Category FLIGHT and M ОТІOIM

In the late 1940s and early 1950s, air forces switched from propeller-driven bombers to jet bombers, such as the U. S. B-47 and British Canberra (built in the United States as the B-57). Both the

United States and the Soviet Union built fleets of very large strategic bombers, designed to carry atomic bombs as well as conventional high explosive bombs. The U. S. Air Force, now a separate arm of the military, set up Strategic Air Command (SAC) in 1946. By 1953, SAC had over 1,000 aircraft. These included the B-36, a giant with six propellers and four jet engines that gave it a speed of 439 miles per hour (706 kilometers per hour).

During the Cold War of the 1940s to the 1980s, Soviet and Western air forces competed in an arms race to build better, faster, and harder-to-catch bombers. Interesting planes from this era include the British Avro Vulcan— a large delta-wing airplane—and the Soviet Tu-95 Bwar, which was the last big bomber with pro­pellers. Some people argued that the age of the bomber was over and that guided missiles were the weapons of the future. Jet bombers flew twice as high and twice as fast as bombers in World War II, but they were still vulnerable to missiles—so why risk pilots’ lives when unmanned missiles could be used instead of bombers?

The success of the B-52 proved that the bomber was still a power­ful weapon. Originally planned as a turboprop bomber in 1948, the B-52 was fitted with jet engines. More than fifty years after it first

flew, it is still in service. In the Vietnam War, B-52s were used alongside smaller, faster airplanes such as the F-4 Phantom and the F-105 Thunderchief, which were able to carry a combination of bombs and missiles.

Building bombers is an expensive business, and many promising designs never get beyond a prototype. The delta­wing B-58 Hustler of 1960 was the first supersonic bomber, but only 116 of them
were built. Even fewer XB-70s were manufactured. First flown in 1964, and able to fly at three times the speed of sound, the XB-70 was canceled before it even got into production. It is unlikely any more big bombers will be built. The need in the twenty-first century is for multi-purpose airplanes that can perform a variety of tasks-dropping bombs is just one of them.

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SEE ALSO:

• Aircraft, Military • Airship

• Mitchell, Billy • World War I

• World War II

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When a plane is flying over an ocean far away from land, pilots used to endure the hissing, crackling noise of their HF radio constantly in case anyone tried to contact them. There is now a system that does the listening for the pilot. When controllers want to contact a pilot, they send a radio signal to the plane. Each aircraft has its own address code. Many airplanes may receive the signal, but the system in only one specific plane recog­nizes the address code and alerts the pilot. It sounds a chime and flashes a light in the cockpit. This tells the pilot that someone is trying to contact that particular plane.

Even when HF radio is being used for long-distance communication, an air­craft’s VHF radio is not switched off. Pilots leave it on and listen for messages from pilots in nearby aircraft. A pilot who suffers serious turbulence, for example, can warn other pilots so that they can find a way around it.

Commercial pilots also can send and receive short text messages. They use this for standard messages, such as weather reports. The messages appear on a screen and can be printed out on paper using the cockpit printer.

The amount of information sent and received by pilots and aircraft has increased over the years, and it will con­tinue to increase. In the future, aircraft may be able to use broadband links that can transmit live video from the cockpit and cabin, as well as giving the crew and passengers access to the Internet during a flight.

In the late twentieth century, with the development of ever smaller electronic systems, the military saw the potential of unmanned aerial vehicles (UAVs) as spy planes. A drone could be fitted with cameras and modern guidance systems to fly on missions over territory where it might be risky to send a piloted airplane. With a drone, there was no risk of a pilot being lost if the vehicle was shot down.

Drones do not have the same limita­tions as people-they do not get tired or hungry—so they can stay in the air for many hours. A solar-powered drone could, in theory, stay in the air for weeks. Modern drones are very small and some can fly low—sneaking around hills rather than flying over them, which makes them hard to spot on radar.

Whereas early drones were always controlled by a person on the ground, modern drones can fly on their own, using built-in control and guidance systems. In the future, drones may be capable of decision making, replacing the human pilot altogether, but this type of technology is still far off.

The turbojet is the simplest jet engine. Air entering the engine is compressed by spinning fans in what is called a com­pressor. The compressed air flows into the engine’s combustion chamber. Here, fuel is sprayed into the air and burned.

The hot gas produced by the burning expands and forces its way out through the back of the engine. On its way out, the jet of hot gas rushes through anoth­er set of fans, called a turbine, and makes them spin. The spinning turbine drives the compressor at the front of the engine. Turbojets are best suited to air­craft flying at about twice the speed of sound. They are also very noisy, so tur­bojets are not used much today.

Most of the jet engines that power airliners and military aircraft today are turbofans. A turbofan engine has a fan at the front. The fans at the front of the engines that power the biggest airliners are enormous. The fan works like a pro­peller with lots of blades. It is powered by a turbine inside the engine. Only a small fraction of the air that goes through the fan enters the engine. Most of the air from the fan is blown around the outside of the engine. This big mass of air moving slowly around the engine
provides most of the engine’s thrust. It also enables turbofans to be quieter than turbojets. Turbofans work best in air­craft flying at 250-1,300 miles per hour (402-2,092 kilometers per hour).

Turbine engines also power some slower planes with propellers. A turbine engine with a propeller is called a turbo­prop. A turbine inside the engine powers the propeller. Turboprops work best for aircraft flying at up to about 450 miles per hour (724 kilometers per hour).

All but the smallest helicopters are now powered by turbine engines. These engines are called turboshafts. A tur­boshaft engine uses the jet of gas from the engine to spin a shaft. The spinning shaft drives the helicopter’s rotors.

Fighter planes sometimes have to make extremely tight turns in combat. The acceleration forces caused by these tight turns are often called g-forces because they are measured by comparing them to the force of gravity at Earth’s sur­face. An acceleration force equal to Earth’s surface gravity is 1g. A force twice as strong as this is 2g, and so on up the g-force scale.

The human body can survive g-forces as high as about 40g, but only for a brief time. People who ride on the most extreme theme park rides normally experience acceleration forces of up to about 4g. Fighter pilots train to withstand g-forces up to about 9g.

Forces as strong as 9g pull blood from a pilot’s head down into the body and legs. Without any protective cloth­ing or training, the pilot would faint from lack of blood in the brain. This type of fainting is also called g-loc, which stands for g-induced loss of conscious­ness. Pilots get some warning of g-loc
because the shortage of blood in their head causes problems with their vision.

Fighter pilots protect themselves from g-loc by wearing an anti-g suit. In a tight turn, air is pumped into the suit’s body and legs. It squeezes the pilot’s body and legs to stop blood from drain­ing down out of his or her head. Pilots also tense the muscles in their bodies to push more blood up into their heads, but this straining maneuver is very tiring. Pilots can be helped by one more system: Oxygen-rich air is forced into their lungs through a facemask. Air also must be pumped into an inflatable vest, which presses the pilot’s chest with equal force.

Fighter pilots can experience nega­tive g-forces, the forces that act in the opposite direction to gravity. A negative g-force forces extra blood up into a pilot’s head. This causes an effect called red-out, because the pilot’s vision turns red. Pilots can only withstand negative g-forces of about -2g or -3g at most.

UNITS OF FORCE

The units used for measuring force include the newton and the pound force. The newton is the internation­al unit of force. It is the force needed to make a mass of 1 kilogram accel­erate at 1 meter per second squared (or per second per second). This force is roughly the same force as the weight of a 3.5-ounce (about 100- gram) object-a small apple, for exam­ple. The pound force is the weight of a mass of 1 pound (0.454 kilogram).

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SEE ALSO:

• Gravity • Jet and Jet Power

• Laws of Motion • Lift and Drag

• Thrust • Weight and Mass

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Late in 1961, NASA chose Glenn to pilot the first American orbital flight. Getting that flight off the ground became a chal­lenge, however. The launch was delayed by problems with the booster rocket and by bad weather. There was even a brief scare over Glenn’s health when he was exposed to children who had the mumps, a disease Glenn had never had. Luckily, he did not become infected.

After ten delays, Glenn finally entered his Friendship 7 space capsule on February 20, 1962. At 10 A. M., the Atlas rocket began to fire and lifted the spacecraft into the air. “We’re under way,” said Glenn.

The flight went smoothly at first. A problem did develop at one point, and Glenn turned off the automatic controls to fly the spacecraft manually for the rest of the trip. Glenn orbited the Earth three times, reporting on what he saw below. Live television coverage carried his words across the country. At one point Glenn said, “I don’t know what you can say about a day in which you have seen four beautiful sunsets.”

During the second orbit, a more seri­ous problem appeared. A warning light suggested that the capsule’s heat shield was loose. This piece on the bottom of the capsule was supposed to protect Glenn when the spacecraft reentered Earth’s atmosphere. If the shield did not remain in place, the capsule-and Glenn-would burn up.

A set of small rockets that sat under­neath the heat shield was supposed to be ejected before reentry began. NASA offi­cials decided to leave them on, hoping that they would help hold the shield in place. In the end, the shield was fine-it turned out the problem was actually with the warning light. Reentry was smooth, although hot, and Glenn’s craft splashed down in the Atlantic Ocean. Soon after, he was picked up by a U. S. Navy ship.

hang glider is a small, light­weight aircraft with no engine. It is controlled by a person who hangs, suspended in a harness, below a triangular wing. The pilot controls the hang glider with body movements and a control bar.

Hang Gliding History

The hang glider concept dates from the pioneer days of aviation at the end of the nineteenth century. German aviator Otto Lilienthal made glider flights, hanging underneath batlike wings that he built himself. His contraptions fitted
the definition of hang glider because Lilienthal controlled them by swinging his body from side to side. He launched himself by running down the slope of a hill. Once in the air, Lilienthal’s control of the glider was always less than com­plete. Although he made more than

2,0 successful glides, a fatal crash in 1896 ended the career of this brave and inventive aviator.

Other inventors saw that the hang glider could lead to larger and more controllable airplanes. Hang gliding
experiments led to the development of larger, person-carrying gliders and then to the first powered airplanes.

Glider, or sailplane, flying developed for sport and recreation during the twentieth century, but hang gliders were mostly forgotten until the 1970s. In that decade, enthusiasts started building them as a cheap, enjoyable way of fly­ing. Their enthusiasm was aided by the availability of lightweight metals, such as aluminum, to construct the frames. New, tough, plastic-based materials were ideal for the wing surfaces. Hang gliding started in the United States, and it soon became popular in other countries.

Today, hang gliding is a popular sport with people who cannot afford to buy or rent a full-size glider. Hang glid­ing equipment is simpler and less costly. These small, portable aircraft are also excellent for people who enjoy flying in places that are not suitable for launch­ing a conventional glider. One of the joys of hang gliding is that the pilot can take the glider almost anyplace flying is permitted. If conditions are suitable, the pilot can be up in the air within a few minutes of unloading the glider from a car trailer. A hang glider is collapsed and folded for transportation and stor­age when not in use.

he Hubble Space Telescope is a reflecting telescope, one that col­lects light from distant objects. Launched into space in 1990, Hubble is run by the U. S. National Aeronautics and Space Administration (NASA) as an orbital observatory. The Hubble tele­scope is named for Edwin Powell Hubble (1889-1953), one of the world’s great astronomers. Its discoveries are valued by astronomers and other space scien­tists all over the world.

Discovering the Universe

At the beginning of the twentieth centu­ry, most astronomers thought there was only one galaxy visible in the universe— the Milky Way—the galaxy of which our Sun and its planets are a tiny part. In 1924, American astronomer Edwin Hubble was using the 100-inch (254- centimeter) Hooker telescope at the Mount Wilson Observatory, near Los Angeles, California. He observed anoth­er galaxy, Andromeda—one of countless galaxies, all of which are apparently moving away from one another at enor­mous speed. Hubble was the first astronomer to propose that the universe was actually expanding. For the first time, scientists realized the true vastness of the universe with its unimaginable number of stars.

Astronomers knew that their optical (light-collecting) telescopes on Earth

HUBBLE FACTS

• Hubble is 43.5 feet (13.3 meters) long-about the length of a school bus-and weighs 24,000 pounds (11,000 kilograms).

• Hubble orbits Earth at a height of about 375 miles (about 600 kilo­meters) and makes one orbit every 97 minutes.

• Compared to the largest telescopes on Earth, Hubble is not especially big-its primary mirror has a dia­meter of 7.9 feet (2.4 meters). It has a secondary mirror, just 12 inches (30 centimeters) in diameter.

• The telescope’s angular resolution, or sharpness of vision, is remarkable.

A person with vision as sharp as Hubble’s could stand in New York City and see bugs on a tabletop as far away as San Francisco.

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could give only a blurred picture of space. Gas and dust in Earth’s atmos­phere make the stars appear to twinkle, but these substances make it difficult to observe faint, distant stars. The atmos­phere also blocks or absorbs electromag­netic radiation from space in wave­lengths other than visible light—radia­tion such as infrared, ultraviolet, gamma rays, and X-rays.

For a clearer view, observatories sited large telescopes on the tops of moun­tains, high above the “optical pollution.”

The idea for a telescope in space, to pro­vide even more clarity, was proposed in 1946 by American scientist Lyman Spitzer. At the time, however, there was no way to get a telescope out there.

Food for the astronauts is brought up from Earth by visiting spacecraft. Most of the food is processed and packaged in pouches or cans, and all the astro­nauts have to do is heat it in a small food warmer or oven. Some food is dehydrated, and the crew adds water to it before eating. Small amounts of fresh food, such as fruit and vegetables, are delivered by spacecraft during their rou­tine trips. Almost all food is stored at room temperature. Although there is a small refrigerator, saving electrical power is a priority, so refrigeration is a luxury in space.

ISS crew members wear casual clothes—often a shirt and shorts or pants. They select their clothing before launch, and often the clothes are sent up to the space station before they arrive there. Astronauts sometimes wear cover­alls for work. There is no washing

О The crew of ISS Expedition Three included two Russians and an American who spent 128 days in 2001 manning the space station.

machine, and so space station crews do not change their clothes very often. Astronauts make their work clothes last, on average, ten days between changes. Underwear and socks are changed every other day. Discarded, dirty clothing is put in a disposal bag and shipped out on the next visit­ing Progress spacecraft. When the unmanned Progress burns up as it reenters Earth’s atmosphere, the dirty cloth­ing, along with the other space station garbage, burns up with it.

When they are off duty,

ISS crew can relax and talk to family and friends on Earth, listen to music, watch movies, play games, read, and work on keeping fit. The human body tends to weaken during long space flights in weight­less conditions, so exercise is a very important part of the astronauts’ routine.

Each crew member is provided with a pair of running shoes to wear when exercising on the treadmill, and another pair of shoes to wear when working out on the exercise bike.

SPACE GOLF

Most of the work done on the space sta­tion is serious science, but in November 2006 two astronauts—Mikhail Tyurin and Mike Lopez-Alegria—finished off a 5/2 hour spacewalk with a golf shot. Wearing Russian Orion spacesuits, the astronauts fixed a tee on a ladder out­side the space station. While Lopez – Alegria held his partner’s feet, the Russian played a one-handed golf shot. This stunt was paid for by a Canadian company in association with the Russian space agency. The ultra-lightweight golf ball (less than 100th the weight of a reg­ular golf ball) was expected to stay in orbit for only a few days.

he great English scientist Sir Isaac Newton (1642-1727) studied the way objects move when forces act on them. His work resulted in three laws of motion that scientists still use today.

On July 5, 1687, three volumes of work by Sir Isaac Newton were pub­lished. The three books were written in Latin, the language of science at that time. Their title is Philosophiae Naturalis Principia Mathematica, which means Mathematical Principles of Natural Philosophy. Natural philosophy was the name in Newton’s time for the science we call physics today. This work is so famous that it is usually simply called the Principia (the Principles).

The three volumes contain details of Newton’s three laws of motion and his law of gravitation. These laws explained and described how all sorts of objects move, even planets. Today, more than 300 years later, Newton’s laws of motion can be used to calculate how aircraft and spacecraft move.

First Law

Newton’s first law of motion says that an object at rest stays at rest, and a moving object moves at a steady speed in a straight line, unless it is acted upon by a force. This is another way of saying that an object does not start moving (or does not change the way it moves) all by itself. If it does start to accelerate, a force must be acting on it. To scientists, the word accelerate does not just mean speed up. It can mean to go faster or slower or to change direction.

An example of Newton’s first law is when an air­craft’s engine power is increased and the extra thrust makes the aircraft accelerate. When a rocket engine fires and a rocket rises off the launch pad, this is Newton’s first law in action as well. The tendency of an object to stay as it is (at rest or moving steadily) unless a force acts on it is known as inertia. Newton’s first law of motion is sometimes called the law of inertia. Inertia increases with

mass. This means that the more mass an object has, the greater the force that is needed to start it moving or stop it again.