Category FLIGHT and M ОТІOIM

Spaceflight began in the mid­dle of the twentieth century, but scientists and writers had imagined the possibility long before. In the seventeenth cen­tury, physicist Sir Isaac Newton set out laws of motion that determine the way in which objects move through space. Fantasies about space travel came from science-fiction writ­ers such as Jules Verne. In his 1865 book From the Earth to the Moon, Verne wrote of people flying to the Moon in a capsule fired from a huge cannon. In 1898, H. G. Wells imagined Martian spacecraft invading Earth in The War of the Worlds. At this time, people could only study the Moon and Mars by peering through optical telescopes, and there were many fanciful notions about alien life-forms on distant worlds.

Russian teacher Konstantin Tsiolkovsky (1857-1935) fig­ured out the mathematical principles of spaceflight by rockets. In 1923, Hermann Oberth (1894-1989) wrote The Rocket into Planetary Space, a book that predicted spaceflight.

Johannes Winkler Oberth (1897-1947), along with other German enthusiasts, formed the Society for Space Travel. One of its members was Wernher von Braun (1912-1977), who helped design the V-2 rocket of World War II and later worked on the U. S. space program. In 1926, American Robert H. Goddard (1882-1945) launched the world’s first liquid-fuel rocket.

The American Interplanetary Society was founded in 1930 by G. Edward Pendray, David Lasser, Laurence Manning, and others. In 1934, it became known as the American Rocket Society.

In 1963, it became part of the American Institute of Aeronautics and Astronautics. The American Rocket Society and the British Interplanetary Society both helped stimulate public interest in space­flight and encouraged test flights of rockets at a time when governments had little interest in spaceflight.

The Space Shuttle design has three main elements: the spacecraft itself, called the orbiter; an external propellant tank; and two solid-fuel rocket boosters. The orbiter looks like a stubby airplane with small, swept-back wings. The external tank holds fuel for the spacecraft’s main engines. The boosters provide most of the lift during the first 2 minutes of flight. All elements of the Space Shuttle are reused except for the external pro­pellant tank. The Space Shuttle’s two

TECHibTALK

THE SPACE SHUTTLE

Length: 122 feet (37 meters). Wingspan: 78 feet (24 meters).

Length with fuel tank and boosters: 184 feet (56 meters).

Cargo bay: 60 feet by 15 feet (18 meters by 4.5 meters).

Maximum payload: 50,000 pounds (22,700 kilograms).

Orbit altitude: about 185-250 miles (300-400 kilometers).

Orbit speed: 17,321 miles per hour (27,870 kilometers per hour).

Landing speed: about 215 miles per hour (345 kilometers per hour).

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solid-fuel boosters burn out 2 minutes after liftoff, at a height of about 28 miles (45 kilometers). They are landed by parachutes and used again. The external tank holds more than 1.57 million pounds (713,000 kilograms) of liquid hydrogen and liquid oxygen. When this fuel is used up, after 8 minutes, the empty tank is jettisoned over the ocean just before the Space Shuttle enters orbit. The tank then burns up in Earth’s atmosphere.

Once in orbit, a Space Shuttle pilot can fire small thruster motors to maneu­ver the craft. The thrusters may be used to change direction and to slow down, for example when docking with the International Space Station.

If an aircraft is to be stable and easily controlled, it must be well balanced. An aircraft balances around a point called its center of gravity, or center of mass. When fuel, passengers, cargo, or any other weight is added to an aircraft, it must be spread evenly throughout the aircraft. Too much weight at the front moves the center of gravity forward and makes the aircraft nose-heavy. Too much weight at the back makes it tail – heavy. More weight on one side than the other side makes it roll. An aircraft’s center of gravity must not be allowed to move too far in front of, or behind, its ideal position. If this happens, the air­craft can become difficult to fly or even dangerously unstable.

Military transport aircraft have a crew member called the loadmaster. Part of the loadmaster’s job is to place the cargo and passengers on board so that the plane’s center of gravity stays within its allowed limits. The center of gravity moves as an aircraft burns off fuel during a flight, so the loadmaster must take this into account.

An airliner’s weight and the position of its center of gravity are calculated before every flight. The amount of fuel it has to carry depends on its weight. A heavier aircraft needs more fuel. To cal­culate the weight and the position of the center of gravity, the crew needs to know approximately how much the fuel, passengers, and baggage weigh.

Most of the weight carried by an air­liner is fuel, and so the amount of fuel pumped into the aircraft’s tanks is meas­ured. The weight of each gallon, or liter, is known, so the weight of the fuel can be calculated. Most of the fuel is stored in the wings on each side of the aircraft.

The baggage is weighed too, but what about the passengers? Passengers are not weighed individually. Instead, air­lines use standard passenger weights, based on an average and multiplied by the number of passengers, to arrive at the total weight of all the passengers.

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HEAVY PASSENGERS

People are getting heavier. The weight of the average person has been increasing since the standard weights used by air­lines were set in the 1990s. Passengers also are bringing more carry-on baggage onto airplanes, and airlines have had to take this extra weight into account. Since the 1990s, the average passenger weight, including carry-on baggage, has increased from 170 pounds (77 kilo­grams) to 190 pounds (86 kilograms).

In winter, passengers wear more clothes, so the average passenger weight in winter increases further to 195 pounds (88 kilograms).

In 2005, because of these changed statistics, the U. S. Federal Aviation Administration (FAA) issued new figures for standard passenger weights. The average weight of an adult man with carry-on baggage was increased from 185 pounds (84 kilograms) to 200 pounds (91 kilograms) in summer and 205 pounds (93 kilograms) in winter. The weight for an average woman with carry-ons was increased from 145 pounds (66 kilograms) to 179 pounds (81 kilograms) in summer and 184 pounds (83 kilograms) in winter. The weight for children age two to twelve years old was increased from 80 pounds (36 kilograms) to 82 pounds (37 kilo­grams) in the summer and 87 pounds (39 kilograms) in winter.

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The tailplane is usually at the bottom of the fin, but some aircraft have theirs fitted halfway up the fin. This type of tail is called a cruciform tail. The word “cruciform” means cross-shaped, and a cruciform tail forms a cross shape when viewed from the front or back.

The tailplane also can be at the top of the fin. This type of tail is called a T-tail because the tail fin and tailplane form a T shape. Cruciform tails and T-tails are common in business jets, which often have their engines mounted on each side of the tail. Mounting the tailplane higher up the tail fin places it out of the way of the engines.

A few aircraft have been built with a V-tail. This has two fins at an angle, forming a V shape. Each fin has a moving part at the back, which is called a ruddervator because it works as both a rudder and an elevator. The F-117 Nighthawk attack plane has a V-tail. The V-tail causes less drag than other designs because it has fewer surfaces, but the aircraft’s tail has to be made stronger, and its control system is more complicated.

The Harrier is coming to the end of its life. It will be replaced by a STOVL ver­sion of the new U. S. fighter plane, the F-35 Lightning II, or Joint Strike Fighter.

The STOVL F-35, called the F-35B, works differently from the Harrier.

The designers of the F-35B faced the problem of producing a supersonic fighter and attack plane that also could manage vertical flight. A jet engine big enough and powerful enough to provide all the lift needed for short takeoff would make the plane too broad and heavy for supersonic flight. A different method had to be found to produce more lift from a smaller engine suitable for supersonic flight. The new aircraft achieves vertical flight by using both vectored thrust and extra vertical thrust from a lift fan.

When the pilot wants to perform short takeoff or vertical landing, the engine nozzle in the aircraft’s tail swivels downward. In addition, doors on the top and bottom of the plane open,
and a spinning fan behind the pilot blows air downward to provide extra lift. The fan is powered by a shaft that comes out of the front of the jet engine. When the fan is not needed, it is discon­nected from the engine and powered down. The F-35B will be the world’s first operational supersonic STOVL aircraft.

SEE ALSO:

• Aircraft, Military • Autogiro

• Helicopter • Lift and Drag

• Propeller • Takeoff and Landing

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During the first months of the fighting in 1914, airplanes buzzed around the skies over the armies below, but pilots had little more to do than the obsolete

cavalry galloping over the fields. Planes were used to observe enemy movements, rather like aerial versions of cavalry scouts on horseback. When opposing pilots met in the air, they waved-at least at first. As the war became serious, they began exchanging shots, first with pis­tols and then with machine guns. Most planes were two-seater biplanes with a pilot and an observer. The observer did the “scouting” and fired the gun.

The machine gun was mounted high to prevent bullets from hitting the pro­peller. Another solution to this problem was to move the propeller, putting it and the engine behind the pilot. This pro­duced “pusher” machines such as the Vickers FB5 Gunbus and the DH-2, one of a series of planes designed by British engineer Geoffrey De Havilland (1882— 1965). The weakness of the pusher was that it was exposed to attack from the
rear. To fire behind himself, the gunner had to stand on his seat and was at risk of falling out of the plane, with no parachute to save him. A device called an interrupter gear, which synchronized the firing of guns with the propeller, solved the propeller positioning problem.

In 1896, the brothers heard of the death of aviation pioneer Otto Lilienthal, who had a fatal accident while gliding. The story renewed the Wright’s interest in flying, and they began learning all they could about the subject. After the Wrights read everything they could find, they realized that many aviation books contradicted each other. They decided to conduct their own experiments.

The Wrights chose to carry out their tests near Kitty Hawk, a small village on the sandy barrier islands off the North Carolina coast. The area was low, with only one small hill, and had no trees.

Glider Experiments

The Wrights arrived at Kitty Hawk in September 1900 and spent several weeks carrying out tests with their first glider. At first, they flew the glider as a kite, with no one on board. Finally, in late October, Wilbur Wright made several flights.

The next year, the Wrights took a larger glider to North Carolina. Wilbur made more than 100 flights that sum­mer. The brothers were puzzled, howev­er, that the behavior of the wings did not match some calculations published by Lilienthal. They returned to Dayton to begin new experiments. The Wright brothers built a wind tunnel, which they used to carry out hundreds of tests of different wing shapes.

Armed with revised theories, the Wrights returned to North Carolina in 1902 with a new glider. This time, the results were spectacular. The Wrights carried out more than 1,000 glider flights. Some carried them more than 600 feet (185 meters), and once their glider stayed in the air for 26 seconds.

In 1947, a WAC-Corporal rocket reached a height of 244 miles (390 kilometers) above the White Sands testing ground in New Mexico. This flight opened the door to space-and encouraged government interest-because it showed that rocket technology could now launch satellites. Ten years later, the Russians launched Sputnik 1, the first artificial satellite. So began the space race between the United States and the Soviet Union. Key figures
in the two rival space programs were Robert Gilruth (1913-2000), appointed to direct the U. S. Mercury astronaut pro­gram in 1958, and Sergei Korolyov (1906-1966), who led the Soviet design team behind the Sputnik program.

Spaceflight was front-page news through the 1960s as the United States and the Soviet Union competed to send astronauts into orbit and probes to the planets. Public interest in space reached a peak during the Apollo Moon landings (1969-1972).

Since the 1970s, spaceflight has developed as a multinational scientific activity and a commercial business.

LIFE BEYOND EARTH

The Planetary Society was founded in 1980 by Carl Sagan, Bruce Murray, and Louis Friedman. Its aim is to "inspire and involve the world’s public in space exploration" and to search for extraterrestrial life (life beyond Earth). A worldwide program known as SETI (Searching for Extra-Terrestrial Intelligence) aims to collect evidence of life on other worlds through detecting radio signals and other forms of transmissions. Currently, Earth is the only planet known to support life, although scientists spec­ulate that life could exist on Earth – type planets orbiting other stars.

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Most satellite launches, for example, are intended for communications and entertainment, such as TV broadcasting. Spaceflight has become almost routine, although tragedies-such as the losses of two U. S. Space Shuttles, Challenger in 1986 and Columbia in 2003-reminded people just how dangerous space can be. Robot space probes have made astonishing voyages, not only to planets but far beyond our solar system. In 1990, NASA’s Voyager 1 probe took a photograph of Earth from a distance of 4 billion miles (6.5 billion kilometers) more than twelve years after it set out on a voyage through space that may well last hundreds of years.

Since the end of the Apollo program in the early 1970s, the most significant manned spacecraft has been the U. S. Space Shuttle. First launched in 1981, the Space Shuttle flies regularly into orbit, delivering supplies to the International Space Station.

The future of spaceflight will proba­bly see a return of astronauts to the Moon and possibly a manned explo­ration trip to Mars. A lunar base might be in existence before the middle of the twenty-first century, and the discovery of water on Mars could even make a Martian colony a possibility.

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SEE ALSO:

• Apollo Program • Astronaut

• Future of Spaceflight • Rocket

• Satellite • Space Probe

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space probe is a robot spacecraft sent far into space. To probe means to investigate, and that is what space probes do. Scientists have sent space probes to the Moon, to the planets, and beyond the solar system into deep space. A probe equipped with sensors, cameras, computers, and a radio transmitter can-within a few hours-discover more about a distant planet than has been gathered in cen­turies of Earth-based astronomy.

A robot space probe needs no air, water, or fuel during its journey through space. Its power comes from tiny nuclear plants or from solar cells that convert sunlight to electrical energy. Once set on its course, a probe can con­tinue to travel through space for years, sending images and data back to Earth.

Flyby probes pass close to their tar – get-a planet, a comet, or an asteroid. Orbital probes go into orbit around a planet or the Sun. Landers descend through the atmosphere to the surface.

Spacelab was a reusable laboratory designed for the Space Shuttle. It allowed scientists to perform experi­ments while orbiting Earth. The labora­tory, mounted inside the Space Shuttle’s cargo bay, was used on many missions. Many experiments tested the effects of weightlessness and space on living things. Spacelab missions have included life science experiments involving human astronauts as well as animals taken into space for scientific research. On April 17, 1998, more than 2,000 living creatures joined the seven crew members of the Space Shuttle Columbia (STS-90) for a sixteen-day mission called Neurolab. During the mission, twenty – six experiments focused on studies of the nervous system and how it develops and functions in space. Test subjects included crew members as well as rats, mice, crickets, snails, and fish. This was Spacelab’s last scheduled flight.

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Shuttle Missions

On a standard mission, the crew com­prises five to seven members. It includes a commander, a pilot, payload special­ists, and mission specialists. The special­ists could be engineers in charge of a piece of equipment or scientists con­ducting experiments. On a rescue mis­sion, a Space Shuttle could be flown by three astronauts to bring back all seven crew members from another Space Shuttle that was in trouble.

The Space Shuttle can be used to launch satellites, to repair faulty equip­ment, to transport supplies and crew to space stations, and to perform experi­ments in space. Its cargo bay can hold up to five satellites. A satellite that needs to be placed in a high orbit above the Space Shuttle’s maximum operating altitude of 400 miles (640 kilometers) is boosted by a small rocket motor. The cargo bay also can carry a space labora­tory, inside which scientists can work comfortably.

The Space Shuttle has performed many significant missions. Scientific experiments performed on board have increased knowledge about space travel, microgravity, and how these affect humans and other living things. Space Shuttles have transported satellites into space, transforming our ability to com­municate and broadcast information. The Space Shuttle is used to carry com­ponents and crew to the International Space Station. Space Shuttle missions have installed, maintained, rescued, and repaired numerous space facilities,

mostly notably the Hubble Space Telescope, which the Shuttle carried into space in 1990.

stall is a sudden loss of lift that can be experienced by an air­craft in some circumstances. Pilots are trained to understand why a stall can happen, how to recognize the early signs of a stall, and how to recov­er from a stall if one occurs.

How It Happens

When a fixed-wing aircraft slows down, the speed of the air flowing over its wings decreases, and the wings produce

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Separated (turbulent) flow

less lift. While flying slowly, the pilot can increase lift by raising the plane’s nose. As the wings tip up, they produce more lift and more drag. The angle of tilt of a wing is called its angle of attack. If the pilot keeps raising a plane’s nose, the angle of attack becomes so great that the air flowing smoothly over the wings suddenly breaks away from them and changes into turbulent, swirling flow. This angle is called the critical angle of attack. When the smooth airflow over the wing breaks down, lift is suddenly lost, and the aircraft drops downward. If one wing stalls before the other, the plane may roll into a spin.

Stall also affects helicopters. When a helicopter’s main rotor spins, the blades moving in the same direction as the air­craft are called the advancing blades, and the blades traveling in the opposite direction are called the retreating blades. Air flows over the advancing blades faster than it flows over the retreating blades, so the advancing blades experi­ence greater lift. If the airflow over the retreating blades is slow enough, they can stall. The helicopter experiences a sudden loss of lift called a retreating blade stall, but only on one side. The advancing blades still produce lift, so the helicopter rolls over to one side.

Recovering from a Stall

A pilot can recover from a stall in two ways. Pushing the control stick forward lowers a plane’s nose, so that it dives and picks up speed. Air flows smoothly over the wing again, and lift returns.

When a piston engine stops unex­pectedly, it is said to have stalled, but this is completely different from the aerodynamic stall that happens to wings. If a piston engine in an air­craft stalls, the plane does not drop like a stone. It becomes a glider. As it glides down, the pilot can look for a suitable landing spot while trying to restart the engine.

Jet engines can suffer from a problem called compressor stall. The spinning compressor blades inside the engine work like small wings.

Just like wings, they can stall. If the smooth airflow entering a jet engine is disturbed, the compressor blades may stall. A common cause of com­pressor stall is a bird strike, when a bird is sucked into an engine. When a compressor stall happens, the engine makes a loud bang and loses thrust, and the aircraft turns toward the affected side.

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The pilot then can raise the nose and fly straight and level again. The other way to recover from a stall is to increase engine power. When a stalled aircraft accelerates, it lowers its nose, and smooth airflow over its wings is restored. The two methods can be used together. A stall-as well as the recovery

from it-always causes some loss of alti­tude, so a stall near the ground can be particularly dangerous.

Large aircraft are equipped with sys­tems that sense when a stall is about to happen. They warn the pilot by shaking the control stick and sounding a warn­ing. If the pilot does nothing, the system may push the control stick forward to automatically lower the plane’s nose.