Category FLIGHT and M ОТІOIM

The U. S. Army obtained its first airplane, a Wright Flyer, in 1909. For almost two years, this was the only plane in what the Washington Star newspaper called the nation’s “aerial fleet.” In 1911 Lieutenant Riley Scott invented a bomb-

sight (a device for aiming bombs) made of nails and wire. He tested it using bombs held in a canvas sling beneath the airplane, and he managed to drop them within 10 feet (3 meters) of a 5-square-foot (0.5-square-meter) target from a height of 400 feet (122 meters). The army was not impressed.

Other people saw a future for bombers, however. In 1911 an Italian army officer named Giulio Douhet described how airplanes could attack an enemy’s communications and supply routes. The Italians were the first to use planes for bombing, in 1911, when one of their airplanes dropped four bombs on a Turkish camp in North Africa dur­ing a war between Italy and Turkey.

ommunication—the conveying of information-is essential to avia­tion and spaceflight. It would be almost impossible to communicate in these fields without radio. Pilots and astronauts use radio to communicate with each other and with air traffic, or mission, controllers on the ground. Aircraft and spacecraft also send and receive text and data by radio.

Commercial aircraft carry a variety of communications equipment. Aircraft crews use some equipment to talk to air traffic controllers and other pilots. Other equipment is used for sending and receiving text messages.

How Radio Works

Information sent by radio travels as a stream of invisible energy waves mov­ing at the speed of light, which is

186,0 miles per second (300,000 kilo­meters per second). A radio wave is actually two waves, one electrical and one magnetic, traveling together. A wave of this kind is called an electro­magnetic wave. Other electromagnetic waves include light and X-rays. The only difference between the different waves is their lengths—radio waves are longer than the other types of waves.

The length of a radio wave is referred to as its wavelength. The number of waves passing by every second is called the frequency. Radio frequency is meas­ured in waves per second, also called cycles per second, or hertz.

Radio signals are divided into fre­quency bands. The high frequency (HF) and very high frequency (VHF) bands are used for aircraft communications. A radio signal is transmitted at a particu­lar frequency, or waves per second. To receive the signal, a radio has to be tuned in to the same frequency. Airports and air traffic control centers have their own radio frequencies. During a flight, a pilot has to keep retuning a plane’s radio to match local frequencies.

VHF signals travel in a straight line from transmitter to receiver. When a transmitter and receiver are no longer in line because an airplane has traveled below the horizon, VHF radio contact is lost. Pilots can use VHF radio to talk to air traffic controllers up to only 230 miles (370 kilometers) or so away.

HF radio is used for communicating over longer distances. HF signals can travel beyond the horizon, because they bounce off a layer of Earth’s atmosphere called the ionosphere.

TECH lbTALK

FREQUENCY BANDS IN AVIATION

Band: High frequency (HF).

Frequency: 3-30 megahertz.

Band: Very high frequency (VHF). Frequency: 30-300 megahertz.

(1 megahertz = 1 million hertz)

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О This diagram shows the wavelength and fre­quency measurements for electromagnetic waves. Radio waves are long compared to X-rays, and so their frequency is comparatively low.

A radio link for sending signals up to an aircraft or spacecraft is called the uplink. A radio link for sending signals from an aircraft or spacecraft down to the ground is the downlink. The infor­mation to be sent by radio-whether a pilot’s voice or data from instruments-is added to a radio signal called a carrier wave. The information changes, or mod­ulates, the carrier wave. When the radio signal is received, the carrier wave is filtered out, leaving the voice or data.

DC-3s flown during the Korean War in the early 1950s and in the Vietnam War of the 1960s and 1970s looked, on the out­side, the same as the DC-3s that flew across the battle­fields of World War II. Inside, many changes were made as technology impro­ved. Radar and electronic equipment were updated. In some military variants, heavy machine guns were fitted so the airplane could operate as a low-flying gunship. There also were many updates to the engines over the years.

The last DC-3 was delivered from the factory in 1946, but there are still hun­dreds of DC-3s flying in many countries around the world, carrying passengers and cargo. Perhaps more than any other airplane, the DC-3 established flying as a safe, affordable, and popular form of transportation.

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SEE ALSO:

• Aerospace Manufacturing

Industry • Aircraft, Commercial

• Aircraft, Military • Aircraft Design

• Boeing • Engine • Materials and

Structures • World War II

After World War I, other types of engines began to replace the rotary engine. One of these was the radial engine. A radial engine looks like a rotary, but the radial engine’s cylinders do not spin.

Radial engines were made smoother and more powerful by adding more

cylinders. The most popular rotary engines of the time had nine cylinders, but the biggest radial engines used in aircraft had up to twenty-eight cylin­ders. Big radial engines caused a lot of air resistance, or drag. The drag was reduced by fitting a streamlined cover, called a cowling, over the engine to deflect air around it.

Radial engines were popular until the 1940s, when there was another change in aircraft design. Designers wanted to create faster, more streamlined planes, so they needed a slimmer engine than the radial to fit inside the slender nose of the aircraft. They chose the inline engine. Its cylinders are in a straight line, like a row of bottles. Bigger inline engines had two rows of cylinders meet­ing at the bottom, forming the shape of a letter V. An inline engine with two rows of six cylinders—twelve cylinders in all—is called a V-12.

When World War II began in 1939, fighters were powered by radial engines. By the end of the war in 1945, faster fighters such as the P-51 Mustang and the Spitfire were using V-12 engines. Radial engines continued to be used by bigger, slower bombers and airliners.

Friction is a force that resists movement. It is caused by surfaces catching or lock­ing together as they try to slide against each other. The size of the force depends on the roughness of the surfaces and on how much force is pushing them together. Friction between objects that are stationary is called static friction. Friction between objects sliding against each other is called dynamic friction, or kinetic friction.

Friction is vital in some places but unwanted, or even damaging, in other places. People, cars, bicycles, and other
land vehicles depend on friction between them and the ground to move around. Friction stops feet and wheels from slipping and gives them something to push against.

Inside engines, however, friction is not wanted. It slows down moving parts as they try to slide over each other. It also causes wear and overheating as sur­faces rub together. One way to reduce friction is to use oil to make surfaces more slippery. Using oil to reduce fric­tion is called lubrication, and the oily liquids used are known as lubricants.

Date of birth: July 18, 1921.

Place of birth: Cambridge, Ohio.

Major contributions: Pilot of first transcontinental flight to average super­sonic speed; first American to orbit Earth; oldest person to fly in space.

Awards: NASA Distinguished Service Medal; Congressional Space Medal of Honor.

John Glenn grew up in the small town of New Concord, Ohio. He became interested in science and aviation as a young boy. After graduat­ing from high school, Glenn studied at Muskingum College in his hometown and gained a degree in engineering.

Becoming a Pilot

In 1942, he joined the U. S. Navy and trained as a pilot. Glenn became an offi­
cer with the U. S. Marines in 1943. Soon after Glenn received his commission in the Marine Corps, he married Annie Castor, the childhood playmate who had become his girlfriend during high school and college.

During World War II, Glenn flew nearly sixty missions as a fighter pilot. After the war, he trained other pilots. When the Korean War broke out in 1950, Glenn volunteered for combat and flew nearly ninety more missions. In the two wars, he won six Distinguished Flying Crosses, along with several other mili­tary honors.

After the Korean War, Glenn became a test pilot. He gained national fame in 1957 by flying a plane from Los Angeles to New York City in less than 3/2 hours. That new speed record marked the first flight across the country with an average speed faster than the speed of sound.

Space probes sent across the solar sys­tem sometimes use the gravity of other planets to help them on their way. As a space probe flies toward a planet, the planet’s gravity pulls the probe and speeds it up. When it flies past the plan­et, gravity acts like a brake and slows it down again. If a planet stood still in space, this is all that would happen, and the probe would not gain or lose any speed. Planets do not stand still, how­ever, they move.

Jupiter flies around the Sun at about

30,0 miles per hour (about 48,000 kilometers per hour). If a space probe is flying in the same direction as Jupiter, it is swept along by the giant planet’s gravity. It speeds up by the amount of Jupiter’s speed, therefore gaining 30,000 miles per hour (48,000 kilometers per hour) without having to use any fuel. A planet’s gravity also can slow a probe

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GRAVITY ON OTHER PLANETS

PLANET GRAVITY

down or bend its flight path to steer it in a different direction. These maneuvers are called “gravity assist.”

Gravity assist enables a small space probe to visit distant planets without having to carry a huge amount of fuel. Space probes going to Mercury use Venus’s gravity to slow them down and set them on course for their destination. Space probes going to the outer planets use planets that they pass on the way to pick up the extra speed they need.

A planet has to be in the right place at the right time to give gravity assist to a space probe exactly when it is needed. For this reason, space probes often have to be launched within a certain period of time, called the launch window.

О Spanish astronaut Pedro Duque watches a water bubble float between himself and the camera on board the International Space Station. The bubble, like a lens, shows the astronaut’s miniature image.

The Hindenburg flew regular passenger services across the north Atlantic Ocean. The east-west trip from Frankfurt,

Germany, to Lakehurst, New Jersey, took 65 hours. Flying in the opposite direc­tion, from North America to Europe, took only 50 hours because of favorable tailwinds. During 1936, the Hindenburg made ten trips across the North Atlantic. The giant airship flew so well that engi­neers decided they could add ten extra passenger cabins, one with four beds, for the 1937 flights.

Passenger airship flights were usual­ly suspended for winter, because the craft flew at low altitude and at low speed and could be affected by bad weather. The Hindenburg’s first trip in

О The vast, complex frame of the Hindenburg fills a giant building during the airship’s construction in 1934.

1937 was scheduled for May, and on May 6, after crossing the Atlantic Ocean, it loomed into sight above Lakehurst, New Jersey. It was an impressive spec­tacle, and a crowd had gathered to watch the airship come in.

Astronauts living on the space station depend on the ISS life – support systems. There is no air in space and no water. Air and water must be transported from Earth or made inside the ISS.

The life-support system pro­vides the crew with oxygen and absorbs the carbon dioxide gas they exhale. The system also has to deal with other gases, such as ammonia, which are

By late 1903 the Wright brothers were ready to try out their invention. On December 14, 1903, Wilbur got ready for the first takeoff. The pilot did not have a seat-he lay stretched out on his front, slightly to the left of center. The engine started, the propellers whirled, but the Flyer refused to lift off the rail.

On December 17, they tried again, this time with Orville as the pilot. It was a cold, windy day. At 10:30 a. m., Orville released the wire that held the Flyer to the launch rail, while Wilbur held the right wing steady. The engine hummed, the propellers whirred once again, and the Flyer rolled slowly along the launch rail and then lifted into the air. At a height of only 10 feet (3 meters) or so, it flew for about 88 feet (27 meters) before swooping back to land safely. Five peo­ple witnessed the historic flight from a lifeboat station nearby.

The Flyer made three more flights that day. On the last flight, Wilbur flew for 853 feet (260 meters). Their longest flight that day lasted just under a minute. It was difficult to

О A replica of the first Flyer is on display at Kitty Hawk, North Carolina, in the Wright Brothers National Memorial visitor center.

О The Wright Brothers Memorial Tower was complete in 1932. It stands at Kitty Hawk on top of Kill Devil Hill. The inscription at its base reads: "In commemoration of the conquest of the air by the brothers Wilbur and Orville Wright-conceived by genius-achieved by dauntless resolution and unconquerable faith."

estimate speed, but the Flyer probably reached about 30 miles per hour (48 kilometers per hour). The Wrights sent a message home, packed up their airplane, and went off for dinner.

Flyer III

Because the Wrights had conducted their experiments away from spectators, their first flight did not create an immediate sensation. The world learned of the breakthrough, however, because the brothers built Flyer II and then the improved Flyer III, which they regarded as the first practical powered airplane.

Flyer III had a wingspan similar to the Flyer, but it was slightly longer and had a more powerful engine. Flyer III made its first flight on June 23, 1905. Between that date and October 16, 1905, the Wrights made nearly fifty flights, some lasting more than 30 minutes. They demonstrated that their airplane could turn, bank, and fly a figure eight pattern with perfect ease. On October 5, 1905, Flyer III flew for 24.2 miles (38.9 kilometers) in 38 minutes.

The brothers were ready to offer their machine for sale, with flying lessons. Wilbur Wright went to France to give demonstrations of flying, while Orville

continued to display the plane in the United States. In September 1908, Orville Wright completed fifty-seven cir­cuits of the drill field at Fort Myer, Virginia, managing to stay in the air for over an hour.

The original Flyer of 1903 was pre­sented to London’s Science Museum by Orville Wright in 1928, but it was returned to the United States in 1948. It is now in the National Air and Space Museum in Washington, D. C.

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SEE ALSO:

• Aerodynamics • Aeronautics

• Biplane • Glider • Lilienthal,

Otto • Propeller • Wind Tunnel

• Wright, Orville and Wilbur

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