Category FLIGHT and M ОТІOIM

Early designs for vertical takeoff air­planes in the 1940s and 1950s tried a type of aircraft called a tail-sitter. The plane sat on the ground on its tail, with its nose pointing straight up in the air. It looked like a rocket with wings. Its propellers lifted it up off the ground. Once the plane was airborne, it slowly tipped over and started to move forward. As it accelerated, its wings generated more and more lift until it was flying normally. The Lockheed XFV-1 and Convair XFY-1 Pogo were tail-sitters.

These planes were very difficult to land because the pilot was facing away from the ground. The tail-sitter design was eventually abandoned.

In the early 1950s, the British compa­ny Rolls-Royce produced two experi­mental, jet-powered, vertical takeoff air­craft called Thrust Measuring Rigs. They were made from a skeleton-like frame with two Rolls-Royce Nene jet engines. These aircraft were so successful that Rolls-Royce went on to develop a new jet engine, the RB108, specially for ver­tical takeoff aircraft.

Some experimental VTOL aircraft built in the 1950s and 1960s tilted their wings with the engines attached. These aircraft, including the Canadair CL-84, LTV-Hiller-Ryan XC-142, and also the Hiller X-18, are called tilt wings. The Vertol 76 VZ-2 also was a tilt wing but its engine was mounted in the center of the fuselage, and it drove two propellers on the wings. This layout meant that the wings and propellers could be tilted without having to tilt the heavy engine as well.

Other researchers, meanwhile, were experimenting with the use of separate engines for lift and forward thrust. The Short Brothers aircraft company in Belfast, Northern Ireland, carried out pioneering research in vertical takeoff in the 1950s. Their Short SC.1 was the first successful British fixed-wing VTOL air­craft. Looking a little like a housefly, it was powered by four Rolls-Royce RB108 jet engines for lift and a fifth RB108 engine for forward thrust.

About the time the early tail-sitting airplanes were being discontinued, the British Hawker company developed a flying test bed for new technologies. It was a vertical takeoff jet plane called the P1127. It was never meant to be an oper­ational aircraft, but it was developed into the most successful vertical takeoff aircraft of all: the Harrier.

When researchers found it difficult to accelerate experimental aircraft through the sound barrier, they looked at the shape of the airplane’s wings. As a normal wing nears the speed of sound, a high-pressure shock wave forms on top

of it. This causes drag, which makes it difficult for an aircraft to go faster with­out using a lot more engine power. It also makes an aircraft harder to control.

Simply by changing the shape of the airfoil, the shock waves can be made smaller. Airfoils changed in this way are called supercritical wings. In a supercrit­ical wing, the upper surface is flattened

The high-pressure air below a wing tries to flow around the wingtip into the low – pressure air above the wing. This makes the air spin off the wingtips and trail behind the plane. The spinning trails are called vortices. The vortices behind a big airliner are powerful enough to flip over a small plane flying behind it. Wingtip vortices also cause extra drag. Some air­planes have wingtips that are specially shaped to reduce the drag caused by vor­tices. Many aircraft use turned-up wingtips called winglets for this purpose.

A few planes have been built with wings that sweep forward to increase maneuver­ability. The first forward-swept wing airplanes were built in the 1940s, but their metal wings could not be made stiff enough, and so they bent. When new materials such as carbon fiber were developed, designers looked at forward-swept wings again. An experimental jet-powered aircraft with forward-swept wings, the Grumman X-29, was built in the 1980s. In Russia, the manufacturer Sukhoi has produced an experi­mental forward-swept wing supersonic fighter, the Su-47 Golden Eagle.

The Wright brothers solved the problem of how to steer a plane by making its wingtips bend, which is called wing warping. By twisting the wingtips on one side of the plane in one direction and the wingtips on the other side in the opposite direc­tion, more lift was produced on one side and less on the other side, so the plane rolled into a turn. Since then, most airplanes have used ailerons instead of wing warping.

Today’s designers are still working on flexible wings, however. They now are called aeroelastic wings. The X-53 is an experimental plane with flexible wings. When wings bend, the result is usually more drag, which is not wanted. The X-53’s wings and the positions of its flaps and ailerons have been designed so that when the wings bend, the result is more lift. One advantage of flexible wings is that they can be up to one – fifth lighter than stiff wings. Flexible wings may enable future aircraft to burn less fuel, carry heavier cargo, or fly farther.

and the curve at the trailing edge is increased. Planes with supercritical wings can go faster with less engine power. Although supercritical wings were developed for supersonic aircraft, they also can produce a lot of lift at low speeds, so they are used by cargo aircraft. The extra lift is good for getting heavy loads off the ground at low speeds.

The V-1 was one of several innovative weapons developed by the Germans. These included the V-2 ballistic missile, anti-aircraft missiles, guided bombs, and the rocket-powered Me-163 interceptor, capable of speeds of 620 miles per hour (1,000 kilometers per hour). The Dornier Do-335 Pfeil “Arrow” was a twin-engine fighter, with one propeller in its nose and another in its tail. This unique air­plane was almost as fast as a jet, but only a handful reached the Luftwaffe before the war ended.

The Germans were the first to use remote-guided rockets, in 1943, firing HS-293 missiles against British ships

KAMIKAZE MISSIONS

As the war swung against Japan, the nation resorted to kamikaze attacks, which started in October 1944. The word kamikaze means "divine wind." Volunteer pilots crash-dived their planes packed with explosives onto U. S. Navy ships, killing themselves and creating as much destruction as possible. Japan even built a rocket-powered suicide plane, the Ohka, which was launched from a carrier plane. An estimated 3,000-4,000 pilots flew kamikaze missions for Japan, sink­ing between thirty and eighty U. S. ships and damaging many more.

in the Atlantic Ocean. Similar radio – controlled missiles, air-launched from Dornier 217 bombers, sank the Italian battleship Roma following Italy’s surren­der to the Allies in 1943.

The Japanese proved resourceful in building robust fighting airplanes, such as the Mitsubishi Zero. The Japanese, like the Germans, had no long-range heavy bombers, but in 1944 they did attack the West Coast of the United States by flying balloons carrying small bombs across the Pacific. About 9,000 balloons were launched; around 1,000 reached the United States, causing 285 recorded incidents and six deaths.

Spaceflight became possible with the development of rockets that had suffi­cient power to break free of Earth’s gravity. To break free, a rocket must reach escape velocity, which is just over

25,0 miles per hour (40,200 kilome­ters per hour). Takeoff and reentry are the two most dangerous times in a spaceflight. Before the 1950s, some sci­entists argued that the human body could not survive the stresses of a space launch. The earliest flights by astro­nauts proved such views wrong. Astronauts have flown faster than any humans have before and have returned back to Earth unharmed.

Conventional rocket motors work both in air (for takeoff) and in space. Most rockets used to launch spacecraft are multistage vehicles propelled by chemical fuel burned in liquid or solid

form. The propellants must include oxy­gen, or the fuel will not burn, because there is no air in space.

Booster rockets provide extra thrust during takeoff. In a multistage rocket, boosters and lower stages separate and fall away as soon as their fuel is burned up. Only the topmost stage reaches space. The load a rocket lifts into space is called its payload-this could be a satellite, a manned spacecraft, or a robot space probe.

A rocket is streamlined for efficient, controlled, high-speed flight through the air. A spacecraft designed to return to Earth, like the Space Shuttle, also is streamlined, but it has wings. The wings help the Space Shuttle land like a con­ventional airplane after it has reentered Earth’s atmosphere.

Returning to Earth from space is potentially as dangerous as leaving it. A spacecraft must decelerate (slow down), using braking rockets, and approach at a precise angle so it does not hit the Earth’s atmosphere too fast. Reentry is accompanied by a rapid rise in tempera­ture. Air gets trapped in front of the spacecraft, which is moving so fast the air cannot escape. Compression (squeez­ing) of the air raises the temperature to more than 10,000°F (5,540°C). Spacecraft would burn up unless protected by a heat shield of tough, insulating material.

The Apollo triumph persuaded many people that the United States had won

the space race. No Soviets flew to the Moon, although unmanned Zond space­craft may have flown test flights for a Moon mission. Soviet plans for a Moon landing were abandoned, prob­ably because of serious problems with the rocket launcher and the lunar space­craft. The closest the Soviet Union came to the Moon was when two small robot vehicles crawled over the dusty lunar surface. Instead, the Soviets turned their attention to orbital space stations, such as Salyut 1 (1971) and later Mir. In 1975, on the Apollo-Soyuz Test Project, American and Soviet astronauts flew together in space. A new era of cooperation had begun.

By the 1980s, the space race was over. Relations between the United States and the Soviet Union improved, with the signing of treaties agreeing to bans on nuclear weapons testing and cut­backs in the production of missiles.

The United States introduced the Space Shuttle in 1981. Although they launched their Buran shuttle in 1988, the Soviets never seriously competed with the new, reusable spacecraft.

In 1989, the Soviet Union broke apart into separate countries. Since then, Russia has worked as a partner with the United States to build and operate the International Space Station. New partic­ipants in space include the European Space Agency (ESA) and China. (China became the third nation to launch an astronaut, in 2003.)

The space race provided significant technological spin-offs (especially in electronics) and led to an increase in sci­ence education. A future space race might be a commercial contest between companies offering space tourism, but most people believe that the future of scientific space exploration lies in inter­national cooperation rather than in a race for the stars.

SEE ALSO:

• Apollo Program • Astronaut

• Gagarin, Yuri • Glenn, John

• Spaceflight • Sputnik

V.

Directional stability keeps a plane flying in a straight line without veering to one side or the other. Early airplanes had lit­tle stability. The pilot had to concentrate extremely hard and constantly make adjustments to keep the plane under control. A gust of wind or a careless maneuver could send the plane spiraling to the ground. Many early aviators died in crashes caused by poor stability and control problems.

A modern plane’s tail fin, or vertical stabilizer, helps to provide directional stability. If the plane’s nose is pushed to one side by a gust of wind, the airflow around the tail fin moves the tail back in line with the nose, so that the plane keeps flying in the same direction instead of veering off course. (Weather vanes keep pointing into the wind for the same reason.)

In 1999, synthetic vision was tested in flight by a modified C-131 military aircraft named the Total In-Flight Simulator (TIFS). For the tests, TIFS was fitted with screens to try a variety of dif­ferent images and data. The research flights were made out of Asheville Regional Airport in North Carolina.

Research pilots using the synthetic vision system reported that they soon forgot they were looking at a computer-generated image and not at the real world.

System designers are already thinking about other ways in which SVS might be used in the future. One possible application is in air traffic control systems at airports.

Airport traffic con­trollers work in a con­trol room that looks out across the airport, but some parts of an airport may be obscured by buildings or bad weather. SVS could provide con­trollers with a clear, computer-generated view of the entire air­port in all conditions. Although synthet­ic vision has been developed for civil aviation, military forces also are interest­ed in the systems. Synthetic vision already has been flight tested in military airplanes and helicopters.

• Air Traffic Control • Avionics

• Cockpit • Global Positioning System • Pilot

The main advantage of a VTOL aircraft is that it does not need a runway, and so it can operate from any small patch of ground, from a road, or even a ship’s deck. One version of the Harrier, the Sea Harrier, was developed for naval use. It could operate from the smallest aircraft carriers. The decks of these ships are too short for most naval jets that require runways, but they are big enough for helicopters and VTOL aircraft.

A Sea Harrier with full fuel tanks and a large weapons load is too heavy to take off vertically, and the deck of a small aircraft carrier is too short to use a normal takeoff run. So small carriers are fitted with a ramp at the end of the deck, also known as a ski jump. As an aircraft accelerates toward the end of the deck, the ski jump gives it an extra push upward into the air.

A Sea Harrier pilot has to calculate the aircraft’s takeoff speed very careful­ly by using its weight and the current wind speed. If takeoff is too slow, the plane might not get airborne. If it is too fast, the Sea Harrier might hit the ski jump too hard and damage its undercar­riage. The Sea Harrier uses a short take­off and vertical landing, making it a STOVL aircraft. It was the first opera­tional STOVL combat aircraft to use vectored thrust.

FLYING BEDSTEADS

When NASA was preparing to send astronauts to the Moon in the 1960s, they developed a strange – looking aircraft to prepare astro­nauts for the task of landing on the lunar surface. The lunar lander, called the Apollo Lunar Excursion Module (LEM), would descend to the Moon balanced on the fiery jet of gas from a rocket engine. The first training vehicle for this event balanced on the jet exhaust from a jet engine instead of a rocket. Called the Lunar Landing Research Vehicle, it led to the development of three Lunar Landing Training Vehicles. Astronauts called them "flying bedsteads" because of their strange appearance.

When the U. S. Marines were looking for a light attack plane, they developed the Harrier to suit their needs. Their work resulted in a new Harrier, the AV – 8B Harrier II. It had bigger, thicker wings and was able to carry a bigger payload over a greater distance.

Fixed-wing airplanes are not the only aircraft that use wings. A helicopter’s rotor blades are actually long, thin wings. High-performance parachutes called parafoils are really inflatable wings. The parachute is made of two layers of fabric with dividers between them, forming a line of pockets, or cells. As the parachute moves along,
air fills the cells and forms a wing shape. The parachutist con­trols and steers the parafoil by pulling control lines that change the wing’s shape.

A flexible fabric hang glider is yet another type of wing. Called a Rogallo wing, this early hang glider was developed in the 1940s by hus­band and wife, Francis and Gertrude Rogallo. When space exploration began, NASA investigated the Rogallo wing as a way of landing the Gemini manned spacecraft. Round parachutes eventually were used instead, but the Rogallo wing was used by other designers, who devel­oped it into the modern hang glider.

Racecars also use wings. However, racecar wings do the opposite job of air­craft wings. They produce a downward force, called downforce, when they cut through air. This pushes the car down harder against the ground, giving its tires better grip, and enabling it to take corners faster without loss of traction.

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SEE ALSO:

• Aerodynamics • Aileron and

Rudder • Bernoulli’s Principle

• Lift and Drag • Stall

Prewar theories that bombing would destroy civilian morale and halt factory production proved inaccurate. The British did not crumble during the Blitz; the Russians moved their factories east out of range of German planes; and German and Japanese workers contin-

WORLD WAR II AVIATION ADVANCES

World War II was a war of air power. During the course of the war, top speeds of fighter aircraft rose from about 350 to 450 miles per hour (563 to 724 kilometers per hour). Bombers flew higher to escape interception: up to 35,000 feet (10,700 meters) by 1945. Naval battles among ships were replaced by long-range air battles between planes flying from aircraft carriers. Factory production methods speeded up manufacture, and technology greatly improved the range, nav­igation, gun power, and bombing accuracy of warplanes. Air transports, such as the C-47 and C-54, carried troops and supplies, and parachutes were used to land them. Radar was the key air invention: It aided ground defenses and also helped pilots locate enemy targets. Air weapons became more destructive as bombs laid waste to cities, and guns and rockets could blow planes apart in midair. For protection, planes had armor plating and self-sealing fuel tanks. By 1944 to 1945, air warfare had been changed forever by new weapons and tech­nology: jet planes, helicopters, the V-1 flying bomb, the V-2 missile, and the atomic bomb.

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