Category FLIGHT and M ОТІOIM

When World War II came to an end, hundreds of DC-3s no longer required by the military were quickly snapped up by airlines desperate for aircraft with which to start postwar passenger services. The DC-3 continued to do a valuable job even in the jet age, being used in civil avia­tion, in the military, and in scientific work. In 1956, a DC-3 flown by the U. S. Navy became the first airplane to land at the South Pole, while assisting an Antarctic expedition named Operation Deep Freeze. The DC-3 design was so effective that it never had to be radically altered. The plane did not change much during its sixty-plus years of service.

THE ADAPTABLE AIRLINER

Very few aircraft have been built in as many versions as the DC-3. It is truly one of the great multipurpose aircraft in aviation history, with about 100 different versions developed over the years for dif­ferent tasks. Some of those versions are:

• TC-47B Navigator trainer.

• XC-47 Experimental floatplane.

• AC-47D 1965 version with three 7.62-millimeter machine guns.

• SC-47D Search and rescue model.

• C-53 Skytrooper with twenty-eight seats and glider-towing hook.

• C-53B 1942 version with special Arctic equipment.

• E4D-4 U. S. Navy model, later adapted for electronic countermeasures.

О In 1946, a C-47 is used to take paratroopers on a practice jump at Fort Benning, Georgia.

The flywheel worked well, but it added a lot of extra weight to the engine. Another type of engine, the rotary engine, solved this problem. The engine’s massive cylinders spun around like the spokes of a wheel. The spinning cylinders did the same job as the fly­wheel, so the heavy flywheel was no longer needed. Famous World War I fighter planes, such as the Sopwith Camel, were powered by rotary engines.

The rotary engine was popular because it produced a lot of power for its weight, but it caused some problems. A heavy weight spinning on the nose of an aircraft affects the way it flies. Pilots who flew the Sopwith Camel found that it turned swiftly to the right, but it was much slower to turn to the left.

It also was difficult to build increas­ingly powerful rotary engines. As the cylinders tried to spin through the air, the air pushed back against them. This air resistance, or drag, slowed the cylin­ders down. The engine had to use some of its power to overcome this drag.

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Spinning the cylinders faster or adding more cylinders to produce more power caused even more drag and wasted more of the engine’s power.

orces are pushes or pulls that can cause objects to accelerate or change shape. Aircraft fly because they produce forces that overcome grav­ity and allow them to rise into the air. They move through the air because of the forces produced by their engines. Spacecraft, which are not traveling in air once they leave Earth’s atmosphere, use the force of gravity to move in a circle.

Basics of Force

In everyday language, acceleration means speeding up. To a scientist or engineer, however, acceleration can mean speeding up, slowing down, or changing direction.

If a force acts on an object that is free to move, it makes the object accelerate. The larger the force, the greater the acceleration. Acceleration also depends on mass. A small mass accelerates faster than a big mass pushed with the same force.

Every force has size and direction. Quantities such as these are called vec­tors. Forces acting in the same direction combine to produce an even larger force. When forces act in opposite direc­tions, they produce a force equal to the difference between them. If the forces acting on something exactly balance each other, there is no overall force, and the forces are said to be in equilibrium.

Some forces, such as friction, act when objects touch each other. These are contact forces. Other forces, such as gravity and magnetic forces, work at a distance. The objects that experience these forces need not touch each other. These are noncontact or distance forces.

Date of birth: March 9, 1934.

Place of birth: Gzhatsk, Soviet Union.

Died: March 27, 1968.

Major contributions: First person to fly in space; first person to orbit Earth. Awards: Order of Lenin; Hero of the Soviet Union.

uri Gagarin was born on a farm in a region west of Moscow in the Soviet Union (now Russia). He learned how to fly as a teen and
began training as a military pilot at the age of twenty-two. Just two years after Gagarin graduated from flight school, the Soviets began looking for candidates to become cosmonauts (the Soviet term for astronauts). Out of 3,000 applicants, they chose twenty men. Gagarin was one of them.

Training in the program was intense. It involved not only technical study and flight training but also physical and psy­chological tests. In January 1961, Gagarin was one of six candidates cho­sen for final testing. As the hopeful cos­monauts prepared for the tests, tragedy touched the Soviet space program. One of the candidates died when fire broke out during a training session. Gagarin and the other four candidates continued with their training.

On April 8, 1961, Soviet offi­cials chose Gagarin to be the first cosmonaut in space. His warm personality was a deciding factor. Officials thought Gagarin would make a good impression in his ensuing wave of public appear­ances as the first person in space. The next day, Gagarin was told of the decision.

On April 12, 1961, Gagarin entered a Vostok spacecraft to fly

О Like many American astronauts, the Soviet cosmonaut Yuri Gagarin trained first as a military pilot.

He returned to aviation after his famous journey into space.

on his mission, named Vostok 1. At 9:07 a. m., the command to ignite the booster rocket was given. Over the radio Gagarin said, “Poyekhali!” (“Here we go!”). The rocket began to rise and the booster was ejected. Gagarin and his capsule were in orbit.

Gagarin orbited Earth once, complet­ing the trip in a little less than an hour – and-a-half. Radio communication was lost briefly between tracking stations, and the lack of contact worried officials. However, communication was soon resumed-to everyone’s great relief.

Gagarin did not actually fly the spacecraft during his trip. Soviet officials worried that the first cosmo­naut might do something wrong, and they locked the controls. He did have a code to unlock them if anything went wrong.

The spacecraft’s reentry into Earth’s atmosphere was difficult. The last set of booster rockets was discarded just before reentry, but they did not completely sep­arate. That caused the spacecraft to jos­tle as it headed back to the ground.

As the spacecraft neared Earth, Gagarin opened a hatch and ejected from the capsule. He opened a parachute and reached the ground in a gentle descent. The historic first spaceflight by humans had been achieved.

After the successful landing, Soviet leaders rushed Gagarin to Moscow. On May 1, 1961, he stood on a platform next to the Soviet leader Nikita Khrushchev as thousands of people paraded on the streets below.

TRIBUTE TO A COMRADE

In 1969, Americans Neil Armstrong and Buzz Aldrin became the first humans to set foot on the Moon. They carried tokens with them to honor three U. S. astronauts and two cosmonauts who had died during the early days of spaceflight. One of those symbols-a medal-honored Yuri Gagarin. The medal is still on the Moon today.

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Fearing losing Gagarin in a fatal space accident, Soviet officials banned him from any more spaceflights. He remained in the space program, helping to train new cosmonauts. In the middle 1960s, Gagarin was promised he could go into space once more, and he began flying planes again to regain his status as a pilot. He died in a training flight in 1968 when his airplane crashed.

The people of the Soviet Union mourned the death of their hero. The Soviet training center for cosmonauts was named for him, and the town of his birth, Gzhatsk, was renamed Gagarin in his honor.

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SEE ALSO:

• Apollo Program • Astronaut

• Spaceflight • Space Race

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The development of the human body was shaped by the conditions on Earth’s surface, including gravity. On Earth, muscles and bones grow strong by working against gravity. Fluids in the body, mainly blood, are pulled down­ward by gravity.

Astronauts in orbit are pulled by gravity almost as strongly as they are on Earth, but the effect of gravity vanishes in orbit because the astronauts and their spacecraft are in a state of free fall. The combination of their speed with the downward pull of gravity means that their curving fall exactly matches the curve of the Earth’s surface. Astronauts in their spacecraft fall without getting any closer to the ground. This effect explains why astronauts float in space.

Gravity tells us which way is up and which way is down. Down is the direc­tion in which gravity pulls us, so down is toward the center of Earth. Up is the opposite direction. When the effect of
gravity is removed, up and down have no meaning. Astronauts sometimes have to take a moment to figure out which is the floor and which is the ceiling because they lose their sense of up and down. When they are in space, they can work, eat, or sleep just as comfortably with their heads pointing at the floor as any other way.

An astronaut’s body is affected by spaceflight. Without gravity to push against, muscles waste away and bones lose calcium. Fluids that are normally pulled downward spread out through the body, making astronauts’ faces fatter and their legs thinner. The balance mechanism in the ear does not work properly, so astronauts can feel dizzy and sick for the first days of a mission.

The Hindenburg had a control car that held the control room or bridge (as in a ship), the navigation room, and an observation area. The control room crew operated rudder and elevator controls. They could also release hydrogen gas (to make the airship lose height) or water ballast (to gain height).

The Germans used hydrogen, which was highly flammable, as a lifting gas. A safer alternative was helium gas, but the

only major producer of helium was the United States. The sale of helium to Germany was prohibited at the time because of political disagreements between the U. S. government and Germany’s Nazi regime. German airship engineers knew that hydrogen gas could be dangerous; there had been many accidents with balloons and airships caused by hydrogen catching fire. Only a spark was needed. To minimize the risk of fire, engineers had built in safety measures that included treating the skin of the airship to prevent any sparks caused by electricity or metal contact. Passengers were permitted to smoke, but only in a pressurized smoking room.

The passenger accommodation was inside the metal body of the airship. The Hindenburg had beds for fifty passen­gers, although more than 100 people could be carried, including the crew. Passenger cabins were small, measuring 6.5 feet by 5.5 feet (1.98 by 1.68 meters). Each was equipped with a sleeping berth, a folding washbasin, and a fold­ing writing table. Passengers spent most of their time in the public areas of the airship, looking out of the windows at the view of mountains, cities, and ocean passing beneath them. At one point, the giant airship even had a grand piano, but this was removed to save weight on the 1937 flights.

On October 31, 2000, the ISS was ready for the arrival of the first astronauts, who came in a Russian Soyuz craft. Expedition One, the first ISS crew, con­sisted of U. S. commander Bill Shepherd and two Russian cosmonauts, Yury Gidzenko and Sergey Krikalyov.

The first crew remained in orbit until March 2001, when Expedition Two arrived in the Space Shuttle Discovery. The crews changed places, and the Expedition One astronauts made a safe return to Earth. The Expedition Two crew remained on the space station until August 2001. Since then, regular exchanges of personnel have been made to maintain a constant three-person crew at the ISS.

О An unpiloted Progress spacecraft approaches the ISS in January 2007, carrying food, fuel, oxy­gen, and other supplies for the ISS crew. Progress spacecraft are destroyed after one mission by burning up on reentry into Earth’s atmosphere.

Today, transportation to and from Earth is supplied by the U. S. Space Shuttle, which will be replaced in the future by the Orion space vehicle. A new Russian shuttle, a European Automated Transfer Vehicle (ATV), and a sim­ilar shuttle spacecraft built by Japan also will take people and supplies to and from the ISS. In addition to the Space Shuttle flights needed to transport new components, fuel, and astro­nauts, unmanned Progress spacecraft arrive at regular intervals to bring supplies and remove waste. Visiting space­craft dock with the ISS, and crew members transfer to the station through an airlock.

Wilbur Wright was born April 16, 1867; Orville on August 19, 1871. As children, the brothers played with a toy helicopter that was driven by a twisted rubber band. Rubber-powered flying machines, invented in the 1870s by Frenchman

Alphonse Penaud, were popular toys. Such toys also helped inspire young inventors, including the Wright brothers. The young Wrights went into business, first as printers and then as bicycle makers. In their spare time, they built and flew kites. They became interested in the possibilities of human flight after reading about the pioneering experi­ments of Otto Lilienthal in Germany and Octave Chanute in the United States.

Lilienthal was killed in 1896 when his glider flipped over in midair. This accident convinced the Wright brothers that Lilienthal’s gliders did not have the right wings or control surfaces for safe, manned flight. They tested different wing shapes in a wind tunnel they built themselves. Then the Wrights brought their gliders from their home in Dayton, Ohio, to Kitty Hawk, North Carolina. Kill Devil Hill, a large sand mound at Kitty

Hawk, was a good place for test flights with few inquisitive spectators.

From 1900 to 1902, the Wrights flew three large gliders that carried a person. Flying the gliders, the brothers learned how to control the flimsy craft, using a system of “wing-warping” (altering the angle of the tips of the wings) to control the balance of the airplane. In the modern airplane, ailerons and elevators are used for this purpose, but the Wrights had to learn by experimenting to overcome the stability problems that had cost Lilienthal his life. In their wing­warping system, wires were attached to the wingtips and fastened to the pilot’s hips. By shifting his body position, the pilot could twist (warp) the tip of the wing to maintain control of the airplane. This method seemed to work in a glider, but would it work in a flying machine powered by an engine?

Building the Flyer

An airplane engine had to be small and light. No vehicle engine of the time was suitable, and so the only option for the Wright brothers was to build their own. They built a gasoline engine with a power output of 12 horse­power (9 kilowatts). The brothers fitted the engine into a flimsy-looking air­plane, much like the gliders they had already flown but with two propellers. They optimistically named their new machine the Flyer.

The Wright Flyer was a biplane with a total wing area of 510 square feet

(47.5 square meters). The wings consist­ed of wood frames covered with cloth. The aircraft’s little gasoline engine was linked by chains to two wooden pro­pellers, each 8.5 feet (2.6 meters) in diameter. One chain was crossed over so that the propeller it drove rotated in the opposite direction to the other. These contra-rotating propellers helped bal­ance the airplane.

The Flyer looked strange compared with most later airplanes. Its “tail” was at the front, and the propellers faced backward, as “pushers.” Very little was known about designing airplane pro­pellers, and the Wrights (who made their own propellers from wood) had to experiment to see which kind worked best. Aviation pioneers copied the screws used on steamships or the sails fitted to windmills, but neither was ideal for an airplane propeller.

To launch the airplane, the Wrights laid down a wooden rail 60 feet (18.3 meters) long. The airplane sat on a dolly-a small cart with two bicycle hubs
for wheels-that ran along the rail. The idea was that, as the engine pushed it along, the Flyer would lift off the dolly into the air and fly.

aterials and structures are gen­eral terms used in flight. They refer to the selection of materi­als used in aircraft and spacecraft and the science of constructing the craft for endurance and safety. Together and sep­arately, the two fields are vital to aero­space engineering.

Wood and Canvas

The first aircraft were made from wood because it was light, fairly strong, avail­able, easily shaped, and easy to repair.

The Wright brothers’ Flyer airplane of 1903 was made mainly from spruce and bamboo covered with canvas.

To save weight, wings were not solid wood. Instead, they had a skeleton-like wooden frame. Long timbers called spars ran the length of the wings. Shorter pieces of wood, called ribs, ran from front to back. Fabric stretched over the ribs gave the wings their shape. Rib­and-spar construction is still used today.

About 170,000 aircraft were built during World War I (1914-1918), and nearly all of them were wooden. Most early planes had biplane wings-one wing above the other-although the first powered monoplane had flown a short distance in 1906. Some were triplanes, with three wings stacked on top of each other. The wings were connected by wooden struts and tight bracing wires that formed a strong structure.

New Materials

Aircraft engines quickly became too large, heavy, and powerful for wooden aircraft. Manufacturers looked for a stronger material that also was light and easy to shape. The first material they chose was aluminum. Aluminum is a lightweight metal that is rustproof, but it is fairly soft and weak.

In the early 1900s, a substance called duralumin was made. It was an alloy, or

О Work begins on the frame of an airship built in the 1930s. The metal ring-frames that give the nose of the giant aircraft its shape are clearly visible.

a metal mixed with other substances. Duralumin was made from aluminum with tiny amounts of copper, man­ganese, and magnesium added. When heated and quickly cooled again, it was soft and easy to bend and shape into parts for aircraft. After being shaped, the duralumin slowly hardened and strengthened over the next few days, becoming much harder and stronger than pure aluminum. This process is called age hardening, and it made dura­lumin an ideal material for aircraft. Duralumin was used to make the metal frames that gave airships their shape.

Duralumin was not perfect, however. Although pure aluminum did not corrode, duralumin did. Corrosion is a chemical reaction that eats away at

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ALLOYS

The properties of a metal can be changed by mixing other substances with it to create an alloy. Brass is an alloy of most­ly copper and zinc, while bronze is made up of copper and tin. Steel is an alloy of iron and carbon, and stainless steel com­prises iron, carbon, and chromium.

Aluminum is alloyed with other met­als to make it stronger. Today, there are dozens of different aluminum alloys for building aircraft and spacecraft. Instead of a name, such as duralumin, each alloy now has a code number that shows what it is made of and what its properties are.

For example, aluminum alloys with num­bers beginning with 2 contain copper.

If the number begins with 7, the alloy contains zinc and magnesium. Other numbers indicate different ingredients.

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a metal. The most familiar example of corrosion is iron turning to rust in damp conditions. A new material called Alclad was invented to deal with the problem of corrosion in duralumin. It was made by coating duralumin with pure aluminum. The pure metal protected the alloy.

Mitchell was promoted to the rank of brigadier general for his service in World War I. After the war, he returned to the United States as second in command of the air service. Mitchell urged research into better bombing sights, more power­ful aircraft engines, and torpedoes that could be dropped by plane. He wanted to build planes that could carry troops and to form a separate air force with an inde­pendent command. He also managed to form an aerial force to fight forest fires.

Mitchell made sure that aviation stayed in the news and in the minds of Americans. He sent his pilots on speed and endurance flights to build publicity. In 1922, Lieutenant James Doolittle became the first person to fly across the United States in less than a day. The next year, Lieutenants John Macready and Oakley Kelly made headlines by fly­ing across the country nonstop. In 1924, Mitchell sent eight airmen in four planes to fly around the world. Two of the planes crashed along the way, but two arrived back in Seattle, Washington State (their departure point), six months and 26,345 miles (42,389 kilometers) after taking off.