Helicopter

For other uses, see Helicopter (disambiguation).

A helicopter is a type of rotorcraft. Its lift and thrust come from rotors that spin flat, like a fan turned sideways. This lets a helicopter take off and land straight up and down, hover in one place, and fly forward, backward, and sideways. Because of this, helicopters can be used in crowded or faraway places where fixed-wing aircraft cannot land without a runway. Some planes that need only a short runway, such as STOL and STOVL aircraft, also need a runway.

The Focke-Wulf Fw 61 was the first helicopter that worked well and could be fully controlled. It flew in 1936. In 1942, the Sikorsky R-4 became the first helicopter made in large numbers. Starting in 1939, Igor Sikorsky worked on the VS-300. After four versions, this design became the model for modern helicopters. It has one main rotor and one small tail rotor.

Most early designs used more than one main rotor. Today, the most common design has one main rotor and a tail rotor that stops the body from spinning. This design is sometimes called a unicopter. Some helicopters have two rotors, in tandem or transverse rotors setups. These can carry more weight than single-rotor designs. Some helicopters with rotors on the same center, tiltrotor aircraft, and compound helicopters also fly today.

Helicopters with four rotors, called quadcopters, were first tried as early as 1907 in France. Along with other multicopters, they are mostly used for special jobs. One example is unmanned aerial vehicles, or drones. Their popularity grew quickly in the early 21st century, as drone racing and aerial photography markets expanded. Recently, some of these craft have been weaponized, meaning they are used as weapons. They have been used for artillery spotting, aerial bombing, and kamikaze drones.

Etymology

The English word helicopter comes from the French word hélicoptère, which Gustave Ponton d'Amécourt created in 1861. It is made from two Ancient Greek words: helix, meaning "spiral" or "whirl," and pteron, meaning "wing."

English speakers often split the word into heli- and -copter, which is not correct from a word-history point of view. This has led to words like helipad and quadcopter. Other English nicknames for the helicopter include "chopper," "copter," "heli," and "whirlybird." In the United States military, a common military slang term is "helo" (pronounced /ˈhiː.loʊ/).

Design

Further information: Tail rotor

Main articles: Aircraft engine and Turboshaft

A helicopter is a type of rotorcraft. It gets its lift and thrust from one or more rotors that spin horizontally. Most helicopters have one main rotor. This rotor creates aerodynamic drag and a turning force that must be balanced. The design that Igor Sikorsky chose for his VS-300 used a smaller tail rotor to push or pull against this turning force. This design has become the most common. Other helicopters use a ducted fan or NOTAR instead. The engines decide what a helicopter can do. Early engines were too weak to lift people, but the internal combustion engine changed that at the end of the 19th century. Today, most larger helicopters are powered by turbine engines. A transmission uses gears and clutches to send power from the engine to the rotors.

A helicopter has four flight controls: the cyclic, the collective, the anti-torque pedals, and the throttle. The cyclic is usually between the pilot's legs. It moves the helicopter forwards, backwards, and from side to side. The collective changes the lift of the main rotor blades. Some helicopters are compound helicopters. They have extra fixed wings and a separate thrust system. This takes some of the work off the rotor during flight and can help the aircraft fly faster.

Flight

A helicopter can fly in three basic ways: hovering, moving forward, and changing between the two. Hovering is the hardest part of flying a helicopter, because the pilot must keep making small corrections to keep it in place. The cyclic control moves the helicopter forward, back, left, and right. The collective keeps the helicopter at a steady height. The pedals control the direction the nose points, which is its heading. Each control affects the others, so when the pilot changes one, the other two must be adjusted too.

A hovering helicopter sits inside a vortex of air that pushes it down. The engine must make enough power to lift the helicopter's weight and push against that downward air. When the helicopter moves forward, it leaves this downward air and enters a state called translational lift. This gives extra lift without using more power. This usually happens at about 16–24 knots (30–44 km/h; 18–28 mph). In forward flight, the controls work more like those of an airplane, and the pedals are usually not needed. The helicopter also does not have a yaw problem in forward flight. If the engine stops, the helicopter enters autorotation. In this state, air moving up through the rotor keeps the main rotor turning.

Uses

Helicopters can take off and land straight up and down, hover in one place for long periods, and fly slowly with good control. This lets them do jobs that other aircraft could not do, or that would take a lot of time or work on the ground. Today, helicopters are used for transportation of people and cargo, military work, construction, firefighting, search and rescue, tourism, medical transport, law enforcement, agriculture, news and media, and aerial observation, among other things.

A helicopter that carries loads on long cables is called an aerial crane. It is used in the logging industry to lift trees from places where roads cannot be built. Helicopters have also given aerial views for electronic news gathering. One of the largest helicopter operations ever done without fighting took place after the 1986 Chernobyl nuclear disaster. Many pilots flew airdrop and observation missions. In firefighting, "Helitack" helicopters help fight wildland fires using aerial firefighting and helibuckets. They can also carry firefighters who rappel down to hard-to-reach areas. Common firefighting models include the Bell 205 and the Erickson S-64 Aircrane. Air ambulances provide emergency medical assistance, often called "MEDEVAC." This use began in the Korean War. Over time, the time needed to reach a medical facility became shorter, from eight hours in World War II to three hours, and then to two hours in the Vietnam War. Police departments use helicopters to follow suspects and watch from above. At night, they often use heat-sensing equipment. Military forces use attack helicopters with missile launchers and miniguns. They also use transport helicopters that can reach places without an airstrip, including for an air assault. Unmanned aerial systems are built for reconnaissance and surveillance, and navy helicopters use dipping sonar for anti-submarine warfare. Oil companies use helicopters to reach oil platforms quickly. NASA developed Ingenuity, a small helicopter that explored Mars. In 2017, Airbus Helicopters sold the most helicopters, followed by Leonardo, Bell Helicopter, and Robinson Helicopter. Among helicopters in use, the most common models are the Robinson R44, the AS350, and the Bell 206. Russian Helicopters, Sikorsky Aircraft, and MD Helicopters also operate many aircraft.

History

See also: Bamboo-copter, Science and inventions of Leonardo da Vinci, and Leonardo's aerial screw

Since around 400 BC, Chinese children have played with bamboo flying toys. These toys are spun like a top and fly when they are let go. A 4th-century AD Chinese book by Ge Hong is said to describe some ideas behind rotary wing aircraft. Later, Leonardo da Vinci designed a machine that could be described as an "aerial screw." In 1754, Mikhail Lomonosov showed a small model that was powered by a spring. People kept working on the idea of flying straight up. Sir George Cayley was inspired by the Chinese flying top when he was a child. The word "helicopter" was first used in 1861 by Gustave de Ponton d'Amécourt. In 1877, Enrico Forlanini built a helicopter powered by steam that had no one on board. It rose 13 meters (43 feet) into the air in Milan. In 1901, Hermann Ganswindt made a flight in Berlin. It was probably the first motor-driven flight carrying people that was heavier than air. In 1905, Ján Bahýľ flew a helicopter that reached 4 meters (13 feet) and flew for over 1,500 meters (4,900 feet).

In 1907, the French brothers Louis Breguet and Jacques built the Gyroplane No.1. It lifted its pilot into the air, but it needed men at each corner to keep it steady. Later that year, Paul Cornu built a helicopter that made the first truly free flight with a pilot. In 1912, another Danish inventor, Jacob Ellehammer, built a helicopter that made several free take-offs.

In the 1920s, Raúl Pateras-Pescara de Castelluccio showed one of the first successful uses of cyclic pitch. This helped control the lift of the rotors. In 1924, Étienne Oehmichen set the first helicopter world record recognized by the FAI. In 1928, Oszkár Asbóth built a prototype that took off and landed at least 182 times. In the early 1920s, Juan de la Cierva invented the autogyro. It became the first practical rotorcraft, but it could not truly fly straight up and down. In 1936, the Focke-Wulf Fw 61 first flew. It was called the world's first practical helicopter. During World War II, Nazi Germany used helicopters in small numbers. In the United States, Igor Sikorsky designed a simpler single-rotor helicopter, the VS-300, in 1939. His R-4 of 1942 was the first large-scale mass-produced helicopter. Bell Aircraft built the Bell 47, which became the first helicopter certified for civilian use in the United States in 1946. In 1951, Charles Kaman built the first turbine-powered helicopter, the K-225. Today, turboshaft engines are the preferred power for helicopters. They allow larger, faster, and higher-performance aircraft.

Safety

Helicopters cannot fly as fast as fixed-wing aircraft. The blade moving forward through the air goes much faster than the helicopter itself and can reach the speed of sound. This causes more drag and shaking. Blades are designed to flap so that the forward blade makes less lift and the backward blade makes more. Because of this, each helicopter has a safe top forward speed called V_NE, which means "velocity, never exceed." Engineers also work on helicopter noise reduction, since many city residents do not like noisy aircraft. Some heliports have closed, and governments have limited flight paths over national parks and other places of natural beauty. To reduce shaking, helicopters are adjusted for height and weight. A poorly adjusted helicopter can shake itself apart. Monitoring systems such as Health and Usage Monitoring Systems (HUMS) help track vibration. Tail rotors can also lose control in some crosswinds, and a ducted tail avoids this problem. Gearboxes have long been a weak point in helicopter reliability. Pascal Chretien designed, built, and flew the world's first man-carrying, free-flying electric helicopter, which was developed in Venelles, France.

Helicopter safety is also supported by volunteer teams, such as the U.S. Helicopter Safety Team (USHST), which publishes accident reviews and encourages better training and safety technology. Pilots must watch for several hazards, including:

• Settling with power, when the helicopter does not have enough power to stop its descent. If not corrected early, it can turn into a vortex ring state.
• Retreating blade stall, which happens at high speed and is the most common limit on forward speed.
• Ground resonance, a self-reinforcing vibration that can occur in an articulated rotor system when the blades become unevenly spaced.
• Low-G condition, a sudden change to negative G-force that causes loss of lift.
• Dynamic rollover, where the helicopter pivots around one skid and tips onto its side, similar to a ground loop in a fixed-wing aircraft.
• Powertrain failures, especially within the shaded area of the height–velocity diagram.
• Brownout in dusty conditions or whiteout in snowy conditions.
• Controlled flight into terrain, when the aircraft is flown into the ground by accident.

World records