Category FLIGHT and M ОТІOIM

n aircraft’s tail helps to keep it stable in the air. The tail’s con­trol surfaces make the aircraft climb, dive, and turn to the left or right.

An airplane’s tail acts like an arrow’s feathers or a firework rocket’s long stick. The tail keeps the plane pointing in the right direction, nose first. Without a tail in place, most airplanes would crash to the ground. The Northrop B-2 Spirit stealth bomber, for example, has no tail and is therefore a very unstable aircraft. It only can be flown with the help of a powerful flight computer.

Stabilizers

A typical airplane tail has a vertical sta­bilizer, or fin, that stands up on top of the fuselage, and a horizontal stabilizer, or tailplane, which sticks out from either side of the tail fin. The fin has a moving part at the back called the rudder. When the rudder is turned to the left, the air
flowing around it pushes the plane’s tail to the right, and the aircraft’s nose turns to the left. When the rudder turns to the right, the aircraft’s nose turns to the right.

The tailplane has moving parts at the back called elevators. The elevators con­trol the aircraft’s pitch. When the eleva­tors tilt up, air flowing around them pushes the aircraft’s tail down and brings the nose up. When the elevators tilt down, the aircraft’s nose tips down as well.

Another method for achieving vertical flight uses separate engines for lift and for forward flight. The lift engines are used to get airborne, and then separate forward thrust engines propel the plane normally. Once the plane is flying forward and the wings are generating lift, the lift engines are shut down. The disadvantage of this design is that the aircraft has to carry the dead weight of the lift engines, which reduces its performance.

One example of this type of aircraft is the Russian Yakovlev Yak-38 Forger. It has three jet engines. Two lift engines behind the pilot blow air straight down. The main engine provides thrust from two nozzles behind the wing. These nozzles can rotate to direct the jet exhaust downward to provide extra lift. The Yak-38 serves on Russia’s Kiev class aircraft carriers.

orld War I began in Europe in 1914, and the United States entered the war in 1917. Remembered for the terrible slaughter of trench warfare on the Western Front, the “Great War,” as World War I became known, was the first war in which air­planes played an important part.

LEARN-EARN

О A World War I poster encourages volunteers to enlist in the Air Service, part of the U. S. Army. At the time, there was no separate U. S. Air Force. The poster reflects the aircraft of the period, including airships.

The Role of Aircraft

Until 1914, military strategists regarded command of the sea as the key factor in international warfare. Britain, Germany, and the United States had the biggest navies. When World War I began, air­planes were still a novelty. The fastest airplane had a top speed of only 100 miles per hour (160 kilometers per hour) and a range of about 100 miles (160 kilometers) before needing to refuel.

In the nineteenth century, balloons and airships had been used in wars, mostly for observation and for evacua­tion of civilians. The military had yet to find uses for the airplane. In 1912, Britain had set up a Royal Flying Corps, but it had very few aircraft. Germany had the largest air force, with more than 200 airplanes plus Zeppelin airships. The U. S. Army had purchased its first air­planes in 1913. No nation had assembled a large air force.

In the four years of World War I (1914-1918), the airplane became a much more formidable weapon. Fighter planes battled in aerial combats called dogfights. For the first time, cities were bombed from the air by airships and air­planes. The warring nations formed air forces or aviation divisions within their armies and navies. War would never be the same again.

Dates of birth: Wilbur: April 16, 1867; Orville: August 19, 1871.

Places of birth: Wilbur: Millville, Indiana; Orville: Dayton, Ohio.

Died: Wilbur: May 30, 1912; Orville: January 30, 1948.

Major contribution: Achieved the first sustained, powered, controlled airplane flight; built the first practical powered airplane; built the first practical passenger-carrying airplane.

Awards: Orville: Collier Trophy.

n December 17, 1903, Wilbur and Orville Wright flew the first sus­tained, powered, controlled air­plane flight at Kitty Hawk, North Carolina. The Wrights continued experi­menting with airplane designs and made several important advances. They helped promote aviation across the United States and in Europe.

Early Life

The Wright brothers were the sons of Milton and Susan Wright. Their father was a church minister. Years after their success, the Wrights said they first became interested in flying in 1878 when their father brought home a toy helicopter powered by a rubber band. Intrigued when the toy flew, the boys played often with it and experimented by making their own versions of it. Their mother, who often made toys and

household appliances herself, encour­aged the brothers’ interest in flight.

Wilbur graduated from high school, but before starting college he suffered a serious injury while playing hockey. He remained at home, helping his father with church business and caring for his sick mother until her death in 1889. During this time, Wilbur read constantly.

By the time their mother died, Wilbur’s younger brother Orville had persuaded Wilbur to join him in opening a print shop in their hometown of Dayton, Ohio. The brothers began pub­lishing a small newspaper, but they failed to make money with the paper and eventually closed the business. In 1892, the brothers opened a successful bicycle shop where they built, sold, and repaired bikes.

Spaceflight began in the mid­dle of the twentieth century, but scientists and writers had imagined the possibility long before. In the seventeenth cen­tury, physicist Sir Isaac Newton set out laws of motion that determine the way in which objects move through space. Fantasies about space travel came from science-fiction writ­ers such as Jules Verne. In his 1865 book From the Earth to the Moon, Verne wrote of people flying to the Moon in a capsule fired from a huge cannon. In 1898, H. G. Wells imagined Martian spacecraft invading Earth in The War of the Worlds. At this time, people could only study the Moon and Mars by peering through optical telescopes, and there were many fanciful notions about alien life-forms on distant worlds.

Russian teacher Konstantin Tsiolkovsky (1857-1935) fig­ured out the mathematical principles of spaceflight by rockets. In 1923, Hermann Oberth (1894-1989) wrote The Rocket into Planetary Space, a book that predicted spaceflight.

Johannes Winkler Oberth (1897-1947), along with other German enthusiasts, formed the Society for Space Travel. One of its members was Wernher von Braun (1912-1977), who helped design the V-2 rocket of World War II and later worked on the U. S. space program. In 1926, American Robert H. Goddard (1882-1945) launched the world’s first liquid-fuel rocket.

The American Interplanetary Society was founded in 1930 by G. Edward Pendray, David Lasser, Laurence Manning, and others. In 1934, it became known as the American Rocket Society.

In 1963, it became part of the American Institute of Aeronautics and Astronautics. The American Rocket Society and the British Interplanetary Society both helped stimulate public interest in space­flight and encouraged test flights of rockets at a time when governments had little interest in spaceflight.

The Space Shuttle design has three main elements: the spacecraft itself, called the orbiter; an external propellant tank; and two solid-fuel rocket boosters. The orbiter looks like a stubby airplane with small, swept-back wings. The external tank holds fuel for the spacecraft’s main engines. The boosters provide most of the lift during the first 2 minutes of flight. All elements of the Space Shuttle are reused except for the external pro­pellant tank. The Space Shuttle’s two

TECHibTALK

THE SPACE SHUTTLE

Length: 122 feet (37 meters). Wingspan: 78 feet (24 meters).

Length with fuel tank and boosters: 184 feet (56 meters).

Cargo bay: 60 feet by 15 feet (18 meters by 4.5 meters).

Maximum payload: 50,000 pounds (22,700 kilograms).

Orbit altitude: about 185-250 miles (300-400 kilometers).

Orbit speed: 17,321 miles per hour (27,870 kilometers per hour).

Landing speed: about 215 miles per hour (345 kilometers per hour).

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solid-fuel boosters burn out 2 minutes after liftoff, at a height of about 28 miles (45 kilometers). They are landed by parachutes and used again. The external tank holds more than 1.57 million pounds (713,000 kilograms) of liquid hydrogen and liquid oxygen. When this fuel is used up, after 8 minutes, the empty tank is jettisoned over the ocean just before the Space Shuttle enters orbit. The tank then burns up in Earth’s atmosphere.

Once in orbit, a Space Shuttle pilot can fire small thruster motors to maneu­ver the craft. The thrusters may be used to change direction and to slow down, for example when docking with the International Space Station.

If an aircraft is to be stable and easily controlled, it must be well balanced. An aircraft balances around a point called its center of gravity, or center of mass. When fuel, passengers, cargo, or any other weight is added to an aircraft, it must be spread evenly throughout the aircraft. Too much weight at the front moves the center of gravity forward and makes the aircraft nose-heavy. Too much weight at the back makes it tail – heavy. More weight on one side than the other side makes it roll. An aircraft’s center of gravity must not be allowed to move too far in front of, or behind, its ideal position. If this happens, the air­craft can become difficult to fly or even dangerously unstable.

Military transport aircraft have a crew member called the loadmaster. Part of the loadmaster’s job is to place the cargo and passengers on board so that the plane’s center of gravity stays within its allowed limits. The center of gravity moves as an aircraft burns off fuel during a flight, so the loadmaster must take this into account.

An airliner’s weight and the position of its center of gravity are calculated before every flight. The amount of fuel it has to carry depends on its weight. A heavier aircraft needs more fuel. To cal­culate the weight and the position of the center of gravity, the crew needs to know approximately how much the fuel, passengers, and baggage weigh.

Most of the weight carried by an air­liner is fuel, and so the amount of fuel pumped into the aircraft’s tanks is meas­ured. The weight of each gallon, or liter, is known, so the weight of the fuel can be calculated. Most of the fuel is stored in the wings on each side of the aircraft.

The baggage is weighed too, but what about the passengers? Passengers are not weighed individually. Instead, air­lines use standard passenger weights, based on an average and multiplied by the number of passengers, to arrive at the total weight of all the passengers.

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HEAVY PASSENGERS

People are getting heavier. The weight of the average person has been increasing since the standard weights used by air­lines were set in the 1990s. Passengers also are bringing more carry-on baggage onto airplanes, and airlines have had to take this extra weight into account. Since the 1990s, the average passenger weight, including carry-on baggage, has increased from 170 pounds (77 kilo­grams) to 190 pounds (86 kilograms).

In winter, passengers wear more clothes, so the average passenger weight in winter increases further to 195 pounds (88 kilograms).

In 2005, because of these changed statistics, the U. S. Federal Aviation Administration (FAA) issued new figures for standard passenger weights. The average weight of an adult man with carry-on baggage was increased from 185 pounds (84 kilograms) to 200 pounds (91 kilograms) in summer and 205 pounds (93 kilograms) in winter. The weight for an average woman with carry-ons was increased from 145 pounds (66 kilograms) to 179 pounds (81 kilograms) in summer and 184 pounds (83 kilograms) in winter. The weight for children age two to twelve years old was increased from 80 pounds (36 kilograms) to 82 pounds (37 kilo­grams) in the summer and 87 pounds (39 kilograms) in winter.

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The tailplane is usually at the bottom of the fin, but some aircraft have theirs fitted halfway up the fin. This type of tail is called a cruciform tail. The word “cruciform” means cross-shaped, and a cruciform tail forms a cross shape when viewed from the front or back.

The tailplane also can be at the top of the fin. This type of tail is called a T-tail because the tail fin and tailplane form a T shape. Cruciform tails and T-tails are common in business jets, which often have their engines mounted on each side of the tail. Mounting the tailplane higher up the tail fin places it out of the way of the engines.

A few aircraft have been built with a V-tail. This has two fins at an angle, forming a V shape. Each fin has a moving part at the back, which is called a ruddervator because it works as both a rudder and an elevator. The F-117 Nighthawk attack plane has a V-tail. The V-tail causes less drag than other designs because it has fewer surfaces, but the aircraft’s tail has to be made stronger, and its control system is more complicated.

The Harrier is coming to the end of its life. It will be replaced by a STOVL ver­sion of the new U. S. fighter plane, the F-35 Lightning II, or Joint Strike Fighter.

The STOVL F-35, called the F-35B, works differently from the Harrier.

The designers of the F-35B faced the problem of producing a supersonic fighter and attack plane that also could manage vertical flight. A jet engine big enough and powerful enough to provide all the lift needed for short takeoff would make the plane too broad and heavy for supersonic flight. A different method had to be found to produce more lift from a smaller engine suitable for supersonic flight. The new aircraft achieves vertical flight by using both vectored thrust and extra vertical thrust from a lift fan.

When the pilot wants to perform short takeoff or vertical landing, the engine nozzle in the aircraft’s tail swivels downward. In addition, doors on the top and bottom of the plane open,
and a spinning fan behind the pilot blows air downward to provide extra lift. The fan is powered by a shaft that comes out of the front of the jet engine. When the fan is not needed, it is discon­nected from the engine and powered down. The F-35B will be the world’s first operational supersonic STOVL aircraft.

SEE ALSO:

• Aircraft, Military • Autogiro

• Helicopter • Lift and Drag

• Propeller • Takeoff and Landing

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During the first months of the fighting in 1914, airplanes buzzed around the skies over the armies below, but pilots had little more to do than the obsolete

cavalry galloping over the fields. Planes were used to observe enemy movements, rather like aerial versions of cavalry scouts on horseback. When opposing pilots met in the air, they waved-at least at first. As the war became serious, they began exchanging shots, first with pis­tols and then with machine guns. Most planes were two-seater biplanes with a pilot and an observer. The observer did the “scouting” and fired the gun.

The machine gun was mounted high to prevent bullets from hitting the pro­peller. Another solution to this problem was to move the propeller, putting it and the engine behind the pilot. This pro­duced “pusher” machines such as the Vickers FB5 Gunbus and the DH-2, one of a series of planes designed by British engineer Geoffrey De Havilland (1882— 1965). The weakness of the pusher was that it was exposed to attack from the
rear. To fire behind himself, the gunner had to stand on his seat and was at risk of falling out of the plane, with no parachute to save him. A device called an interrupter gear, which synchronized the firing of guns with the propeller, solved the propeller positioning problem.