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A helicopter is a type of
rotorcraft A rotary-wing aircraft, rotorwing aircraft or rotorcraft is a heavier-than-air aircraft with rotor wing, rotary wings that spin around a vertical mast to generate lift (force), lift. Part 1 (Definitions and Abbreviations) of Subchapter A of Chapt ...
in which lift and
thrust Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that ...
are supplied by horizontally spinning
rotor ROTOR was an elaborate air defence radar system built by the British Government in the early 1950s to counter possible attack by Soviet bombers. To get it operational as quickly as possible, it was initially made up primarily of WWII-era syst ...
s. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward and laterally. These attributes allow helicopters to be used in congested or isolated areas where
fixed-wing aircraft A fixed-wing aircraft is a heavier-than-air aircraft, such as an airplane, which is capable of flight using aerodynamic lift. Fixed-wing aircraft are distinct from rotary-wing aircraft (in which a rotor mounted on a spinning shaft generate ...
and many forms of short take-off and landing (
STOL A short takeoff and landing (STOL) aircraft is a fixed-wing aircraft that can takeoff/land on short runways. Many STOL-designed aircraft can operate on airstrips with harsh conditions (such as high altitude or ice). STOL aircraft, including tho ...
) or short take-off and vertical landing (
STOVL A short take-off and vertical landing aircraft (STOVL aircraft) is a fixed-wing aircraft that is able to take off from a short runway (or take off vertically if it does not have a heavy payload) and land vertically (i.e. with no runway). The ...
) aircraft cannot perform without a
runway In aviation, a runway is an elongated, rectangular surface designed for the landing and takeoff of an aircraft. Runways may be a human-made surface (often asphalt concrete, asphalt, concrete, or a mixture of both) or a natural surface (sod, ...
. The
Focke-Wulf Fw 61 The Focke-Wulf Fw 61 was the first successful, practical, and fully controllable helicopter, first flown in 1936. It was also known as the Fa 61, as Focke began a new company— Focke-Achgelis—in 1937. Design and development Professor Henri ...
was the first successful, practical, and fully controllable helicopter in 1936, while in 1942, the Sikorsky R-4 became the first helicopter to reach full-scale production. Starting in 1939 and through 1943, Igor Sikorsky worked on the development of the VS-300, which over four iterations, became the basis for modern helicopters with a single main rotor and a single tail rotor. Although most earlier designs used more than one main rotor, the configuration of a single main rotor accompanied by a vertical anti-torque tail rotor (i.e. ''unicopter'', not to be confused with the single-blade
monocopter A monocopter or gyropter is a rotorcraft that uses a single rotating blade. The concept is similar to the whirling helicopter seeds that fall from some trees. The name gyropter is sometimes applied to monocopters in which the entire aircraft rota ...
) has become the most common helicopter configuration. However, twin-rotor helicopters (bicopters), in either
tandem Tandem, or in tandem, is an arrangement in which two or more animals, machines, or people are lined up one behind another, all facing in the same direction. ''Tandem'' can also be used more generally to refer to any group of persons or objects w ...
or
transverse rotors A transverse-rotor aircraft is an aircraft with two large Horizontal plane, horizontal helicopter rotor, rotor assemblies mounted side by side. Single-rotor helicopters (unicopters) need an additional tail rotor or NOTAR, tail exhaust to neut ...
configurations, are sometimes in use due to their greater payload capacity than the monorotor design, and coaxial-rotor,
tiltrotor A tiltrotor is an aircraft that generates lift (force), lift and thrust, propulsion by way of one or more powered Helicopter rotor, rotors (sometimes called ''proprotors'') mounted on rotating shaft (mechanical engineering), shafts or nacelles ...
and compound helicopters are also all flying today. Four-rotor helicopters (
quadcopter A quadcopter, also called quadrocopter, or quadrotor is a type of helicopter or multicopter that has four rotors. Although quadrotor helicopters and convertiplanes have long been flown experimentally, the configuration remained a curiosity ...
s) were pioneered as early as 1907 in France, and along with other types of
multicopter A multirotor or multicopter is a rotorcraft with more than two lift (force), lift-generating helicopter rotor, rotors. An advantage of multirotor aircraft is the simpler rotor mechanics required for flight control. Unlike single- and double-rot ...
s, have been developed mainly for specialized applications such as commercial
unmanned aerial vehicle An unmanned aerial vehicle (UAV) or unmanned aircraft system (UAS), commonly known as a drone, is an aircraft with no human pilot, crew, or passengers onboard, but rather is controlled remotely or is autonomous.De Gruyter Handbook of Dron ...
s (drones) due to the rapid expansion of
drone racing Drone racing is a motorsport where participants operate radio-controlled aircraft (typically small quadcopter unmanned aerial vehicle, drones) equipped with onboard digital camera, digital video cameras, with the operator looking at a compa ...
and
aerial photography Aerial photography (or airborne imagery) is the taking of photographs from an aircraft or other flight, airborne platforms. When taking motion pictures, it is also known as aerial videography. Platforms for aerial photography include fixed-wi ...
markets in the early 21st century, as well as recently
weapon A weapon, arm, or armament is any implement or device that is used to deter, threaten, inflict physical damage, harm, or kill. Weapons are used to increase the efficacy and efficiency of activities such as hunting, crime (e.g., murder), law ...
ized utilities such as artillery spotting,
aerial bomb An aerial bomb is a type of Explosive weapon, explosive or Incendiary device, incendiary weapon intended to travel through the Atmosphere of Earth, air on a predictable trajectory. Engineers usually develop such bombs to be dropped from an aircra ...
ing and suicide attacks.


Etymology

The English word ''helicopter'' is adapted from the French word , coined by Gustave Ponton d'Amécourt in 1861, which originates from the
Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...
' (), ''genitive'' ''helikos'' (ἕλῐκος), "helix, spiral, whirl, convolution" and ' () "wing". In a process of
rebracketing Rebracketing (also known as resegmentation or metanalysis) is a process in historical linguistics where a word originally derived from one set of morphemes is broken down or bracketed into a different set. For example, '' hamburger'', originally ...
, the word is often (erroneously, from an etymological point of view) perceived by English speakers as consisting of ''heli-'' and ''-copter'', leading to words like ''helipad'' and ''quadcopter''. English language nicknames for "helicopter" include "chopper", "copter", "heli", and "whirlybird". In the
United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
military, the common slang is "helo" pronounced /ˈhiː.loʊ/.


Design

A helicopter is a type of
rotorcraft A rotary-wing aircraft, rotorwing aircraft or rotorcraft is a heavier-than-air aircraft with rotor wing, rotary wings that spin around a vertical mast to generate lift (force), lift. Part 1 (Definitions and Abbreviations) of Subchapter A of Chapt ...
in which lift and thrust are supplied by one or more horizontally-spinning rotors. By contrast the
autogyro An autogyro (from Greek and , "self-turning"), gyroscope, gyrocopter or gyroplane, is a class of rotorcraft that uses an unpowered rotor in free autorotation to develop lift. A gyroplane "means a rotorcraft whose rotors are not engine-d ...
(or gyroplane) and gyrodyne have a free-spinning rotor for all or part of the flight envelope, relying on a separate thrust system to propel the craft forwards, so that the airflow sets the rotor spinning to provide lift. The compound helicopter also has a separate thrust system, but continues to supply power to the rotor throughout normal flight. U.S. federal regulations state that "helicopter" means a rotorcraft that, for its horizontal motion, depends principally on its engine-driven rotors.


Rotor system

The rotor system, or more simply ''rotor'', is the rotating part of a helicopter that 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 horizontal thrust to counteract torque from the main rotors. The rotor consists of a mast, hub and rotor blades. The mast is a cylindrical metal shaft that extends upwards from the transmission. At the top of the mast is the attachment point for the rotor blades called the hub. Main rotor systems are classified according to how the rotor blades are attached and move relative to the hub. There are three basic types: hingeless, fully articulated, and teetering; although some modern rotor systems use a combination of these.


Anti-torque

Most helicopters have a single main rotor, but torque created by its
aerodynamic drag In fluid dynamics, drag, sometimes referred to as fluid resistance, is a force acting opposite to the direction of motion of any object moving with respect to a surrounding fluid. This can exist between two fluid layers, two solid surfaces, or b ...
must be countered by an opposed torque. The design that
Igor Sikorsky Igor Ivanovich Sikorsky, (25 May 1889 – 26 October 1972) was a Russian-American aviation pioneer in both helicopters and fixed-wing aircraft. His first success came with the Sikorsky S-2, the second aircraft of his design and construc ...
settled on for his VS-300 was a smaller tail rotor. The tail rotor pushes or pulls against the tail to counter the torque effect, and this has become the most common configuration for helicopter design, usually at the end of a ''tail boom''. Some helicopters use other anti-torque controls instead of the tail rotor, such as the
ducted fan In aeronautics, a ducted fan is a thrust-generating mechanical fan or Propeller (aeronautics), propeller mounted within a cylindrical wiktionary:duct, duct or shroud. Other terms include ducted propeller or shrouded propeller. When used in vertic ...
(called '' Fenestron'' or ''FANTAIL'') and NOTAR. NOTAR provides anti-torque similar to the way a wing develops lift through the use of the Coandă effect on the tail boom.Frawley 2003, p. 151. The use of two or more horizontal rotors turning in opposite directions is another configuration used to counteract the effects of torque on the aircraft without relying on an anti-torque tail rotor. This allows the power normally required to be diverted for the tail rotor to be applied fully to the main rotors, increasing the aircraft's power efficiency and lifting capacity. There are several common configurations that use the counter-rotating effect to benefit the rotorcraft: * Tandem rotors are two counter-rotating rotors with one mounted behind the other. *
Transverse rotors A transverse-rotor aircraft is an aircraft with two large Horizontal plane, horizontal helicopter rotor, rotor assemblies mounted side by side. Single-rotor helicopters (unicopters) need an additional tail rotor or NOTAR, tail exhaust to neut ...
are pair of counter-rotating rotors transversely mounted at the ends of fixed wings or outrigger structures. Now used on
tiltrotor A tiltrotor is an aircraft that generates lift (force), lift and thrust, propulsion by way of one or more powered Helicopter rotor, rotors (sometimes called ''proprotors'') mounted on rotating shaft (mechanical engineering), shafts or nacelles ...
s, some early model helicopters had used them. *
Coaxial rotors A coaxial-rotor aircraft is an aircraft whose helicopter rotor, rotors are mounted one above the other on Concentric objects, concentric shafts, with the same axis of rotation, but turning in opposite directions (contra-rotating). This rotor co ...
are two counter-rotating rotors mounted one above the other with the same axis. * Intermeshing rotors are two counter-rotating rotors mounted close to each other at a sufficient angle to let the rotors intermesh over the top of the aircraft without colliding. An aircraft utilizing this is known as a synchropter. * Multirotors make use of three or more rotors. Specific terms are also used depending on the exact amount of rotors, such as tricopter,
quadcopter A quadcopter, also called quadrocopter, or quadrotor is a type of helicopter or multicopter that has four rotors. Although quadrotor helicopters and convertiplanes have long been flown experimentally, the configuration remained a curiosity ...
, hexacopter and octocopter for three rotors, four rotors, six rotors and eight rotors respectively, of which quadcopter is the most common. Multirotors are primarily used on drones and use on aircraft with a human pilot is rare. Tip jet designs let the rotor push itself through the air and avoid generating torque.


Engines

The number, size and type of engine(s) used on a helicopter determines the size, function and capability of that helicopter design. The earliest helicopter engines were simple mechanical devices, such as rubber bands or spindles, which relegated the size of helicopters to toys and small models. For a half century before the first airplane flight, steam engines were used to forward the development of the understanding of helicopter aerodynamics, but the limited power did not allow for manned flight. The introduction of the
internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal comb ...
at the end of the 19th century became the watershed for helicopter development as engines began to be developed and produced that were powerful enough to allow for helicopters able to lift humans. Early helicopter designs utilized custom-built engines or rotary engines designed for airplanes, but these were soon replaced by more powerful automobile engines and radial engines. The single, most-limiting factor of helicopter development during the first half of the 20th century was that the amount of power produced by an engine was not able to overcome the engine's weight in vertical flight. This was overcome in early successful helicopters by using the smallest engines available. When the compact,
flat engine A flat engine is a piston engine where the cylinders are located on either side of a central crankshaft. Flat engines are also known as horizontally opposed engines, however this is distinct from the less common opposed-piston engine design, ...
was developed, the helicopter industry found a lighter-weight powerplant easily adapted to small helicopters, although radial engines continued to be used for larger helicopters. Turbine engines revolutionized the aviation industry; and the turboshaft engine for helicopter use, pioneered in December 1951 by the aforementioned Kaman K-225, finally gave helicopters an engine with a large amount of power and a low weight penalty. Turboshafts are also more reliable than piston engines, especially when producing the sustained high levels of power required by a helicopter. The turboshaft engine was able to be scaled to the size of the helicopter being designed, so that all but the lightest of helicopter models are powered by turbine engines today. Special jet engines developed to drive the rotor from the rotor tips are referred to as tip jets. Tip jets powered by a remote compressor are referred to as cold tip jets, while those powered by combustion exhaust are referred to as hot tip jets. An example of a cold jet helicopter is the Sud-Ouest Djinn, and an example of the hot tip jet helicopter is the YH-32 Hornet. Some radio-controlled helicopters and smaller, helicopter-type
unmanned aerial vehicle An unmanned aerial vehicle (UAV) or unmanned aircraft system (UAS), commonly known as a drone, is an aircraft with no human pilot, crew, or passengers onboard, but rather is controlled remotely or is autonomous.De Gruyter Handbook of Dron ...
s, use
electric motor An electric motor is a machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a electromagnetic coil, wire winding to gene ...
s or motorcycle engines. Radio-controlled helicopters may also have
piston engine A reciprocating engine, more often known as a piston engine, is a heat engine that uses one or more Reciprocating motion, reciprocating pistons to convert high temperature and high pressure into a Circular motion, rotating motion. This article ...
s that use fuels other than gasoline, such as
nitromethane Nitromethane, sometimes shortened to simply "nitro", is an organic compound with the chemical formula . It is the simplest organic nitro compound. It is a polar liquid commonly used as a solvent in a variety of industrial applications such as in ...
. Some turbine engines commonly used in helicopters can also use biodiesel instead of jet fuel. There are also human-powered helicopters.


Transmission

The transmission is a mechanical system that transmits power from the engine(s) to the rotors. The transmission is a system of gears, bearings,
clutch A clutch is a mechanical device that allows an output shaft to be disconnected from a rotating input shaft. The clutch's input shaft is typically attached to a motor, while the clutch's output shaft is connected to the mechanism that does th ...
es and shafts that performs several functions (1) Translates the alignment of the
drive shaft A drive shaft, driveshaft, driving shaft, tailshaft (Australian English), propeller shaft (prop shaft), or Cardan shaft (after Girolamo Cardano) is a component for transmitting mechanical power (physics), power, torque, and rotation, usually ...
to match the alignment of the rotor shafts; (2) Reduces the RPM of the drive shaft to the lower RPMs of the rotors; and (3) Enables the engine to engage or disengage from the rotors. For helicopters with tail rotors, the transmission
drivetrain A drivetrain (also frequently spelled as drive train or sometimes drive-train) or transmission system, is the group of components that deliver mechanical power from the prime mover to the driven components. In automotive engineering, the driv ...
forks into two paths: one leading to the main rotor, and one leading to the tail rotor.''Helicopter Flying Handbook'', FAA, 2024, Chaper 4 "Helicopter Components, Sections, and Systems" https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/helicopter_flying_handbook The drive shafts of helicopter engines are typically not aligned with the rotor shafts, so the transmission must translate the alignment of the drive shaft to match the shafts of the rotors. Many engine drive shafts are aligned horizontally, yet the main rotor shaft ("mast") is usually vertical, and the tail rotor shaft is often perpendicular to the engine's drive shaft. The transmission contains a series of gears, usually bevel gears, that translate the alignment of the drive shaft to the alignment of the rotor shafts. The transmission also reduces the RPMs of the engine to the lower RPMs required by the rotors. The output drive shaft of the engine, before any gearing is applied, is typically between 3,000 and 50,000 RPM ( turbine engines typically have higher RPM than
piston engine A reciprocating engine, more often known as a piston engine, is a heat engine that uses one or more Reciprocating motion, reciprocating pistons to convert high temperature and high pressure into a Circular motion, rotating motion. This article ...
s). The main rotor typically rotates between 300 and 600 RPM. The tail rotor, if present, usually rotates between 1,000 and 5,000 RPM. (The RPMs of a given model of helicopter are usually fixed the RPM ranges listed above represent a variety of helicopter models). The transmission contains a series of reduction gears to reduce the engine RPM to the rotor RPMs. Several types of reduction gears may be used, including bevel gears,
planetary gear An epicyclic gear train (also known as a planetary gearset) is a Reduction drive, gear reduction assembly consisting of two gears mounted so that the center of one gear (the "planet") revolves around the center of the other (the "sun"). A carri ...
s, helical gears, and spur gears. Most transmissions contain several reduction gears: the engine itself may contain reduction gears (often spur gears) between the engine's internal shaft and the output drive shaft; the main rotor may have a reduction gear at its base (typically a planetary gear); and there may be reduction gears at the tail rotor, and on the shaft leading to the tail rotor. The transmission often includes one or more
clutch A clutch is a mechanical device that allows an output shaft to be disconnected from a rotating input shaft. The clutch's input shaft is typically attached to a motor, while the clutch's output shaft is connected to the mechanism that does th ...
es, which permit the rotors to engage or disengage from the engine. A clutch is required so the engine can start up and gain speed before taking the load of the rotors. A clutch is also required in the case of engine failure: in that situation, the rotors must disengage from the engine so that the rotors can continue spinning and perform autorotation. Helicopter clutches are usually
freewheel image:Freewheel en.svg, Freewheel mechanism In mechanical engineering, mechanical or automotive engineering, a freewheel or overrunning clutch is a device in a transmission (mechanics), transmission that disengages the driveshaft from the driv ...
clutches relying on centrifugal forces ( sprag clutchs are commonly used), but belt drive clutches are also used.


Flight controls

A helicopter has four flight control inputs. These are the cyclic, the collective, the anti-torque foot 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'' or ''stick'' and moves forwards and backwards and side to side. On most helicopters, the cyclic is similar to a
joystick A joystick, sometimes called a flight stick, is an input device consisting of a stick that pivots on a base and reports its angle or direction to the device it is controlling. Also known as the control column, it is the principal control devic ...
. However, the Robinson R22, Robinson R44 and Robinson R66 have a unique teetering-bar cyclic control system and a few helicopters have a cyclic control that descends into the cockpit from overhead. The cyclic is called the cyclic because it cyclically changes the pitch of the main rotor blades. In a forward flight state, as the blades rotate, the blade rotating forward will see higher speed and a corresponding increase in lift compared to the retreating blade. As such, the angle of attack of the forward rotating blade has to be lower than the retreating blade or the helicopter will roll to the retreating blade side. This happens cyclically as the blades rotate through a complete rotation leading to the naming of this control as the cyclic. The cyclic controls this differential angle. The cyclic controls the tilt of the rotor. In hover, the cyclic controls motion of the helicopter over the ground. In flight, the cyclic controls the pitch and roll of the helicopter. In a hover, if the pilot pushes the cyclic forward, the rotor disk tilts forward, and the rotor produces a thrust in the forward direction. If the pilot pushes the cyclic to the side, the rotor disk tilts to that side and produces thrust in that direction, causing the helicopter to move sideways. Because of
precession Precession is a change in the orientation of the rotational axis of a rotating body. In an appropriate reference frame it can be defined as a change in the first Euler angle, whereas the third Euler angle defines the rotation itself. In o ...
, the cyclic moves the
swashplate A swashplate, also known as slant disk, is a mechanical engineering device used to translate the motion of a rotating shaft into reciprocating motion, or vice versa. The working principle is similar to crankshaft, Scotch yoke, or wobble, nutat ...
90 degrees before the desired main rotor tilt. This can be seen when the rotor is stopped. With the blades aligned fore/aft, moving the cyclic forward does not change the blade angle but moving the cyclic to the side will change the blade angle. In flight, the cyclic acts like the stick in an airplane. Moving the cyclic forward pitches the nose down for more speed. Moving the cyclic aft lifts the nose to slow the aircraft. Moving the cyclic to the side rolls the helicopter in that direction which generally leads to turning in that direction, assuming coordinated flight. The collective pitch control or ''collective'' is located on the left side of the pilot's seat with an adjustable friction control to prevent inadvertent movement freeing the pilot's left hand for other uses. The collective changes the pitch angle of all the main rotor blades collectively (i.e. all at the same time) and independently of their rotational position. Therefore, if an up collective input is made, all the blades increase angle of attack equally, and the result is additional lift (power) to the main rotor system which can increase helicopter speed or altitude. Lowering the collective results in less lift from the main rotor system. A
swashplate A swashplate, also known as slant disk, is a mechanical engineering device used to translate the motion of a rotating shaft into reciprocating motion, or vice versa. The working principle is similar to crankshaft, Scotch yoke, or wobble, nutat ...
controls the collective and cyclic pitch of the main blades. The swashplate moves up and down, along the main shaft, to change the pitch of the blades. The stick is connected to the swash plate through the collective and cyclic systems allowing both systems to independently control the angle of the blades. The anti-torque pedals are located in the same position as the
rudder A rudder is a primary control surface used to steer a ship, boat, submarine, hovercraft, airship, or other vehicle that moves through a fluid medium (usually air or water). On an airplane, the rudder is used primarily to counter adverse yaw ...
pedals in a fixed-wing aircraft, and serve a similar purpose, namely to control the yaw or direction in which the nose of the aircraft is pointed. Application of the pedal in a given direction changes the pitch of the tail rotor blades, increasing or reducing the thrust produced by the tail rotor and causing the nose to yaw in the direction of the applied pedal. The pedals mechanically change the pitch of the tail rotor altering the amount of thrust produced. Helicopters do not exhibit
adverse yaw Adverse yaw is the natural and undesirable tendency for an aircraft to yaw in the opposite direction of a roll. It is caused by the difference in lift and drag of each wing. The effect can be greatly minimized with ailerons deliberately designed ...
as seen in airplanes and the pedals are not generally required when turning in forward flight. Use of the pedals is closely related to the collective in hover. For example, increasing collective increases aerodynamic drag on the main rotor system causing a yaw of the helicopter. The pedals are used to counter that yaw. Both the cyclic and collective can have a wide variety of toggles and switches available to the pilot to control such things as aerodynamic trim, engine speed trim, radio and intercom, hook release, water release, etc. This allows the pilot to control these functions without removing their hands from the controls. Helicopter rotors are designed to operate in a narrow range of
RPM Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or r⋅min−1) is a unit of rotational speed (or rotational frequency) for rotating machines. One revolution per minute is equivalent to hertz. Standards ISO 80000-3:2019 def ...
.Croucher, Phil
Professional helicopter pilot studies
page 2-11. . Quote: otor speed"is constant in a helicopter".
Johnson, Pam
Delta D2
page 44 ''Pacific Wings''. Retrieved 2 January 2010
John M. Seddon, Simon Newman
Basic Helicopter Aerodynamics
p. 216, ''
John Wiley and Sons John Wiley & Sons, Inc., commonly known as Wiley (), is an American multinational publishing company that focuses on academic publishing and instructional materials. The company was founded in 1807 and produces books, journals, and encyclop ...
'', 2011. Retrieved 25 February 2012. . Quote: "The rotor is best served by rotating at a constant rotor speed"
The throttle controls the power produced by the engine, which is connected to the rotor by a fixed ratio transmission. The purpose of the throttle is to maintain enough engine power to keep the rotor RPM within allowable limits so that the rotor produces enough lift for flight. The throttle control is a motorcycle-style twist grip mounted on the collective control.


Compound helicopter

A compound helicopter has an additional system for thrust and, typically, small stub fixed wings. This offloads the rotor in cruise, which allows its rotation to be slowed down, thus increasing the maximum speed of the aircraft. The Lockheed AH-56A Cheyenne diverted up to 90% of its engine power to a pusher propeller during forward flight.


Flight

There are three basic flight conditions for a helicopter: hover, forward
flight Flight or flying is the motion (physics), motion of an Physical object, object through an atmosphere, or through the vacuum of Outer space, space, without contacting any planetary surface. This can be achieved by generating aerodynamic lift ass ...
and the transition between the two.


Hover

Hovering is the most challenging part of flying a helicopter. Required are constant control inputs and corrections by the pilot to keep the helicopter where it is required to be. Despite the complexity of the task, the control inputs in a hover are simple. The cyclic is used to eliminate drift in the horizontal plane, that is to control forward and back, right and left. The collective is used to maintain altitude. The pedals are used to control nose direction or heading. It is the interaction of these controls that makes hovering so difficult, since an adjustment in any one control requires an adjustment of the other two, creating a cycle of constant correction. In addition, the center of lift of the main rotor system is significantly above the center of gravity (CG) of the helicopter. Thus, any lateral perturbation of the helicopter in a hover will tend to increase as the rotor lift will increasingly roll or pitch the helicopter in a positive-feedback rotor-lift versus helicopter CG situation. The lateral motion of the helicopter lags behind the roll induced by the rotor lift side vector which will lead an inexperienced pilot into a pilot induced oscillation (PIO) and eventual loss of control.


Transition from hover to forward flight

A hovering helicopter is surrounded by a vortex of air pushing the helicopter down. This can be a hover in ground effect or out of ground effect. Thus, when in a hover, the engine needs to provide enough power to both counter helicopter weight as well as counter this downward flow of air into the rotor system. As a helicopter moves from hover to forward flight it flies out of this downward flowing vortex and enters a state called translational lift which provides extra lift without increasing power. This state, most typically, occurs when the airspeed reaches approximately , and may be necessary for a helicopter to obtain flight. A maneuver called a running take off involves sliding the helicopter on the ground at increasing speed until sufficient lift is achieved for flight.


Forward flight

In forward flight a helicopter's flight controls behave more like those of a fixed-wing aircraft. Applying forward pressure on the cyclic will cause the nose to pitch down, with a resultant increase in airspeed and loss of altitude. Aft cyclic will cause the nose to pitch up, slowing the helicopter and causing it to climb. Increasing collective (power) while maintaining a constant airspeed will induce a climb while decreasing collective will cause a descent. Coordinating these two inputs, down collective plus aft cyclic or up collective plus forward cyclic, will result in airspeed changes while maintaining a constant altitude. Helicopters do not exhibit adverse yaw and the pedals are not generally needed for forward flight, even when turning.


Autorotation

If the engine fails or is disconnected from the rotor system, the helicopter will enter an autorotation, where the helicopter's main rotor turns due to air moving up through the rotor, instead of engine power driving the rotor.


Uses

Due to the operating characteristics of the helicopter—its ability to take off and land vertically, and to hover for extended periods of time, as well as the aircraft's handling properties under low
airspeed In aviation, airspeed is the speed of an aircraft relative to the air it is flying through (which itself is usually moving relative to the ground due to wind). In contrast, the ground speed is the speed of an aircraft with respect to the sur ...
conditions—it has proved advantageous to conduct tasks that were previously not possible with other aircraft, or were time- or work-intensive to accomplish on the ground. Today, helicopter uses include
transport Transport (in British English) or transportation (in American English) is the intentional Motion, movement of humans, animals, and cargo, goods from one location to another. Mode of transport, Modes of transport include aviation, air, land tr ...
ation of people and cargo, military uses, construction, firefighting,
search and rescue Search and rescue (SAR) is the search for and provision of aid to people who are in distress or imminent danger. The general field of search and rescue includes many specialty sub-fields, typically determined by the type of terrain the search ...
,
tourism Tourism is travel for pleasure, and the Commerce, commercial activity of providing and supporting such travel. World Tourism Organization, UN Tourism defines tourism more generally, in terms which go "beyond the common perception of tourism as ...
, medical transport, law enforcement, agriculture,
news News is information about current events. This may be provided through many different Media (communication), media: word of mouth, printing, Mail, postal systems, broadcasting, Telecommunications, electronic communication, or through the te ...
and
media Media may refer to: Communication * Means of communication, tools and channels used to deliver information or data ** Advertising media, various media, content, buying and placement for advertising ** Interactive media, media that is inter ...
, and aerial observation, among others. A helicopter used to carry loads connected to long cables or slings is called an aerial crane. Aerial cranes are used to place heavy equipment, like radio transmission towers and large air conditioning units, on the tops of tall buildings, or when an item must be raised up in a remote area, such as a radio tower raised on the top of a hill or mountain. Helicopters are used as aerial cranes in the logging industry to lift trees out of terrain where vehicles cannot travel and where environmental concerns prohibit the building of roads. These operations are referred to as longline because of the long, single sling line used to carry the load. In military service helicopters are often useful for delivery of outsized slung loads that would not fit inside ordinary cargo aircraft: artillery pieces, large machinery (field radars, communications gear, electrical generators), or pallets of bulk cargo. In military operations these payloads are often delivered to remote locations made inaccessible by mountainous or riverine terrain, or naval vessels at sea. In electronic news gathering, helicopters have provided aerial views of some major news stories, and have been doing so, from the late 1960s. Helicopters have also been used in films, both in front and behind the camera. The largest single non-combat helicopter operation in history was the disaster management operation following the 1986 Chernobyl nuclear disaster. Hundreds of pilots were involved in
airdrop An airdrop is a type of airlift in which items including weapons, equipment, humanitarian aid or leaflets are delivered by military or civilian aircraft without their landing. Developed during World War II to resupply otherwise inaccessible tr ...
and observation missions, making dozens of sorties a day for several months. " Helitack" is the use of helicopters to combat wildland fires.Butler, Bret W. et al
"Appendix A: Glossary: Fire Behavior Associated with the 1994 South Canyon Fire on Storm King Mountain, Colorado research paper"
''U.S. Dept. of Agriculture, Forest Service'', September 1998. Retrieved 2 November 2008.
The helicopters are used for
aerial firefighting Aerial firefighting, also known as waterbombing, is the use of aircraft and other aerial resources to Wildfire suppression, combat wildfires. The types of aircraft used include fixed-wing aircraft and helicopters. Smokejumpers and rappellers ar ...
(water bombing) and may be fitted with tanks or carry helibuckets. Helibuckets, such as the Bambi bucket, are usually filled by submerging the bucket into lakes, rivers, reservoirs, or portable tanks. Tanks fitted onto helicopters are filled from a hose while the helicopter is on the ground or water is siphoned from lakes or reservoirs through a hanging snorkel as the helicopter hovers over the water source. Helitack helicopters are also used to deliver firefighters, who rappel down to inaccessible areas, and to resupply firefighters. Common firefighting helicopters include variants of the Bell 205 and the Erickson S-64 Aircrane helitanker. Helicopters are used as air ambulances for emergency medical assistance in situations when an
ambulance An ambulance is a medically-equipped vehicle used to transport patients to treatment facilities, such as hospitals. Typically, out-of-hospital medical care is provided to the patient during the transport. Ambulances are used to respond to ...
cannot easily or quickly reach the scene, or cannot transport the patient to a medical facility in time. Helicopters are also used when patients need to be transported between medical facilities and air transportation is the most practical method. An air ambulance helicopter is equipped to stabilize and provide limited medical treatment to a patient while in flight. The use of helicopters as air ambulances is often referred to as "
MEDEVAC Medical evacuation, often shortened to medevac or medivac, is the timely and efficient movement and en route care provided by medical personnel to patients requiring evacuation or transport using medically equipped air ambulances, helicopters an ...
", and patients are referred to as being "airlifted", or "medevaced". This use was pioneered in the
Korean War The Korean War (25 June 1950 – 27 July 1953) was an armed conflict on the Korean Peninsula fought between North Korea (Democratic People's Republic of Korea; DPRK) and South Korea (Republic of Korea; ROK) and their allies. North Korea was s ...
, when time to reach a medical facility was reduced to three hours from the eight hours needed in
World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
, and further reduced to two hours by the
Vietnam War The Vietnam War (1 November 1955 – 30 April 1975) was an armed conflict in Vietnam, Laos, and Cambodia fought between North Vietnam (Democratic Republic of Vietnam) and South Vietnam (Republic of Vietnam) and their allies. North Vietnam w ...
. In naval service a prime function of rescue helicopters is to promptly retrieve downed aircrew involved in crashes occurring upon launch or recovery aboard aircraft carriers. In past years this function was performed by destroyers escorting the carrier, but since then helicopters have proved vastly more effective. Police departments and other law enforcement agencies use helicopters to pursue suspects and patrol the skies. Since helicopters can achieve a unique aerial view, 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. Military forces use
attack helicopter An attack helicopter is an armed helicopter with the primary role of an attack aircraft, with the offensive (military), offensive capability of engaging ground targets such as enemy infantry, military vehicles and fortifications. Due to their ...
s to conduct aerial attacks on ground targets. Such helicopters are mounted with
missile launchers A rocket launcher is a weapon that launches an unguided, rocket-propelled projectile. History The earliest rocket launchers documented in imperial China consisted of arrows modified by the attachment of a rocket motor to the shaft a few i ...
and miniguns. Transport helicopters are used to ferry troops and supplies where the lack of an
airstrip An aerodrome, airfield, or airstrip is a location from which aircraft flight operations take place, regardless of whether they involve air cargo, passengers, or neither, and regardless of whether it is for public or private use. Aerodromes in ...
would make transport via fixed-wing aircraft impossible. The use of transport helicopters to deliver troops as an attack force on an objective is referred to as "
air assault Air assault is the movement of ground-based military forces by vertical take-off and landing (VTOL) aircraft, such as helicopters, to seize and hold key terrain that has not been fully secured, and to directly engage enemy forces behind enemy l ...
". Unmanned aerial systems (UAS) helicopter systems of varying sizes are developed by companies for military
reconnaissance In military operations, military reconnaissance () or scouting is the exploration of an area by military forces to obtain information about enemy forces, the terrain, and civil activities in the area of operations. In military jargon, reconnai ...
and
surveillance Surveillance is the monitoring of behavior, many activities, or information for the purpose of information gathering, influencing, managing, or directing. This can include observation from a distance by means of electronic equipment, such as ...
duties. Naval forces also use helicopters equipped with dipping sonar for
anti-submarine warfare Anti-submarine warfare (ASW, or in the older form A/S) is a branch of underwater warfare that uses surface warships, aircraft, submarines, or other platforms, to find, track, and deter, damage, or destroy enemy submarines. Such operations ar ...
, since they can operate from small ships. Oil companies charter helicopters to move workers and parts quickly to remote drilling sites located at sea or in remote locations. The speed advantage over boats makes the high operating cost of helicopters cost-effective in ensuring that
oil platform An oil platform (also called an oil rig, offshore platform, oil production platform, etc.) is a large structure with facilities to extract and process petroleum and natural gas that lie in rock formations beneath the seabed. Many oil platforms w ...
s continue to operate. Various companies specialize in this type of operation.
NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...
developed '' Ingenuity'', a helicopter used to survey
Mars Mars is the fourth planet from the Sun. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...
(along with a rover). It began service in February 2021 and was retired due to sustained rotor blade damage in January 2024 after 73 sorties. As the Martian atmosphere is 100 times thinner than Earth's, its two blades spin at close to 3,000 revolutions a minute, approximately 10 times faster than that of a terrestrial helicopter.


Market

In 2017, 926 civil helicopters were shipped for $3.68 billion, led by
Airbus Helicopters Airbus Helicopters SAS (formerly Eurocopter S.A., trading as Eurocopter Group) is the helicopter manufacturing division of Airbus. It is the largest in the industry in terms of revenues and turbine helicopter deliveries, holding 48% of the wo ...
with $1.87 billion for 369 rotorcraft, Leonardo Helicopters with $806 million for 102 (first three-quarters only), Bell Helicopter with $696 million for 132, then Robinson Helicopter with $161 million for 305. By October 2018, the in-service and stored helicopter fleet of 38,570 with civil or government operators was led Robinson Helicopter with 24.7% followed by Airbus Helicopters with 24.4%, then Bell with 20.5 and Leonardo with 8.4%,
Russian Helicopters JSC Russian Helicopters () is a helicopter design and manufacturing company headquartered in Moscow, Russia. The company designs and manufactures civilian and military helicopters. The company's principal shareholder is Rostec. It is the world's ...
with 7.7%,
Sikorsky Aircraft Sikorsky Aircraft is an American aircraft manufacturer based in Stratford, Connecticut. It was established by the Russian-American aviation pioneer Igor Sikorsky in 1923, and was among the first companies to manufacture helicopters for civilian ...
with 7.2%, MD Helicopters with 3.4% and other with 2.2%. The most widespread model is the piston Robinson R44 with 5,600, then the H125/ AS350 with 3,600 units, followed by the Bell 206 with 3,400. Most were in North America with 34.3% then in Europe with 28.0% followed by Asia-Pacific with 18.6%, Latin America with 11.6%, Africa with 5.3% and Middle East with 1.7%.


History


Early design

The earliest references for vertical flight came from China. Since around 400 BC,Leishman, J. Gordon. ''Principles of Helicopter Aerodynamics''. Cambridge aerospace series, 18. Cambridge:
Cambridge University Press Cambridge University Press was the university press of the University of Cambridge. Granted a letters patent by King Henry VIII in 1534, it was the oldest university press in the world. Cambridge University Press merged with Cambridge Assessme ...
, 2006. . Web extract
Chinese children have played with bamboo flying toys (or Chinese top). This bamboo-copter is spun by rolling a stick attached to a rotor. The spinning creates lift, and the toy flies when released. The 4th-century AD
Daoist Taoism or Daoism (, ) is a diverse philosophical and religious tradition indigenous to China, emphasizing harmony with the Tao ( zh, p=dào, w=tao4). With a range of meaning in Chinese philosophy, translations of Tao include 'way', 'road', ' ...
book '' Baopuzi'' by
Ge Hong Ge Hong (; b. 283 – d. 343 or 364), courtesy name Zhichuan (稚川), was a Chinese linguist, philosopher, physician, politician, and writer during the Eastern Jin dynasty. He was the author of '' Essays on Chinese Characters'', the '' Baopu ...
( "Master who Embraces Simplicity") reportedly describes some of the ideas inherent to rotary wing aircraft.Fay, John
"Helicopter Pioneers – Evolution of Rotary Wing Aircraft"
''Helicopter History Site''. Retrieved: 28 November 2007
Designs similar to the Chinese helicopter toy appeared in some Renaissance paintings and other works. In the 18th and early 19th centuries Western scientists developed flying machines based on the Chinese toy. It was not until the early 1480s, when Italian polymath
Leonardo da Vinci Leonardo di ser Piero da Vinci (15 April 1452 - 2 May 1519) was an Italian polymath of the High Renaissance who was active as a painter, draughtsman, engineer, scientist, theorist, sculptor, and architect. While his fame initially rested o ...
created a design for a machine that could be described as an " aerial screw", that any recorded advancement was made towards vertical flight. His notes suggested that he built small flying models, but there were no indications for any provision to stop the rotor from making the craft rotate.Rumerman, Judy
"Early Helicopter Technology"
''Centennial of Flight Commission'', 2003. Retrieved 12 December 2010
Pilotfriend.co

''Pilotfriend.com''. Retrieved 12 December 2010
As scientific knowledge increased and became more accepted, people continued to pursue the idea of vertical flight. In July 1754, Russian
Mikhail Lomonosov Mikhail Vasilyevich Lomonosov (; , ; – ) was a Russian polymath, scientist and writer, who made important contributions to literature, education, and science. Among his discoveries were the atmosphere of Venus and the law of conservation of ...
had developed a small coaxial modeled after the Chinese top but powered by a wound-up spring deviceLeishman, J. Gordon (2006)
Principles of Helicopter Aerodynamics
. Cambridge University Press. p. 8.
and demonstrated it to the
Russian Academy of Sciences The Russian Academy of Sciences (RAS; ''Rossíyskaya akadémiya naúk'') consists of the national academy of Russia; a network of scientific research institutes from across the Russian Federation; and additional scientific and social units such ...
. It was powered by a spring, and was suggested as a method to lift
meteorological Meteorology is the scientific study of the Earth's atmosphere and short-term atmospheric phenomena (i.e. weather), with a focus on weather forecasting. It has applications in the military, aviation, energy production, transport, agriculture ...
instruments. In 1783, Christian de Launoy, and his
mechanic A mechanic is a skilled tradesperson who uses tools to build, maintain, or repair machinery, especially engines. Formerly, the term meant any member of the handicraft trades, but by the early 20th century, it had come to mean one who works w ...
, Bienvenu, used a coaxial version of the Chinese top in a model consisting of contrarotating
turkey Turkey, officially the Republic of Türkiye, is a country mainly located in Anatolia in West Asia, with a relatively small part called East Thrace in Southeast Europe. It borders the Black Sea to the north; Georgia (country), Georgia, Armen ...
flight feathers as rotor blades, and in 1784, demonstrated it to the
French Academy of Sciences The French Academy of Sciences (, ) is a learned society, founded in 1666 by Louis XIV at the suggestion of Jean-Baptiste Colbert, to encourage and protect the spirit of French Scientific method, scientific research. It was at the forefron ...
. Sir George Cayley, influenced by a childhood fascination with the Chinese flying top, developed a model of feathers, similar to that of Launoy and Bienvenu, but powered by rubber bands. By the end of the century, he had progressed to using sheets of tin for rotor blades and springs for power. His writings on his experiments and models would become influential on future aviation pioneers. Alphonse Pénaud would later develop coaxial rotor model helicopter toys in 1870, also powered by rubber bands. One of these toys, given as a gift by their father, would inspire the
Wright brothers The Wright brothers, Orville Wright (August 19, 1871 – January 30, 1948) and Wilbur Wright (April 16, 1867 – May 30, 1912), were American aviation List of aviation pioneers, pioneers generally credited with inventing, building, and flyin ...
to pursue the dream of flight. In 1861, the word "helicopter" was coined by Gustave de Ponton d'Amécourt, a French inventor who demonstrated a small steam-powered model. While celebrated as an innovative use of a new metal, aluminum, the model never lifted off the ground. D'Amecourt's linguistic contribution would survive to eventually describe the vertical flight he had envisioned. Steam power was popular with other inventors as well. In 1877, the Italian engineer, inventor and aeronautical pioneer Enrico Forlanini developed an unmanned helicopter powered by a
steam engine A steam engine is a heat engine that performs Work (physics), mechanical work using steam as its working fluid. The steam engine uses the force produced by steam pressure to push a piston back and forth inside a Cylinder (locomotive), cyl ...
. It rose to a height of , where it remained for 20 seconds, after a vertical take-off from a park in
Milan Milan ( , , ; ) is a city in northern Italy, regional capital of Lombardy, the largest city in Italy by urban area and the List of cities in Italy, second-most-populous city proper in Italy after Rome. The city proper has a population of nea ...
. Milan has dedicated its city airport to Enrico Forlanini, also named
Linate Airport Milan Linate Airport is a city airport located in Milan, the second-largest city and largest urban area of Italy. It served 10.6 million passengers and recorded 118,060 aircraft movements in 2024, making it one of the busiest airports in Ital ...
, as well as the nearby park, the Parco Forlanini. Emmanuel Dieuaide's steam-powered design featured counter-rotating rotors powered through a hose from a boiler on the ground. In 1887 Parisian inventor, Gustave Trouvé, built and flew a tethered electric model helicopter. In July 1901, the maiden flight of Hermann Ganswindt's helicopter took place in Berlin-Schöneberg; this was probably the first heavier-than-air motor-driven flight carrying humans. A movie covering the event was taken by
Max Skladanowsky Max Skladanowsky (30 April 1863 – 30 November 1939) was a German people, German inventor and early filmmaker. Along with his brother Emil, he invented the Bioscop, an early movie projector the Skladanowsky brothers used to display a moving pict ...
, but it remains lost. In 1885,
Thomas Edison Thomas Alva Edison (February11, 1847October18, 1931) was an American inventor and businessman. He developed many devices in fields such as electric power generation, mass communication, sound recording, and motion pictures. These inventions, ...
was given US$1,000 (equivalent to $ today) by James Gordon Bennett, Jr., to conduct experiments towards developing flight. Edison built a helicopter and used the paper for a stock ticker to create
guncotton Nitrocellulose (also known as cellulose nitrate, flash paper, flash cotton, guncotton, pyroxylin and flash string, depending on form) is a highly flammable compound formed by nitrating cellulose through exposure to a mixture of nitric acid and ...
, with which he attempted to power an internal combustion engine. The helicopter was damaged by explosions and one of his workers was badly burned. Edison reported that it would take a motor with a ratio of three to four pounds per horsepower produced to be successful, based on his experiments. Ján Bahýľ, a Slovak inventor, adapted the
internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal comb ...
to power his helicopter model that reached a height of in 1901. On 5 May 1905, his helicopter reached in altitude and flew for over . In 1908, Edison patented his own design for a helicopter powered by a gasoline engine with box kites attached to a mast by cables for a rotor, but it never flew.


First flights

In 1906, two French brothers, Jacques and Louis Breguet, began experimenting with airfoils for helicopters. In 1907, those experiments resulted in the ''Gyroplane No.1'', possibly as the earliest known example of a quadcopter. Although there is some uncertainty about the date, sometime between 14 August and 29 September 1907, the Gyroplane No. 1 lifted its pilot into the air about for a minute.Munson 1968.Hirschberg, Michael J. and David K. Dailey
"Sikorsky"
. ''US and Russian Helicopter Development in the 20th Century'', American Helicopter Society, International. 7 July 2000.
The Gyroplane No.1 proved to be extremely unsteady and required a man at each corner of the airframe to hold it steady. For this reason, the flights of the Gyroplane No.1 are considered to be the first manned flight of a helicopter, but not a free or untethered flight. That same year, fellow French inventor Paul Cornu designed and built the Cornu helicopter which used two counter-rotating rotors driven by a Antoinette engine. On 13 November 1907, it lifted its inventor to and remained aloft for 20 seconds. Even though this flight did not surpass the flight of the Gyroplane No. 1, it was reported to be the first truly free flight with a pilot.Leishman, J. Gordon, Technical Fellow of AHS International
"Paper"
64th Annual Forum of the American Helicopter Society International, on the aerodynamic capability of Cornu's design, arguing that the aircraft lacked the power and rotor loading to lift free of the ground in manned flight.
Cornu's helicopter completed a few more flights and achieved a height of nearly , but it proved to be unstable and was abandoned. In 1909, J. Newton Williams of Derby, Connecticut, and
Emile Berliner Emile Berliner (May 20, 1851 – August 3, 1929) originally Emil Berliner, was a German-American inventor. He is best known for inventing the lateral-cut flat disc gramophone record, record (called a "gramophone record" in British and American En ...
of Washington, D.C., flew a helicopter "on three occasions" at Berliner's lab in Washington's Brightwood neighborhood. In 1911, Slovenian philosopher and economist Ivan Slokar patented a helicopter configuration. The Danish inventor Jacob Ellehammer built the
Ellehammer helicopter __NOTOC__ The Ellehammer helicopter was an otherwise-unnamed experimental aircraft built in Denmark in 1912. Based on experiments with models, Jacob Ellehammer constructed a full-size machine equipped with two contra-rotating discs, each of whi ...
in 1912. It consisted of a frame equipped with two counter-rotating discs, each of which was fitted with six vanes around its circumference. After indoor tests, the aircraft was demonstrated outdoors and made several free take-offs. Experiments with the helicopter continued until September 1916, when it tipped over during take-off, destroying its rotors. During
World War I World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a World war, global conflict between two coalitions: the Allies of World War I, Allies (or Entente) and the Central Powers. Fighting to ...
,
Austria-Hungary Austria-Hungary, also referred to as the Austro-Hungarian Empire, the Dual Monarchy or the Habsburg Monarchy, was a multi-national constitutional monarchy in Central Europe#Before World War I, Central Europe between 1867 and 1918. A military ...
developed the PKZ, an experimental helicopter prototype, with two aircraft built.


Early development

In the early 1920s, Argentine Raúl Pateras-Pescara de Castelluccio, while working in Europe, demonstrated one of the first successful applications of cyclic pitch. Coaxial, contra-rotating, biplane rotors could be warped to cyclically increase and decrease the lift they produced. The rotor hub could also be tilted forward a few degrees, allowing the aircraft to move forward without a separate propeller to push or pull it. Pateras-Pescara was also able to demonstrate the principle of autorotation. By January 1924, Pescara's helicopter No.1 was tested but was found to be underpowered and could not lift its own weight. His 2F fared better and set a record.FAI Record ID #13094 – Straight distance. Class E former G (Helicopters), piston
" ''Fédération Aéronautique Internationale''. Retrieved: 21 September 2014.
The British government funded further research by Pescara which resulted in helicopter No. 3, powered by a radial engine which could fly for up to ten minutes. In March 1923 ''
Time Time is the continuous progression of existence that occurs in an apparently irreversible process, irreversible succession from the past, through the present, and into the future. It is a component quantity of various measurements used to sequ ...
'' magazine reported Thomas Edison sent George de Bothezat a congratulations for a successful helicopter test flight. Edison wrote, "So far as I know, you have produced the first successful helicopter." The helicopter was tested at McCook's Field and remained airborne for 2 minutes and 45 seconds at a height of 15 feet. On 14 April 1924, Frenchman Étienne Oehmichen set the first helicopter world record recognized by the ''
Fédération Aéronautique Internationale The World Air Sports Federation (; FAI) is the world governing body for air sports, and also stewards definitions regarding human spaceflight. It was founded on 14 October 1905, and is headquartered in Lausanne, Switzerland. It maintains worl ...
'' (FAI), flying his quadrotor helicopter .FAI Record ID #13093 – Straight distance. Class E former G (Helicopters), piston
" ''Fédération Aéronautique Internationale''. Retrieved: 21 September 2014.
On 18April 1924, Pescara beat Oemichen's record, flying for a distance of (nearly ) in 4 minutes and 11 seconds (about ), maintaining a height of .Rumerman, Judy

. Centennial of Flight Commission. Retrieved 28 November 2007.
On 4May, Oehmichen completed the first closed-circuit helicopter flight in 7 minutes 40 seconds with his No. 2 machine. In the US, George de Bothezat built the quadrotor helicopter de Bothezat helicopter for the United States Army Air Service but the Army cancelled the program in 1924, and the aircraft was scrapped. Albert Gillis von Baumhauer, a Dutch aeronautical engineer, began studying rotorcraft design in 1923. His first prototype "flew" ("hopped" and hovered in reality) on 24 September 1925, with Dutch Army-Air arm Captain Floris Albert van Heijst at the controls. The controls that van Heijst used were von Baumhauer's inventions, the cyclic and collective.H.J.G.C. Vodegel and K.P. Jessurun. ''A Historical Review of Two Helicopters Designed in the Netherlands''. 21st European Rotocraft Forum, 1995, Saint Petersburg, Russia
web extract
/ref>Alex de Voogt. ''The Transmission of Helicopter Technology, 1920-1939: Exchanges with von Baumhauer''. Int. j. for the history of eng. & tech., Vol. 83 No. 1, January 2013, 119–40
web extract
Patents were granted to von Baumhauer for his cyclic and collective controls by the British ministry of aviation on 31January 1927, under patent number 265,272. In 1927, Engelbert Zaschka from Germany built a helicopter, equipped with two rotors, in which a
gyroscope A gyroscope (from Ancient Greek γῦρος ''gŷros'', "round" and σκοπέω ''skopéō'', "to look") is a device used for measuring or maintaining Orientation (geometry), orientation and angular velocity. It is a spinning wheel or disc in ...
was used to increase stability and serves as an energy accumulator for a
gliding Gliding is a recreational activity and competitive air sports, air sport in which pilots fly glider aircraft, unpowered aircraft known as Glider (sailplane), gliders or sailplanes using naturally occurring currents of rising air in the atmospher ...
flight to make a landing. Zaschka's aircraft, the first helicopter, which ever worked so successfully in miniature, not only rises and descends vertically, but is able to remain stationary at any height. In 1928, Hungarian aviation engineer Oszkár Asbóth constructed a helicopter prototype that took off and landed at least 182 times, with a maximum single flight duration of 53 minutes. In 1930, the Italian engineer Corradino D'Ascanio built his D'AT3, a coaxial helicopter. His relatively large machine had two, two-bladed, counter-rotating rotors. Control was achieved by using auxiliary wings or servo-tabs on the trailing edges of the blades,Spenser 1998 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 or 59 ft), duration (8 minutes 45 seconds) and distance flown (1,078 m or 3,540 ft).FAI Record ID #13086 – Straight distance. Class E former G (Helicopters), piston
" ''Fédération Aéronautique Internationale''. Retrieved: 21 September 2014.


First practical rotorcraft

Spanish aeronautical engineer and pilot
Juan de la Cierva Juan de la Cierva y Codorníu, 1st Count of la Cierva (; 21 September 1895 – 9 December 1936), was a Spanish civil engineer, pilot and a self-taught aeronautical engineer. His most famous accomplishment was the invention in 1920 of a rotorcr ...
invented the
autogyro An autogyro (from Greek and , "self-turning"), gyroscope, gyrocopter or gyroplane, is a class of rotorcraft that uses an unpowered rotor in free autorotation to develop lift. A gyroplane "means a rotorcraft whose rotors are not engine-d ...
in the early 1920s, becoming the first practical rotorcraft. In 1928, de la Cierva successfully flew an autogyro across the English Channel, from London to Paris. In 1934, an autogyro became the first rotorcraft to successfully take off and land on the deck of a ship. That same year, the autogyro was employed by the Spanish military during the Asturias revolt, becoming the first military deployment of a rotocraft. Autogyros were also employed in
New Jersey New Jersey is a U.S. state, state located in both the Mid-Atlantic States, Mid-Atlantic and Northeastern United States, Northeastern regions of the United States. Located at the geographic hub of the urban area, heavily urbanized Northeas ...
and
Pennsylvania Pennsylvania, officially the Commonwealth of Pennsylvania, is a U.S. state, state spanning the Mid-Atlantic (United States), Mid-Atlantic, Northeastern United States, Northeastern, Appalachian, and Great Lakes region, Great Lakes regions o ...
for delivering mail and newspapers prior to the invention of the helicopter. Though lacking true vertical flight capability, work on the autogyro forms the basis for helicopter analysis.


Single lift-rotor success

In the Soviet Union, Boris N. Yuriev and Alexei M. Cheremukhin, two aeronautical engineers working at the '' Tsentralniy Aerogidrodinamicheskiy Institut'' (TsAGI or the Central Aerohydrodynamic Institute), constructed and flew the TsAGI 1-EA single lift-rotor helicopter, which used an open tubing framework, a four-blade main lift rotor, and twin sets of diameter, two-bladed anti-torque rotors: one set of two at the nose and one set of two at the tail. Powered by two M-2 powerplants, up-rated copies of the Gnome ''Monosoupape'' 9 Type B-2 100 CV output rotary engine of World War I, the TsAGI 1-EA made several low altitude flights. By 14 August 1932, Cheremukhin managed to get the 1-EA up to an unofficial altitude of , shattering d'Ascanio's earlier achievement. As the Soviet Union was not yet a member of the FAI, however, Cheremukhin's record remained unrecognized. Nicolas Florine, a Russian engineer, built the first twin tandem rotor machine to perform a free flight. It flew in Sint-Genesius-Rode, at the ''Laboratoire Aérotechnique de Belgique'' (now von Karman Institute) in April 1933, and attained an altitude of and an endurance of eight minutes. Florine chose a co-rotating configuration because the gyroscopic stability of the rotors would not cancel. Therefore, the rotors had to be tilted slightly in opposite directions to counter torque. Using hingeless rotors and co-rotation also minimised the stress on the hull. At the time, it was one of the most stable helicopters in existence.Watkinson 2004, p. 358. The Bréguet-Dorand '' Gyroplane Laboratoire'' was built in 1933. It was a coaxial helicopter, contra-rotating. After many ground tests and an accident, it first took flight on 26 June 1935. Within a short time, the aircraft was setting records with pilot Maurice Claisse at the controls. On 14 December 1935, he set a record for closed-circuit flight with a diameter.FAI Record ID #13059 – Straight distance. Class E former G (Helicopters), piston
" ''
Fédération Aéronautique Internationale The World Air Sports Federation (; FAI) is the world governing body for air sports, and also stewards definitions regarding human spaceflight. It was founded on 14 October 1905, and is headquartered in Lausanne, Switzerland. It maintains worl ...
''. Retrieved: 21 September 2014.
The next year, on 26 September 1936, Claisse set a height record of .FAI Record ID #13084 – Altitude. Class E former G (Helicopters), piston
" ''Fédération Aéronautique Internationale''. Retrieved: 21 September 2014.
And, finally, on 24 November 1936, he set a flight duration record of one hour, two minutes and 50 secondsFAI Record ID #13062 – Duration in closed circuit. Class E former G (Helicopters), piston
" ''Fédération Aéronautique Internationale''. Retrieved: 21 September 2014.
over a closed circuit at 44.7 kilometres per hour (27.8 mph). The aircraft was destroyed in 1943 by an Allied
airstrike An airstrike, air strike, or air raid is an offensive operation carried out by aircraft. Air strikes are delivered from aircraft such as blimps, balloons, fighter aircraft, attack aircraft, bombers, attack helicopters, and drones. The official d ...
at Villacoublay airport.


American single-rotor beginnings

American inventor Arthur M. Young started work on model helicopters in 1928 using converted electric hover motors to drive the rotor head. Young invented the stabilizer bar and patented it shortly after. A mutual friend introduced Young to Lawrence Dale, who once seeing his work asked him to join the Bell Aircraft company. When Young arrived at Bell in 1941, he signed his patent over and began work on the helicopter. His budget was US$250,000 (equivalent to $ million today) to build two working helicopters. In just six months they completed the first Bell Model 1, which spawned the Bell Model 30, later succeeded by the Bell 47.


Birth of an industry

Heinrich Focke Henrich Focke (8 October 1890 – 25 February 1979) was a German aviation pioneer from Bremen and also a co-founder of the Focke-Wulf company. He is best known as the inventor of the Fw 61, the first successful, practical, and fully contro ...
at Focke-Wulf had purchased a license from
Cierva Autogiro Company The Cierva Autogiro Company was a British firm established in 1926 to develop the autogyro. The company was set up to further the designs of Juan de la Cierva, a Spanish engineer and pilot, with the financial backing of James George Weir, a Scot ...
, which according to Frank Kingston Smith Sr., included "the fully controllable cyclic/collective pitch hub system". In return, Cierva Autogiro received a cross-license to build the Focke-Achgelis helicopters. Focke designed the world's first practical helicopter, the transverse twin-rotor
Focke-Wulf Fw 61 The Focke-Wulf Fw 61 was the first successful, practical, and fully controllable helicopter, first flown in 1936. It was also known as the Fa 61, as Focke began a new company— Focke-Achgelis—in 1937. Design and development Professor Henri ...
, which first flew in June 1936. It was demonstrated by
Hanna Reitsch Hanna Reitsch (29 March 1912 – 24 August 1979) was a German Pilot (aeronautics), aviator and test pilot. Along with Melitta von Stauffenberg, she flight-tested many of Germany's new aircraft during World War II and received many hono ...
in February 1938 inside the
Deutschlandhalle Deutschlandhalle was an arena located in the Westend (Berlin), Westend neighbourhood of Berlin, Germany. It was inaugurated on 29 November 1935 by Adolf Hitler. The building was granted landmark status in 1995, but was demolished on 3 December 20 ...
in
Berlin Berlin ( ; ) is the Capital of Germany, capital and largest city of Germany, by both area and List of cities in Germany by population, population. With 3.7 million inhabitants, it has the List of cities in the European Union by population withi ...
. The Fw 61 set a number of FAI records from 1937 to 1939, including: maximum altitude of , maximum distance of , and maximum speed of . Autogiro development was now being bypassed by a focus on helicopters. During World War II,
Nazi Germany Nazi Germany, officially known as the German Reich and later the Greater German Reich, was the German Reich, German state between 1933 and 1945, when Adolf Hitler and the Nazi Party controlled the country, transforming it into a Totalit ...
used helicopters in small numbers for observation, transport, and medical evacuation. The Flettner Fl 282 ''Kolibri'' synchropter—using the same basic configuration as
Anton Flettner Anton Flettner (1 November 1885 – 29 December 1961) was a German Aerospace engineering, aviation engineer and inventor. Born in Hattersheim am Main#Eddersheim, Eddersheim (today a district of Hattersheim am Main), Flettner made important contri ...
's own pioneering Fl 265—was used in the
Baltic Baltic may refer to: Peoples and languages *Baltic languages, a subfamily of Indo-European languages, including Lithuanian, Latvian and extinct Old Prussian *Balts (or Baltic peoples), ethnic groups speaking the Baltic languages and/or originatin ...
,
Mediterranean The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern ...
, and Aegean Seas. The Focke-Achgelis Fa 223 Drache, like the Fw 61, used two transverse rotors, and was the largest rotorcraft of the war. Extensive bombing by the Allied forces prevented Germany from producing helicopters in large quantities during the war. In the United States, Russian-born engineer
Igor Sikorsky Igor Ivanovich Sikorsky, (25 May 1889 – 26 October 1972) was a Russian-American aviation pioneer in both helicopters and fixed-wing aircraft. His first success came with the Sikorsky S-2, the second aircraft of his design and construc ...
and
Wynn Laurence LePage The Platt-LePage Aircraft Company was a manufacturer of aircraft for the armed forces of the United States of America. Based in Eddystone, Pennsylvania, the company produced the first helicopter to be officially acquired by the United States Army A ...
competed to produce the U.S. military's first helicopter. LePage received the
patent A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an sufficiency of disclosure, enabling discl ...
rights to develop helicopters patterned after the Fw 61, and built the XR-1Francillon 1997 in 1941. Meanwhile, Sikorsky settled on a simpler, single-rotor design, the VS-300 of 1939, which turned out to be the first practical single lifting-rotor helicopter design. After experimenting with configurations to counteract the torque produced by the single main rotor, Sikorsky settled on a single, smaller rotor mounted on the tail boom. Developed from the VS-300, Sikorsky's R-4 of 1942 was the first large-scale mass-produced helicopter, with a production order for 100 aircraft. The R-4 was the only Allied helicopter to serve in World War II, used primarily for
search and rescue Search and rescue (SAR) is the search for and provision of aid to people who are in distress or imminent danger. The general field of search and rescue includes many specialty sub-fields, typically determined by the type of terrain the search ...
(by the
USAAF The United States Army Air Forces (USAAF or AAF) was the major land-based aerial warfare service component of the United States Army and ''de facto'' aerial warfare service branch of the United States during and immediately after World War II ...
1st Air Commando Group) in the
Burma campaign The Burma campaign was a series of battles fought in the British colony of British rule in Burma, Burma as part of the South-East Asian theatre of World War II. It primarily involved forces of the Allies of World War II, Allies (mainly from ...
; in Alaska; and in other areas with harsh terrain. Total production reached 131 helicopters before the R-4 was replaced by other Sikorsky helicopters such as the R-5 and the R-6. In all, Sikorsky produced over 400 helicopters before the end of World War II.Day, Dwayne A
"Igor Sikorsky – VS 300"
''Centennial of Flight Commission'', 2003. Retrieved 9 December 2007.
While LePage and Sikorsky built their helicopters for the military,
Bell Aircraft The Bell Aircraft Corporation was an American aircraft manufacturer, a builder of several types of fighter aircraft for World War II but most famous for the Bell X-1, the first supersonic aircraft, and for the development and production of many i ...
hired Arthur Young to help build a helicopter using Young's two-blade teetering rotor design, which used a weighted stabilizer bar placed at a 90° angle to the rotor blades. The subsequent Model 30 helicopter of 1943 showed the design's simplicity and ease of use. The Model 30 was developed into the
Bell 47 The Bell 47 is a single-rotor single-engine light helicopter manufactured by Bell Helicopter. It was based on the third Bell 30 prototype, which was the company's first helicopter designed by Arthur M. Young. The 47 became the first heli ...
of 1945, which became the first helicopter certified for civilian use in the United States (March 1946). Produced in several countries, the Bell 47 was 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 Kaman modified his K-225 synchropter—a design for a twin-rotor helicopter concept first pioneered by
Anton Flettner Anton Flettner (1 November 1885 – 29 December 1961) was a German Aerospace engineering, aviation engineer and inventor. Born in Hattersheim am Main#Eddersheim, Eddersheim (today a district of Hattersheim am Main), Flettner made important contri ...
in 1939, with the aforementioned Fl 265 piston-engined design in Germany—with a new kind of engine, the
turboshaft A turboshaft engine is a form of gas turbine that is optimized to produce shaft horsepower rather than jet thrust. In concept, turboshaft engines are very similar to turbojets, with additional turbine expansion to extract heat energy from the ex ...
engine. This adaptation of the turbine engine provided a large amount of power to Kaman's helicopter with a lower weight penalty than piston engines, with their heavy engine blocks and auxiliary components. On 11December 1951, the Kaman K-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 Sud Aviation (, 'Southern Aviation') was a French state-owned aircraft manufacturer, originating in the merger of Sud-Est ( SNCASE, or ''Société nationale des constructions aéronautiques du sud-est'') and Sud-Ouest ( SNCASO or ''Société nat ...
Alouette II that would become the first helicopter to be produced with a turbine-engine. Reliable helicopters capable of stable hover flight were developed decades after fixed-wing aircraft. This is largely due to higher engine power density requirements than fixed-wing aircraft. Improvements in fuels and engines during the first half of the 20th century were a critical factor in helicopter development. The availability of lightweight
turboshaft A turboshaft engine is a form of gas turbine that is optimized to produce shaft horsepower rather than jet thrust. In concept, turboshaft engines are very similar to turbojets, with additional turbine expansion to extract heat energy from the ex ...
engines in the second half of the 20th century led to the development of larger, faster, and higher-performance helicopters. While smaller and less expensive helicopters still use piston engines, turboshaft engines are the preferred powerplant for helicopters today.


Safety


Maximum speed limit

There are several reasons a helicopter cannot fly as fast as a fixed-wing aircraft. When the helicopter is hovering, the outer tips of the rotor travel at a speed determined by the length of the blade and the rotational speed. 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 speed. 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 The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elasticity (solid mechanics), elastic medium. More simply, the speed of sound is how fast vibrations travel. At , the speed of sound in a ...
, and thus produce vastly increased drag and vibration. At the same time, the advancing blade creates more lift traveling forward, the retreating blade produces less lift. If the aircraft were to accelerate to the air speed that the blade tips are spinning, the retreating blade passes through air moving at the same speed of the blade and produces no lift at all, resulting in very high torque stresses on the central shaft that can tip down the retreating-blade side of the vehicle, and cause a loss of control. Dual counter-rotating blades prevent this situation due to having two advancing and two retreating blades with balanced forces. Because the advancing blade has higher airspeed than the retreating blade and generates a dissymmetry of lift, rotor blades are designed to "flap" – lift and twist in such a way that the advancing blade flaps up and develops a smaller angle of attack. Conversely, the retreating blade flaps down, develops a higher angle of attack, and generates more lift. At high speeds, the force on the rotors is such that they "flap" excessively, and the retreating blade can reach too high an angle and stall. For this reason, the maximum safe forward airspeed of a helicopter is given a design rating called VNE, ''velocity, never exceed''. In addition, it is possible for the helicopter to fly at an airspeed where an excessive amount of the retreating blade stalls, which results in high vibration, pitch-up, and roll into the retreating blade.


Noise

At the end of the 20th century, designers began working on helicopter noise reduction. Urban communities have often expressed great dislike of noisy aviation or noisy aircraft, and police and passenger helicopters can be unpopular because of the sound. The redesigns followed the closure of some city
heliport A heliport is a small airport which has a helipad, suitable for use by helicopters, powered lift, and various types of vertical lift aircraft. Designated heliports typically contain one or more touchdown and liftoff areas and may also hav ...
s and government action to constrain flight paths in
national parks A national park is a nature park designated for conservation (ethic), conservation purposes because of unparalleled national natural, historic, or cultural significance. It is an area of natural, semi-natural, or developed land that is protecte ...
and other places of natural beauty.


Vibration

To reduce vibration, all helicopters have rotor adjustments for height and weight. A maladjusted helicopter can easily vibrate so much that it will shake itself apart. Blade height is adjusted by changing the pitch of the blade. Weight is adjusted by adding or removing weights on the rotor head and/or at the blade end caps. 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 In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a Airfoil#Airfoil terminology, reference line on a body (often the chord (aircraft), chord line of an airfoil) and the vector (geometry), vector representing the relat ...
to counter the vibration. Adjustment can be difficult in part because measurement of the vibration is hard, usually requiring sophisticated accelerometers mounted throughout the airframe and gearboxes. The most common blade vibration 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. Health and Usage Monitoring Systems (HUMS) provide vibration monitoring and rotor track and balance solutions to limit vibration. Gearbox vibration most often requires a gearbox overhaul or replacement. Gearbox or drive train vibrations can be extremely harmful to a pilot. The most severe effects are pain, numbness, and loss of tactile discrimination or dexterity.


Loss of tail-rotor effectiveness

For a standard helicopter with a single main rotor, the tips of the main rotor blades produce a vortex ring in the air, which is a spiraling and circularly rotating airflow. As the craft moves forward, these vortices trail off behind the craft. When hovering with a forward diagonal crosswind, or moving in a forward diagonal direction, the spinning vortices trailing off the main rotor blades will align with the rotation of the tail rotor and cause an instability in flight control. When the trailing vortices colliding with the tail rotor are rotating in the same direction, this causes a loss of thrust from the tail rotor. When the trailing vortices rotate in the opposite direction of the tail rotor, thrust is increased. Use of the foot pedals is required to adjust the tail rotor's angle of attack, to compensate for these instabilities. These issues are due to the exposed tail rotor cutting through open air around the rear of the vehicle. This issue disappears when the tail is instead ducted, using an internal impeller enclosed in the tail and a jet of high pressure air sideways out of the tail, as the main rotor vortices can not impact the operation of an internal impeller.


Critical wind azimuth

For a standard helicopter with a single main rotor, maintaining steady flight with a crosswind presents an additional flight control problem, where strong crosswinds from certain angles will increase or decrease lift from the main rotors. This effect is also triggered in a no-wind condition when moving the craft diagonally in various directions, depending on the direction of main rotor rotation. This can lead to a loss of control and a crash or hard landing when operating at low altitudes, due to the sudden unexpected loss of lift, and insufficient time and distance available to recover.


Transmission

Conventional rotary-wing aircraft use a set of complex mechanical gearboxes to convert the high rotation speed of gas turbines into the low speed required to drive main and tail rotors. Unlike powerplants, mechanical gearboxes cannot be duplicated (for redundancy) and have always been a major weak point in helicopter reliability. In-flight catastrophic gear failures often result in gearbox jamming and subsequent fatalities, whereas loss of lubrication can trigger onboard fire. Another weakness of mechanical gearboxes is their transient power limitation, due to structural fatigue limits. Recent EASA studies point to engines and transmissions as prime cause of crashes just after pilot errors. By contrast, electromagnetic transmissions do not use any parts in contact; hence lubrication can be drastically simplified, or eliminated. Their inherent redundancy offers good resilience to single point of failure. The absence of gears enables high power transient without impact on service life. The concept of electric propulsion applied to helicopter and electromagnetic drive was brought to reality by
Pascal Chretien Pascal Chrétien (born 7 April 1968) is a French-Australian commercial helicopter Pilot (aeronautics), pilot and engineer with degrees in electronics and aerospace who designed, built and test flew the world’s first crewed Electric aircraft#R ...
who designed, built and flew world's first man-carrying, free-flying electric helicopter. The concept was taken from the conceptual
computer-aided design Computer-aided design (CAD) is the use of computers (or ) to aid in the creation, modification, analysis, or optimization of a design. This software is used to increase the productivity of the designer, improve the quality of design, improve c ...
model on 10 September 2010 to the first testing at 30% power on 1 March 2011 – less than six months. The aircraft first flew on 12 August 2011. All development was conducted in Venelles, France.


Hazards

As with any moving vehicle, unsafe operation could result in loss of control, structural damage, or loss of life. The following is a list of some of the potential hazards for helicopters: * Settling with power is when the aircraft has insufficient power to arrest its descent. This hazard can develop into vortex ring state if not corrected early. * Vortex ring state is a hazard induced by a combination of low airspeed, high power setting, and high descent rate. Rotor-tip vortices circulate from the high pressure air below the rotor disk to low pressure air above the disk, so that the helicopter settles into its own descending airflow. Adding more power increases the rate of air circulation and aggravates the situation. It is sometimes confused with settling with power, but they are aerodynamically different. *
Retreating blade stall Retreating blade stall is a hazardous flight condition in helicopters and other rotary wing aircraft, where the retreating rotor blade has a lower relative blade speed, combined with an increased angle of attack, causing a stall and loss of lift ...
is experienced during high speed flight and is the most common limiting factor of a helicopter's forward speed. * Ground resonance is a self-reinforcing vibration that occurs when the lead/lag spacing of the blades of an articulated rotor system becomes irregular. * Low-G condition is an abrupt change from a positive G-force state to a negative G-force state that results in loss of lift (unloaded disc) and subsequent roll over. If aft cyclic is applied while the disc is unloaded, the main rotor could strike the tail causing catastrophic failure. * Dynamic rollover in which the helicopter pivots around one of the skids and 'pulls' itself onto its side (almost like a fixed-wing aircraft ground loop). *
Powertrain In a motor vehicle, the powertrain comprises the main components that generate engine power, power and deliver that power to the road surface, water, or air. This includes the internal combustion engine, engine, transmission (mechanics), trans ...
failures, especially those that occur within the shaded area of the height-velocity diagram. * Tail rotor failures which occur from either a mechanical malfunction of the tail rotor control system or a loss of tail rotor thrust authority, called "loss of tail-rotor effectiveness" (LTE). * Brownout in dusty conditions or whiteout in snowy conditions. * Low rotor RPM, is when the engine cannot drive the blades at sufficient RPM to maintain flight. * Rotor overspeed, which can over-stress the rotor hub pitch bearings (brinelling) and, if severe enough, cause blade separation from the aircraft. * Wire and tree strikes due to low altitude operations and take-offs and landings in remote locations. *
Controlled flight into terrain In aviation, a controlled flight into terrain (CFIT; usually ) is an aviation accidents and incidents, accident in which an airworthy aircraft, fully under pilot control, is unintentionally flown into the ground, a body of water or other obstac ...
in which the aircraft is flown into the ground unintentionally due to a lack of situational awareness. * Mast bumping in some helicoptersFAA RFH, page 11-10


List of fatal crashes


World records


See also


References


Notes


Footnotes


Bibliography

* Chiles, James R. ''The God Machine: From Boomerangs to Black Hawks: The Story of the Helicopter''. New York: Bantam Books, 2007. . * Cottez, Henri. ''Dictionnaire des structures du vocabulaire savant''. Paris: Les Usuels du Robert. 1980. . * Francillon, René J. ''McDonnell Douglas Aircraft since 1920: Volume II''. London: Putnam, 1997. . * Frawley, Gerard. ''The International Directory of Civil Aircraft, 2003–2004''. Fyshwick, Canberra, Act, Australia: Aerospace Publications Pty Ltd., 2003, p. 155. . * Munson, Kenneth. ''Helicopters and other Rotorcraft since 1907''. London: Blandford Publishing, 1968. .
''Rotorcraft Flying Handbook''
Washington: Skyhorse Publishing, Inc., 2007. .
''Rotorcraft Flying Handbook: FAA Manual H-8083-21''
Washington, D.C.: Federal Aviation Administration (Flight Standards Division), U.S. Dept. of Transportation, 2001. . * Thicknesse, P. ''Military Rotorcraft'' (Brassey's World Military Technology series). London: Brassey's, 2000. . * Watkinson, John. Art of the Helicopter. Oxford: Elsevier Butterworth-Heinemann, 2004. * Wragg, David W. ''Helicopters at War: A Pictorial History''. London: R. Hale, 1983. . * Zaschka, Engelbert. ''Drehflügelflugzeuge. Trag- und Hubschrauber''. Berlin-Charlottenburg: C. J. E. Volckmann Nachf. E. Wette, 1936. .


External links


"Helicopterpage.com – How Helicopters Work"
Complete site explaining different aspects of helicopters and how they work.
"Planes That Go Straight Up"
1935 article about early development and research into helicopters.
"Flights — of the Imagination"
1918 article on helicopter design concepts.
"Twin Windmill Blades Fly Wingless Ship"
''Popular Mechanics'', April 1936
Silent (Russian-language intertitled) video about the Cheremukhin/Yuriev TsAGI 1-EA pioneer helicopter

American Helicopter Society
* {{Authority control Aircraft configurations Articles containing video clips