Category FLIGHT and M ОТІOIM

The Global Positioning System, or GPS, is a network of satellites that enables anyone on Earth’s surface, or flying above it, to find out exactly where they are. The system belongs to the United States, but it is not the only satellite positioning system. Russia has developed a similar system, called the Global Navigation Satellite System

О The first satellite positioning systems were set up by the United States and the Soviet Union to give their submarines a way of figuring out exactly where they were during long patrols of the vast oceans. In 1989, this sailor on the USS Alabama checks information provided by GPS to pinpoint the submarine’s location.

(GLONASS). A group of nations in Europe and elsewhere in the world is developing a satellite positioning system named Galileo.

The Idea

When the first satellites were launched into space in the late 1950s, scientists were able to locate them and follow their movements through radio signals the satellites sent back to Earth. They soon realized that this might work in reverse. A satellite’s radio signal could be used to figure out the location on Earth of the radio that received it.

Three satellites would enable a radio receiver to calculate its position on the ground. A fourth satellite would enable the receiver’s altitude to be calculated as well. In order to have four satellites in view above the horizon all the time,

there would have to be at least twenty – four satellites orbiting the planet. A pro­gram based on this idea, the Global Positioning System (GPS), was devel­oped by the U. S. Department of Defense.

First, scientists had to prove that such a system would really work. Two experimental satellites, Timation 1 and Timation 2, were launched in 1967 and 1969. In 1974, a third experimental satellite, Navigation Technology Satellite 1 (NTS-1), was the first satellite to carry an atomic clock. Finally, NTS-2 was launched in 1977 to test all the systems and software before the first GPS satel­lite was launched in 1978. The whole network of twenty-four satellites was completed in 1994.

Ever since the first reliable helicopters took to the air, these rotary-wing air­craft have been widely used all over the world for both military and commercial purposes. Helicopters are not cheap to operate, and they are noisy, but their flexibility has made them extremely useful that it is hard to imagine a world without them.

A disadvantage of a helicopter is that it is slower than a fixed-wing aircraft. Most helicopters travel at speeds of less than 200 miles per hour (320 kilometers
per hour). One way to make a helicopter go faster is to add jet-thrust engines or propellers for forward flight. This pro­duces a compound helicopter that can fly at more than 340 miles per hour (550 kilometers per hour).

The first helicopters had piston engines, but most modern helicopters are powered by a gas turbine jet engine called a turboshaft. Some helicopters, especially military craft, have short stubby wings that provide extra lift dur­ing forward flight. The wings also are used for attaching payloads and as mounts for missiles and other weapons.

The Soviet Union has built some of the world’s biggest helicopters, such as the Mil Mi-26, probably the heaviest helicopter ever flown. A rival U. S. heli­copter, the Sikorsky CH-53E Super Stallion (1974), used just one extra-large rotor with a diameter of 79 feet (24.08 meters). It could carry a crew of three and up to fifty-five troops.

While setting these aviation records, Hughes was building a powerful aircraft company, Hughes Aircraft, founded in 1932. When World War II broke out, Hughes hoped to produce aircraft for the U. S. war effort. Other manufacturers won the contracts for this work, howev­er, and Hughes only received a contract for two experimental planes.

The experimental aircraft Hughes produced were both innovative, but they were unsuccessful. The first crashed while Hughes was flying it. The second

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ACCIDENT AND INJURIES

Hughes’s first experimental plane, the XF-11, nearly killed him. It was meant to be a high-altitude spy plane that could be used to take photographs without being seen by enemy radar. Before it was finished, World War II ended. Hughes contin­ued working on the plane, however.

On July 7, 1946, he took it on a test flight that developed problems. The plane crashed, destroying three homes in Beverly Hills, California, in the process. The crash and resulting fire left Hughes with many injuries and severe burns. He began taking powerful painkillers while recovering from these injuries—drugs that led to an addiction that plagued him for the rest of his life.

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experimental aircraft was a flying boat so large that it could carry more than 700 passengers. The U. S. military hoped to use the giant aircraft to carry troops across the Atlantic Ocean without wor­rying about attacks by German sub­marines. Unable to get aluminum need­ed to build the plane, Hughes built it of wood. That produced the plane’s nick­name, the Spruce Goose (although it was actually made of birch, not spruce). Its official name was the Hughes H-4 Hercules. The Spruce Goose had a wingspan of 320 feet (98 meters), longer than a football field. The plane was flown only once, on November 2, 1947. That day, Hughes piloted it a distance of 1 mile (1.6 kilometers) in the harbor of Long Beach, California. The plane did not rise above 80 feet (25 meters). It remained in the harbor at the cost of a million dollars a year until Hughes’s death. The Spruce Goose is now dis­played in the Evergreen Aviation Museum in McMinnville, Oregon.

Personal jetpacks have become a reality in space. On Earth, a successful jetpack has proved harder to achieve, although the devices have featured in lots of sci­ence fiction stories. In stories set in the future, a character straps a jetpack on his back, fires up the engine, and takes off.

A few personal jetpacks have been built and used in real life. The 1984 Summer Olympic Games in Los Angeles,

California, began with a pilot wearing a real jetpack flying into the stadium.

Most of the personal jetpacks devel­oped so far, however, are not powered by jet engines. Their jet thrust is supplied by a small, powerful rocket. These devices also are known as rocket belts, or rocket packs. When the wearer wants to take off, a liquid called hydrogen peroxide is forced from tanks in the backpack into a reaction chamber. Hydrogen peroxide is similar to water, but it contains extra

oxygen. Inside the reaction chamber, a chemical reaction changes the hydrogen per­oxide into steam at a temperature of 1370°F (743°C). The steam jets out of two pipes that point downward, pushing the flier up off the ground. The jetpack is steered by means of tilting the jet pipes.

Even the most advanced model built so far can be flown for no more than about 30 seconds. Jetpacks powered by jet engines can make longer flights, but they are far more complicated to build and much more expensive.

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The astronauts also are anchored to the spacecraft by their boots or with a line.

Objects experience lift and drag when they travel through all kinds of gases, not just air. A spacecraft entering anoth­er planet’s atmosphere experiences drag. If it were the right shape, it could also
produce lift. Objects moving through liq­uids also experience lift and drag. The streamlined shape of a fish enables it to slip through water easily with minimum drag. Ships and submarines experience drag as they move through water. Ships called hydrofoils have underwater wings. As a hydrofoil accelerates, its underwater wings produce lift, and the ship’s hull rises up out of the water.

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SEE ALSO:

• Aerodynamics • Aircraft Design

• Bernoulli’s Principle • Force

• Glider • Laws of Motion • Thrust

• Weight and Mass • Wing

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Modern cruise missiles (missiles with wings and small jet engines) can trace their history back to the flying bombs built during World War II (1939-1945). The V-1 flying bomb was a jet-powered plane without a pilot. It was given the name of “Buzz Bomb” or “Doodlebug”
because of the characteristic buzzing noise its engine produced.

The engine used in the V-1 was a type of jet called a pulsejet. Air entered the engine through shutters, and then fuel was sprayed into it and ignited. The explosion snapped the shutters closed at the front and forced the hot gases out of the engine’s tailpipe. Then the shutters opened, and the process started over again. This happened about 100 times every second.

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STINGERS

The smallest missiles are light enough to be carried by a soldier. Stinger is a portable missile system that soldiers can use to shoot down low-flying air­craft. A soldier holds the launcher on his shoulder and waits for the missile to lock onto the target. When the mis­sile is fired, a small rocket hurls it out of the launch tube. Then the launch rocket falls away, and the main rocket fires at a safe distance from the soldier. The missile accelerates to twice the speed of sound, guiding itself toward the heat given out by the target.

missile test range in New Mexico.

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When the V-1 had flown the right distance to reach the target, a guillotine (sharp blade) cut the cable linked to its elevator, a flap in the V-1’s tail that tilted to control its height. Once the cable was cut, a spring pulled the eleva­tor down and sent the bomb into a dive.

A classic collection of stories from medieval times is One Thousand and One Nights. These tales from Southwest Asia relate the adventures of kings and councillors, fishermen and merchants, soldiers and slaves. In this world of magic and mys­tery, some stories involve that age-old dream of humans flying.

О By the 1800s and 1900s, science fiction had replaced ancient myths and legends about flight. Author Jules Verne described a journey to the Moon and back in From the Earth to the Moon (1865). The launch of Verne’s fictional craft (illustrated here) took place in Florida, which later became the real launch site for the U. S. space program.

MODERN MYTHS

Myths from many different cultures tell of gods who come down to Earth to meet with humans. Some people claim that these stories reveal vis­its from space travelers in ancient times and that some ancient drawings show gods in spaceships or wearing helmets. Scientists dis­miss these claims, however. Today, stories about aliens from other planets focus on unidentified flying objects, or UFOs. Since UFO sightings in Washington and Idaho gained great media attention in 1947, sightings of UFOs have increased dramatically. By the 1950s, some people were beginning to connect UFOs with religious and supernatural beliefs. Claims of UFO sightings are most common in the United States. The kinds of UFOs people report most frequently are flying saucers or moving lights.

О A photograph from the files of the Central Intelligence Agency (CIA) shows what the photographer claimed was a UFO over New Jersey in 1952.

Many UFO images appeared in the period, and there was much doubt about the authen­ticity of the images.

Even a handkerchief will act as a para­chute if strings are tied from each corner to a small weight. The idea may have struck someone far back in history. The Chinese invented the umbrella, and they may have adapted the umbrella shape to try parachuting 1,000 years ago. In around 1485, Italian artist and inventor Leonardo da Vinci drew a cone-shaped

parachute, but it is not known whether his device was ever tested.

The first parachute jumps recorded in Europe were made in 1783 by Sebastien Lenormand of France, who dropped weights and animals from a tower using a parachute that looked rather like a lampshade. In 1797, Andre Jacques Garnerin made a circular parachute of cotton cloth, from which hung a basket for a passenger. On October 22, 1797, he and his parachute were carried aloft by a balloon. Garnerin descended safely from about 2,000 feet (610 meters) above the city of Paris.

In the nineteenth century, parachute jumping from balloons became a popu­lar form of entertainment. Balloon jumper Charles Broadwick invented the first body-pack parachute in 1905. The parachute pack was fastened to the balloon by a line. As the jumper fell, the line tightened and pulled the para­chute canopy open. In 1912, Captain Albert Berry made the first parachute jump from an airplane, at a height of 1,500 feet (460 meters) above St. Louis, Missouri. Georgie Thompson, a teenager who jumped with Broadwick, was the first woman to jump from an airplane and land using a parachute, in 1913.

During World War I (1914-1918) few pilots had parachutes. Generals (and many pilots) argued that parachutes were too cumbersome. Military person­nel who went up in observation balloons did have parachutes, however, so they could leap out if their balloons were hit by enemy gunfire.

HOW A PARACHUTE WORKS

When a parachute opens, air pushes up to fill the canopy. The air acts against the force of gravity and slows the fall of the object to which it is attached. A parachute increases air resistance because it offers a large surface area that produces friction with the air. At first, friction is greater than gravity, so the parachutist slows down. When the friction decreases to the point at which it is equal to the force of gravity, the parachutist descends at a constant speed. In cer­tain weather conditions, the upward force of air may push the parachutist upward for a short time.

Pressure is the pressing effect of a force acting on a surface. Scientifically expressed, pressure is the force per unit area acting on a surface. Pressure (P) is defined as the force applied (F) divided by the area (A) of application. The equation for pressure is: P=F/A.

When a force acts on a material (solid, liquid, or gas), the result is pres­sure. The causes of pressure are as var­ied as the causes of forces. The force of a party balloon squeezing the air inside it produces pressure. The weight of a book pressing down onto a table pro­duces pressure. Oil forced through the pipes of an aircraft’s hydraulic system produces pressure. Gravity pulling air against Earth’s surface produces atmospheric pressure.

Atmospheric Pressure

Atmospheric pressure, or air pressure, can be measured in various ways. The weight of air pressing down on the Earth’s surface produces an air pressure at sea level of 14.7 pounds per square inch (psi), or about 100 kilopascals (100,000 pascals). Meteorologists (weath­er scientists) measure pressure in bars. The air pressure at sea level is about 1 bar, or 1,000 millibars. This pressure also is known as “1 atmosphere.”

Air pressure in the atmosphere falls with increasing height. Gravity pulls air against Earth’s surface. Air at Earth’s surface has the weight of all the rest of

THE BAROMETER

Atmospheric pressure is measured with an instrument called a barome­ter. The first barometer was made in 1643 by an Italian scientist named Evangelista Torricelli (1608-1647). He filled a long glass tube with mer­cury. Then he turned the tube upside down with its open mouth in a bowl of mercury. Some of the mercury ran down into the bowl, but not all of it. A column of mercury about 30 inches (76 centimeters) high stayed in the tube. Its weight was balanced by air pressure acting on the mercury in the bowl. Torricelli realized that changes in the column’s level were due to changes in atmospheric pressure. Mercury barometers work in this way.

An aneroid barometer works in a different way. It is a sealed can with some air taken out. Atmospheric pressure squashes the can. The amount of squashing changes when the air pressure changes. These small movements are linked to a needle pointing at a press scale. Because they do not need a tall tube of mercury, aneroid barome­ters are much smaller than mer­cury barometers.

the air above it bearing down on it, so the pressure is greatest here. Air higher in the atmosphere has less air from above pressing down on it, so the air pressure higher above the ground is lower. This is an important factor to consider for a person flying high in the atmosphere or going into space.

One-fifth of air, or about 20 percent, is oxygen. The thin, low-pressure air at the top of a high mountain contains the same percentage of oxygen as air near the ground, but because there is less air at high altitude, there is also less oxy­gen. The human body is very sensitive to sudden, even small, changes in pressure. Going up a tall building in a fast eleva­tor can make someone’s ears pop. The shortage of oxygen in low-pressure air at high altitudes can cause more severe effects. When people go higher in the atmosphere, they may experience a vari­ety of problems due to low air pressure.

Mountain climbers can suffer headaches, nausea, and dizziness when at altitude.

Controlled spaceflight needs a rocket in which the power can be varied and turned on and off. Liquid-fuel rockets can be controlled in this way. Liquid-fuel rockets are more complicated than solid rockets, because piping, valves, and pumping systems are needed to move the liquid propellants from their storage tanks to the engines. A type of kerosene called RP-1 (Refined Petroleum-1) is a commonly used liquid rocket fuel.

Unlike RP-1, some liquid propellants have to be kept very cold. Hydrogen and oxygen are common rocket propellants. They are normally gases, but they can be packed into very small tanks by chang­ing them into liquids. Hydrogen becomes liquid below a temperature of -423°F (-253°C). Oxygen becomes liquid
below -298°F (-183°C). Liquid oxygen also is called LOX. Propellants that have to be kept super-cold are known as cryo­genic propellants. They are not suitable for most military rockets and missiles because it is difficult to keep them sufficiently cold for long periods, and military equipment always must be kept ready to use. Instead, cryogenic propel­lants are used for civilian spaceflight, such as the Space Shuttle missions, because they are highly efficient, yield­ing a lot of power per gallon.

Some small rockets use propellants that ignite as soon as they meet. These are called hypergolic propellants. Rocket engines that use hypergolic pro­pellants can be very simple and reliable, because they do not need complicated ignition systems. Small rockets called thrusters use hypergolic propellants.

Strange materials have been used as rocket propellants. The Mythbusters tele­vision program, which aims to prove or disprove myths, built a working rocket fueled by a salami. SpaceShipOne, the first privately funded manned space

plane and winner of the Ansari X-Prize, burns rubber as its fuel. The rubber is solid, and the oxidizer, nitrous oxide, is liquid. A rocket like this, with a mixture of solid and liquid (or gas) propellants, is called a hybrid rocket.