Category FLIGHT and M ОТІOIM

Modern propeller planes have their pro­pellers at the front, pulling the plane through the air. These are called tractor
propellers. In the early days of aviation, it was just as common for planes to have their propellers at the back, pushing the aircraft. The first successful powered air­plane, the Wright brothers’ Flyer, had two pusher propellers behind the wings.

Pusher propellers were popular because they did not get in the way of the air flowing over the wings. Without an engine or propeller in the way, the pilot had a great view ahead. It also was eas­ier to fit guns in the nose of a fighter

PROPROTORS

The strangest propellers are called proprotors. They have this name because they work like helicopter rotors part of the time and like propellers the rest of the time. Compared to regular propellers, proprotors are enormous. The propellers of a C-130 Hercules cargo plane, for example, are 13.5 feet (4 meters) across. The V-22 Osprey’s proprotors are nearly three times as big: 38 feet (12 meters) across. When the Osprey is on the ground, its engines are tipped up, pointing straight up in the air. Its two propellers look like helicopter rotors, and they work in the same way-when they spin, they lift the Osprey straight up into the air. Then the engines swivel forward, and the rotors work like propellers.

C The Osprey’s engines and pro­pellers tilt up (top left) for vertical takeoff. The engines tilt down and the propellers face forward (bottom left) for level flight.

plane that had its engine and propeller mounted in back.

Pusher propellers had drawbacks, however. They made it harder for pilots to escape from planes in the air without hitting a propeller. Also, the heavy weight of an engine at the back of a plane could be dangerous in a crash. It could move forward and crush the cock­pit. The problem of fitting guns to fight­er planes with propellers at the front was solved during World War I (1914-1918) by a device called an interrupter gear. It stopped a machine gun from firing when a propeller blade was in front of the gun barrel. The gun was synchronized to fire through the spaces between the blades. By the end of the war, nearly all fighter planes had their propellers at the front.

The idea of “artificial moons” orbiting Earth was put forward by a few scien­tists and science-fiction writers in the early 1900s. In 1945, British science fic­tion writer Arthur C. Clarke suggested in a magazine article that three satellites orbiting Earth could act as relay trans­mitters for worldwide communications. The visionary Clarke now has a satellite orbit named after him.

By the 1950s, there were rockets capable of launching satellites, although these were being developed primarily as military missiles. The American Rocket Society and the National Science Foundation both suggested using satel­lites for the scientific study of space. These groups proposed that, to mark International Geophysical Year (1957­1958), the United States should launch a science satellite.

The Soviet Union announced that it also would launch a satellite, but few people in the West took this claim seriously. So it was a great surprise when, on October 4, 1957, the Russians launched the world’s first satellite, Sputnik 1. Orbiting Earth every 96 minutes, Sputnik 1 caused a sensation. An even greater surprise followed on November 3, 1957, with the launch of Sputnik 2, which was bigger still and carried a dog named Laika. The United

О The first satellite launched by the United States was Explorer 1, seen here being installed on its launch vehicle in January 1958.

States launched its first satellite, Explorer 1, early in 1958. The “space race” had begun in earnest.

The Soviet Union launched hundreds of Cosmos satellites and also Molniya communications satellites, but seldom released much information about them. U. S. space launches were more public, and satellites were usually designated by their function: scientific, weather, com­munications, navigation, or Earth obser­vation. Only satellites for military use were kept secret.

Since the 1960s, France, China, Japan, Britain, India, and Israel have launched satellites with their own launch vehicles. Other nations have hired launches to put satellites into space. Once front-page news, satellites are now routine, with many commercial and multinational launches each year.

The first parachutists usually fell “like a sack being hurled out of a window,” in the words of Leo Valentin, a parachute jumper. (Valentin wore suits with batlike wings in an attempt to imitate bird flight. Wing suits often broke in midair, and Valentin was killed in an accident in 1956.) Parachutists soon found, howev­er, that by adopting a box position as they fell-stomach-down, with arms and legs bent slightly backward-they could soar like a bird rather than drop like a sack until their parachute opened.

Modern skydivers are taught to fall in the box position, although experi­enced divers also adopt other positions. The spread-eagle body acts like a wing, so a skydiver can fly around, and teams can formate (group together). Groups of as many as 282 divers have achieved formation in free fall.

An amazing demonstration of free fall maneuvering took place in 1987, in the sky above Arizona, when skydiver Gregory Robertson saved the life of fel­low parachutist Debbie Williams. She was knocked unconscious after colliding with another jumper, and she fell for

6,0 feet (1,830 meters). Robertson dived alongside her and opened her parachute at 3,500 feet (1,070 meters) above the ground. Only then did he open his own parachute.

Most airplanes are designed to be aero­dynamically stable. A stable airplane is one that is steady in the air. If it is rocked by a gust of wind, it steadies itself without the pilot having to do any­thing. Stability makes an airplane safer and easier to fly, but it also makes it more difficult to maneuver. Stable air­craft are designed to fly straight and level. That stability works well for a plane like an airliner, because passengers want to fly in planes that feel steady and turn gently.

A fighter plane that performed like an airliner, however, would not last long in an air battle. Fighters have to be able
to maneuver fast to chase other planes and escape danger. The way to make fighter planes more maneuverable is to make them less stable.

The latest fighters are highly unsta­ble. Sometimes, a pilot needs to make a sudden turn, climb, or dive. A fighter plane’s instability enables it to respond quickly to controls and make such a move much faster than a more stable aircraft. In fact, these extraordinary planes are able to fly only with the help of computers that constantly make

FLYING WINGS

Most planes have the same basic layout, with a pair of wings sticking out from a central fuselage (body) and a small tail unit at the back. The B-2 bomber (below) is different. It is a type of aircraft called a flying wing. The whole plane is one big wing. There is no tail. A flying wing is very streamlined, but it is also very unstable. If the nose of a flying wing tips up or down even a little, the plane can suddenly flip over. Most planes have a tail unit that prevents this from happening. A flying wing needs a control system to keep it under control in the air.

Flying wing aircraft have been built since the 1930s, but they never became very popular or widespread, because their lack of stability made them difficult to fly. The control systems available then were not able to tame their wild behavior. Control systems developed since the late 1980s work much better. The B-2 bomber, which first flew in 1989, relies on four flight computers to stop it from tumbling out of con­trol. The pilot operates the computers, and the computers fly the plane.

split-second adjustments to keep them under control. Without their flight com­puters, these planes would be impossible to control.

Scientists know a lot more about aerodynamics today than they did in the early days of aviation, but there is still a lot to learn. The development of new aircraft and faster aircraft, together with the use of new materials, continue to
present aerospace engineers with new challenges in aerodynamics.

SEE ALSO:

• Aircraft Design • Bird • Glider

• Lift and Drag • Materials and Structures • Wind Tunnel • Wing

• Wright, Orville and Wilbur

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The uppermost layer of the atmosphere is the thermosphere. It stretches from the top of the mesosphere up to a height of about 400 miles (640 kilometers). Temperature levels rise dramatically in the thermosphere, up to approximately 3630°F (about 2000°C).

THE OZONE HOLE

Some of the chemicals we use, espe­cially chlorofluorocarbons (CFCs), damage the ozone layer by breaking down the ozone. In the 1970s, scien­tists found a hole forming in the ozone layer over the South Pole. Measurements made by satellites confirmed this in the 1980s. To save the ozone layer, CFCs were banned by most countries. New measure­ments show that the damage is slowing down, although it may take up to 100 years for the ozone layer to recover completely.

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A spectacular light display sometimes occurs in the thermosphere. Near the North Pole, the light patterns are known as the northern lights, or aurora borealis. The southern lights, or aurora australis, are seen near the South Pole. Auroras are caused by particles of energy from the Sun. These particles stream through space past Earth. The Earth’s magnetism pushes them away everywhere except at the poles. As the particles dive into the atmosphere, they crash into gases in the thermosphere and create a glow.

Outside the atmosphere, the last remaining wisps of gas form the exos­phere. This may extend to about 6,200 miles (about 10,000 kilometers) from

Earth. The gases in this layer are mainly hydrogen and helium. The exosphere is so thin and the Earth’s gravity has such a weak hold on it that the gas particles can escape into space.

The thermosphere and exosphere contain part of the atmosphere known as the ionosphere. This layer contains particles with an electrical charge called ions. Some radio signals bounce off the

О The northern lights, or aurora borealis, occur in the thermosphere, the atmosphere layer that lies between 53 miles (85 kilometers) and 400 miles (644 kilometers) from Earth’s surface. The colorful ribbons and clouds of light can be seen regularly in northern regions of the world.

ionosphere. They can travel long dis­tances around the world by bouncing between the ground and ionosphere over and over again. Very short radio waves pass through the ionosphere instead of bouncing off it. These radio waves can be used to communicate with spacecraft.

The first airlines started operating with both airships and airplanes. Companies began selling tickets for regular passen­ger flights. The world’s oldest airline is the Dutch airline KLM, which started in 1919. Another pioneer airline was Australia’s Qantas (Queensland and Northern Territory Aerial Service), which

was founded in 1920. Two early U. S. airlines were Pan American World Airways (1927) and Trans World Airlines (founded as Western Air Express in 1925).

In the early days, airplanes had lim­ited endurance, and airfields were few. Flying boats, however, were aircraft that could land anywhere there was water. They were used for the long routes that traveled over oceans. In 1936 Pan American Airways began a passenger service across the Pacific Ocean using the China Clipper flying boat. The China Clipper carried forty-three passengers on day flights. On night flights, the number was reduced to eighteen passengers, who were provided with beds.

Some of the first land-based passen­ger planes were large biplanes, such as Britain’s HP-42, an airliner with four engines that flew from 1930 to 1939. It carried thirty-eight passengers at around 100 miles per hour (160 kilometers per hour). The HP-42 had to land every

500 miles (805 kilometers) to refuel on flights between England and India.

In the 1920s and 1930s, flights were often interrupted by unplanned land­ings, usually because of engine failure or bad weather. Pilots had just a few, basic instruments to guide them, radio was unreliable, airfields were few, and even heavy rain could cause a flight to be canceled.

In the 1930s manufacturers began to build all-metal monoplanes. Boeing’s Model 247 (1933) carried ten passengers at 180 miles per hour (290 kilometers per hour). The reliable Douglas DC-3 (1935) popularized air travel, becoming one of the most famous airliners. Some DC-3s are still flying today. The world’s first pressurized airliner, the Boeing 307, was able to fly above most of the bad weather that made flights uncomfort­ably bumpy for passengers.

World War II (1939-1945) inter­rupted all commercial aviation. When the war ended, airlines resumed flights with converted warplanes. The British Lancastrian was a civil version of the Lancaster bomber,

О The first interior created for a U. S. passenger jet was displayed in New York City in 1956, when the manu­facturer Boeing showed off its 707 Jet Stratoliner cabin, complete with models posing as flight attendants.

while the Boeing Stratocruiser was based on the B-29 bomber. New planes of the 1950s included the last of the long – range propeller-driven airliners, such as the Lockheed Constellation. This air­plane carried up to 100 passengers from New York to London at 340 miles per hour (550 kilometers per hour), cruising at 23,000 feet (7,000 meters).

Small aircraft also developed for commercial use in this period. The Cessna 152 of the 1950s, for example, was a two-seat monoplane with a piston engine that gave it a top speed of 125 miles per hour (200 kilometers per hour).

A carrier is controlled from a tall struc­ture, similar to an airfield control tower, known as the island. The island is on the starboard (right) side of the ship, leaving most of the deck clear for airplanes.

A carrier’s airplanes are usually stored on the hangar deck, from where

they are raised to the flight deck by an elevator. Aircraft may also be parked on the flight deck. The wings of many car­rier planes can be folded to save space.

Specialized airplanes, such as the tilt-rotor V-22 Osprey and the AV-8B Harrier jump jet, have V/STOL (short for vertical/short takeoff and landing) capability, which makes them especially useful for ships. Fast jets, such as the Navy’s F-14 Tomcats and F/A-18 Hornets, are launched by catapult to boost their speed for takeoff from the short aircraft carrier deck.

The carrier heads into the wind when planes are taking off or landing so that the force of the wind provides extra lift. Some naval aircraft have extra large

wing flaps to give the pilot good control at slow speeds. Some, such as the F-14, have variable-geometry wings. The pilot takes off and lands with wings in the extended position for slow flying, then moves the wings to the backward posi­tion for supersonic flight.

Landing on a carrier can be tricky for a naval pilot, even with modern radar and computer aids. There is a lot of ocean and only a narrow strip of flattop to aim for. As the plane touches down, a tailhook on its underside catches in one of four steel cables stretched across the deck, bringing it to a stop quickly. This device, essential to landing on an air­craft carrier, is called an arresting gear. Planes usually land on an angled land­ing section of the deck, situated on the port (left) side of the ship, so they can take off again if they miss the cables.

Carriers Today

Aircraft carriers are the biggest ships in the U. S. Navy. Today’s nuclear-powered carriers are able to travel up to 1 million miles (1.6 million kilometers) without refueling. Other countries operate air­craft carriers, too, although some of these are medium-sized ships operating only helicopters or V/STOL jets that can take off from a short “ski-jump” ramp and land vertically.

SEE ALSO:

• Aircraft, Military • Bomber

• Fighter Plane • Helicopter • VTOL, V/STOL, and STOVL • World War II

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The first airship filled with helium was the Goodyear C7 (1921). Helium is safer than hydrogen, because it does not burn in air and cause explosions. Helium became standard on U. S. airships, for example the Shenandoah (1923). Accidents still occurred, usually caused by bad weather. Airships did not fly high enough to travel above a storm, and their slow speed made them diffi­cult to control in high winds. The Shenandoah was destroyed in a storm over Ohio in 1925. The British R-101 crashed over France in 1930 on its first flight to India, killing forty-eight of its fifty-four passengers and crew. After this crash, Britain abandoned its airship program.

The U. S. Navy ordered two Goodyear rigid airships that used helium, the Akron (1931) and the Macon (1933). The Akron carried 207 people in November 1931, a record for an airship. These eight-engine airships were flying aircraft carriers—each was equipped to carry four small fighter planes. The two were identical in size: 785 feet (239 meters) long, and they were the largest airships operated by the United States.

GRAF ZEPPELIN

Gas capacity: 3,708,040 cubic feet (105,000 cubic meters)

Length: 776 feet (236.6 meters)

Speed: about 68 miles per hour (about 110 kilometers per hour)

The most successful passenger airship was the German Graf Zeppelin, which was named for Ferdinand von Zeppelin (Graf, meaning "Count," was von Zeppelin’s title). Between 1928 and 1937 the airship carried more than 13,000 passengers without a single accident. Whenever it flew low over a city, excited crowds gathered to see the long, gray – colored shape pass slowly overhead. In 1928, piloted by Hugo Eckener, the Graf Zeppelin set a record by cruising almost

4,0 miles (6,436 kilometers). In 1929, it flew around the world in 21 days, 5 hours, and 31 minutes. The journey, cov­ering a distance of approximately 20,000 miles (about 32,000 kilometers), began and ended

Both giant airships were wrecked in accidents within two years of entering service, however. The Akron went down during a storm in the Atlantic Ocean in 1933, killing seventy-three men. Two years later, in February 1935, the Macon crashed into the Pacific Ocean.

The Zeppelins and most other big air­ships were filled with hydrogen gas. Hydrogen gas gives more lift than other gases, but it catches fire easily when mixed with air. Although hydrogen was
known to be dangerous, its lightness and cheapness made it attractive to air­ship designers.

The German airship Hindenburg, sister ship of the Graf Zeppelin, began passenger flights between Germany and the United States. On May 6, 1937, the Hindenburg exploded and caught fire while docking at Lakehurst, New Jersey. The cause was the ignition of the hydro­gen gas by sparks. Of the ninety-seven people on board, thirty-five were killed.

The terrible end of this great aircraft destroyed passengers’ faith in airship travel. Commercial use faded as airships were replaced by airplanes.

The Apollo 17 mission returned with a record amount of Moon rock—256 pounds (116 kilograms). This material, together with earlier soil samples and scientific data from the Moon landings, was eagerly studied by scientists all over the world. By the 1970s, however, the public had become less excited about manned spaceflights. Politicians also lost interest. NASA turned its attention to more practical space travel in the form of a reusable spacecraft, the Space Shuttle. Since 1972, there have been no further Moon landings.

Leftover Apollo equipment was used in 1973 in Skylab, an orbital space sta­tion used as a science laboratory. Three crews of U. S. astronauts visited Skylab, the third crew making the longest visit of eighty-four days.

The last Apollo spacecraft flew in 1975. Astronauts Tom Stafford, Donald Slayton, and Vance Brand docked in Earth orbit with a Soviet Soyuz space­craft carrying cosmonauts Alexei Leonov and Valery Kubasov. This mission, the Apollo-Soyuz Test Project, was intended to further U. S.-Soviet collaboration in space. With this project, the Apollo pro­gram came to a positive end.

The Apollo missions captured the imaginations of millions of people around the world who watched the Apollo 11 astronauts on television, from the thrilling moment of launch to their Moon walks and final splashdown.

The Apollo program was also an immense technical and industrial achievement. Thousands of workers in dozens of companies and research insti­tutes worked together to build the necessary rockets, spacecraft, and equip­ment. The program also boosted progress in microelectronics and com­puters. This important new technology would soon come to be used in further space exploration and on Earth.

Balloons were soon flying over the ocean. Frenchman Jean – Pierre Blanchard and American John Jeffries flew across the English Channel in 1785. In 1793 Blanchard completed the first balloon flight in the United States, traveling from Pittsburgh, Pennsylvania, to Gloucester County, New Jersey.

Early balloonists learned to control flight upward or down­ward. By letting out air or gas, the balloonist could descend. Throwing out ballast (sand or lead weights) enabled the balloon (now lighter) to rise. The dis­advantage of a balloon is that it cannot be steered-it drifts with the wind. Sails, oars, and even paddlewheels were tried for steering, all without success.

Balloon flights became popular entertainment, but they also had serious uses. The U. S. Army’s Balloon Corps used balloons for observation during the Civil War (1861-1865). Balloonists made the first scientific researches into the upper atmosphere. In the 1930s, Auguste

Piccard, a Swiss scientist, rode in a sealed cabin beneath a hydrogen bal­loon. He rose more than 50,000 feet (15,240 meters). In 1935 American bal­loonists Albert W. Stevens and Orvil A. Anderson ascended to 72,395 feet (22,066 meters). This record remained unbroken until the 1960s, when other balloonists in the United States reached

over 100,000 feet (30,480 meters). Unmanned balloons have flown as high as 170,000 feet (51,816 meters).