Category FLIGHT and M ОТІOIM

Aircraft and spacecraft are not the only vehicles that make use of jet power. Some battle tanks and fast warships are propelled by gas turbines. It is not the jet thrust of the engine that propels these vehicles, however. The Abrams tank’s gas turbine engine drives its tracks. A warship’s gas turbine drives its propellers.

Other vehicles do use jet thrust to accelerate to very high speeds. The fastest cars in the world are powered by thrust. The problems designers face in
creating thrust-powered cars are similar to those faced by aircraft designers. The shape of the car is very important, because drag must be cut to a minimum.

The world’s fastest car has traveled faster than the speed of sound. On October 15, 1997, Thrust SSC, driven by British fighter pilot Andy Green, set a land speed record of 763 miles per hour (1,228 kilometers per hour) in the Black Rock Desert, Nevada. It was powered by two Rolls-Royce Spey fighter engines, which, together, were more powerful than 150 Indy racecars.

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SEE ALSO:

• Engine • Force • Laws of

Motion • Rocket • Whittle, Frank

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Date of birth: May 23, 1848.

Place of birth: Anklam, Germany.

Died: August 10, 1896.

Major contribution: Researched and wrote about many principles of aero­dynamics and aeronautics; first person photographed flying a successful heavier-than-air aircraft.

tto Lilienthal became attracted to the idea of flying as a teenager. In his first attempts at flying, he tried to mimic the method used by birds. Lilienthal built two pairs of 6.5-foot-long (1.9-meter-long) wings. He strapped one pair on his brother’s arms and the second pair on himself. The two ran down a hill flapping the wings, hoping to take off into the air. The experiment failed, but Lilienthal remained committed to flying.

In 1870, Lilienthal graduated with a degree in mechanical engineering from the University of Berlin, Germany. While heading a factory that made engines, he devoted his spare time to studying the flight of birds.

In 1891, Lilienthal built his first glid­er. The frame was made of willow wood covered by cotton fabric. The wings were 25 feet (7.6 meters) long from tip to tip. Lilienthal bounced off a springboard to launch himself into the air. On the first attempt, he traveled only a few feet. Lilienthal made repeated experiments, increasing the height of the springboard and then shortening the wingspan.

Eventually, he glided as far as 80 feet (24 meters).

Over the next few years, Lilienthal continued tinkering with gliders. From 1891 to 1896 he took more than 2,000 glider flights. Lilienthal tried covering both sides of the wings and adjusting wingspan. Most of his designs were monoplanes, with single wings, but some were biplanes. In most of his air­craft, Lilienthal stood in a harness between the wings, with his torso above the wings and his legs below. Once aloft, he maneuvered the glider by shifting his weight from one side to another or by leaning to the front or the back.

AN IMPORTANT PUBLICATION

In 1889, Otto Lilienthal published a book summarizing his research into how birds fly. Called Bird Flight as the Basis of Aviation, it was a brilliant work for its time. Lilienthal conclud­ed that the curved shape of birds’ wings was the secret to their flying ability. He proposed that a flat sur­face would offer less wind resistance and prevent lift. He also calculated how long wings would have to be to carry a human into flight.

Although effective, the technique was difficult and required great strength. Lilienthal tried adding devices to make it easier to guide the glider.

By 1894, Lilienthal had decided that he needed a better launching area. He mounded dirt into a hill and built a shed on top, where he stored his equipment. The hill allowed Lilienthal to launch no matter which way the wind was blow – ing—he could simply run down the appropriate side of the hill. He always chose to run into the wind to get the needed lift.

Lilienthal was able to glide more than 150 feet (46 meters) from his new launching site, but he wanted to go even farther. As a result, he began launching himself from some higher hills near Berlin. On one trip, Lilienthal traveled 1,150 feet (350 meters).

Continued tests led to a fatal disaster. On August 9, 1896, Lilienthal took a glider flight in the midst of heavy wind gusts. One gust caught the glider and sent it crashing to the ground from 50 feet (15 meters) up. Lilienthal broke his back and died the next day.

Lilienthal’s work in aviation was of great importance. His writings influ­enced others interested in flying, including Orville and Wilbur Wright. Photographs taken of his glider flights inspired many early aviation pioneers by showing that a man could, indeed, build and fly a heavier-than-air aircraft.

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SEE ALSO:

• Aerodynamics • Aeronautics

• Aircraft Design • Glider • Lift

and Drag

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Missiles that spend most of their flight falling through the air without power are called ballistic missiles. A rocket launches them high in the air, or even into space, and then gravity pulls them back down to the ground again. A track­ing system finds the target and locks onto it. The tracking system gives the target’s location to the missile’s guid­ance system, which then works out the flight path the missile needs to follow. The guidance system commands the flight system to steer the missile, usual­ly by moving fins on the missile’s body.

Small ballistic missiles are mounted on mobile launchers that can be moved from place to place. The biggest ballistic missiles—intercontinental ballistic mis­siles (ICBMs)-can fly more than 3,300 miles (5,300 kilometers) from one conti­nent to another. These missiles are too big and heavy to be moved around by trucks, but they would be easy to attack if they stood out in the open. One way to hide large missiles from enemies is to keep them in launch tubes, called silos, buried in the ground. As missiles have become more accurate and more power­ful, however, silos provide less protec­tion. Another way to protect missiles

from enemy attack is to put them in nuclear submarines, which can stay sub­merged in the ocean for weeks at a time.

he National Aeronautics and Space Administration (NASA) is the U. S. national space agency. It was formed in 1958 for advanced aero­nautics research and space exploration. NASA is a federally funded organiza­tion, employing thousands of engineers, scientists, and professionals in aerospace research. Its work includes developing new airplanes and spacecraft and testing new technologies.

NASA has been associated with many of the most dramatic and historic episodes in the history of spaceflight-it achieved worldwide recognition in the 1960s when it sent astronauts to the Moon. NASA’s work continues into the twenty-first century, with manned spaceflights and with space probes that explore the Solar System. It is the world’s leading space agency, ahead of the Russian federal space agency and the European space agency.

NASA scientists and engineers are also engaged in research projects concerning transportation and the envi­ronment. Images taken from NASA sources, such as space telescopes and probes, have excited the imaginations of people around the world. NASA’s exten­sive educational and media programs provide information about space and space technology.

NACA

The predecessor to NASA was known as the National Advisory Committee for

Aeronautics (NACA), which was founded in 1915. This body was responsible for important early research into airplane flight, using research airplanes and wind tunnels. By modern standards NACA was small-in 1938 it had a staff of just over 400 people.

After World War II (1939-1945), NACA expanded its activities into the realm of supersonic flight, working closely with the U. S. Air Force on the record-breaking X-1 airplane and other projects. In the late 1940s, the Department of Defense urged scientists to work with the military on missile experiments. At the same time, scientists were pressing for rockets to be sent into space for research. President Dwight D. Eisenhower approved a plan to launch a science satellite as part of the International Geophysical Year, sched­uled for July 1957 to December 1958. The chosen rocket vehicle for the satel­lite launch was the Naval Research Laboratory’s Vanguard rocket.

The Vanguard Project was under­funded and slow to get off the ground. The United States was shocked when, in October 1957, news broke that the Soviet Union had beaten America into space by launching the world’s first arti­ficial satellite, Sputnik 1. Many people in the United States became concerned that there was a widening gap between Soviet and U. S. space science. American scientists quickly responded to the chal­lenge, launching the nation’s first satel­lite, Explorer 1, in January 1958. Despite this achievement, however, there were
calls for a new agency to drive forward the national effort in the “space race.”

In 1919, the forerunner of the modern parachute was tested in the United States by a group of jumpers, including James Floyd Smith, Leo Stevens, and Leslie Irvin. The new parachute had a circular canopy and a smaller parachute called a pilot chute. Both parachutes and their lines were folded and stowed in a cloth pack. The pack was held closed by three metal pins attached to a wire rip­cord. When the jumper tugged a handle on the harness, the ripcord ripped the pins free, and the pack opened. The pilot chute flew out, acted as a brake, and pulled out the main canopy. On April 28, 1919, Leslie Irvin tested the parachute after jumping out of a plane over McCook Field in Ohio. In 1922, came the first use of a parachute in an emergency when an American military pilot, Lieutenant Harold Harris, bailed out of a test plane over North Dayton, Ohio. Throughout the 1920s, barnstormers and show jumpers made parachute jumps to entertain crowds at flying shows.

Most jumps were from low level. Doctors warned that parachuting from great heights, or falling at high speed before the parachute opened, would kill the jumper. In fact, such fears were proved wrong. In 1945, Lieutenant Colonel William Lovelace jumped from a B-17 bomber at a height of 40,000 feet (12,190 meters). Although he wore breathing apparatus, Lovelace became unconscious, but his parachute opened, and he landed safely.

Big drops in air pressure are even more serious. Pilots and passengers of high­flying aircraft need protection from the low air pressure outside of the plane. Early airliners did not fy higher than about 10,000 feet (3,050 meters)-above that height, some passengers began to feel faint. To fy higher safely, an aircraft has to be pressurized. Extra air is pumped inside a modern airliner to raise the pressure. The air inside a pressurized airliner is not at sea level pressure. It is the same as the pressure at an altitude of about 8,000 feet (2,500 meters), which is about 11 psi, or 75.8 kilopascals.

Fighter pilots sit in a pressurized cockpit, but they also wear an oxygen mask in case the canopy shatters and the cockpit loses pressure.

If an airliner suffers a sudden loss of pressure at its cruising altitude of about

35,0 feet (10,600 meters), oxygen masks drop down automatically from the ceiling. The crew and passengers have about 30 seconds to put them on before losing consciousness.

The Space Shuttle and International Space Station (ISS) are both pressurized to sea level pressure. The spacesuits worn by astronauts, however, are pres­surized to only 4.3 psi (about 30 kilopas – cals) to prevent them from blowing up like a balloon. If an astronaut breathed air at such a low pressure, there would not be enough oxygen, so the suit is supplied with pure oxygen.

Because the pressure in a spacesuit is much lower than the pressure inside the spacecraft, the air pressure around astronauts preparing to leave their spacecraft is lowered in stages so that they can adjust safely. The day before a spacewalk, the air pressure inside the Space Shuttle is lowered to 10.2 psi (70 kilopascals). Space Station astro­nauts spend several hours inside an air­lock where the air pressure is even lower, to prepare for the lower pressure inside their spacesuits.

HIGH RISKS

Early balloonists were the first avia­tors to discover the hazards of high – altitude flight. On September 5, 1862, Henry Coxwell and James Glaisher made a balloon ascent to more than 30,000 feet (9,100 meters). No manned balloon had flown as high before. As they passed

29,0 feet (8,850 meters), Glaisher became paralyzed. Then he lost con­sciousness. Coxwell lost the use of his arms and had to use his teeth to pull the rope that released hydrogen from the balloon and let them descend. They both survived.

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Using Pressure

Aircraft and spacecraft can use different kinds of pressure in their operations. When a large liquid-fuel rocket is fired, pumps feed fuel to the engine. Pumps are too big and heavy for small rockets and spacecraft, so they use pressure instead. A high-pressure gas, such as helium, pushes the fuel from its storage tank to the engine.

Aircraft use high-pressure oil in their hydraulic systems. Hydraulic systems are those operated by liquid. Liquids cannot be squashed as much as gases because their molecules are already close together. This causes liquids under pressure to transmit force from one place to another. A digging machine

works in this way. Oil pumped through flexible hoses operates mechanical pushers called rams, which move the digger’s arm. Modern automobile brakes also work by hydraulic power. An air­craft’s hydraulic system uses oil pressure to move its control surfaces and raise its landing gear. Cargo planes use hydraulic pressure to operate their cargo doors and loading ramps. Rockets use hydraulic power, too, when they swivel their engine nozzles for steering.

SEE ALSO:

• Air and Atmosphere • Altitude

• Astronaut

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There are several ways of steering a rocket or rocket-powered spacecraft. One way is to use swiveling fins, like an airplane’s control surfaces, in the atmos­phere. A rocket must be traveling fast before its fins begin to work, because they only work when air is flowing over them very quickly. Other rockets have swiveling vanes in the rocket exhaust. When the vanes swivel, they deflect some of the engine’s exhaust jet. The entire jet can be deflected by swiveling the engine itself or just the nozzle. Most modern rockets have swiveling engines, also called gimbaled engines. The Space Shuttle’s main engines are gimbaled.

A rocket or spacecraft also can be turned or steered by means of thrusters.

When the Space Shuttle’s solid rocket boosters fall away, thrusters push them away from the spacecraft. The Space Shuttle uses forty-four thrusters in its nose and tail for attitude control when flying in space.

Rockets are used for braking as well as steering. Braking rockets also are called retro-rockets. When an orbiting spacecraft is ready to land, it fires off rockets in the direction in which it is traveling. The thrust slows the space­craft, and gravity begins to pull it down.

The Soyuz spacecraft uses retro-rock­ets for landing. It fires retro-rockets just before it touches down on the ground to cushion its landing.

United Aircraft discontinued the Clippers, but the company funded Sikorsky’s effort to achieve his long-

"I have never been in the air in a machine that was as pleasant to fly as the helicopter. It is a dream to feel the machine lift you gently up in the air, float smoothly over one spot for indefinite periods, move up or down under good control, as well as move not only forward or backward but in any direction."

Igor Sikorsky

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held dream of building a helicopter. This time, that effort succeeded, with the help of new, lightweight materials and a staff of engineers.

On September 14, 1939, Sikorsky climbed into the first helicopter model, the VS-300. He always insisted on tak­ing the first flight of any completely new design. The helicopter worked— it rose vertically, hovered, and returned to land. The flying machine had a single rotor with three blades driven by a 75-horsepower engine. Sikorsky’s heli­copter was not the first to reach the air, but it was the first successful flight of a helicopter with a single rotor. Because most helicopters follow that design, Sikorsky is considered the leading pioneer of the helicopter industry.

The design needed improvement, however. Sikorsky tried another version with two small rotor blades in the rear. On May 13, 1940, that machine rose into the air, but was difficult to move for-

ward. The next model had just one smaller rotor blade in the rear. This ver­sion flew smoothly and on May 6, 1941, it set a record by staying aloft for more than an hour.

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