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 Greek words meaning spiral and wing. Nicknames for the helicopter include “chopper,” “eggbeater,” and “whirlybird.”
A helicopter can fly straight up or straight down, forward, backward, or sideways. It can even hover (stay in one spot in the air). Unlike most airplanes, helicopters can take off and land in a small space. In addition, they can fly safely at much slower speeds and lower altitudes than airplanes. However, they cannot fly as fast as most planes. Most helicopters cannot exceed 200 miles (320 kilometers) per hour. At faster flight speeds, the velocity of the rotor blade tips approaches the speed of sound, and it becomes difficult to rotate the rotor. At high speeds, strong vibrations also develop that could damage the blades. Helicopters also use more fuel than airplanes to travel the same distance. In general, helicopters can fly only two to three hours—or less than 600 miles (970 kilometers)—without refueling.
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Helicopters range in size from tiny, single-seat models to huge transports that can carry two trucks in their cargo hold. The heaviest helicopter ever manufactured is the Mil Mi-26, built in Russia. It weighs 31 tons (28 metric tons) and can carry 22 tons (20 metric tons) of cargo.
Uses of helicopters
Because of helicopters’ ability to hover in midair and to take off and land in small areas, they can be used for many tasks. 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.
Helicopters have rescued many people. A helicopter can hover above a disaster scene and lower a sling or harness to endangered people below. The rescuers can then pull the people up and fly them to safety. Helicopters have plucked 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 automobile or airplane 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, the police use helicopters to trail fleeing suspects and direct squad cars on the ground. Law enforcement agents in helicopters look for lost people and escaped convicts. Such agents also patrol national borders on the lookout for smugglers and illegal immigrants.
Many radio and television stations use helicopters to cover news events. In large cities, helicopter pilots observe the flow of traffic and broadcast radio reports warning drivers of traffic jams. Motion-picture companies often film from helicopters to give audiences a bird’s-eye view of a scene. Helicopter pilots fly low along pipelines, railroad tracks, and power lines to look 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 fish.
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) atop downtown office buildings, 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 antennas and huge air conditioners atop tall buildings and erect preassembled electric power transmission towers. Workers also use helicopters to pour concrete in hard-to-reach places and to put bridge sections in position.
For agricultural and forestry operations.
Farmers use helicopters to spread seeds, fertilizers, weedkillers, and insecticides over large areas. The downdraft caused by the rotors can aid in these applications. 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. Military helicopters carry artillery to key battle positions and transport jeeps, tanks, and other equipment. 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, also called _gunships,_ may carry cannons, machine guns, rockets, or missiles. Their main targets are enemy ground vehicles, particularly 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 with both lift and propulsion. The tail rotor has from 2 to 13 blades. It is usually mounted vertically on either side of the tail at a right angle to the main rotor. The tail rotor overcomes the tendency of a helicopter to spin in the direction opposite to that of the main rotor and helps control direction. Some helicopters have the tail rotor mounted inside a duct that goes through the tail. Such a system is called a fenestron or fan-in-fin. On some single-rotor helicopters, a system that uses jets of pressurized air, rather than a tail rotor, helps control the craft.
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 coaxial-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 airplane has fixed (immovable) wings that create lift as the airplane moves forward. Helicopter rotor blades are rotary wings. An engine turns the rotor, and the blades generate lift as they whirl through the air.
Experts disagree on the best way to explain lift. According to one explanation, lift is produced by a difference in air pressure above and below a wing. As a helicopter blade whirls through the air, the air flows more quickly over its curved upper surface and more slowly over its flatter bottom surface. This difference in air speed creates a difference in air pressure above and below the blade. There is less pressure on the upper surface than on the lower surface. Air pushes more strongly against the bottom of the blade than against the top, producing lift.
According to another explanation, a wing generates lift by deflecting (turning) the airflow downward. A helicopter blade deflects the airflow by guiding the air along its curved surface and by meeting the air at an angle. Deflection produces lift according to English scientist Isaac Newton’s third law of motion. This law states that, for every action, there is an equal and opposite reaction. Thus, as the blade deflects the airflow downward, the air pushes the blade upward. See Aerodynamics (Lift) .
Helicopter pilots, like airplane pilots, can control the amount of lift by changing the angle that the wing makes with the airflow. This angle is called the angle of attack. By increasing the angle of attack, the pilot can increase the amount of lift generated by the rotor. Decreasing the angle of attack decreases the amount of lift the rotor produces.
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 the aircraft 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, a stick between the knees. The pilot can tilt the control column in any direction, and the helicopter responds by moving in the same direction. 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. But gravity counteracts the upward pull, 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.
If the main rotor of a single-rotor helicopter spins in a counterclockwise direction, the push of the torque is clockwise. The tail rotor counteracts the torque and enables the pilot to change the helicopter’s 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, the main rotors turn in opposite directions. The torque generated by one rotor thus cancels out that generated by the other. To turn the craft, the pilot changes the pitch of the rotors so that the torque of one rotor is greater than that of the other.
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 known only by their last names, 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 gasoline engines had been developed that made human helicopter flight possible. The first piloted 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 about 2 feet (60 centimeters) 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. He flew his tandem-rotor aircraft to a height of about 6 feet (1.8 meters) 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, Henrich Focke, a German inventor, built a twin-rotor helicopter that was even further advanced. The following year, it reached a speed of 76 miles (122 kilometers) per hour and an altitude of about 8,000 feet (2,400 meters). 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 the enemy and the transportation of troops and supplies to hard-to-reach areas. During the Vietnam War (1957-1975), thousands of armed U.S. attack helicopters, also called gunships, flew combat missions. During the Persian Gulf War of 1991 and the Iraq War (2003-2011), the U.S. military used helicopters that could fire missiles at Iraqi targets, wait to see the results, and then fire again if the target was not destroyed.
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 engines previously 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 and wooden blades have been replaced with more durable blades made from composite materials, usually plastic reinforced with carbon fibers.
Recent developments
include efforts to increase the speed and range of helicopters and to design and build helicopters that do not need a pilot. A tiltrotor aircraft combines features of both helicopters and airplanes. It has a wing like an airplane’s and two main rotors, one at each wing tip. The tiltrotor can take off, hover, fly, and land like a helicopter. But by moving the rotors from a horizontal to a vertical position, the tiltrotor can fly like an airplane. This feature gives the tiltrotor higher speeds and a longer range than a traditional helicopter.
Manufacturers are also developing helicopters for use as drones (unmanned aerial vehicles). These unpiloted vehicles can fly missions that are too dangerous or too tedious for pilots.
