Category FLIGHT and M ОТІOIM

In the late 1950s, the U. S. government began planning a space program. Officials looked for test pilots with at least 1,500 hours of flight experience, a college degree, and certain physical requirements. Glenn was one of 110 mil­itary officers who met these standards. After interviews and tests, he was one of only seven to be named to the first U. S. space program, Project Mercury.

Training began in early 1959 and continued for two years. Early in 1961, officials chose Alan Shepard, Virgil “Gus” Grissom, and John Glenn as the candidates for the first flights. The plan called for the astronauts to fly brief sub­orbital missions (suborbital flights go to very high altitudes, but do not go into orbit). At first they simply would be launched into space and return to Earth. Later, they would be sent on orbital flights, during which they would travel around the planet.

On April 12, 1961, the Soviet Union announced that it had launched Yuri Gagarin into space and that he had orbited the Earth once. U. S. leaders were bitterly disappointed by the Soviets claiming the first such success. They quickly followed Yuri Gagarin’s historic flight by sending Shepard into space. But while Gagarin had orbited Earth, Shepard just went up and came back down again. The Soviet achievement was much greater.

American frustration increased later in 1961. Grissom took a suborbital flight in July, but in August the Soviet pilot,

Gherman Titov orbited Earth for an entire day, circling the planet seventeen times. In view of this success, NASA officials dropped plans for any more suborbital flights.

The gravitational pull of other bodies also affects Earth. Twice a day, the sea rises up and washes up onto the coast. These daily rises and falls of the sea are the tides. They are caused mostly by the Moon’s gravity and, to a lesser extent, by the Sun’s gravitational pull. The Moon pulls water on Earth toward it, and a big bulge of water forms. As Earth spins, the high water moves around the world, causing one of the day’s tides. A smaller bulge left behind on the opposite side of the world causes the second tide

Just as the massive gray shape was close to its mooring mast, spectators were horrified to see flames erupt and spread rapidly through the fabric. Engulfed in flames, the giant airship crashed to the ground. In little more than 30 seconds, the greatest airship the world had ever seen had become nothing more than a red – hot mass of twisted metal.

It was amazing that anyone could survive such an inferno, but most of the crew and passengers did. Thirty-five of the ninety-seven people on board were killed: thirteen of the thirty-six passen­gers and twenty-two of the sixty-one crew members. Many died when they leapt from the airship. Those who stayed onboard as it crumpled to the ground were mostly able to scramble clear.

The horror of the Hindenburg’s end was broadcast on live radio, and this report, together with the press photo­graphs of the burning airship, had a worldwide impact.

How the Hindenburg fire started is not clear. Possible causes include a spark or a lightning strike, although the paint on the skin also has been blamed. There have even been allegations of sabotage. Whatever the cause, the consequence of the accident is undisputed. The loss of the Hindenburg meant the end of the air-

ship era. Other airship disasters, such as the loss of the USS Akron in 1933, already had shaken the public’s faith in airships. The Hindenburg tragedy was the final blow that effectively put an end to the historic age of the great passenger-carrying airships.

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SEE ALSO:

• Airship • Engine • Materials and

Structures • World War I

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During their stay on the ISS, astro­nauts carry out various experiments designed to study Earth from space. They also test and extend scientific and medical knowledge about the effects of spaceflight travel on the human body, animals, and plants.

The ISS is a science laboratory in orbit, with ongoing experiments in astronomy, physics, crystal growing, metallurgy, biology, and space engineering. Scientists in the space station can do research under the microgravity conditions that do not exist on Earth.

A new way to produce oxygen in space could be from plants, which release oxygen naturally during their food-making process, photosynthe­sis. One objective of sending astro­nauts to the ISS is to develop "space­gardening." A journey to and from Mars would take eighteen months – if astronauts are to build bases on Mars and stay there for months, they will need to make their own air. They could grow plants, both for food and to generate oxygen. The ISS has greenhouses in both the Destiny lab­oratory and in the Zvezda service module for plant experiments. The astronauts keep a record of the plants’ growth and harvest samples of their crops to send back to Earth.

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given off in small quantities by the human body, to prevent these gases from building up to unpleasant or dan­gerous levels.

Most of the oxygen inhaled by ISS astronauts is made by electrolysis, using electricity from the station’s solar pan­els. In the process of electrolysis, water is split into hydrogen gas and oxygen gas. Water is made of these two gases: each molecule of water contains two hydrogen atoms and one oxygen atom. Passing an electrical current through water causes these atoms to separate and to recombine as hydrogen and oxygen.

or takeoff and landing-and for taxiing around the airfield-air­planes need landing gear. Usually, landing gear consists of a set of wheels attached to struts that absorb the impact of landing. Some airplanes have skis for landing on snow or floats for landing on water. Helicopters have skids or (for
water landings) pontoons. Another name for an aircraft’s landing gear is the undercarriage.

Pioneer aviators used wheels, like automobile wheels, that created drag (air resistance) in flight. One way to reduce drag was to enclose the wheels in a streamlined shape. A better way to reduce drag – and thus boost lift-was to make landing gear retractable. To achieve this, a mechanism was added to raise the wheels out of the way after takeoff and lower them for landing. The machin­ery added weight, however, and so the extra speed came at a cost. At speeds of around 200 miles per hour (about 320 kilo­meters per hour), the advan­tages of retractable gear were not that great. Retractable gear was introduced on 1930s planes such as Boeing’s Monomail (1930), but many smaller planes kept fixed landing gear, which was cheaper, lighter, and reli­able. By the 1940s most military airplanes and passenger planes had fully retractable landing gear. The faster the airplanes flew, the more useful retractable gear became.

Conventional “tail-dragging” landing gear has three wheels. Two wheels, or sets of wheels,

О A close-up view of a landing gear bay during inspection shows how large some landing gear can be.

are positioned just in front of the air­plane’s center of gravity, usually under the wings, with a smaller wheel fixed beneath the tail. On the ground, the air­plane sits with its nose angled upward, resting on its tail wheel.

An airplane with “tricycle” landing gear also has three sets of wheels, but they are arranged differently. Two wheels-or up to twenty sets of wheels – are located between the center and rear of the aircraft, and a third wheel, or set of wheels, is beneath the nose. Tricycle landing gear keeps the plane horizontal on the ground, giving the pilot a better view. An aircraft with tricycle gear is also less likely to tip forward onto its nose when landing. An additional tail wheel or skid may be added to prevent damage to the tail during takeoff.

Tandem gear is used on heavy air­planes, such as the B-52. This bomber airplane has two sets of wheels, one behind the other. This tandem arrange­ment leaves the wings more flexible. To prevent damage to its long wings, the B-52 has a small, stabilizing wheel under each wing tip.

Mechanisms to operate the wheels include electric and hydraulic systems. Landing an airliner at over 100 miles per hour (160 kilometers per hour) puts a huge strain on the landing gear and on the wheels, which start spinning before touchdown. The struts that hold the wheels have very effective shock absorbers—hydraulic cylinders filled with oil and air-to absorb the impact of landing.

LANDING ON AN AIRCRAFT CARRIER

Airplanes such as the Hornet, designed for landing on the short runways of aircraft carriers, have tail hooks to slow them down. As they land, the tail hook catches one of several cables stretched across the deck. The cable acts like an extra brake to help stop the plane.

Landing gear takes up considerable space inside an aircraft. Some cargo planes, such the C-5 transport, have their landing gear installed in bulges on the outside of the fuselage, keeping the interior space free for freight.

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SEE ALSO:

• Aerodynamics • Aircraft Carrier ____ . /

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.