![LAPD Bell 206 Jetranger](https://upload.wikimedia.org/wikipedia/commons/7/78/LAPD_Bell_206_Jetranger.jpg)
A helicopter is a type of
rotorcraft
A rotorcraft or rotary-wing aircraft is a heavier-than-air aircraft with rotary wings or rotor blades, which generate lift by rotating around a vertical mast. Several rotor blades mounted on a single mast are referred to as a rotor. The Internat ...
in which
lift
Lift or LIFT may refer to:
Physical devices
* Elevator, or lift, a device used for raising and lowering people or goods
** Paternoster lift, a type of lift using a continuous chain of cars which do not stop
** Patient lift, or Hoyer lift, mobil ...
and
thrust are supplied by horizontally spinning
rotor
Rotor may refer to:
Science and technology
Engineering
* Rotor (electric), the non-stationary part of an alternator or electric motor, operating with a stationary element so called the stator
*Helicopter rotor, the rotary wing(s) of a rotorcraft ...
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 and many forms of
STOL (Short TakeOff and Landing) or
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 ...
(Short TakeOff and Vertical Landing) aircraft cannot perform without a
runway.
In 1942, the
Sikorsky R-4
The Sikorsky R-4 is a two-seat helicopter that was designed by Igor Sikorsky with a single, three-bladed main rotor and powered by a radial engine. The R-4 was the world's first large-scale mass-produced helicopter and the first helicopter used by ...
became the first helicopter to reach full-scale
production
Production may refer to:
Economics and business
* Production (economics)
* Production, the act of manufacturing goods
* Production, in the outline of industrial organization, the act of making products (goods and services)
* Production as a stati ...
.
[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.
Although most earlier designs used more than one main rotor, the configuration of a single
main rotor
A helicopter main rotor or rotor system is the combination of several rotary wings (rotor blades) with a control system, that generates the aerodynamic lift force that supports the weight of the helicopter, and the thrust that counteracts aerody ...
accompanied by a vertical anti-torque
tail rotor
The tail rotor is a smaller rotor mounted vertically or near-vertically at the tail of a traditional single-rotor helicopter, where it rotates to generate a propeller-like horizontal thrust in the same direction as the main rotor's rotation. Th ...
(i.e. unicopter, not to be confused with the single-blade
monocopter) has become the most common helicopter configuration. However, twin-main rotor helicopters (bicopters), in either
tandem
Tandem, or in tandem, is an arrangement in which a team of machines, animals or people are lined up one behind another, all facing in the same direction.
The original use of the term in English was in ''tandem harness'', which is used for two ...
or
transverse rotors configurations, are sometimes in use due to their greater payload capacity than the monorotor design, and
coaxial-rotor,
tiltrotor
A tiltrotor is an aircraft which generates lift and propulsion by way of one or more powered rotors (sometimes called ''proprotors'') mounted on rotating shafts or nacelles usually at the ends of a fixed wing. Almost all tiltrotors use a trans ...
and
compound helicopter
A helicopter is a type of rotorcraft in which lift and thrust are supplied by horizontally spinning rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward and laterally. These attributes ...
s are also all flying today.
Quadrotor helicopters (
quadcopter
A quadcopter or quadrotor is a type of helicopter with four rotors.
Although quadrotor helicopters and convertiplanes have long been flown experimentally, the configuration remained a curiosity until the arrival of the modern UAV or drone. T ...
s) were pioneered
as early as 1907 in France, and along with other types of
multicopters, have been developed mainly for specialized applications such as
drones.
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:
Greece
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 ...
' () "helix, spiral, whirl, convolution" and ' () "wing". For various reasons, the word is often erroneously, from an etymological point of view, analysed by English speakers into ''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 (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...
military, the common slang is "helo" pronounced with a long "e".
Design characteristics
![Rotor Antitorque System](https://upload.wikimedia.org/wikipedia/commons/2/22/Rotor_Antitorque_System.svg)
A helicopter is a type of
rotorcraft
A rotorcraft or rotary-wing aircraft is a heavier-than-air aircraft with rotary wings or rotor blades, which generate lift by rotating around a vertical mast. Several rotor blades mounted on a single mast are referred to as a rotor. The Internat ...
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"), also known as a ''gyroplane'', is a type of rotorcraft that uses an unpowered rotor in free autorotation to develop lift. Forward thrust is provided independently, by an engine-driven propeller. Whi ...
(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.
Rotor system
The rotor system, or more simply ''rotor'', is the rotating part of a helicopter that generates
lift
Lift or LIFT may refer to:
Physical devices
* Elevator, or lift, a device used for raising and lowering people or goods
** Paternoster lift, a type of lift using a continuous chain of cars which do not stop
** Patient lift, or Hoyer lift, mobil ...
. 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 must be countered by an opposed torque. The design that
Igor Sikorsky 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 mounted within a cylindrical duct or shroud. Other terms include ducted propeller or shrouded propeller. When used in vertical takeoff and landing
(VTOL) applicati ...
(called ''
Fenestron'' or ''FANTAIL'') and
NOTAR
NOTAR ("no tail rotor") is a helicopter system which avoids the use of a tail rotor. It was developed by McDonnell Douglas Helicopter Systems (through their acquisition of Hughes Helicopters). The system uses a fan inside the tail boom to build ...
. 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.]
![Belgium Police 520N (cropped)](https://upload.wikimedia.org/wikipedia/commons/b/b9/Belgium_Police_520N_%28cropped%29.jpg)
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 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 which generates lift and propulsion by way of one or more powered rotors (sometimes called ''proprotors'') mounted on rotating shafts or nacelles usually at the ends of a fixed wing. Almost all tiltrotors use a trans ...
s, some early model helicopters had used them.
*
Coaxial rotors
Coaxial rotors or coax rotors are a pair of helicopter rotors mounted one above the other on concentric shafts, with the same axis of rotation, but turning in opposite directions ( contra-rotating). This rotor configuration is a feature of helicop ...
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. Aircraft utilizing this is known as a synchropter.
*
Multirotor
A multirotor or multicopter is a rotorcraft with more than two lift-generating rotors. An advantage of multirotor aircraft is the simpler rotor mechanics required for flight control. Unlike single- and double-rotor helicopters which use complex ...
s 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 or quadrotor is a type of helicopter with four rotors.
Although quadrotor helicopters and convertiplanes have long been flown experimentally, the configuration remained a curiosity until the arrival of the modern UAV or drone. T ...
, 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
A tip jet is a jet nozzle at the tip of some helicopter rotor blades, used to spin the rotor, much like a Catherine wheel firework. Tip jets replace the normal shaft drive and have the advantage of placing no torque on the airframe, thus not re ...
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 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.
![CH-53G engine](https://upload.wikimedia.org/wikipedia/commons/3/32/CH-53G_engine.jpg)
Early helicopter designs utilized custom-built engines or
rotary engine
The rotary engine is an early type of internal combustion engine, usually designed with an odd number of cylinders per row in a radial configuration. The engine's crankshaft remained stationary in operation, while the entire crankcase and its ...
s designed for airplanes, but these were soon replaced by more powerful automobile engines and
radial engines
The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders "radiate" outward from a central crankcase like the spokes of a wheel. It resembles a stylized star when viewed from the front, and is cal ...
. 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 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 jet
A tip jet is a jet nozzle at the tip of some helicopter rotor blades, used to spin the rotor, much like a Catherine wheel firework. Tip jets replace the normal shaft drive and have the advantage of placing no torque on the airframe, thus not re ...
s. 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
The Sud-Ouest SO.1221 Djinn (alternatively written S.O.1221) is a French two-seat light helicopter designed and manufactured by aircraft manufacturer Sud-Ouest (SNCASO), which was later merged into Sud Aviation. It was the first production French ...
, and an example of the hot tip jet helicopter is the
YH-32 Hornet.
Some
radio-controlled helicopters and smaller, helicopter-type
unmanned aerial vehicles, use
electric motors or motorcycle engines.
Radio-controlled helicopters may also have
piston engines 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 helicopter
A human-powered helicopter (HPH) is a helicopter powered solely by one or more humans carried on board. As in other human-powered aircraft, the power is usually generated by pedalling. It remains a considerable engineering challenge to obtain bo ...
s.
Flight controls
![Helicopter controls layout](https://upload.wikimedia.org/wikipedia/commons/9/99/Helicopter_controls_layout.svg)
A helicopter has four flight control inputs. These are the cyclic, the collective, the anti-torque pedals, and the throttle. The cyclic control is usually located between the pilot's legs and is commonly called the ''cyclic stick'' or just ''cyclic''. On most helicopters, the cyclic is similar to a joystick. However, the
Robinson R22
The Robinson R22 is a two-seat, two-bladed, single-engine light utility helicopter manufactured by Robinson Helicopter Company. It was designed in 1973 by Frank D. Robinson, and has been in production since 1979.
Development
The majority of fl ...
and
Robinson R44
The Robinson R44 is a four-seat light helicopter produced by Robinson Helicopter Company since 1992. Based on the company's two-seat Robinson R22, the R44 features hydraulically assisted flight controls. It was first flown on 31 March 1990 a ...
have a unique teetering bar cyclic control system and a few helicopters have a cyclic control that descends into the cockpit from overhead.
The control is called the cyclic because it changes
cyclic pitch of the main blades. The result is to tilt the rotor disk in a particular direction, resulting in the helicopter moving in that direction. 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 hover sideways.
The collective pitch control or ''collective'' is located on the left side of the pilot's seat with a settable friction control to prevent inadvertent movement. The collective changes the pitch angle of all the main rotor blades collectively (i.e. all at the same time) and independently of their position. Therefore, if a collective input is made, all the blades change equally, and the result is the helicopter increasing or decreasing in altitude.
A
swashplate 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 both blades. This causes the helicopter to push air downward or upward, depending on the
angle of attack. The swashplate can also change its angle to move the blades angle forwards or backwards, or left and right, to make the helicopter move in those directions.
The anti-torque pedals are located in the same position as the
rudder pedals in a fixed-wing aircraft, and serve a similar purpose, namely to control the 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.
Helicopter rotors are designed to operate in a narrow range of
RPM.
[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
p216, '' John Wiley and Sons'', 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. In single-engine helicopters, the throttle control is a motorcycle-style
twist grip mounted on the collective control, while dual-engine helicopters have a power lever for each engine.
Compound helicopter
A compound helicopter has an additional system for thrust and, typically, small stub
fixed wing
A fixed-wing aircraft is a heavier-than-air flying machine, such as an airplane, which is capable of flight using wings that generate lift caused by the aircraft's forward airspeed and the shape of the wings. Fixed-wing aircraft are distin ...
s. 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 process by which an object moves through a space without contacting any planetary surface, either within an atmosphere (i.e. air flight or aviation) or through the vacuum of outer space (i.e. spaceflight). This can be a ...
and the transition between the two.
Hover
![Advanced Helicopter Rescue School (cropped)](https://upload.wikimedia.org/wikipedia/commons/7/7e/Advanced_Helicopter_Rescue_School_%28cropped%29.jpg)
Hovering is the most challenging part of flying a helicopter. This is because a helicopter generates its own gusty air while in a hover, which acts against the
fuselage and flight control surfaces. The end result is 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.
Transition from hover to forward flight
As a helicopter moves from hover to forward flight it 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.
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. The pedals serve the same function in both a helicopter and a fixed-wing aircraft, to maintain balanced flight. This is done by applying a pedal input in whichever direction is necessary to center the ball in the
turn and bank indicator
In aviation, the turn and slip indicator (T/S, a.k.a. turn and bank indicator) and the turn coordinator (TC) variant are essentially two aircraft flight instruments in one device. One indicates the rate of turn, or the rate of change in the aircr ...
.
Uses
![Kfd-205-N408KC-050428-26cr](https://upload.wikimedia.org/wikipedia/commons/0/0a/Kfd-205-N408KC-050428-26cr.jpg)
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. Among the common conventions for qualifying airspeed are:
* Indicated airspeed ("IAS"), what is read on an airspeed gauge connected to a Pitot-static system;
* Calibrated ...
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
transportation of people and cargo, military uses, construction, firefighting,
search and rescue,
tourism, medical transport, law enforcement, agriculture,
news and
media
Media may refer to:
Communication
* Media (communication), tools used to deliver information or data
** Advertising media, various media, content, buying and placement for advertising
** Broadcast media, communications delivered over mass e ...
, and
aerial observation
Aerial reconnaissance is reconnaissance for a military or strategic purpose that is conducted using reconnaissance aircraft. The role of reconnaissance can fulfil a variety of requirements including artillery spotting, the collection of imagery ...
, among others.
A helicopter used to carry loads connected to long cables or slings is called an
aerial crane
An aerial crane or flying crane is a helicopter used to lift heavy or awkward loads. As aerial cranes, helicopters carry loads connected to long cables or slings in order to place heavy equipment when other methods are not available or economically ...
. 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.
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
Helitack crews are teams of wildland firefighters who are transported by helicopter to wildfires. Helicopters provide rapid transport, enabling helitack crews to quickly respond and assess a wildfire situation. Helitack crews may land near a w ...
" 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 (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
The Bell 204 and 205 are the civilian versions of the UH-1 Iroquois single-engine military helicopter of the Huey family of helicopters. They are type-certificated in the transport category and are used in a wide variety of applications, inc ...
and the
Erickson S-64 Aircrane helitanker.
Helicopters are used as
air ambulance
Air medical services is a comprehensive term covering the use of air transportation, aeroplane or helicopter, to move patients to and from healthcare facilities and accident scenes. Personnel provide comprehensive prehospital and emergency and cri ...
s for
emergency medical assistance in situations when an
ambulance 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 wounded being evacuated from a battlefield, to injured patients being evacuated from the scene of a ...
", and patients are referred to as being "airlifted", or "medevaced". This use was pioneered in the
Korean War, 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, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...
, and further reduced to two hours by the
Vietnam War. 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. 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.
![KPRC - IAH (cropped)](https://upload.wikimedia.org/wikipedia/commons/f/f8/KPRC_-_IAH_%28cropped%29.jpg)
Military forces use
attack helicopters to conduct aerial attacks on ground targets. Such helicopters are mounted with
missile launchers and
minigun
The M134 Minigun is an American 7.62×51mm NATO six-barrel rotary machine gun with a high rate of fire (2,000 to 6,000 rounds per minute). It features a Gatling-style rotating barrel assembly with an external power source, normally an electric ...
s.
Transport helicopters are used to ferry troops and supplies where the lack of an
airstrip 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".
Unmanned aerial systems (UAS) helicopter systems of varying sizes are developed by companies for military
reconnaissance and
surveillance duties. Naval forces also use helicopters equipped with
dipping sonar
Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, measure distances (ranging), communicate with or detect objects on or ...
for
anti-submarine warfare, 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 platforms 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 US federal government responsible for the civil List of government space agencies, space program ...
is developing the
Mars Helicopter, a helicopter to be launched to survey Mars (along with a rover) in 2020. Given that the Martian atmosphere is 100 times thinner than that of Earth's, its two blades will spin at close to 3,000 revolutions a minute, approximately 10 times faster than that of a terrestrial helicopter.
In
electronic news-gathering
Electronic news-gathering (ENG) or electronic journalism (EJ) is usage of electronic video and audio technologies by reporters to gather and present news instead of using film cameras. The term was coined during the rise of videotape techn ...
, 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.
Market
In 2017, 926 civil helicopters were shipped for $3.68 billion, led by
Airbus Helicopters with $1.87 billion for 369 rotorcraft,
Leonardo Helicopters with $806 million for 102 (first three-quarters only),
Bell Helicopter
Bell Textron Inc. is an American aerospace manufacturer headquartered in Fort Worth, Texas. A subsidiary of Textron, Bell manufactures military rotorcraft at facilities in Fort Worth, and Amarillo, Texas, as well as commercial helicopters in M ...
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 with 7.7%,
Sikorsky Aircraft with 7.2%,
MD Helicopters with 3.4% and other with 2.2%.
The most widespread model is the piston
Robinson R44
The Robinson R44 is a four-seat light helicopter produced by Robinson Helicopter Company since 1992. Based on the company's two-seat Robinson R22, the R44 features hydraulically assisted flight controls. It was first flown on 31 March 1990 a ...
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
![Leonardo da Vinci helicopter](https://upload.wikimedia.org/wikipedia/commons/3/37/Leonardo_da_Vinci_helicopter.jpg)
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, 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 () refers to either a school of philosophical thought (道家; ''daojia'') or to a religion (道教; ''daojiao''), both of which share ideas and concepts of Chinese origin and emphasize living in harmony with the '' Tao ...
book ''
Baopuzi'' by
Ge Hong ( "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 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 had developed a small coaxial modeled after the Chinese top but powered by a wound-up spring device
[Leishman, J. Gordon (2006)]
Principles of Helicopter Aerodynamics
. Cambridge University Press. p. 8. and demonstrated it to the
Russian Academy of Sciences. It was powered by a spring, and was suggested as a method to lift
meteorological instruments. In 1783,
Christian de Launoy
Christians () are people who follow or adhere to Christianity, a monotheistic Abrahamic religion based on the life and teachings of Jesus Christ. The words ''Christ'' and ''Christian'' derive from the Koine Greek title ''Christós'' (Χρισ ...
, and his
mechanic, Bienvenu, used a coaxial version of the Chinese top in a model consisting of contrarotating
turkey flight feathers
as rotor blades, and in 1784, demonstrated it to the
French Academy of Sciences.
Sir George Cayley
Sir George Cayley, 6th Baronet (27 December 1773 – 15 December 1857) was an English engineer, inventor, and aviator. He is one of the most important people in the history of aeronautics. Many consider him to be the first true scientific aeri ...
, 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 to pursue the dream of flight.
![Elicottero sperimentale Enrico Forlanini 1877 Museo scienza e tecnologia Milano](https://upload.wikimedia.org/wikipedia/commons/d/d7/Elicottero_sperimentale_Enrico_Forlanini_1877_Museo_scienza_e_tecnologia_Milano.jpg)
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 1878 the Italian
Enrico Forlanini
Enrico Forlanini (13 December 1848 – 9 October 1930) was an Italian engineer, inventor and aeronautical pioneer, known for his works on helicopters, aeroplanes, hydrofoils and dirigibles. He was born in Milan. His older brother Carlo Forlanini ...
's unmanned vehicle, also powered by a steam engine, rose to a height of , where it hovered for some 20 seconds after a vertical take-off. 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
Gustave Pierre Trouvé (2 January 1839 – 27 July 1902) was a French electrical engineer and inventor in the 19th century.
Trouvé was born on 2 January 1839 in La Haye-Descartes (Indre-et-Loire, France) and died on 27 July 1902 in Paris. A pol ...
, 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 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 picture show to a p ...
, but it remains
lost.
In 1885,
Thomas Edison 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, 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 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.
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.
![HE2G8](https://upload.wikimedia.org/wikipedia/commons/f/fa/HE2G8.jpg)
That same year, fellow French inventor
Paul Cornu designed and built the
Cornu helicopter which used two counter-rotating rotors driven by a
Antoinette
Antoinette is a given name, that is a diminutive feminine form of Antoine and Antonia (from Latin ''Antonius'').
People with the name include:
Nobles
* Antoinette de Maignelais, Baroness of Villequier by marriage (1434–1474), mistress of C ...
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, Dr. 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 record (called a "gramophone record" in British and American English) used with a ...
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
Jacob Christian Hansen-Ellehammer (14 June 1871 – 20 May 1946) was a Danish watchmaker and inventor born in Bakkebølle, Denmark. He is remembered chiefly for his contributions to powered flight.
Following the end of his apprenticeship as a ...
built the
Ellehammer helicopter 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 (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...
,
Austria-Hungary 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
Autorotation is a state of flight in which the main rotor system of a helicopter or other rotary-wing aircraft turns by the action of air moving up through the rotor, as with an autogyro, rather than engine power driving the rotor. Bensen, Ig ...
. 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 continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future. It is a component quantity of various measurements used to sequence events, ...
'' magazine reported Thomas Edison sent Dr.
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'' (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
/ref> 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 was used to increase stability and serves as an energy accumulator for a gliding 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 invented the autogyro
An autogyro (from Greek and , "self-turning"), also known as a ''gyroplane'', is a type of rotorcraft that uses an unpowered rotor in free autorotation to develop lift. Forward thrust is provided independently, by an engine-driven propeller. Whi ...
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 and Pennsylvania 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
The rotary engine is an early type of internal combustion engine, usually designed with an odd number of cylinders per row in a radial configuration. The engine's crankshaft remained stationary in operation, while the entire crankcase and its ...
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''. 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 seconds[FAI 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 kilometers per hour (27.8 mph). The aircraft was destroyed in 1943 by an Allied airstrike 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 German helicopter.
Biography ...
at Focke-Wulf had purchased a license from Cierva Autogiro Company, 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 transverse twin-rotor helicopter, the Focke-Wulf Fw 61
The Focke-Wulf Fw 61 is often considered the first practical, functional 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 Henrich Foc ...
, which first flew in June 1936. The Fw 61 had flown higher than at speeds of . Autogiro development was now being bypassed by a focus on helicopters.
During World War II, Nazi Germany
Nazi Germany (lit. "National Socialist State"), ' (lit. "Nazi State") for short; also ' (lit. "National Socialist Germany") (officially known as the German Reich from 1933 until 1943, and the Greater German Reich from 1943 to 1945) was ...
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 (November 1, 1885 – December 29, 1961) was a German aviation engineer and inventor. Born in Eddersheim (today a district of Hattersheim am Main), Flettner made important contributions to airplane, helicopter, vessel, and automob ...
's own pioneering Fl 265—was used in the Mediterranean, while the Focke Achgelis Fa 223 ''Drache'' twin-rotor helicopter was used in Europe. Extensive bombing by the Allied forces prevented Germany from producing any helicopters in large quantities during the war.
In the United States, Russian-born engineer Igor Sikorsky and Wynn Laurence LePage competed to produce the U.S. military's first helicopter. LePage received the patent rights to develop helicopters patterned after the Fw 61, and built the XR-1.[Francillon 1997] Meanwhile, Sikorsky settled on a simpler, single rotor design, the VS-300
The Vought-Sikorsky VS-300 (or S-46) is an American single-engine helicopter designed by Igor Sikorsky. It had a single three-blade rotor originally powered by a 75 horsepower (56 kW) engine. The first "free" flight of the VS-300 was on 13 ...
, 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 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, primarily for search and rescue (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; 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 man ...
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 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 he ...
, which became the first helicopter certified for civilian use in the United States. 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 (November 1, 1885 – December 29, 1961) was a German aviation engineer and inventor. Born in Eddersheim (today a district of Hattersheim am Main), Flettner made important contributions to airplane, helicopter, vessel, and automob ...
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 shaftpower rather than jet thrust. In concept, turboshaft engines are very similar to turbojets, with additional turbine expansion to extract heat energy from the exhaust ...
engine. This adaptation of the turbine engine
A gas turbine, also called a combustion turbine, is a type of continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas generator or core) and are, in the directi ...
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 Kaman may refer to:
* Kaman (surname)
* Kamein (Kaman), an ethnic group in Burma
* Kaman Aircraft, an American aerospace company and helicopter manufacturer
* Kaman Music Corporation, a company of several musical instrument manufacturers
* 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 Alouette II
Alouette or alouettes may refer to:
Music and literature
* "Alouette" (song), a French-language children's song
* Alouette, a character in ''The King of Braves GaoGaiGar''
Aerospace
* SNCASE Alouette, a utility helicopter developed in France i ...
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 shaftpower rather than jet thrust. In concept, turboshaft engines are very similar to turbojets, with additional turbine expansion to extract heat energy from the exhaust ...
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 elastic medium. At , the speed of sound in air is about , or one kilometre in or one mile in . It depends strongly on temperature as w ...
, 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
Dissymmetry of lift (also known as asymmetry of lift or asymmetric lift) in rotorcraft aerodynamics refers to an unequal amount of lift on opposite sides of the rotor disc. It is a phenomenon that affects single-rotor helicopters and autogyros i ...
, 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
During the closing years of the 20th century designers began working on helicopter noise reduction
Helicopter noise reduction is a topic of research into designing helicopters which can be operated more quietly, reducing the public-relations problems with night-flying or expanding an airport. In addition, it is useful for military applicat ...
. 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 suitable for use by helicopters and some other vertical lift aircraft. Designated heliports typically contain one or more touchdown and liftoff areas and may also have limited facilities such as fuel or hangars. I ...
s and government action to constrain flight paths in national parks
A national park is a natural park in use for conservation purposes, created and protected by national governments. Often it is a reserve of natural, semi-natural, or developed land that a sovereign state declares or owns. Although individua ...
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 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 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 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
The vortex ring state (VRS) is a dangerous aerodynamic condition that may arise in helicopter flight, when a vortex ring system engulfs the rotor, causing severe loss of lift. The vortex ring state is sometimes referred to as settling with powe ...
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
A vortex ring, also called a toroidal vortex, is a torus-shaped vortex in a fluid; that is, a region where the fluid mostly spins around an imaginary axis line that forms a closed loop. The dominant flow in a vortex ring is said to be toroidal, ...
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 Ground resonance is an imbalance in the rotation of a helicopter rotor when the blades become bunched up on one side of their rotational plane and cause an oscillation in phase with the frequency of the rocking of the helicopter on its landing gear. ...
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
A helicopter is susceptible to a rolling tendency,
called dynamic rollover, when close to the ground,
especially when taking off or landing.
For dynamic rollover to occur, some factor has to first
cause the helicopter to roll or pivot around a ski ...
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
A drivetrain (also frequently spelled as drive train or sometimes drive-train) is the group of components that deliver mechanical power from the prime mover to the driven components. In automotive engineering, the drivetrain is the components o ...
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 accident in which an airworthy aircraft, under pilot control, is unintentionally flown into the ground, a mountain, a body of water or an obstacle. In a typical CFIT scenario, ...
in which the aircraft is flown into the ground unintentionally due to a lack of situational awareness.
* Mast bumping in some helicopters[FAA 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
"www.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