Category FLIGHT and M ОТІOIM

The weight of a whole airplane acts as if all of its mass were concentrated at one point. This point is called the center of gravity. If an airplane could hang from a wire at this point, it would hang perfect­ly level. A flying airplane is held up by lift. All the lift acts at one point called the center of pressure. Airplanes are designed so that the center of pressure and center of gravity are close to each other, but it is not possible to get them in exactly the same place. Both of them move during a flight as a plane’s speed and attitude change and as it uses up fuel. Passengers walking about in an air­liner move its center of gravity as well.

If the center of pressure is in front of the center of gravity, it pulls the plane’s nose up and the plane is said to be tail – heavy. If the center of pressure is behind the center of gravity, it pulls the plane’s nose down. Then the plane becomes nose-heavy. If a plane were consistently
nose-heavy or tail-heavy, the pilot would have to keep pulling or pushing the con­trol stick for long periods to stay level. To avoid this, planes have trim control. This is usually a wheel, lever, or group of switches in the cockpit. Pilots use trim control to move the center of pressure forward or backward until it lines up with the center of gravity, making the aircraft level. Small airplanes have panels in the tail, called trim tabs. They tilt up or down to move the tail up or down until the plane is level. Larger airliners trim their pitch by tilting the horizontal stabilizers in their tail. A level plane is called a trimmed plane.

rocket is a type of jet engine. It has three main parts: its struc­ture, a guidance system, and a propulsion system. The structure is the basic frame of a rocket. The guidance system keeps the rocket on course. The propulsion system comprises the rocket’s engines. A rocket carries a payload-the spacecraft that is launched by the rocket. Rockets contain everything they need to work and do not need to take in air.

The History of Rockets

It is not known who built the very first rocket, but it is believed that some form
of rocket was made in China sometime before 1200, perhaps as long ago as 200 b. c.e. Early rockets were like fireworks, propelled by a mixture of chemicals called black powder. The first recorded use of rockets in war was at the Battle of Kai-Feng in 1232, when a Mongol attack on the Chinese city of Kai-Feng was fought off with the help of rockets.

In the eighteenth century, British forces came under rocket attack in India. They were so impressed with the rockets that a British artillery officer, Sir William Congreve, developed solid fuel military rockets for the British army. Congreve’s rockets were used during the Napoleonic Wars in Europe.

KONSTANTIN TSIOLKOVSKY (1857-1935)

Konstantin Tsiolkovsky, spaceflight’s earliest pioneer, was a Russian schoolteacher who wrote scientific studies of rockets and space travel. In 1898, Tsiolkovsky wrote an article entitled "Investigating Space with Rocket Devices" that presented the scienti­fic principles of spaceflight. Over the next thirty or so years, Tsiolkovsky wrote a series of scientific and mathematical studies of rocket engines, rocket fuels, spacecraft in

orbit, space stations, and even spacesuits. The many honors he was awarded included a lifetime pension from the Soviet state that enabled him to retire from teaching and work full-time on spaceflight. All of Tsiolkovsky’s work was theoretical. He never carried out any experiments with rockets, but rocket scientists and engineers in the Soviet Union and other countries have studied Tsiolkovsky’s work.

These early rockets were very inaccu­rate. Like firework rockets, they relied on a long stick to keep them pointing in the right direction and to stop them from tumbling. This was improved upon in 1844, when William Hale designed a rocket that spun as it flew through the air. The spinning kept it flying straight and true. These early military rockets were overtaken by advances in artillery.

In 1898, a Russian schoolteacher named Konstantin Tsiolkovsky wrote the first serious study of spaceflight using rockets. In the 1920s, rocket research flourished in several countries. In the United States, Robert H. Goddard launched the first liquid-fuel rocket. Amateur rocket scientists in Germany began developing rockets that led to the first modern rocket-propelled weapons in World War II.

Shock waves also affect spacecraft returning to Earth. When a space­craft plunges back into Earth’s atmosphere from space, it compresses the air in front of it, and a shock wave is formed.

When air is compressed, it heats up. The shock wave created by a spacecraft reentering the atmosphere at high speed is very hot. The Mercury, Gemini, and Apollo manned space capsules, were designed to reenter the atmos­phere blunt end first.

This blunt shape helped to push the super-hot shock wave forward, away from the capsule. A heat shield protect­ed the astronauts and spacecraft from the heat that remained.

Today, the Russian Soyuz capsules use this method, and so does the Space Shuttle. The Space Shuttle reenters the atmosphere with its nose tipped up and its large underside facing the direction of flight. This deflects most of the heat­ed shock wave around the spacecraft.

As the Space Shuttle descends lower in the atmosphere, nose and tail shock

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waves form on it. They spread out and reach the ground, where people hear two sonic booms. All supersonic aircraft form two shock waves. Unlike the Space Shuttle, however, most of these aircraft are so small, and the shock waves they create are so close together that only one bang is audible.

SEE ALSO:

• Air and Atmosphere • Pressure

• Supersonic Flight

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In the 1930s the agile biplane was replaced by the much faster monoplane. This new kind of aircraft had an enclosed cockpit, a streamlined metal body, and a high-performance engine. Fighter planes such as the German Messerschmitt Bf 109 and Curtiss P-40 had a top speed of over 350 miles per hour (563 kilometers per hour). Bombers, such as Boeing’s B-17, were slower at around 280 miles per hour (450 kilo­meters per hour), but they could fly for 2,000 miles (3,220 kilometers). The bombers carried 6,000 pounds (2,725 kilograms) of bombs that could be dropped accurately on city targets.

O (From left) An A-10 Thunderbolt II, F-86 Sabre, P-38 Lightning and P-51 Mustang fly in a flight formation during an air show at Langley Air Force Base, Virginia, on May 21, 2004. The formation displayed four generations of U. S. Air Force fighters.

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Length: 31 feet (9.45 meters)

Wingspan: 28 feet (8.53 meters) Weight: 12,250 pounds (5,557 kilograms)

Motor: Reaction Motors XLR-11- RM-3 four-chamber rocket engine Fuel: Mixture of alcohol and liquid oxygen

Thrust: 6,000 pounds

(2,722 kilograms/26,500 newtons)

The Bell X-1 was shaped like a bullet for maximum streamlining. Its wings and tail plane were conventional in design. (In the 1940s, other experi­mental high-speed aircraft had strange shapes.) The stubby-winged X-1, however, had hidden secrets. Its wings were thin but very strong. A stabilizer, which the pilot could move up and down, improved stability and control. Later supersonic planes were also fitted with stabilizers.

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By 1930, about 400,000 people a year were flying on U. S. domestic airlines. Bigger, faster planes were needed to carry more people. Worldwide, passen­ger flights rose to 3 million in 1938.

By the late 1930s, most airplanes were built in factories, yet designs were

still often the work of one person. The British Spitfire fighter of World War II, for example, was the brainchild of designer Reginald J. Mitchell.

When World War II began in Europe in 1939, U. S. factories were turning out just over 2,000 new airplanes a year. U. S. aircraft production rose enormously during the war. From early 1942, U. S. aircraft factories operated twenty-four hours a day, often seven days a week. In 1941, it took 55,000 hours of labor to build a B-17 bomber. In 1944, it took only 19,000 hours, which meant that three planes were being built in about the time it had taken to turn out one. By 1944, U. S. factories were building 96,000 aircraft per year-more than Germany and Japan together.

By the end of the 1940s, high demand from the military and civil sec­tors had changed the face of the aircraft manufacturing industry. The introduc­tion of jet airplanes in the 1940s and 1950s brought a huge increase in civil air
travel, and business boomed again. Space exploration in the 1960s and 1970s coincided with the Cold War, a period of hostility between the West (led by the United States) and communist nations (led by the Soviet Union). Both the space age and the Cold War brought new demands from government cus­tomers. Satellites, spacecraft, rockets, and missiles became important products of the aerospace manufacturing indus­try. Aerospace research and technology grew to keep up with new demands.

In some countries air traffic control is run by the military. In others, civilian air traffic controllers may work for the gov­ernment or for a privatized company. The Federal Aviation Administration (FAA) is the national agency responsible for civil­ian aircraft and air safety in the United States. It sets the rules for all commercial aircraft operators and private pilots fly­ing in U. S. airspace. The FAA also certi­fies pilots. Air traffic controllers must undergo a training course before they, too, are certified by the FAA.

The FAA runs a network of twenty Air Route Traffic Control Centers (ARTCCs) across the continental United States. Most centers are named for major cities—although located outside them—

and they are identified by a code. Center code names are prefixed by the letter K, followed by a three-letter identifying tab, such as KZBW (Boston) and KZAU (Chicago). There are also centers outside the continental United States in Alaska, Guam, and Puerto Rico. The Air Traffic Control System Command Center over­sees the national picture.

National airspace is the air above a nation’s territory, which may include stretches of ocean. Each ARTCC has responsibility for its own area, and some have responsibility for airspace over international areas of ocean, allocated to them by the ICAO. (Much of the airspace above oceans, however, is not controlled by any one nation.)

Each center takes charge of an air­plane from the time the pilot enters its area until the airplane is handed off to the next control center. Near the end of its flight, usually at a distance of 5 miles (8 kilometers) from the airfield, the plane is handed over to an air traffic controller at the airport terminal for landing.

The first aircraft used in warfare was the tethered balloon. It was used for obser­vation, rising above battlefields so observers could get a view of the action below. The balloon was later developed into the airship, and airships were also used by the military for observation.

The first gasoline-powered military airplanes were known as scouts because reconnaissance (flying on missions to gather information) was their chief pur­pose. Other uses were soon found for military airplanes. They dropped bombs, fired at enemy ships, and shot down enemy aircraft. Special airplanes, most­ly biplanes, were built for these tasks.

The first air combat took place dur­ing World War I (1914-1918). Pilots shot at one another with pistols, shot­guns, and machine guns. The next step was to attach a machine gun, which the pilot aimed at an enemy, to the airplane itself. By 1915 fighter planes had been developed with synchronized machine guns that fired bullets between the whirling propeller blades. Celebrated fighter pilots, known as aces, created successful air fighting tactics.

By the end of World War I, there were two main types of military air­plane. Fighters flew at around 125 miles per hour (200 kilometers per hour) at heights of up to 22,000 feet (6,700 meters). Larger, heavier bombers flew more slowly, around 100 miles per hour (160 kilometers per hour), but they could fly for up to 8 hours.

In the 1930s the agile biplane was replaced by the much faster monoplane. This new kind of aircraft had an enclosed cockpit, a streamlined metal body, and a high-performance engine. Fighter planes such as the German Messerschmitt Bf 109 and Curtiss P-40 had a top speed of over 350 miles per hour (563 kilometers per hour). Bombers, such as Boeing’s B-17, were slower at around 280 miles per hour (450 kilo­meters per hour), but they could fly for 2,000 miles (3,220 kilometers). The bombers carried 6,000 pounds (2,725 kilograms) of bombs that could be dropped accurately on city targets.

O (From left) An A-10 Thunderbolt II, F-86 Sabre, P-38 Lightning and P-51 Mustang fly in a flight formation during an air show at Langley Air Force Base, Virginia, on May 21, 2004. The formation displayed four generations of U. S. Air Force fighters.

THE VERACRUZ INCIDENT

The first military operation involving U. S. airplanes was during the Veracruz Incident, a dispute between the United States and Mexico that began in April 1914. Five Curtiss flying boats were carried into the Mexican port of Veracruz by U. S. naval ships. The aircraft flew mis­sions to search for mines in the harbor. On May 6, 1914, the airplane flown by Lieutenant Patrick N. L. Bellinger (1885-1962) was shot at from the ground by Mexican forces.

This was the first time that a U. S. military plane was hit by enemy fire while on active service. Bellinger survived and went on to become a distinguished admiral.

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As air travel has grown more popular, some airports have grown so large that
they resemble small cities. A very large international airport, or primary hub, usually covers between 1.5 and 5 square miles (3.9 and 13 square kilometers). Some occupy much more space. The air­port that occupies the most land is King Khalid International Airport in Riyadh, Saudi Arabia, which covers more than 80 square miles (207 square kilometers).

Most airports are located away from the centers of cities, partly because they need so much space for their runways, but also because of noise. Aircraft are noisy, and flights over residential dis­tricts or at night may be limited. Good highways, together with rapid transit systems, are essential for a large airport to work efficiently. These road and rail networks move passengers and freight to and from airports, but they are also necessary to transport the thousands of workers who keep airports running.

Founded in 1958, the National Aero­nautics and Space Administration

The huge Saturn V rocket that took Apollo 11 into space weighed 5.8 million pounds (2.6 million kilograms). It stood 363 feet (110.6 meters) high. The rocket had three stages. The first and second stage took the spacecraft up into orbit around Earth, while the third stage sent the spacecraft traveling toward the Moon. The five first-stage engines burned liquid oxygen and kerosene. The five second – stage engines burned liquid oxygen and nitrogen. The third – stage engine burned liquid oxy­gen. In the first 2.5 minutes of flight, Saturn V burned about

528,0 gallons (about 2 million liters) of fuel.

The Apollo 11 spacecraft weighed about 103,000 pounds (46,762 kilograms) at launch. The cone-shaped command module Columbia was 12 feet (3.7 meters) high. The cylinder­shaped service module stood 22 feet (6.7 meters) high. The lunar module, the Eagle, was 21 feet (6.4 meters) high. It weighed 29,983 pounds (13,612 kilo­grams). The lunar module had two engines: one for descent and one for leaving the Moon.

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Avionics equipment has to keep working in all conditions. An aircraft could be sitting on the ground on a hot day at more than 104°F (40°C), and a few min­utes later it could be flying through air as cold as -76°F (-60°C). Turbulent (rough) air and hard landings can shake up a plane considerably. Lightning can strike and shock a plane with millions of volts. Avionics have to work reliably through all of this.

If part of an avionics system does break down, however, it is designed to fail in a way that does not put an air­craft in danger. The most important sys­tems have at least one backup. If the main or primary system fails, the back­up takes over. There is often more than one backup, so if the first backup fails, yet another backup can take over. This is called “failsafe operation.”

The Space Shuttle has five flight computers. Four of the computers work together, and they constantly check each other. If one computer fails, the other three vote it out of the system and ignore it so that it cannot command the spacecraft to do anything dangerous. If a second computer fails, the other two can still land the Space Shuttle safely. If all four computers fail, the fifth com­puter takes over. If all five computers were programmed with the same soft­ware, they could all crash because of the same fault in their programming. The fifth computer, therefore, is programmed with different software.