In September 2007, Fossett disappeared in a small airplane while in a scouting flight over the Nevada desert. He was officially pronounced dead in February 2008.

A modern aircraft is a highly com­plex, computerized machine. To fly it properly, a pilot needs technical as well as piloting skills. A first officer and other cabin crew assist the captain of an airliner. Most large commercial airplanes have two pilots. (General aviation airplanes and helicopters are usually flown by a single pilot.)

The invention of radar can be traced back to experiments with radio waves carried out by physicist, Heinrich Hertz (1857-1894). Hertz discovered that radio waves passed through some materials and were reflected by others. In 1904, scientist Christian Hulsmeyer showed that radio waves could detect ships, and

О Dish antennae such as these at a tracking station in California swivel to pick up signals.

he suggested that this ability might be used to avoid collisions at sea, but there was no interest in his idea.

In 1922, the effect was rediscovered when a ship on the Potomac River in Washington, D. C., caused a disturbance to radio signals being sent across the river. An airplane was detected by radar for the first time in 1930.

As World War II approached, scien­tists in Britain and Germany stepped up their research into radar. The first prac­tical radar system for air defense was developed in Britain by Sir Robert Watson-Watt in 1935. During the war, the British coastline was protected by a system called Chain Home. When the system detected approaching aircraft, the planes’ positions were plotted on a map in a control room. Fighter pilots

were then given instructions by radio to guide them toward the incoming enemy aircraft. Germany also developed an air defense radar system, called Freya, dur­ing World War II. In addition, radar was also used to guide searchlights and anti­aircraft guns.

These early radar systems were too big and heavy to install in an aircraft. In 1939, however, scientists at Birmingham University, England, invented a device called a cavity magnetron, which enabled radar equipment to transmit and receive much shorter radio waves. This made it possible to build smaller and more powerful radar equipment, light enough to be carried by aircraft. As they developed, these systems had been known as RDF (radio direction finding). In 1942, the term radar (short for radio detection and ranging) came into use.

In 1943, British bombers were equipped with a radar system named H2S. It pointed downward and showed a map of the ground on a screen inside the aircraft. It enabled bombers to find their targets through the cloud cover. An improved U. S. system called H2X was developed in 1945.

The United States and the Soviet Union tested anti-satellite (ASAT) missile systems back in the 1980s. In 1985, a U. S. F-15 fighter fired a missile that flew into space and destroyed a U. S. solar observa­tory satellite orbiting 375 miles (600 kilometers) from Earth. After this one suc­cess, the ASAT project was abandoned, partly because of concerns that such mis­siles violated the 1967 Outer Space Treaty. The treaty requires nations to refrain from placing weapons into space-such as nuclear warheads, lasers, and other high – energy weapons-that could be used to destroy satellites or aimed at ground targets. In 2007, China claimed to have test-fired a missile that destroyed an obsolete weather satellite, raising a new debate about ASAT usage. As increasing numbers of satellites are launched, the question of how to regulate ASAT systems remains unresolved.

in wilderness and cities. Space cameras provide images from which mapmakers create accurate maps. They even can give computer users instant images of their own location over the Internet.

Weather satellites have revolution­ized meteorology. They provide the daily TV weather images, and they alert fore­casters to developing global weather situations, such as hurricanes. The National Oceanic and Atmospheric Administration (NOAA) runs a national weather service from satellite data pro­vided by the National Environmental Satellite Data and Information Service.

Short-range weather forecasting uses data from geostationary operational environmental satellites (GOES). Long – range weather forecasts use data from polar-orbiting operational environmen­tal satellites (POES). NOAA also operates a search-and-rescue satellite-aided tracking system, known as SARSAT,
which can locate a person in trouble at almost any location on the planet.

kyjacking is the illegal seizure of an airplane. It is a crime similar to hijacking a truck or taking over a ship at sea. Skyjackers may demand that the plane be flown to a destination of their choice or demand a ransom for the release of passengers. They may use the airplane as a weapon of destruction.

How Skyjacking Began

The first recorded skyjacking was in 1931 in Peru. Rebel soldiers forced two American pilots to fly a plane over the city of Lima to drop propaganda leaflets. The first skyjack in the United States

DISAPPEARING AIR PIRATE

Probably the most famous criminal sky­jacking in the United States happened in 1971. A man known as Dan or D. B. Cooper took over a Northwest Orient Airlines Boeing 727. After forcing the plane to land, he demanded $200,000 as ransom for the release of the passen­gers. When he had received the money and four parachutes (one each for him­self and the three remaining crew mem­bers), Cooper ordered the airplane to take off again. He parachuted from the rear of the Boeing 727 over the Cascade Mountains of the northwestern United States and was never seen again. There have been many suspects, but no certain culprit has ever been found.

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took place in 1961, when a passenger on a commercial flight from Miami to Key West, Florida, ordered the pilot to divert the aircraft to Communist-ruled Cuba.

With lax security at airports in the 1960s, it was relative­ly easy for a terrorist to smuggle a gun onto an air­liner to threaten the pilots and passengers. Skyjackers often had political motives.

Taking over an airliner ensured publicity for their cause. Less often, a skyjacker was a criminal who hoped to extort money by air piracy.

In the 1970s, when tension between Israel and its Arab neighbors was high, terrorists based in the Middle East made several attacks on airliners. Their usual practice was to seize an airliner in flight, force the pilot to land, and then broad­cast their demands by radio. Skyjackers held passengers inside the airplane as hostages, hoping to bargain for the release from jail of fellow terrorists or other prisoners.

In September 1970, a spectacular skyjacking took place in the Middle East, when Palestinian terrorists seized three airliners simultaneously. All three air­craft were landed in the Jordan desert at Dawson’s Field (a former British air force base) and then blown up after most of the hostages had been released. An attack on a fourth airplane was foiled by Israeli security guards. A fifth airplane was hijacked three days later.

Meanwhile, the airplane took the lead. When Giffard was making the first airship flight in France in 1852, Englishman George Cayley had already begun a scientific study of the forces produced by moving air, or aerodynam­ics. Cayley was interested in how these forces could be used by heavier-than-air flying machines.

He wrote that the challenge was “to make a surface support a given weight
by the application of power to the resist­ance of air.” He was talking about lift and drag, the aerodynamic forces that act on aircraft. Cayley’s work resulted in the first manned gliders in the middle of the nineteenth century.

The invention of the steam engine in the nineteenth century awakened interest in developing steam-powered airplanes. The steam engines of the day were too heavy, however. Powered air­planes had to wait until smaller, lighter engines powered by gasoline were developed in the late 1800s. That would

О The Giffard steam-powered balloon made the first successful powered flight. The engine, pro­peller, and platform for the pilot hang beneath the 144-foot (44-meter) hydrogen-filled balloon. This model of Giffard’s balloon is now on display at the Science Museum in London, England.

lead to a usable engine for airplanes. Aeronautical pioneers, meanwhile, con­centrated on learning to build stable gliders and control them in the air.

The brothers Orville and Wilbur Wright experimented with kites and gliders in a very methodical way. Each time they encountered a problem, they worked at it until they found a solution. They also designed a gasoline engine light enough to power an airplane based on one of their gliders. The brothers were finally ready to fly the world’s first successful powered airplane in 1903.

The Wright brothers had developed the airplane and shown that controlled flight was possible. Other engineers and inventors reshaped the airplane and otherwise improved it with their own ideas. The age of modern aeronautics had begun.

Otto Lilienthal (1848-1896) in Germany made more than 2,000 glider flights. Other aeronautical engineers and inventors around the world avidly read Lilienthal’s books and essays on aeronautics. The read­ers included Percy Pilcher in Britain and the Wright brothers and Octave Chanute in the United States. These innovators flew gliders similar to modern hang gliders. They steered by shifting their weight to one side.

Aeronautical research at that time was very risky, and accidents were common. Flimsy aircraft made of wood and fabric could fall apart, or they could spin out of control and plunge to the ground. Lilienthal and Pilcher both died as a result of aircraft crashes.

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Into the Modern World

The fixed-wing aircraft was not the only way to fly. Other aeronautical engineers struggled with the problems of building craft with spinning wings, called rotors. Their work led to the development of autogiros and helicopters.

All sorts of new technologies were applied to the airplane-new wing shapes, new engines, metal structures instead of wood, monoplanes instead of biplanes, more efficient propellers, more streamlined aerodynamics, and so on. Piece by piece, these and many other advances in aeronautics transformed the fragile wood-and-wire flying machines of the early twentieth century into the amazing aircraft we have today.

An ACV is an aircraft only in the sense that it is lifted off the surface supported by the air beneath it. Air can exert a lot of power when it is under pressure, for example when it is blasted into an enclosed space. An ACV uses this power to lift itself, floating on a cushion of air created by powerful fans. In this way, it is able to move smoothly over land or water. An ACV cannot fly at height. Depending on the vehicle, the amount of lift is between 6 inches and 100 inches (15.2 centimeters and 254 centimeters).

Some ACVs have wings, designed to generate just enough lift to raise the vehicle above the surface when it has reached a sufficient speed. Wings are not essential, however. An ACV will float on the compressed air that is sucked in by the fans and held in place beneath it. The air is contained either by a rigid sidewall or by a flexible skirt fixed around the lower edges of the vehicle. It is this air that gives the ACV its lift.

For forward propulsion, some ACVs use propellers turning in the air (like some airplanes). Others are driven for­ward by propellers turning underwater or by a high-powered water jet.

О This diagram shows the basic parts of a hovercraft. A fan sucks in air to create lift.

A propeller creates the thrust to move the craft forward, while a rudder is used to steer.

EXPERIMENTING WITH GROUND EFFECT

The principle of ground-effect flight was first suggested in 1716 by Swedish scientist and philoso­pher Emanuel Swedenborg. In the 1870s, British engineer Sir John Thornycroft experimented with model vehicles that floated on air.

He concluded that, instead of a ship having a conventional sealed hull, it could be designed with a plenum chamber-a box filled with air and open at the bottom. (A plenum is an enclosed space in which the air pressure is greater than the air pressure that surrounds the space.)

The air would reduce the drag from the water, allowing the ship to travel faster on less power. Unfortunately, the technology required to build a full-sized ACV did not exist at the time. In the 1920s, however, German engineers proved that a flying boat could achieve greater range and speed by flying very close to the water, making use of ground effect.

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ACV Pioneers

The modern ACV owes much to the pio­neer work of three inventors: British engineer Christopher Cockerell and two Americans: airspace engineer Walter A. Crowley and U. S. Navy designer Colonel

Melville Beardsley. Cockerell had the idea that a vehicle would float on a ring-shaped curtain of air. He proved it with experiments using two empty coffee cans and a hair dryer. Crowley, meanwhile, was inspired by his dis­covery that a household lampshade could be made to float on air. In 1957 he built a hover-chair, which was not unlike a giant lampshade. He and Beardsley separately came up with the invention of a flexible skirt to stop air from escaping beneath the ACV. This escaped air had been the chief weakness of Cockerell’s design.

A skirt was fitted to the first practical ACV, Cockerell’s SR-N1 hovercraft. Big enough to carry three men, this vehicle crossed the English Channel in 1959. The SR-N1 skimmed across the sea at almost 30 miles per hour (48 kilo­meters per hour). It offered the prospect of an entirely new kind of ferry.

Experimental

n experimental aircraft is one that is designed to try out new ideas and investigate unknown areas of flight. It may have been designed to fly faster or higher than existing types. It may have been built to test a new wing shape, control system, or engine. Experimental aircraft, often identified as X-planes, sometimes look unlike any airplane flown before.

Many experimental aircraft are intended for military use. The military is constantly looking for new ideas, per­haps to combat a new threat or to take advantage of a new technology. Civil airliners, cargo planes, and light aircraft change less dramatically.

Every new aircraft is to some degree experimental, no matter how much test­ing and computer simulation has been done. The preflight design stage and
ground test program may last several years, but the moment of truth comes when a test pilot flies a new airplane for the first time. Sometimes, experimental craft succeed beyond expectations. A new production line of airplanes may follow. Others are failures. The history of aviation is littered with planes that crashed the first time they were flown. Yet even a failure has its uses, because good designers can learn from mistakes.