Category FLIGHT and M ОТІOIM

Some shapes move through air more easily than others. Angular, boxy shapes catch more air. They also break up the smooth flow of the air, making it turbu­lent and chaotic. Slender, gently curving shapes create less drag than angular shapes, because air can flow around them more smoothly. Objects that air flows around smoothly are described as streamlined.

Airplanes are streamlined. Anything on their surface that might stick out into the air and cause unnecessary drag is smoothed out wherever possible to reduce drag. A plane’s metal skin is held

in place by fastenings called rivets. Airplanes used to be held together by rivets with round heads. The round heads stuck out and caused some drag. Today, the most streamlined aircraft are held together by rivets with flat heads that do not stick out. A plane’s metal skin is also polished or painted to give it a smooth surface that air can flow over easily.

All but the smallest and slowest planes have wheels that fold up inside them after takeoff. Doors close over the wheels to give the plane’s body a smooth, streamlined shape. If the wheels stayed down, they would spoil the plane’s streamlined shape and create a lot of drag. The doors and windows are also designed to be level with the plane’s skin.

When an object tries to move through air, the air pushes back. This resistance to motion is called drag. All aircraft experience drag as they move through air. When an airplane turns, the rising wing experiences more drag than the falling wing. The extra drag is caused by

SPECIAL AILERONS

Light aircraft and planes with long wings, such as gliders, suffer from the worst adverse yaw. Designers can make adverse yaw less of a problem by using special ailerons.

One type, called a Frise aileron, cre­ates more drag when it tilts up than when it tilts down. When a plane with Frise ailerons turns, both wings create extra drag, and so there is little or no adverse yaw.

Another way to deal with the problem is to make the aileron in one wing tilt down just a little, while the aileron in the other wing tilts up a lot. These ailerons are known as differential ailerons. The rising wing creates less drag because the aileron is not tilted downward as much. As a result, the yaw problem is reduced.

The Tiger Moth biplane had differen­tial ailerons. More modern light air­craft, such as the Cessna 152, also use differential ailerons.

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the downward-tilted aileron. This force, called aileron drag, acts like a brake, slowing down one side of the plane. It turns the plane’s nose in the wrong direction-the opposite direction to the turn. This effect is called adverse yaw. Yaw means turning to the left or right.

An airplane’s rudder is used to con­trol yaw. The rudder swivels to the left or right. A pilot corrects adverse yaw by turning the rudder to point the plane’s nose in the correct direction. If a plane banks to the right in order to turn right, for example, its nose yaws to the left. Adding some right rudder corrects this.

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SEE ALSO:

• Aerodynamics • Biplane • Lift and Drag • Pitch, Roll, and Yaw • Tail

• Wing

Airport controllers work from a control tower, a tall building with a good view of the run­ways. They use their eyes, as well as radar, to scan airspace. Incoming airplanes waiting to

О In the United States, military airplanes are controlled by military air traffic centers based on land and on ships at sea. These U. S. Navy controllers are monitoring incoming aircraft aboard the aircraft carrier USS Abraham Lincoln.

land circle in a vertical “holding stack” above the airfield. When a controller directs the lowest plane in the stack to start its landing approach, the next plane descends to take its place.

Once an airplane has touched down, the controller directs it to an exit taxi­way, clearing the runway for the next landing. At large, busy airports, for extra safety, radar also tracks planes on the ground. With an increasing number of flights every year-and tightened security checks at airports-air traffic controllers have a heavy workload. Delays at airports may happen when there are simply too many aircraft for the controllers to handle smoothly.

Modern navigational aids have increased air safety. The first naviga­tional aids for pilots were illuminated beacons on the ground. Next came radio
stations transmitting signals, which a pilot could use to fix a course. Modern airplanes have onboard radar and iner­tial guidance navigation systems, with computers that can fly the plane and plot a course automatically, using data from the satellites of the Global Positioning System (GPS) and other navigation systems. Most modern airliners can, if necessary, land automat­ically without any help from the pilot.

SEE ALSO:

• Airport • Altitude • Communication

• Navigation • Pilot • Radar

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One of the most useful military aircraft is the helicopter. Developed toward the end of World War II, helicopters were used in the Korean War (1950-1953) and the Vietnam War (1954-1975). They have been used in all conflicts since.

Helicopters can land combat troops, carry weapons and supplies, evacuate wounded, and fly around a battlefield to support ground troops and destroy tanks. Helicopters rescue air force pilots shot down over enemy territory as well as civilians in trouble on land or off­shore. Naval helicopters may take off from the decks of naval ships to carry out reconnaissance and anti-submarine patrols and to attack enemy ships.

Transportation

The aircraft used by the military to carry troops and equipment are known as transports. Some transports are huge. The U. S. Air Force’s biggest transport is the C-5 Galaxy; only slightly smaller is the C-141 Starlifter. During the Gulf War (1990-1991), the U. S. Air Force air­lifted more than 577,000 tons (523,340 metric tons) of supplies and nearly 500,000 personnel over distances of up to 7,000 miles (11,260 kilometers) to the Middle East combat zone.

The C-130 Hercules is used on shorter – range missions. This sturdy four-engine turboprop transport has been around since 1954. One of its jobs is to drop paratroops, but it also flies as a heavily armed “gunship.” To extend their range, many military airplanes can be refueled in the air by flying tankers, such as the U. S. Air Force’s KC-10.

Military airplanes provide trans­portation wherever people are in danger or in trouble. They fly emergency aid to the victims of hurricanes, earthquakes, and other natural disasters. They evacu­ate civilians from war zones. They bring food, medicines, tents, and other sup­plies wherever there are floods, famines, or fighting.

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SEE ALSO:

• AWACS • Bomber • Fighter Plane

• Helicopter • Missile • Radar

• Stealth

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n airship is a lighter-than-air craft that can be propelled, like a balloon with an engine. An air­ship also has a rudder and fins for steer­ing. Some airships have rigid sides, while others are soft until filled with gas, like a balloon. Airships were used in the first controlled, powered flights.

The First Airships

Before airships were invented, people had developed balloons for air travel. Balloons, however, are not steerable, and they drift with the wind. In the nine­teenth century, aviators tried to build balloons that could be controlled.

French inventor Henri Giffard (1825-1882) built the first airship in 1852. He constructed a cucumber­shaped balloon 144 feet (44 meters) long. The only engine available at the time was a steam engine. Suspended beneath the balloon was a platform on which Giffard fixed a small steam engine that he designed himself to make it as light as possible. The engine drove a propeller, which pushed the airship along at 5 miles per hour (8 kilometers per hour). In this airship, Giffard flew

for 17 miles (27 kilometers). His airship had no way of turning in flight, unfor­tunately, because it had no steering mechanism.

Charles Renard and Arthur Krebs addressed this drawback in 1884. Their airship, La France, had an electric motor plus a rudder and elevator for steering. The inventors proved their airship’s superiority by flying a circular course over Paris, which no balloon could do. This airship was known as a dirigible, from a French word meaning “steer­able.” The name dirigible came to be used for airships in general.

Other airships soon took to the skies. In 1888, Dr. Karl Wolfert of Germany tested the first airship powered by a gasoline engine-an engine already being tested in early automobiles.

The lunar module began its descent toward the target landing site on an area of the Moon called the Sea of Tranquility. By gazing out of the small window, Armstrong was able to choose a
flat landing area. Probes on the lunar module’s legs signaled when it was about 5 feet (1.5 meters) above the dusty surface. The engine cut out, and the Eagle landed on the Moon at 4:17 p. m. (Eastern Daylight Time) on July 20. After touchdown, Armstrong radioed to Mission Control in Houston, Texas: “Houston, Tranquility base here. The Eagle has landed.”

Armstrong and Aldrin wore space – suits to protect them from the Moon’s environment. There is no atmosphere on the Moon—to survive, the men needed the oxygen and steady temperature and air pressure provided by the suits.

Armstrong opened a hatch and climbed down a ladder onto the powdery surface, followed by Aldrin. The astro­nauts’ first steps on the Moon were recorded by a TV camera on the side of the lunar module. Armstrong said,

“That’s one small step for man, one giant leap for mankind.” The astronauts spent two hours on the Moon’s surface, collecting rock samples and setting up scientific equipment. Mission accom­plished, they reentered the Eagle.

The first manned Mercury spaceflight, launched by the United States in 1961, was ballistic. A rocket carried the space capsule into space. Forty-two seconds after liftoff, the rocket shut down, and the capsule separated from it. The cap­sule’s momentum carried it on upward. The capsule did not go into orbit around Earth. Gravity slowed its upward flight until, at a height of 118 miles (190 kilometers), it stopped climbing and began falling. Parachutes opened to slow the capsule’s fall before splashdown in the Atlantic Ocean.

THE BALLISTA

The word ballistic comes from a Greek word meaning "to throw." A weapon called the ballista was invented in ancient Greece in about 400 b. c.e. It was a throwing machine, like a huge crossbow. It hurled heavy stone balls or spears.

A spacecraft coming back to Earth can follow a ballistic trajectory, which simply means that it falls through the atmosphere. A ballistic reentry is uncomfortable for astronauts, however. The strong forces produced by drag slow the spacecraft down suddenly, like a car braking hard. Also, once the spacecraft begins its return to Earth on a ballistic reentry, it cannot be steered toward a particular landing area.

Another way to return to Earth is to use the spacecraft’s shape to create lift instead of letting it fall back to Earth. A spacecraft produces lift simply by tilt­ing, like a kite. As it plunges through the atmosphere, its angle to the oncoming air lifts it up.

A spacecraft returning from space in this way slows down more gently than in a ballistic reentry. By changing the amount and direction of its tilt, the
spacecraft can then be steered through the atmosphere toward a chosen landing site. The Space Shuttle comes back to Earth in this way.

SpaceShipOne, the first private spacecraft, uses a ballistic reentry. When its rocket engine shuts down after launch, at a height of 150,000 feet (45,720 meters), the spacecraft’s momen­tum carries it up another 150,000 feet (45,720 meters). From that point, SpaceShipOne falls back through the atmosphere. The pilot then retakes control and flies the spaceship like a glider to a landing on a runway.

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SEE ALSO:

• Gravity • Lift and Drag • Space­flight • Space Shuttle • Takeoff and Landing

A number of biplane types were still in military service when World War II began in 1939. Most were soon with­drawn, although there were exceptions. The last frontline biplane with the U. S.

Navy was the Curtiss SBC Helldiver, a dive bomber that was still flying at the time of the Japanese attack on Pearl Harbor in 1941. The Curtiss Seagull scout plane served with the U. S. Navy from 1933 until the end of World War II. This aircraft had the unusual distinction of outlasting at least two later designs intended to replace it. So did the Fairey Swordfish torpedo plane, which flew from British aircraft carriers during World War II naval battles, despite hav­ing a top speed of only 138 miles per hour (222 kilometers per hour).

Many wartime pilots learned to fly in a two-seater biplane. The De Havilland Tiger Moth, first flown in 1931, was still in use in the early twenty-first century.

Another very successful trainer biplane was the Boeing/Stearman Model 75, which became the standard World War II trainer for the U. S. military.

О Vintage biplanes are used today for recreation and for aerobatics demonstrations. These airplanes are flying while tied together.

Lloyd Stearman started building biplanes in 1927, and the Stearman Company became part of Boeing in 1939. Being slow and safe to handle, the Boeing/Stearman Model 75 was ideal for pilots who were learning basic flying skills. Ten thousand Model 75s, known unofficially as Kaydets, were built before 1945. After the war, many Model 75s were sold to the air forces of other nations, while others ended up as agri­cultural airplanes.

William Boeing still dreamed of a new, fast airliner. This dream came true in

1933 with the Boeing 247. The 247 is widely regarded as the first “modern” airliner. It was a low-wing, twin-engine monoplane, made completely of metal and with retractable landing gear. The 247 was flown by a pilot and copilot, while a flight attendant catered to the ten passengers. Two Pratt & Whitney Wasp radial engines gave the 247 a speed of 200 miles per hour (320 kilome­ters per hour), and it could fly for 745 miles (1,200 kilometers) before refueling.

By 1934, Boeing was operating an airline and manufacturing aircraft, which was prohibited by a new law (the

1934 Air Mail Act). The federal govern­ment ordered that Boeing be divided, and the company was split into United Aircraft, United Air Lines, and the Boeing Airplane Company.

О Workers install fixtures to the tail fuselage of a B-17 bomber in 1942.

In 1939 Boeing released the elegant 314 Clipper flying boat. Designed for passenger routes over the oceans, the Clipper had a range of 3,500 miles (5,630 kilometers). The same year, how­ever, World War II halted commercial flying between the United States and Europe and brought an end to the flying boat era.

Aircraft manufacturers had begun to design new warplanes some years before World War II began in Europe in September 1939. In May 1934 the U. S. Army issued a specification for a new bomber, and Boeing came up with the four-engine 299, which was first flown on July 28, 1935. Three weeks later, the 299 flew nonstop for 2,100 miles (3,380 kilometers) at an average speed of 252 miles per hour (406 kilometers per hour). Boeing’s delight at this success turned to gloom when, in October, the bomber crashed on takeoff. New prototypes were quickly in the air, however; the Y1B-17, first flown on December 2, 1936, became the B-17 Flying Fortress.

The cockpit is the compartment in an aircraft’s nose where pilots sit to fly the aircraft. It contains the flight controls, engine controls, and instruments that show information about the aircraft. An airliner’s cockpit is also known as the flight deck.

Flight and Engine Controls

Most aircraft have two seats in the cock­pit, side by side. Each seat has its own set of flight controls, so the aircraft can be flown from either one. There is one set of engine controls between the seats.

There are two main flight controls: the control yoke and a pair of foot ped­als. The yoke looks like a car’s steering wheel with the top cut off. Turning the yoke makes a plane bank to one side. Pushing on the yoke makes an airplane’s nose tip down so the plane loses height.

Pulling the yoke back tips a plane’s nose up and makes the plane climb. The pedals control the rudder that is in the tail of an airplane.

Pushing the left pedal turns the plane’s nose to the left. Pushing the right pedal turns the nose to the right.

The main engine control is called the throttle, or power

lever. If the aircraft has more than one engine, there is a power lever for each engine. Moving the power levers changes the amount of fuel supplied to each engine. Giving an engine more fuel makes it run faster and pro­duce more power.

Airbus airliners are unusual because they have no control yokes for steering the plane.

Instead, they are steered by small hand controllers, called side-stick controllers, that look like com­puter game joysticks. There is one on each side of the cockpit.