Category FLIGHT and M ОТІOIM

Like all airplanes, a glider must maintain a flow of air over its wings to sustain lift. Lacking a motor, a glider cannot fly level for long and still maintain that airflow. In calm air, the pilot must keep the nose of the air­craft angled slightly toward the ground-as the glider flies in a gentle dive, gaining speed, the airflow around the wings pro­vides lift. Having built up speed, it can rise up before descending again. A glider can soar to great heights if the pilot can locate rising air currents, known as thermals or updrafts. Carried up by such currents, the plane spirals upward, just as a vulture or buzzard soars on widespread wings and can fly for many hours in this way.

A glider has a high glide ratio, which determines the distance it can travel forward compared to its height loss. If a particular aircraft has a glide ratio of 40:1, it can glide 40 miles (64 kilo­meters) forward for every mile of altitude it loses. Once this glider has reached an altitude of around 3,000 feet (915 meters), the pilot has a good chance of flying around 120,000 feet (36,600 meters) in distance. If the pilot can gain greater height by soaring in a rising air current, the length of the flight will be

much longer. Some gliders have a glide ratio of 70:1. The Space Shuttle, by con­trast, has a glide ratio of only 4:1.

In 1936, a helicopter flown in Germany became the forerunner of the modern helicopter. The Focke-Achgelis FW-61

THE CONVERTIPLANE

A variation on the helicopter princi­ple is the convertiplane. This concept dates back to the autogiro of the 1920s. A convertiplane is capable of vertical takeoff and landing (VTOL) using rotary-wing flight, but then switches to normal layout for for­ward flight at speeds matching those of conventional airplanes. The idea was demonstrated in 1957 by the British Rotodyne, a helicopter-like airliner with wings and engines for normal flight. An example of a modern convertiplane is the tilt-wing CV-22 Osprey.

had two rotors mounted on outriggers (metal frames) on either side of the fuselage. This aircraft could take off and land vertically, it could hover, and it could fly at 76 miles per hour (122 kilo­meters per hour) during flights of over an hour in duration.

Igor Sikorsky, who had left Russia in 1919 and had become a U. S. citizen, was still busy working on ideas for heli­copters. In 1940, his new helicopter, the VS-300, made its first flight without being tethered to the ground. It was a

BELL HELICOPTERS

The Bell Aircraft Corporation was founded by American Lawrence Bell (1894-1956). The company made its name with airplanes, such as the record-breaking X-1, but became equally famous for helicopters, start­ing with the Bell Model 47 (1945). This small, bubble-nosed whirlybird stayed in production until 1973 and was used by armed forces all over the world. Its original piston engine gave the Model 47 a top speed of 105 miles per hour (169 kilometers per hour).

small, single-seat machine with a single rotor. The VS-300 was followed in 1942 by the XR-4, the first military helicopter to be put into production. A small number of XR-4s were flown by Allied forces during World War II (1939-1945). In 1943, an XR-4 became the first heli­copter to take off from a ship.

Date of birth: December 24, 1905.

Place of birth: Houston, Texas.

Died: April 5, 1976.

Major contributions: Set speed records for flying across the United States and around the world; founded Hughes Aircraft Company, a major producer of airplanes and satellites; built the world’s largest fly­ing boat; expanded TransWorld Airlines (TWA) into a major airline.

Awards: Harmon Trophy (twice); Collier Trophy; Octave Chanute Award; Congressional Gold Medal; member of Aviation Hall of Fame.

oward Hughes had a remarkable career that including setting world speed records as a pilot, creating one of the giant companies of the aerospace industry, and building a major airline. In the later decades of his
life, he lived almost completely isolated from other people.

Making Movies

Hughes was the son of a Texas oilman. The family became wealthy when Hughes’s father invented a drill bit that could dig deep through rock for oil. The company that made the drill bit—the Hughes Tool Company—generated huge profits that funded other business ven­tures. In 1924, at age eighteen, Howard Hughes gained control of his family for­tune when his father died.

Two years later, Hughes moved to Hollywood in Los Angeles, California, to follow his passion for movies. He began producing movies and took over direct­ing his favorite, Hell’s Angels. The movie portrayed air combat during World War I. Hughes bought nearly ninety vintage planes (forming the largest private air fleet in the world as a result) and filmed hours of aerial com­bat scenes. Released in 1930, the movie was a box-office success, but it came nowhere near earning back its stunning cost, $3.8 million (which would be ten times that amount today). From the late 1940s to the late 1950s, he owned a major motion pic­ture studio called RKO Pictures.

О After making the movie Hell’s Angels, Howard Hughes went on to make Sky Devils, a comedy about World War I aviation. Hughes reused many of the airplanes from his large fleet. He is shown here on the Sky Devils set in 1931.

in space in the form of rockets, which propel spacecraft by using jet thrust. Rockets carry the oxygen needed to burn their fuel. The fuel and oxygen-or a chemical containing oxygen-are mixed and burned, producing lots of hot gas. The gas rushes out of the rocket’s noz­zle as a fast jet, thrusting the rocket in the opposite direction.

Rocket-powered fighter planes were built in the 1940s, but they proved unpopular because of their short range and explosive fuel. Today, rockets are mainly used for launching spacecraft and missiles.

There are other ways of using jet power in space. Ed White made the first spacewalk by a U. S. astronaut during the Gemini 4 mission of 1965. He carried a gas gun called a handheld maneuvering unit (HHMU). As he floated in space, tied safely to the spacecraft by a tether, White squeezed the trigger to make gas squirt out of the gun. These tiny jets of gas were powerful enough to move him around. White found that he was able to maneuver easily with the gun, although it ran out of gas quickly. A similar device was tested during later Gemini missions. This time, the gun was supplied with gas by a hose from the spacecraft, so it worked longer.

The shape of a wing, curved on top and flatter underneath, is called an airfoil. When it slices through air, some of the air rises up over the curved top of the wing and down the other side.

The air that travels over the top of the wing speeds up and, according to a scientific law known as Bernoulli’s Principle, the pressure above the wing falls. In addition, air flowing over the wing is directed downward by the wing’s shape. According to another sci­entific law, Newton’s third law of motion, this downward motion of the air results in an upward motion of the wing. The force that pushes a wing upward is lift. If a wing is tilted up at the front, air is deflected downward even more pow­erfully by the curved top and also by the angled bottom of the wing. This pro­duces more lift.

Types of Drag

For a plane flying slower than the speed of sound, there are three main types of drag. They are induced drag, form drag, and skin friction drag. Induced drag is also known as lift-induced drag. It hap­pens when wings produce lift, and it is increased at low speeds.

Form drag depends on the size and shape of an aircraft. It increases as an airplane flies faster. This kind of drag can be reduced by making a plane slender and streamlined. A streamlined
shape is one that lets air flow around it smoothly and easily.

Skin friction drag depends on how smooth the surface of an aircraft is. It is greater at high speeds. Designers can reduce skin friction drag by making an aircraft as smooth as possible. Form drag and skin friction drag added together are sometimes called parasitic drag, or parasite drag.

With induced drag increasing at low speeds and parasitic drag increasing at high speeds, there is a speed in the mid­dle at which both types of drag are lower; the total drag, in other words, is the lowest it can be. An aircraft’s L/D number is highest at this speed, and its wings are working most efficiently. When designers produce a new airplane, they try to ensure that its cruising speed is the same as this minimum drag speed. The cruising speed is the speed at which

a plane usually flies, so aircraft design­ers want its wings to be most efficient at this speed.

Aircraft that fly faster than the speed of sound suffer from additional types of drag: wave drag and ram drag. Wave drag happens because high-pressure waves called shock waves form in the air around the airplane and slow it down. Ram drag is caused by air being slowed down as it enters the plane’s engines.

In the United States, microlight sport flying is controlled by the United States Ultralight Association (USUA), which was formed in 1985 and is based in Gettysburg, Pennsylvania. The associa­tion aims to encourage flying for fun as well as the promotion of good safety procedures and instruction by profes­sional flight instructors.

Every two years, the U. S. National Microlight Championships take place at a different location. The 2006 champi­onships were jointly promoted by the USUA and Aero Sports Connection (ASC), the two biggest microlight flying organizations in the United States. A

T E

U. S. team competes in the World Microlight Championships, in which there are four categories: airplane, weight-shift trike, powered parachute, and powered paraglider classes. Such competitions challenge the skills of the microlight pilot and the performance of the aircraft in various ways, including navigation tasks using GPS technology and precision landings.

N

SEE ALSO:

• Aileron and Rudder • Hang Glider

• Materials and Structures • Pitch,

Roll, and Yaw

_____________________________________________ /

Stories about people who fly appear in cultures across the world. People of East Africa imagined Kibaga, a warrior hero, who soared over his enemies, dropping rocks on their heads. The Incas of ancient Peru told of Ayar Utso, who grew wings and flew up to the Sun. Koroglu, of Azerbaijan, mounted a horse that grew wings and carried him into the sky. Gatutkaca, from Java, had a magi­cal jacket that allowed him to fly.

Perhaps the most famous myth about flying is the ancient Greek story of Daedalus and his son, Icarus. Daedalus had been brought by King Minos to the
island of Crete to work for him. After Daedalus helped Minos’s rival, Theseus, Daedalus knew that he and his son were in danger. For years, the two had secret­ly been making two pairs of wings out of eagle feathers attached to reeds by string and beeswax. Although the wings had not yet been tested, Daedalus and Icarus decided to use them to escape.

Before setting out, Daedalus warned his son not to fly too close to the sea, lest the spray of the waves wet the wings and cause him to fall. He also cautioned Icarus not to soar too high, which would allow the Sun’s heat to melt the wax and

destroy the wings. With those warnings, father and son put on the wings, climbed to a tower, and launched themselves.

The two soared over the sea, but Icarus was soon overcome with the thrill of flying. Forgetting his father’s cau­tions, he began to climb higher and higher. Just as Daedalus had warned, the Sun’s heat melted the wax holding his wings together. As the feathers fell off his arms, Icarus plunged into the sea and drowned.

The Greek hero Perseus fared some­what better. His quest was to kill Medusa, a monstrous woman with

JATAYU AND SAMPAATI

Hindu mythology has a story similar to that of Daedalus and Icarus. The brothers Jatayu and Sampaati were the children of the flying god Garuda. Half-gods, they had the form of vultures. The two brothers competed to see who could fly the highest. One day Jatayu soared higher than his older brother. Sampaati feared that the Sun would scorch his brother’s wings. He climbed above Jatayu to protect him. Jatayu was saved, but Sampaati’s wings were scorched off his back, causing him to fall to Earth.

______________________________________ /

SANTA CLAUS

Based on the story of a Christian saint, the legend of Santa Claus draws on elements from Holland, Germany, and Russia. Although this legend is hundreds of years old, Santa Claus’s ability to fly is rather recent. In 1823 an American named Clement Moore published a poem called "A Visit from Saint Nicholas." In the poem, Moore described how reindeer fly through the sky to take Santa from rooftop to rooftop, enabling him to reach every house. This airborne means of travel has become an important part of the Santa Claus myth.

_______________________________________ J

snakes for hair who was so ugly and evil that anyone who looked at her face turned to stone. With help from the

gods, Perseus obtained a pair of winged sandals that he used to fly to Medusa’s lair. He also borrowed the helmet of Hades, the god of the underworld, which made him invisible. With that ability, he could approach the monster unseen. As he arrived, Perseus looked at the mon­ster’s reflection in his shield, rather than directly at her face. Thus protected from her power, he was able to slay her.

Perseus did not suffer any evil conse­quences as a result of his flying. Unlike Bellerophon, he did not risk the gods’ anger. Instead, he gave the winged san­dals to the god Hermes.

The German legend of Wieland fea­tures an ironworker who fell in love with a beautiful swan-maiden. They married and lived happily for a time, but the swan-maiden yearned again for the freedom of flight and left him. Wieland was captured by an evil king who forced him to make weapons and other goods. Eventually, Wieland fashioned a suit with wings, which he used to escape from the evil king’s dungeon. After killing the king with arrows and gaining his revenge, he fulfilled his other goal by joining his swan-wife in the sky.

n ornithopter is a machine with flapping wings. Early inventors tried to copy bird flight by designing and building these aircraft, but their designs failed to get off the ground. Small ornithopters have flown as toy models and research experiments.

The principle behind the ornithopter is that the flapping wings provide both lift and propulsion. When people first dreamed of flying, they naturally tried to imitate birds, and some tried strap­ping wings to their arms. In about 1500, Italian artist and inventor, Leonardo da Vinci, made a sketch of a practical-look­ing ornithopter, but it never flew. One of
the first toy airplanes was a model flown at the court of the King of Poland in 1647, by an Italian inventor named Titus Burratini. His model apparently had fixed and flapping wings.

Flapping wings were not the answer for human flight, as glider pioneer Sir George Cayley (1773-1857) realized. Cayley decided that if an aircraft needed wings for lift, some other means must be found for propulsion. The answer was the fixed-wing airplane with a propeller. Cayley never flew a powered plane, however, and people continued to design flapping-wing machines.

A model ornithopter, flown in 1870 by Gustave Trouve (1839-1902), was powered by revolver cartridges. The exploding cartridge forced the wings down, and springs pushed the wings up again. Trouve’s ornithopter apparently flew for 230 feet (70 meters). Another French inventor, Alphonse Penaud (1850-1880), designed an ornithopter as well as model gliders. His models flew well and later inspired Orville and Wilbur Wright. Unfortunately, when his clever designs for flying machines were not taken up by the authorities, Penaud became depressed and committed sui­cide. In the 1890s, Australian Lawrence Hargrave built an ornithopter powered by using steam or compressed air to flap one set of small wings, while relying on large, fixed wings for lift.

A toy ornithopter flies because it is so lightweight. By the 1930s, rubber – powered model “flapping birds” were popular toys. These ornithopters could fly well in calm air for a short period of time. A small ornithopter, made from wood, wire, paper, or plastic, needs only a taut, twisted rubber band for power to make the wings flap. Model ornithopters fly best in the calm air inside a large building-rubber-powered ornithopters have achieved inside flight durations of more than 20 minutes. For outside use, there are radio-controlled ornithopter kits that are usually powered by a small electric motor.

The problem with ornithopters is finding a power plant that will make the wings beat up and down with sufficient

TECH^TALK

HOW AN ORNITHOPTER FLIES

An ornithopter creates all its thrust— and most of its lift—by flapping its wings. The wings beat in a twisting motion rather than directly up and down. They are joined by a center section that is moved up and down by the drive mechanism from the engine. The thrust comes from a low-pressure zone around the lead­ing edge of the wing that generates leading-edge suction. Many toy ornithopters fly nose-up to ensure enough lift. The tail is usually set at a steep angle of incidence, angled up.

_____________________________________________ /

power to generate both lift and propul­sion but is not so heavy that the machine cannot leave the ground. A leading designer of ornithopters is Dr. James Delaurier of the University of Toronto’s Institute for Aerospace Studies in Canada. His team has flown several small flapping-wing designs. In 2006 they successfully flew a larger machine, using a jet-assisted takeoff.

SEE ALSO:

• Aerodynamics • Bird • Cayley,

George • Da Vinci, Leonardo • Wing

_________________ J

Helicopters also change their attitude by pitch, roll, and yaw motions, but they do it differently from fixed-wing airplanes. Unlike airplanes, helicopters do not have wings, ailerons, elevators, or a rudder. Instead, they use their main rotor, the spinning blades on top, for pitch and roll move­ments. Tilting the whole rotor forward or back­ward changes the pitch of a helicopter. Tilting the rotor to one side or the other makes the air-

POINTING AT THE HORIZON

During daylight, pilots often keep an aircraft’s attitude under control by simply looking out of the window.

To keep an airplane flying straight and level, the pilot keeps its nose pointing at the horizon and the wings level with the horizon. This is called visual flight. If the horizon is not visible because of darkness or clouds, an instrument in the cockpit called the artificial horizon is used instead. It shows an outline of the plane’s wings in front of a ball with the horizon marked on it. Whatever way the plane moves, the ball rotates to keep its artificial horizon in line with the real horizon. A glance at this instrument shows whether or not the plane is level.

4_____________________________________________ J

craft roll. Speeding up or slowing down the small rotor in the helicopter’s tail makes the aircraft yaw to the left or right.

The Space Shuttle looks like a delta­wing airplane. It uses elevons in its wings to control pitch and roll. A rudder in its tailfin controls yaw. It also has a hinged panel called the body flap under its tail. No other aircraft or spacecraft has this control surface, which is used to trim the Space Shuttle’s pitch. In space, the Space Shuttle is unable to change its attitude in the same way as a plane
because elevons and rudders do not work in space. Instead, it fires small rocket thrusters in its nose and tail.

N

SEE ALSO:

• Aileron and Rudder • Control System • Lift and Drag • Tail

_____________________________________________ )

The force produced by a rocket engine is called thrust. The upward force of thrust must be greater than the downward force of gravity if a rocket is to take off. One measure of an engine’s power and efficiency is its thrust-to-weight ratio. Rockets have the highest thrust-to – weight ratios of all engines.

Most rockets work by means of chem­ical reactions, combining two chemicals, or propellants: a fuel and an oxidizer. The oxidizer, consisting of oxygen or a

О A rocket must produce huge upward thrust to get into space. It does this by producing a high – pressure jet of hot gases.

chemical containing oxygen, is needed to burn the fuel. Burning produces hot gases that expand rapidly and rush out of the engine nozzle at high speed. According to Newton’s third law of motion, the gas jet pushes against the rocket, and the rocket pushes back against the gas jet with the same force. The result is that the rocket is thrust in one direction as the gas flies in the opposite direction.

Other types of rockets produce thrust from a high-pressure jet of water, air, steam, or another gas. Ion engines pro­duce thrust by accelerating electrically charged gas particles.

One way to make a rocket accelerate faster, go farther, or carry a heavier pay­load is to make it lighter. For this reason, large rockets usually are built as a series of rockets standing on top of each other. The individual rockets are called stages. When each stage uses up its fuel, it falls away and the next stage fires. This enables the rocket to get rid of unneces­sary weight that would slow it down.