Helicopter

Types of helicopters - (1) Single-Rotor, (2) Tandem-Rotor, and (3) Coaxial-Rotor Helicopter.

A heavily armed attack helicopter on a mission          

A helicopter hovering over a logging site

A transport helicopter flying supplies to an oil rig      

A business helicopter landing on a city rooftop

Helicopters can do jobs that aeroplanes cannot do. Unlike planes, military attack helicopters can turn instantly to fire weapons in almost any direction. Helicopters can hover in midair and take off and land in small areas, such as forest clearings, drilling platforms, and rooftops.

Helicopter rescue missions have saved the lives of thousands of people. A coast guard helicopter above has picked up the crew members from a sinking ship.

Helicopter rescue missions have saved the lives of thousands of people. A coast guard helicopter above has picked up the crew members from a sinking ship.

Crop-dusting by helicopter enables farmers to spray agricultural chemicals exactly where they are needed. This specially equipped helicopter is spraying a field with insecticide.     

An antisubmarine helicopter, armed with torpedoes, takes off from a navy ship. Such helicopters carry electronic devices to locate and track submarines.

A rotor blade's shape creates lift. As the blade moves, air flows faster over its curved upper surface than under its flat lower surface. Air pressure is thereby reduced over the blade but unchanged under it. This difference in pressure produces lift.

Greater lift can be created by increasing the angle of attack- the angle the rotor blade makes with the air flowing past it. Increasing the angle causes air to push against the bottom of the blade, which in­creases the air pressure and thereby the lift.

Helicopter controls. Moving the collective pitch lever makes the helicopter climb, hover, or descend. Tilting the control col­umn causes forward, backward, or sideways flight. Pushing the rudder pedals controls the direction the helicopter points. 

Piloting a helicopter - A pilot flies a helicopter by varying the pitch (angle) of the rotor blades. The lift of the main rotor counteracts gravity. The force of the tail rotor counteracts torque, a force that tends to spin the air­craft in the direction opposite to that of the main rotor. In the diagrams below, the pitch of the blades is indicated by the thickness of the circles showing the area swept by the rotor.

The first practical single-rotor helicopter was built and flown by Igor Sikorsky. Its first flight, was in 1939.

Helicopters in combat were first used on a massive scale by United States armed forces during the Vietnam War (1957-19751).

An experimental compound helicopter has coaxial rotors to provide lift. However, it uses jet engines for forward movement. Such aircraft can fly much faster than regular helicopters.

What is a Helicopter?
Helicopter is a type of aircraft that derives both lift and propulsion from one or more sets of horizontally revolving overhead rotors. It is capable of moving vertically and horizontally, the direction of motion being controlled by the pitch of the rotor blades.
Facts, History and Types. Helicopter, aircraft with one or more power-driven horizontal propellers or rotors that enable it to take off and land vertically, to move in any direction, or to remain stationary in the air. Other vertical-flight craft include autogiros, convertiplanes, and V/STOL aircraft of a number of configurations...

Helicopter is an aircraft that is lifted into the air and kept aloft by one or two powerful whirling rotors. A hel­icopter rotor resembles a huge propeller that is parallel to the ground. However, the rotor is actually a rotating wing. The name helicopter refers to the rotor. It comes from the Greek words helix, meaning spiral, and pteron, meaning wing. Nicknames for the helicopter include "chopper," "eggbeater," and "whirlybird."

A helicopter can fly straight up or straight down, for- ward, backward, or-sideways. It can even hover (stay in one spot in the air). Unlike most aeroplanes, helicopters need no runway. They can take off and land in a very small space. In addition, helicopters can fly safely at much slower speeds and lower altitudes than aero­planes. However, they cannot fly as fast as most planes. Most helicopters cannot exceed 320 kilometres per hour. At faster speeds, strong vibrations develop that could damage the rotor blades. Helicopters also use more fuel than aeroplanes to travel the same distance, and so are less economical than aeroplanes. In general, helicopters can fly for only two to three hours-or less than 1000 kilometres—without refuelling. Aeroplanes can travel much further without refuelling.

Helicopters range in size from tiny, single-seat mod­els to huge transports that can carry two trucks in their cargo hold. The heaviest helicopter is the Mil Mi-26, built by the Soviet Union. It weighs 28 metric tons and can carry 20 metric tons of cargo.

Uses of helicopters

Helicopters can be used for many tasks that cannot be performed by other types of aircraft, because they are able to hover in midair and take off and land in small areas. They are particularly useful (1) for rescue mis­sions, (2) for aerial observation, (3) for transportation and construction work, (4) for agricultural and forestry oper­ations, and (5) for military missions.

For rescue missions. Many early developers of heli­copters intended them to be used for saving lives. A hel­icopter can hover above the scene of a disaster. A sling or harness can then be lowered from the craft to endan­gered people below. They are then pulled up and flown to safety. Helicopters have been used to pluck people from burning skyscrapers, sinking ships, and rising floodwaters. They have flown stranded mountain climb­ers and injured skiers to safety. Serving as flying ambu­lances, helicopters can land near car or aeroplane crashes and rush the injured to hospitals. Helicopters can also deliver food and medicine to areas that other vehicles cannot reach because of earthquakes, floods, or storms.

For aerial observation. In many cities, police use helicopters to trail fleeing suspects and direct police cars on the ground. Law enforcement agents in helicop­ters look for lost people and escaped convicts. They may patrol national borders on the lookout for smugglers and illegal immigrants. Helicopters are also used to patrol motorways and identify speeding cars.

Many radio and television stations use helicopters to cover news events from the air. In large cities, helicop­ter pilots observe the flow of traffic and broadcast radio reports warning drivers of traffic jams. Film companies often film from helicopters to give audiences a bird's- eye view of a scene. Helicopter pilots fly low along pipe­lines, railway tracks, and power lines to inspect them for damage.

Helicopters are used to explore wilderness areas, to survey land, and to help locate oil and other resources. From helicopters, scientists count wildlife populations and chart the migration routes of wild animals. Some fishing fleets use helicopters to spot schools of tuna.

For transportation and construction work. Heli­copter transportation is expensive. However, the con­venience of helicopter flight makes "choppers" ideal transport vehicles for certain uses. The flexibility, secu­rity, and speed of helicopter travel have made it a major method of transportation for political leaders in many countries. Helicopter travel saves business executives time that they otherwise might waste in using slow-moving ground transportation. From heliports (airports for helicopters) on city office buildings, business execu­tives may fly directly to nearby cities for meetings.

Helicopter service is essential to many offshore oil-drilling operations. Numerous offshore wells are in rough ocean waters that make it hazardous to bring in replacement crews and supplies by ship. However, heli­copters can land on the drilling platforms and so pro­vide much faster and safer delivery than ships.

Helicopters are often used to transport cargo that is too large or awkward for other vehicles to haul. The cargo is carried in a sling hanging below the craft.

Powerful helicopters are used in construction work as "flying cranes." Workers in helicopters install aerials and huge air conditioners on top of tall buildings and erect preassembled electric power transmission towers. Workers also use helicopters to pour concrete in hard- to-reach places and to put long bridge sections in posi­tion.

For agricultural and forestry operations. Farmers use helicopters to spread seeds, fertilizers, weedkillers, and insecticides over large areas. Instead of building roads, some companies that manufacture forest prod­ucts depend on helicopters to transport logging crews into and out of forests and to carry out logs.

For military missions. In the armed forces, helicop­ters serve as flying ambulances and as troop transports. Powerful military helicopters carry artillery to key battle positions and fly jeeps, tanks, and other equipment wherever they are needed. Helicopters equipped with electronic gear pick up and disrupt enemy communica­tions signals. The armed forces also use helicopters to observe the movements of enemy troops and ships. Many naval helicopters have devices to locate and track submarines. They may also be armed with depth charges, missiles, or torpedoes. Army attack helicopters may carry bombs, cannons, machine guns, or missiles. Their main targets are enemy tanks.

Types of helicopters

Single-rotor helicopters are the most common type of helicopters. A single-rotor helicopter has one main rotor mounted above its body. Although such an aircraft is called a single-rotor helicopter, it also has a second, smaller rotor mounted on its tail. The main rotor may have from 2 to 8 blades. It provides the helicopter's lifting power. The tail rotor has from 2 to 13 blades. It is mounted vertically on either side of the tail and so spins at a right angle to the main rotor. The tail rotor is used to control direction. It also overcomes the tendency of the helicopter to spin around in the direction opposite to that of the main rotor.

Twin-rotor helicopters have two main rotors. The rotors turn in opposite directions and so eliminate the need for a tail rotor. Two basic types of twin-rotor heli­copters are widely used: tandem-rotor helicopters and coaxial-rotor helicopters. A tandem-rotor helicopter has a main rotor mounted above each end of its body. A co-axial-rotor helicopter has one rotor above the other. The rotors are mounted above the middle of the helicopter's body. The shaft of the upper rotor turns inside the shaft of the lower rotor.

How helicopters fly

Lift is the force that causes an aircraft to overcome gravity, climb into the air, and stay aloft. Most aircraft rely on wings to produce lift. An aeroplane has fixed (im­movable) wings that create lift as the aeroplane moves forward. Helicopter rotor blades are rotary wings. An engine turns the rotor, and the blades generate lift as they whirl through the air.

The special shape of wings helps them create lift. A wing's upper surface is curved, and its lower surface is less curved or flat. As a wing moves or whirls through the air, air flows over and under the wing. In the same amount of time, the air flowing over the curved upper surface travels farther than the air flowing under the wing. The air thus flows faster over the wing than under it. This difference in air speed creates a difference in air pressure above and below the wing. There is less pres­sure on the upper surface than on the lower surface. Be­cause air is pushing more strongly against the bottom of the wing than against the top, lift is created. For addi­tional information, see the article Aerodynamics (Princi­ples of aerodynamics).

Helicopter pilots, like aeroplane pilots, can control the amount of lift by changing the angle that the wings make with the airflow. This angle is called the angle of attack. You can demonstrate the relation between lift and the angle of attack by using a kite to serve as a sim­ple wing. Hold the kite flat and point it into the wind. If you then slightly raise the front of the kite, you increase the angle of attack. You will feel a force trying to push the kite upward. This force is the lift created by the wind as it pushes against the bottom surface, if you decrease the angle of attack, the force becomes weaker.

Piloting a helicopter. The pilot of a single-rotor heli­copter operates three basic controls inside the cockpit.

(1) The collective pitch lever makes the helicopter climb, hover, or descend. (2) The control column, also called the cyclic pitch control, causes it to fly forward, back­ward, or sideways. (3) The rudder pedals swing the tail around so that the helicopter can turn. Each control var­ies the pitch (angle) of the main rotor or tail rotor blades.

A system of cables, rods, and other devices leads from the controls in the cockpit to the rotor blades.

Climbing, hovering, and descending. The pilot's left hand moves the collective pitch lever up and down. By raising the lever, the pilot increases the pitch of all main rotor blades equally. The increased pitch, in turn, in­creases the lift generated by the spinning rotor. When lift exceeds the force of gravity, the helicopter goes straight up. After reaching a particular altitude, the pilot may want to hover. The pilot then lowers the lever to de­crease the pitch of the rotor blades and so reduce the amount of lift. When the rotor's lifting force has been reduced just enough to counteract the pull of gravity, the craft will maintain a constant altitude. To de­scend, the pilot lowers the collective pitch lever farther, thereby decreasing the lift. When lift becomes weaker than the force of gravity, the craft descends.

Flying forward, backward, and sideways. The pilot's right hand operates the control column. The control col­umn is a stick between the pilot's knees. It can be tilted in any direction. The helicopter moves in whatever di­rection the pilot tilts the column.

When the control column is tilted, the pitch of the main rotor blades alternately increases and decreases as they sweep through opposite sections of their circular path. To fly forward, the pilot pushes the column ahead. This causes the pitch to be greatest just before the blades pass over the tail. The blades have the least pitch just before they reach the nose. These changes in pitch cause the rotor blades to rise slightly in the rear. The rotor then tries to pull the helicopter both upward and ahead. Gravity counteracts the upward pull, however, and so the aircraft moves forward in level flight.

To fly backward, the pilot pulls back on the control column. This gives the blades the most pitch as they ap­proach the nose and the least pitch as they approach the tail. The nose rises, the tail dips, and the helicopter flies backward. The aircraft can be made to fly sideways in a similar manner.

Turning. As a helicopter's main rotor spins in one di­rection, it creates a force that pushes against the body of the craft in the opposite direction. This twisting force is called torque. It must be overcome or the helicopter will be out of control and simply turn in circles.

The main rotor of a single-rotor helicopter spins in a counterclockwise direction, and so the push of the torque is clockwise. The pilot of a single-rotor craft uses the tail rotor to counteract torque and to change direc­tion. The pilot controls the tail rotor by stepping on two rudder pedals. If neither pedal is depressed, the tail rotor blades spin at just the right pitch to produce ex­actly enough sideways force to counteract the torque. The helicopter then points straight ahead. To swing left, the pilot steps on the left rudder pedal, thereby increas­ing the pitch of the tail rotor blades. The increased force of the rotor pushes the tail in the direction opposite to the clockwise push of the torque. The helicopter then turns to the left. To turn right, the pilot depresses the right rudder pedal and so decreases the pitch—and thus the force—of the tail rotor blades. The torque itself then swings the tail in a clockwise direction, which turns the helicopter to the right.

On a twin-rotor helicopter, one main rotor turns clockwise and the other turns counterclockwise. As a re­sult, the torque generated by one rotor cancels out that generated by the other. The pilot turns the craft by changing the pitch of the main rotors.

Development of the helicopter

Early designs and experiments. The earliest known mention of a rotor-powered flying machine appears in a Chinese text written about A.D. 320. The design of this machine may have been based on a Chinese toy called the flying top. Such toys flew by means of feather rotors. In 1483, the great Italian artist and scientist Leonardo da Vinci sketched a design for a helicopter. It had a large screwlike wing made of starched linen. In 1784, two Frenchmen named Launoy and Bienvenu built the first model helicopter in Europe that could fly. Based on the Chinese flying top, it had two rotors made of feathers. Throughout the 1800's, inventors in Europe and the United States experimented with model helicopters. The steam engines and electric motors of that time were too weak or too heavy to power a full-sized helicopter.

By the early 1900's, small, powerful petrol engines had been developed that made manned helicopter flight possible. The first manned flight took place in 1907. The craft was a four-rotor helicopter built by Louis Breguet, a French inventor. The helicopter lifted one of Breguet's assistants 61 centimetres into the air for a minute. Assist­ants on the ground steadied the helicopter during the flight. Later in 1907, a French mechanic named Paul Cornu made the first free flight in a helicopter. Fie flew his tandem-rotor aircraft to a height of about 2 metres for about 20 seconds.

The first practical helicopters. Early helicopters were difficult to control, and their flight was wobbly. In 1935, Breguet and another Frenchman, Rene Dorand, built a coaxial-rotor helicopter that was easier to control and flew far more steadily. In 1936, Heinrich Focke, a German inventor, built a twin-rotor helicopter that was even further advanced. The following year, it reached a speed of 122 kilometres per hour and an altitude of about 2,400 metres. It could stay aloft for 1 hour and 20 minutes.

The first flight of a practical single-rotor helicopter took place in the United States in 1939. The craft was built and flown by Igor I. Sikorsky, a Russian engineer who had moved to the United States in 1919. The British and the U.S. armed forces used an improved version of Sikorsky's helicopter during World War II (1939-1945).

Further improvements. During the mid-1900's, the military use of helicopters began to increase greatly, which led to major improvements in their design. Helicopters had been used mainly for patrol and rescue mis­sions in World War II. New tasks for the helicopter dur­ing the Korean War (1950-1953) included armed observa­tion of enemy positions and strength and transporting troops and supplies to hard-to-reach areas. During the Vietnam War (1957-1975), thousands of armed U.S. attack helicopters flew combat missions.

The ever-expanding military use of helicopters en­couraged the development of faster, larger, and more powerful craft. In the 1940's and 1950's, engineers adapted the jet engine for use in helicopters. Jet engines were lighter and more powerful than the previous en­gines used to turn the rotor shafts. They enabled heli­copters to fly faster and higher and to carry heavier loads. In addition, the use of new construction materials made helicopters lighter, safer, and stronger. For exam­ple, metal or wooden rotor blades were replaced by longer-lasting plastic blades. Such improvements also made helicopters suitable for more civilian uses.

Recent developments include efforts by manufac­turers to simplify the complicated operation of helicop­ters and to increase their speed. One manufacturer has developed a single-rotor helicopter that needs no tail rotor. Instead, the craft uses jets of air to counteract torque and to change direction. Attempts to increase the speed of helicopters have led to the development of ex­perimental compound helicopters. These vehicles do not depend entirely on rotors to provide forward move­ment as well as lift. Instead, compound helicopters also have jet or propeller systems to help push or pull them ahead. One compound helicopter has reached the speed of 555 kilometres per hour. Related articles: Aerodynamics, Sikorsky, Igor I; Autogiro; Cayley, Sir George; and V/STOL

Outline:

Uses of helicopters: For rescue missions; For aerial observation; For agricultural and forestry operations; For transportation and for construction work; and For military missions

Types of helicopters: Single-rotor helicopters; and Twin-rotor helicopters

How helicopters fly: Lift, and Piloting a helicopter

Development of the helicopter

Questions

What kind of wings does a helicopter have?

How are helicopters used in the construction industry?

What is a tandem-rotor helicopter? A coaxial-rotor helicopter? Who built and flew the first practical single-rotor helicopter? What are some military uses of the helicopter?

Why does a single-rotor helicopter have a tail rotor?

What is a compound helicopter?

In what ways can a helicopter fly that an aeroplane cannot?

What happens when a helicopter pilot raises the collective pitch lever?

Why is helicopter service essential to many offshore oil-drilling operations?

Helicopter Crash

Update: Victim identified in Skagway helicopter crash

A Skagway helicopter pilot is dead following a crash outside Skagway Friday evening. The pilot was 59-year-old Christopher Maggio of Skagway. Maggio was the only person on board. According to an Alaska State Trooper report, the U.S. Coast Guard contacted troopers Friday evening around 8:30 to report that a helicopter had gone down near the upper portion of the Denver Glacier, 6 miles east of Skagway.

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New debris found, search on for last victim of Sarawak helicopter crash

The Straits Times - 20 hours ago - KUCHING (THE STAR/ASIA NEWS NETWORK) - New debris believed to be from the Sarawak helicopter that crashed and killed a Malaysian ...

Norway helicopter crash kills - CNN.com

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Helicopter pilot dies in crash in Skagway | Alaska Dispatch News

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WBAY‑TV: 4 days ago - A pilot helping with the installation of transmission lines was killed when the helicopter crashed in Manitowoc County Wednesday morning.

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A French reality series has suffered a devastating accident. On Monday, 10 people died when two helicopters collided into one another during the creation of the ...