AskDefine | Define helicopter

Dictionary Definition

helicopter n : an aircraft without wings that obtains its lift from the rotation of overhead blades [syn: chopper, whirlybird, eggbeater]

User Contributed Dictionary



From French hélicoptère, from Greek ελικόπτερον italbrac helikopteron, from Ancient Greek έλιξ (genitive έλικος) italbrac helix, italbrac helikos “turning, revolving, rotating, spinning” + πτερόν italbrac pteron “wing” or “anything winged”.


  • IPA (UK):
  • IPA (US):
  • IPA (Australia):
  • SAMPA (Australia): /"heli%kopt@(r)/


  1. An aircraft that is borne along by one or more sets of long rotating blades which allow it to hover, move in any direction including reverse, or land; and having a smaller set of blades on its tail that stabilize the aircraft.
    We flew over the city in a helicopter.
  2. a powered trowelling machine with spinning blades used to spread concrete.





  1. To transport by helicopter

Extensive Definition

A helicopter is an aircraft that is lifted and propelled by one or more horizontal rotors, each rotor consisting of two or more rotor blades. Helicopters are classified as rotorcraft or rotary-wing aircraft to distinguish them from fixed-wing aircraft because the helicopter derives its source of lift from the rotor blades rotating around a mast. The word 'helicopter' is adapted from the French hélicoptère, coined by Gustave de Ponton d'Amecourt in 1861. It is linked to the Greek words helix/helik- () = "spiral" or "turning" and pteron () = "wing".
As an aircraft, the primary advantages of the helicopter are due to the rotor blades that revolve through the air, providing lift without requiring the aircraft to move forward. This creates the ability for the helicopter to take off and land vertically without the need for runways. For this reason, helicopters are often used in congested or isolated areas where fixed-wing aircraft are not able to take off or land. The lift from the rotor also allows the helicopter to hover in one area and to do so more efficiently than other forms of vertical takeoff and landing (VTOL) aircraft, allowing it to accomplish tasks that fixed-wing aircraft are unable to perform.
Although helicopters were developed and built during the first half-century of flight, some even reaching limited production, it was not until 1942 that a helicopter designed by Igor Sikorsky reached full-scale production, with 131 aircraft built. Even though most previous designs used more than one main rotor, it was the single main rotor with antitorque tail rotor configuration of this design that would come to be recognized worldwide as the helicopter.


Since 400 AD, Chinese children have played with bamboo flying tops. This toy made its way to Europe and is depicted in a 1463 European painting. Pao Phu Tau (抱朴子) was a 4th-century book in China reported to describe some of the ideas inherent to rotary wing aircraft:
Leonardo da Vinci conceived a machine that could be described as an "aerial screw". He wrote that he made small flying models but could not stop the rotor from making the whole craft rotate. Later machines would more closely resemble the ancient bamboo flying top, with spinning wings rather than screws.
In July 1754, Mikhail Lomonosov showed the Russian Academy of Sciences a small coaxial rotor powered by a wound-up spring, intended to lift meteorological instruments.

First flights

In 1906, two French brothers, Jacques and Louis Breguet, began experimenting with airfoils for helicopters and in 1907, those experiments resulted in the Gyroplane No.1. Although there is some uncertainty about the dates, sometime between 14 August and 29 September 1907, the Gyroplane No. 1 lifted its pilot up into the air about two feet (0.6 meters) for a minute. Not to be outdone, Oemichen reclaimed the world record on 4 May when he flew his No. 2 machine again for a 14-minute flight covering 5,550 feet (1.05 mi, 1.692 km) while climbing to a height of 50 feet (15 meters). Cierva had discovered aerodynamic and structural deficiencies in his early designs that could cause his autogyros to flip over after takeoff. The flapping hinges that Cierva designed for the C.4 allowed the rotor to develop lift equally on the left and right halves of the rotor disk. A crash in 1927 led to the development of a drag hinge to relieve further stress on the rotor from its flapping motion. a concept that was later adopted by other helicopter designers, including Bleeker and Kaman. Three small propellers mounted to the airframe were used for additional pitch, roll, and yaw control. The D'AT3 held modest FAI speed and altitude records for the time, including altitude (18 m), duration (8 minutes 45 seconds) and distance flown (1,078 m). Meanwhile, Sikorsky, had settled on a simpler, single rotor design, the VS-300. After experimenting with configurations to counteract the torque produced by the single main rotor, he settled on a single, smaller rotor mounted vertically on the tailboom.
Developed from the VS-300, Sikorsky's R-4 became the first mass produced helicopter with a production order for 100 aircraft. The R-4 was the only Allied helicopter to see service in World War II, primarily being used for rescue in Burma, Alaska, and other areas with harsh terrain. Total production would reach 131 helicopters before the R-4 was replaced by other Sikorsky helicopters such as the R-5 and the R-6. In all, Sikorsky would produce over 400 helicopters before the end of World War II.
As LePage and Sikorsky were building their helicopters for the military, Bell Aircraft hired Arthur Young to help build a helicopter using Young's semi-rigid, teetering-blade rotor design, which used a weighted stabilizing bar. The subsequent Model 30 helicopter demonstrated the simplicity and ease of the design. The Model 30 was developed into the Bell 47, which became the first aircraft certificated for civilian use in the United States. Produced in several countries, the Bell 47 would become the most popular helicopter model for nearly 30 years.

Turbine age

In 1951, at the urging of his contacts at the Department of the Navy, Charles H. Kaman modified his Ka-225 helicopter with a new kind of engine, the turboshaft engine. This adaptation of the turbine engine provided a large amount of horsepower to the helicopter with a lower weight penalty than piston engines, with their heavy engine blocks and auxiliary components. On 11 December 1951, the Ka-225 became the first turbine-powered helicopter in the world. Two years later, on 26 March 1954, a modified Navy HTK-1, another Kaman helicopter, became the first twin-turbine helicopter to fly. However, it was the Sud Aviation Alouette II that would become the first helicopter to be produced with a turbine-engine.


Due to the unique operating characteristics of the helicopter—its ability to takeoff and land vertically, and to hover for extended periods of time, as well as the aircraft's handling properties under low airspeed conditions—it has been chosen to conduct tasks that were previously not possible with other aircraft, or were time- or work-intensive to accomplish on the ground. Today, helicopters are used for transportation, for construction, for firefighting, search and rescue, and a variety of other jobs that require its special capabilities.
Helicopters are used as air ambulances for emergency medical assistance in situations when an ambulance cannot easily or quickly reach the scene. Helicopters are also used when a patient needs to be transported between medical facilities and air transportation is the most practical method for the safety of the patient. Air ambulance helicopters are equipped to provide medical treatment to a patient while in flight. The use of helicopters as an air ambulance is often referred to as MEDEVAC, and patients are referred to as being "airlifted", or "medevaced".
Oil companies charter helicopters to move workers and parts quickly to remote drilling sites located out to sea or in remote locations. The speed over boats makes the high operating cost of helicopters cost effective to ensure that oil platforms continue to flow. Companies such as CHC Helicopter, Bristow Helicopters, and Air Logistics specialize in this type of operation.
Police departments and other law enforcement agencies use helicopters to pursue suspects. Since helicopters can achieve a unique aerial view and don't need to negotiate ground obstacles, they are often used in conjunction with police on the ground to report on suspects' locations and movements. They are often mounted with lighting and heat-sensing equipment for night pursuits.

Rotor configurations

Most helicopters have a single, main rotor but require a separate rotor to overcome torque. This is accomplished through a variable pitch, antitorque rotor or tail rotor. This is the design that Igor Sikorsky settled on for his VS-300 helicopter and it has become the recognized convention for helicopter design, although designs do vary. When viewed from above, designs from Germany, United Kingdom and the United States are said to rotate counter-clockwise, all others are said to rotate clockwise. This can make it difficult when discussing aerodynamic effects on the main rotor between different designs, since the effects may manifest on opposite sides of each aircraft.

Single main rotor

With a single main rotor helicopter, the creation of torque as the engine turns the rotor creates a torque effect that causes the body of the helicopter to turn in the opposite direction of the rotor. To eliminate this effect, some sort of antitorque control must be used, with a sufficient margin of power available to allow the helicopter to maintain its heading and provide yaw control. The three most common controls used today are the traditional tail rotor, Eurocopter's Fenestron (also called a fantail), and MD Helicopters' NOTAR.
Fenestron and FANTAIL are trademarks for a ducted fan mounted at the end of the tail boom of the helicopter and used in place of a tail rotor. Ducted fans have between eight and 18 blades arranged with irregular spacing, so that the noise is distributed over different frequencies. The housing is integral with the aircraft skin and allows a high rotational speed, therefore a ducted fan can have a smaller size than a conventional tail rotor.
The Fenestron was used for the first time at the end of the 1960s on the second experimental model of Sud Aviation's SA 340, and produced on the later model Aérospatiale SA 341 Gazelle. Besides Eurocopter and its predecessors, a ducted fan tail rotor was also used on the canceled military helicopter project, the United States Army's RAH-66 Comanche, as the FANTAIL.


NOTAR, an acronym for NO TAil Rotor, is a helicopter anti-torque system that eliminates the use of the tail rotor on a helicopter. Although the concept took some time to refine, the NOTAR system is simple in theory and works to provide antitorque the same way a wing develops lift using the Coandă effect. A variable pitch fan is enclosed in the aft fuselage section immediately forward of the tail boom and driven by the main rotor transmission. This fan forces low pressure air through two slots on the right side of the tailboom, causing the downwash from the main rotor to hug the tailboom, producing lift, and thus a measure of antitorque proportional to the amount of airflow from the rotorwash. This is augmented by a direct jet thruster (which also provides directional yaw control) and vertical stabilizers.
Development of the NOTAR system dates back to 1975 when engineers at Hughes Helicopters began concept development work. A more heavily modified prototype demonstrator first flew in March 1986 and successfully completed an advanced flight-test program, validating the system for future application in helicopter design. There are currently three production helicopters that incorporate the NOTAR design, all produced by MD Helicopters. This antitorque design also improves safety by eliminating the opportunity for personnel to walk into the tail rotor.

Tip jets

Another single main rotor configuration without a tail rotor is the tip jet rotor, where the main rotor is not driven by the mast, but from nozzles on the tip of the rotor blade; which are either pressurized from a fuselage-mounted gas turbine or have their own turbojet, ramjet or rocket thrusters. Although this method is simple and eliminates torque, the prototypes that have been built are less fuel efficient than conventional helicopters and produce more noise. One example, the Percival P.74, was not even able to leave the ground, and the Hiller YH-32 Hornet had good lifting capability but was otherwise poor. The Fairey Jet Gyrodyne and 40-seat Fairey Rotodyne flew very well indeed. Possibly the most unusual was the rocket tipped Rotary Rocket Roton ATV. None have made it into production.

Dual rotors (contra-rotating)

Contra-rotating rotors, are rotorcraft configurations with a pair or more of large horizontal rotors turning in opposite directions to counteract the effects of torque on the aircraft without relying on an antitorque tail rotor. Primarily, there are three common configurations that use the contra-rotating effect to benefit the rotorcraft; tandem rotors are two rotors with one mounted behind the other, coaxial rotors are two rotors that are mounted one above the other with the same axis, and intermeshing rotors are two rotors that are mounted close to each other at enough angle to allow the rotors to intermesh over the top of the aircraft. Another configuration found on tiltrotors and some earlier helicopters is called transverse rotors where the pair of rotors is mounted at each end of a wing-type structure or outriggers.


Tandem rotors are two horizontal main rotor assemblies mounted one behind the other. Tandem rotors achieve pitch attitude changes to accelerate and decelerate the helicopter through a process called differential collective pitch. To pitch forward and accelerate, the rear rotor increases collective pitch, raising the tail and the front rotor decreases collective pitch, simultaneously dipping the nose. To pitch upward while decelerating (or moving rearward), the front rotor increases collective pitch to raise the nose and the rear rotor decreases collective pitch to lower the tail. Yaw control is developed through opposing cyclic pitch in each rotor; to pivot right, the front rotor tilts right and the rear rotor tilts left, and to pivot left, the front rotor tilts left and the rear rotor tilts right.


Coaxial rotors are a pair of rotors turning in opposite directions on the same masthead. The advantage of the coaxial rotor is that, in forward flight, the lift provided by the advancing halves of each rotor compensates for the retreating half of the other, eliminating one of the key effects of dissymmetry of lift: retreating blade stall. However, other design considerations plague coaxial rotors. There is an increased mechanical complexity of the rotor system because it requires linkages and swashplates for two rotor systems. Add that each rotor system needs to be turned in opposite directions means that the mast itself is more complex, and provisions for making pitch changes to the upper rotor system must pass through the lower rotor system.


Intermeshing rotors on a helicopter are a set of two rotors turning in opposite directions, with each rotor mast mounted on the helicopter with a slight angle to the other so that the blades intermesh without colliding. This configuration is sometimes referred to as a synchropter. Intermeshing rotors have high stability and powerful lifting capability. The arrangement was successfully used in Nazi Germany for a small anti-submarine warfare helicopter, the Flettner Fl 282 Kolibri. During the Cold War, the American company, Kaman Aircraft produced the HH-43 Huskie for the USAF firefighting and rescue missions. The latest Kaman model, the Kaman K-MAX, is a dedicated sky crane design.


Transverse rotors are mounted on the end of wings or outriggers, perpendicular to the body of the aircraft. Similar to tandem rotors and intermeshing rotors, the transverse rotor also uses differential collective pitch. But like the intermeshing rotors, the transverse rotors use the concept for changes in the roll attitude of the rotorcraft. This configuration is found on two of the first viable helicopters, the Focke-Wulf Fw 61 and the Focke-Achgelis Fa 223, as well as the world's largest helicopter ever built, the Mil Mi-12. It is also the configuration found on tiltrotors, such as Bell's XV-15 and the newer V-22 Osprey.

Helicopter rotor system

The rotor system, or more simply rotor, is the rotating part of a helicopter which generates lift. A rotor system may be mounted horizontally as main rotors are, providing lift vertically, or it may be mounted vertically, such as a tail rotor, to provide lift horizontally as thrust to counteract torque effect. In the case of tiltrotors, the rotor is mounted on a nacelle that rotates at the edge of the wing to transition the rotor from a horizontal mounted position, providing lift horizontally as thrust, to a vertical mounted position providing lift exactly as a helicopter.
The rotor consists of a mast, hub and rotor blades. The mast is a cylindrical metal shaft which extends upwards from and is driven by the transmission. At the top of the mast is the attachment point for the rotor blades called the hub. The rotor blades are then attached to the hub by a number of different methods. Main rotor systems are classified according to how the main rotor blades are attached and move relative to the main rotor hub. There are three basic classifications: semirigid, rigid, or fully articulated, although some modern rotor systems use an engineered combination of these types.


A semirigid rotor system allows for two different movements, flapping and feathering. This system is normally comprised of two blades, which are rigidly attached to the rotor hub. The hub is then attached to the rotor mast by a trunnion bearing or teetering hinge and is free to tilt with respect to the main rotor shaft. This allows the blades to see-saw or flap together. As one blade flaps down, the other flaps up. Feathering is accomplished by the feathering hinge, which changes the pitch angle of the blade. Since there is no vertical drag hinge, lead-lag forces are absorbed through blade bending.
Helicopters with semi-rigid rotors are vulnerable to a condition known as mast bumping which can cause the rotor flap stops to shear the mast. Mast bumping is normally encountered during low-G maneuvers, so it is written into the operator's handbook to avoid any low-G conditions.

Fully articulated

In a fully articulated rotor system, each rotor blade is attached to the rotor hub through a series of hinges, which allow the blade to move independently of the others. These rotor systems usually have three or more blades. The blades are allowed to flap, feather, and lead or lag independently of each other. The horizontal hinge, called the flapping hinge, allows the blade to move up and down. This movement is called flapping and is designed to compensate for dissymmetry of lift. The flapping hinge may be located at varying distances from the rotor hub, and there may be more than one hinge. The vertical hinge, called the lead-lag or drag hinge, allows the blade to move back and forth. This movement is called lead-lag, dragging, or hunting. Dampers are usually used to prevent excess back and forth movement around the drag hinge. The purpose of the drag hinge and dampers is to compensate for the acceleration and deceleration caused by Coriolis Effect. Each blade can also be feathered, that is, rotated around its spanwise axis. Feathering the blade means changing the pitch angle of the blade. By changing the pitch angle of the blades you can control the thrust and direction of the main rotor disc.


In a rigid rotor system, the blades, hub, and mast are rigid with respect to each other. The rigid rotor system is mechanically simpler than the fully articulated rotor system. There are no vertical or horizontal hinges so the blades cannot flap or drag, but they can be feathered. Operating loads from flapping and lead/lag forces must be absorbed by bending rather than through hinges. By flexing, the blades themselves compensate for the forces which previously required rugged hinges. The result is a rotor system that has less lag in the control response, because the rotor has much less oscillation. The rigid rotor system also negates the danger of mast bumping inherent in semi-rigid rotors.


Modern rotor systems may use the combined principles of the rotor systems mentioned above. Some rotor hubs incorporate a flexible hub, which allows for blade bending (flexing) without the need for bearings or hinges. These systems, called "flextures", are usually constructed from composite material. Elastomeric bearings may also be used in place of conventional roller bearings. Elastomeric bearings are bearings constructed from a rubber type material and have limited movement that is perfectly suited for helicopter applications. Flextures and elastomeric bearings require no lubrication and, therefore, require less maintenance. They also absorb vibration, which means less fatigue and longer service life for the helicopter components.

Controlling flight

A helicopter has four flight control inputs. These are the cyclic, the collective, the anti-torque pedals, and the throttle. The cyclic control is usually located between the pilot's legs and is commonly called the cyclic stick or just cyclic. On most helicopters, the cyclic is similar to a joystick. Although, the Robinson R22 and R44 have a unique teetering bar cyclic control system and a few helicopters have a cyclic control that descends into the cockpit from overhead.
Helicopter rotors are designed to operate at a specific RPM. The throttle controls the power produced by the engine, which is connected to the rotor by a transmission. The purpose of the throttle is to maintain enough engine power to keep the rotor RPM within allowable limits in order to keep the rotor producing enough lift for flight. In single-engine helicopters, the throttle control is a motorcycle-style twist grip mounted on the collective control, while dual-engine helicopters have a power lever for each engine.

Flight conditions

There are two basic flight conditions for a helicopter; hover and forward flight.
  • ; Hover
  • ;Forward flight

Alternative power sources

The Rotomotion SR20 is a small, unmanned helicopter which is powered by electric batteries. The SR20 can carry a payload of 10 pounds for 12 to 24 minutes based on battery configuration.


The main limitation of the helicopter is its slow speed. There are several reasons why a helicopter cannot fly as fast as a fixed wing aircraft. When the helicopter is at rest, the outer tips of the rotor travel at a speed determined by the length of the blade and the RPM. In a moving helicopter, however, the speed of the blades relative to the air depends on the speed of the helicopter as well as on their rotational velocity. The airspeed of the advancing rotor blade is much higher than that of the helicopter itself. It is possible for this blade to exceed the speed of sound, and thus produce vastly increased drag and vibration. See Wave drag.
Helicopters vibrate. An unadjusted helicopter can easily vibrate so much that it will shake itself apart. To reduce vibration, all helicopters have rotor adjustments for height and pitch. Most also have vibration dampers for height and pitch. Some also use mechanical feedback systems to sense and counter vibration. Usually the feedback system uses a mass as a "stable reference" and a linkage from the mass operates a flap to adjust the rotor's angle of attack to counter the vibration. Adjustment is difficult in part because measurement of the vibration is hard. The most common adjustment measurement system is to use a stroboscopic flash lamp, and observe painted markings or coloured reflectors on the underside of the rotor blades. The traditional low-tech system is to mount coloured chalk on the rotor tips, and see how they mark a linen sheet.

Hazards of helicopter flight

As with any moving vehicle, unsafe operation could result in loss of control, structural damage, or fatality. The following is a list of some of the potential hazards for helicopters:

Deadliest helicopter crashes

  1. Khankala attack - Mi-26 shot down over Chechnya in 2002; 127 killed.
  2. 1997 Israeli helicopter disaster - MH-53 crash in Israel in 1997; 73 killed.
  3. 1977 Israeli CH-53 crash - CH-53 crash near Yitav in the Jordan Valley on 10 May 1977; 54 killed.
  4. 1986 Sumburgh disaster - a British International Helicopters Boeing 234LR Commercial Chinook, Shetland Islands; 45 killed.
  5. 1968 Los Angeles Airways Flight 417 - a Los Angeles Airways Sikorsky S-61L crashed enroute to the Disneyland Heliport; 21 killed.




  • Cottez, Henri. Dictionnaire des structures du vocabulaire savant. Paris: Les Usuels du Robert. 1980. ISBN 0-851-77827-5.
  • Flight Standards Service. Rotorcraft Flying Handbook: FAA Manual H-8083-21. Washington, DC: Federal Aviation Administration, U.S. Dept. of Transportation, 2001. ISBN 1-56027-404-2.
  • Francillon, René J. McDonnell Douglas Aircraft since 1920: Volume II. London: Putnam, 1997. ISBN 0-851-77827-5.
  • Frawley, Gerard. The International Directory of Civil Aircraft, 2003-2004. Fyshwick, Canberra, Act, Australia: Aerospace Publications Pty Ltd., 2003, p. 155. ISBN 1-875671-58-7.
  • Munson, Kenneth. Helicopters and other Rotorcraft since 1907. London: Blandford Publishing, 1968. ISBN 978-0-713-70493-8.
  • Thicknesse, P. Military Rotorcraft (Brassey's World Military Technology series). London: Brassey's, 2000. ISBN 1-857533-25-9.
  • Wragg, David W. Helicopters at War: A Pictorial History. London: R. Hale, 1983. ISBN 0-709-00858-9.

External links

helicopter in Arabic: مروحية
helicopter in Min Nan: Ti̍t-seng-ki
helicopter in Bosnian: Helikopter
helicopter in Bulgarian: Хеликоптер
helicopter in Catalan: Helicòpter
helicopter in Czech: Vrtulník
helicopter in Danish: Helikopter
helicopter in German: Hubschrauber
helicopter in Estonian: Helikopter
helicopter in Modern Greek (1453-): Ελικόπτερο
helicopter in Spanish: Helicóptero
helicopter in Esperanto: Helikoptero
helicopter in Basque: Helikoptero
helicopter in Persian: بالگرد
helicopter in French: Hélicoptère
helicopter in Irish: Ingearán
helicopter in Scottish Gaelic: Heileacoptair
helicopter in Galician: Helicóptero
helicopter in Korean: 헬리콥터
helicopter in Croatian: Helikopter
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helicopter in Icelandic: Þyrla
helicopter in Italian: Elicottero
helicopter in Hebrew: מסוק
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helicopter in Lithuanian: Sraigtasparnis
helicopter in Lingala: Elikɔptɛ́lɛ
helicopter in Hungarian: Helikopter
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helicopter in Japanese: ヘリコプター
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helicopter in Uzbek: Vertolyot
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helicopter in Portuguese: Helicóptero
helicopter in Romanian: Elicopter
helicopter in Russian: Вертолёт
helicopter in Simple English: Helicopter
helicopter in Slovak: Vrtuľník
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helicopter in Serbian: Хеликоптер
helicopter in Finnish: Helikopteri
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helicopter in Thai: เฮลิคอปเตอร์
helicopter in Vietnamese: Máy bay trực thăng
helicopter in Tajik: Чархбол
helicopter in Turkish: Helikopter
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helicopter in Chinese: 直升機
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