Category FLIGHT and M ОТІOIM

Drone

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rone is a short name for a remotely piloted aircraft, also known as a remotely piloted vehicle (RPV). It is a small airplane that can be controlled by radio from the ground. A drone also can fly itself using data programmed into its com­puter system.

The main task of a drone is to fly reconnaissance missions, photographing enemy positions, but it also can be used as an attack weapon. The advantage of drones over manned aircraft is that they can operate over dangerous terri­tory without risk to a human pilot. Some drones have long endurance and can stay in the air for as long as two days.

Drone Development

A drone resembles a large model air­plane. Model enthusiasts build and fly radio-controlled airplanes, and the first drones were developed from this hobby. One of the first drones was the Hewitt- Sperry Automatic Airplane, which was developed during and after World War I (1914-1918).

During World War II (1939-1945), the U. S. Army used the Radioplane Target Drone, invented by Walter H. Righter and Reginald Denny. (Denny was at that time better known as a Hollywood actor.) The army used these miniature, unmanned airplanes as flying targets for pilots and antiaircraft gun­ners. Because they were meant to be destroyed by gunfire, the drone vehicles

VARIOUS ROLES

Modern drones have five main roles:

• As targets for gunnery practice by ground guns or pilots.

• For reconnaissance (obtaining information) over the battlefield.

• In combat, where there is high risk to human pilots.

• In research and development.

• In civilian use-for example, by police, or for geological surveys and environmental research.

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had to be cheap-the first Radioplanes cost $600 each in 1938 (which would be about $8,000 today).

Later models, such as the OQ-3 of 1943, could fly at 102 miles per hour (164 kilometers per hour). More than

9,0 OQ-3s were built, and all but six were destroyed during target practice.

Another kind of drone used in World War II was the German V-1 flying bomb. Its mission was offensive: It was basi­cally an unguided missile-a bomb with stubby wings and a pulse-jet motor (a kind of jet engine). The V-1 had a simple guidance system that determined how far it would fly before its engine cut out and it crashed to the ground, exploding on impact. The V-1 was fired from a launch ramp and flew at about 340 miles per hour (about 547 kilo­meters per hour). From June 1944, V-1s based in Nazi-occupied Europe were used to attack Britain. They were terrify­ing but relatively easy to shoot down because they flew in a straight line and had no way to alter their course after launch. The modern equivalent of the V-1 is the cruise missile.

Jet Engines

Propellers did not work well when the tips of their blades reached the high speeds that airplane manufacturers wanted. Companies looked for a type of engine that did not use a propeller.

In the 1920s, an aircraft engineer called Frank Whittle had produced plans for a new type of aircraft engine. Instead of using a propeller, it produced a jet of gas. His first jet engine was working by 1937. One of his engines was fitted to an aircraft, which made its first flight on May 15, 1941.

Although Whittle had invented the jet engine, his was not the first jet plane to fly. In Germany, Hans von Ohain had

THE AEOLIPILE

A man named Hero of Alexandria made a very simple jet engine about

2,0 years ago. It was called the aeolipile, which means wind ball.

It was a hollow metal ball with small nozzles (pipes), one on each side. The two nozzles pointed in opposite directions. The ball was supported so that it was free to spin. When the ball was filled with water and heated over a fire, the water changed to steam. The steam jetted out of the nozzles and made the ball spin.

been working on jet engines separately from Whittle. One of his jet engines was fitted to a Heinkel He-178 aircraft, which made the world’s first jet-powered flight on August 27, 1939.

The jet engine belongs to a family of engines called gas turbines, or turbine engines. Today, all but the smallest air­planes and helicopters are powered by turbine engines, because they pack a lot of power into a small space.

Thrust

The force that drives a jet plane forward is the thrust of its engine or engines. A jet engine produces forward thrust by accelerating gas backward. The forward thrust is a reaction to the backward force of the jet. Because of this, jet engines and rockets also are called reaction engines. A spinning propeller thrusts an airplane forward by accelerating the air backward.

Thrust is one of four forces that act on every powered aircraft. The other forces are drag, lift, and weight. Drag acts in the opposite direction to thrust. Weight is the force of gravity acting on the mass of the plane, pulling it down­ward. Lift is the upward force produced by a plane’s wings, a helicopter’s rotor blades, or the lifting gas of an airship.

Moving in a Circle

A force that acts in the same direction as an object’s movement can make it go

FORCE IN SPACE

Outside the atmosphere there is no air, so there is no lift or drag. Once a spacecraft is in space, it uses rockets to produce the thrust needed to change speed or direction. Without drag, a spacecraft does not have to keep firing its rockets to maintain its speed. Not all spacecraft travel completely outside the atmosphere. Spacecraft orbiting at a low altitude pass through the outer atmosphere.

The atmosphere causes drag, which slows spacecraft down, and they slowly lose altitude. To maintain orbit, they fire rockets to move back up to a higher orbit.

Spacecraft turn in space by firing small rockets or gas jets called thrusters. A spacecraft will continue to turn, even when a thruster stops firing, because there is nothing to stop it from doing so. A second thruster has to be fired in the oppo­site direction to stop it from turning.

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faster in a straight line. A force also can make something move in a circle. A turning force is also called torque or moment—the force applied by a wrench to tighten a nut, for example, is torque.

Earth’s surface and everything on it constantly moves in a circle. Spacecraft orbiting Earth are moving in a circle, too, or in an elongated circle shape

Thrustcalled an ellipse. An object can be made to move in a circle by a force directed toward the center of the circle. This sort of force is called centripetal force.

If a ball is whirled around at the end of a piece of string, the pull of the string provides the centripetal force that keeps the ball flying in a circle. The centripetal force that keeps everything on Earth’s surface and keeps orbiting spacecraft moving in a circle is gravity.

О The Moon stays in orbit around Earth because of Earth’s gravity, which is a centripetal force.

Project Mercury

In the late 1950s, the U. S. government began planning a space program. Officials looked for test pilots with at least 1,500 hours of flight experience, a college degree, and certain physical requirements. Glenn was one of 110 mil­itary officers who met these standards. After interviews and tests, he was one of only seven to be named to the first U. S. space program, Project Mercury.

Training began in early 1959 and continued for two years. Early in 1961, officials chose Alan Shepard, Virgil “Gus” Grissom, and John Glenn as the candidates for the first flights. The plan called for the astronauts to fly brief sub­orbital missions (suborbital flights go to very high altitudes, but do not go into orbit). At first they simply would be launched into space and return to Earth. Later, they would be sent on orbital flights, during which they would travel around the planet.

On April 12, 1961, the Soviet Union announced that it had launched Yuri Gagarin into space and that he had orbited the Earth once. U. S. leaders were bitterly disappointed by the Soviets claiming the first such success. They quickly followed Yuri Gagarin’s historic flight by sending Shepard into space. But while Gagarin had orbited Earth, Shepard just went up and came back down again. The Soviet achievement was much greater.

American frustration increased later in 1961. Grissom took a suborbital flight in July, but in August the Soviet pilot,

Project Mercury

О John Glenn gives a "ready" sign as part of prelaunch activities during the Mercury missions.

Gherman Titov orbited Earth for an entire day, circling the planet seventeen times. In view of this success, NASA officials dropped plans for any more suborbital flights.

Tides

Подпись: of the day. At regular intervals, the Sun adds to the Moon’s gravity to produce the highest tides or opposes the Moon’s gravity to produce lower tides.Подпись:The gravitational pull of other bodies also affects Earth. Twice a day, the sea rises up and washes up onto the coast. These daily rises and falls of the sea are the tides. They are caused mostly by the Moon’s gravity and, to a lesser extent, by the Sun’s gravitational pull. The Moon pulls water on Earth toward it, and a big bulge of water forms. As Earth spins, the high water moves around the world, causing one of the day’s tides. A smaller bulge left behind on the opposite side of the world causes the second tide

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The Crash

Just as the massive gray shape was close to its mooring mast, spectators were horrified to see flames erupt and spread rapidly through the fabric. Engulfed in flames, the giant airship crashed to the ground. In little more than 30 seconds, the greatest airship the world had ever seen had become nothing more than a red – hot mass of twisted metal.

It was amazing that anyone could survive such an inferno, but most of the crew and passengers did. Thirty-five of the ninety-seven people on board were killed: thirteen of the thirty-six passen­gers and twenty-two of the sixty-one crew members. Many died when they leapt from the airship. Those who stayed onboard as it crumpled to the ground were mostly able to scramble clear.

The horror of the Hindenburg’s end was broadcast on live radio, and this report, together with the press photo­graphs of the burning airship, had a worldwide impact.

Подпись: О As the Hindenburg came near to landing in Lakehurst, New Jersey, the giant airship erupted into flames in its rear section. It hit the ground almost immediately.

How the Hindenburg fire started is not clear. Possible causes include a spark or a lightning strike, although the paint on the skin also has been blamed. There have even been allegations of sabotage. Whatever the cause, the consequence of the accident is undisputed. The loss of the Hindenburg meant the end of the air-

ship era. Other airship disasters, such as the loss of the USS Akron in 1933, already had shaken the public’s faith in airships. The Hindenburg tragedy was the final blow that effectively put an end to the historic age of the great passenger-carrying airships.

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SEE ALSO:

• Airship • Engine • Materials and

Structures • World War I

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SCIENTIFIC EXPERIMENTS

During their stay on the ISS, astro­nauts carry out various experiments designed to study Earth from space. They also test and extend scientific and medical knowledge about the effects of spaceflight travel on the human body, animals, and plants.

The ISS is a science laboratory in orbit, with ongoing experiments in astronomy, physics, crystal growing, metallurgy, biology, and space engineering. Scientists in the space station can do research under the microgravity conditions that do not exist on Earth.

A new way to produce oxygen in space could be from plants, which release oxygen naturally during their food-making process, photosynthe­sis. One objective of sending astro­nauts to the ISS is to develop "space­gardening." A journey to and from Mars would take eighteen months – if astronauts are to build bases on Mars and stay there for months, they will need to make their own air. They could grow plants, both for food and to generate oxygen. The ISS has greenhouses in both the Destiny lab­oratory and in the Zvezda service module for plant experiments. The astronauts keep a record of the plants’ growth and harvest samples of their crops to send back to Earth.

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given off in small quantities by the human body, to prevent these gases from building up to unpleasant or dan­gerous levels.

Most of the oxygen inhaled by ISS astronauts is made by electrolysis, using electricity from the station’s solar pan­els. In the process of electrolysis, water is split into hydrogen gas and oxygen gas. Water is made of these two gases: each molecule of water contains two hydrogen atoms and one oxygen atom. Passing an electrical current through water causes these atoms to separate and to recombine as hydrogen and oxygen.

Landing Gear

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or takeoff and landing-and for taxiing around the airfield-air­planes need landing gear. Usually, landing gear consists of a set of wheels attached to struts that absorb the impact of landing. Some airplanes have skis for landing on snow or floats for landing on water. Helicopters have skids or (for
water landings) pontoons. Another name for an aircraft’s landing gear is the undercarriage.

Pioneer aviators used wheels, like automobile wheels, that created drag (air resistance) in flight. One way to reduce drag was to enclose the wheels in a streamlined shape. A better way to reduce drag – and thus boost lift-was to make landing gear retractable. To achieve this, a mechanism was added to raise the wheels out of the way after takeoff and lower them for landing. The machin­ery added weight, however, and so the extra speed came at a cost. At speeds of around 200 miles per hour (about 320 kilo­meters per hour), the advan­tages of retractable gear were not that great. Retractable gear was introduced on 1930s planes such as Boeing’s Monomail (1930), but many smaller planes kept fixed landing gear, which was cheaper, lighter, and reli­able. By the 1940s most military airplanes and passenger planes had fully retractable landing gear. The faster the airplanes flew, the more useful retractable gear became.

Conventional “tail-dragging” landing gear has three wheels. Two wheels, or sets of wheels,

О A close-up view of a landing gear bay during inspection shows how large some landing gear can be.

are positioned just in front of the air­plane’s center of gravity, usually under the wings, with a smaller wheel fixed beneath the tail. On the ground, the air­plane sits with its nose angled upward, resting on its tail wheel.

An airplane with “tricycle” landing gear also has three sets of wheels, but they are arranged differently. Two wheels-or up to twenty sets of wheels – are located between the center and rear of the aircraft, and a third wheel, or set of wheels, is beneath the nose. Tricycle landing gear keeps the plane horizontal on the ground, giving the pilot a better view. An aircraft with tricycle gear is also less likely to tip forward onto its nose when landing. An additional tail wheel or skid may be added to prevent damage to the tail during takeoff.

Tandem gear is used on heavy air­planes, such as the B-52. This bomber airplane has two sets of wheels, one behind the other. This tandem arrange­ment leaves the wings more flexible. To prevent damage to its long wings, the B-52 has a small, stabilizing wheel under each wing tip.

Mechanisms to operate the wheels include electric and hydraulic systems. Landing an airliner at over 100 miles per hour (160 kilometers per hour) puts a huge strain on the landing gear and on the wheels, which start spinning before touchdown. The struts that hold the wheels have very effective shock absorbers—hydraulic cylinders filled with oil and air-to absorb the impact of landing.

LANDING ON AN AIRCRAFT CARRIER

Airplanes such as the Hornet, designed for landing on the short runways of aircraft carriers, have tail hooks to slow them down. As they land, the tail hook catches one of several cables stretched across the deck. The cable acts like an extra brake to help stop the plane.

Landing Gear

О Tricycle landing gear and tail hooks can be seen on these F/A-18C Hornet air­craft used by the U. S. Navy’s Blue Angels team as they approach for a landing.

Landing gear takes up considerable space inside an aircraft. Some cargo planes, such the C-5 transport, have their landing gear installed in bulges on the outside of the fuselage, keeping the interior space free for freight.

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SEE ALSO:

• Aerodynamics • Aircraft Carrier ____ . /

The Heat Factor

Some aircraft, especially fast military aircraft, cannot be made from aluminum alloys. Airplanes heat up as they fly faster because they both compress the air they fly through and create friction as they rub against it. Planes flying faster than about two-and-a-half times the speed of sound heat up so much that an aluminum body would become danger­ously soft and weak. Aluminum melts at a temperature of about 1220°F (660°C).

The Heat FactorО A worker at the Douglas Aircraft Company in California during World War II fastens the frame of an A-20 bomber with thousands of rivets.

An aircraft that flies faster than three times the speed of sound reaches nearly 1000°F (538°C). These planes are built from a metal called tita­nium. The Lockheed SR-71 Blackbird spy plane was the first to be built from titanium in the 1960s. It could fly at three-and-a-half times the speed of sound.

The first manned space capsules used in the Mercury and Gemini space proj­ects also were made from titanium. The Apollo command module was made of a lightweight aluminum honeycomb sand­wiched between aluminum sheets. It had a heat shield to protect it from the high temperatures of reentry. The Space Shuttle is made of aluminum protected by insulation material.

Momentum

M

omentum is a property of all moving objects, including both aircraft and spacecraft. An object’s momentum is calculated by multiplying its mass by its velocity. Velocity is a vector-it has direction as well as size. Momentum, therefore, is also a vector.

A ball rolling down a hill gathers momentum as it goes faster and faster. A skydiver jumping out of a plane gath­ers momentum as gravity accelerates his or her rate of motion toward the ground.

Momentum depends on mass as well as speed, so a massive aircraft, such as a jumbo jet, has a lot more momentum

О Marbles on a slope gather momentum as they roll. Objects with higher mass have more momentum.

Momentum

than a smaller, lighter plane flying at the same speed. If an aircraft speeds up, its momentum increases. If it slows down, its momentum decreases. When it lands and comes to a stop, its momen­tum falls to zero.