HOME

TheInfoList



OR:

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 allow helicopters to be used in congested or isolated areas where
fixed-wing aircraft 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 distinc ...
and many forms of
STOL A short takeoff and landing (STOL) aircraft is a conventional fixed-wing aircraft that has short runway requirements for takeoff and landing. Many STOL-designed aircraft also feature various arrangements for use on airstrips with harsh conditio ...
(Short TakeOff and Landing) or STOVL (Short TakeOff and Vertical Landing) aircraft cannot perform without a runway. In 1942, the Sikorsky R-4 became the first helicopter to reach full-scale production.Munson 1968.Hirschberg, Michael J. and David K. Dailey
"Sikorsky"
. ''US and Russian Helicopter Development in the 20th Century'',
American Helicopter Society American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the "United States" or "America" ** Americans, citizens and nationals of the United States of America ** American ancestry, pe ...
, International. 7 July 2000.
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-main rotor helicopters (bicopters), in either tandem or
transverse rotors Transverse rotor aircraft have two large horizontal rotor assemblies mounted side by side. Single-rotor helicopters (unicopters) need an additional tail rotor or tail exhaust to neutralize the reactional angular momentum produced by the mai ...
configurations, are sometimes in use due to their greater payload capacity than the monorotor design, and coaxial-rotor, tiltrotor and compound helicopters are also all flying today. Quadrotor helicopters ( quadcopters) were pioneered as early as 1907 in France, and along with other types of multicopters, have been developed mainly for specialized applications such as
drone Drone most commonly refers to: * Drone (bee), a male bee, from an unfertilized egg * Unmanned aerial vehicle * Unmanned surface vehicle, watercraft * Unmanned underwater vehicle or underwater drone Drone, drones or The Drones may also refer to: ...
s.


Etymology

The English word ''helicopter'' is adapted from the French word , coined by Gustave Ponton d'Amécourt in 1861, which originates from the Greek ' () "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 military, the common slang is "helo" pronounced with a long "e".


Design characteristics

A helicopter is a type of rotorcraft in which lift and thrust are supplied by one or more horizontally-spinning rotors. By contrast the autogyro (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. 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 called air resistance, a type of friction, or fluid resistance, another type of friction or fluid friction) is a force acting opposite to the relative motion of any object moving with respect to a surrounding fl ...
must be countered by an opposed torque. The design that Igor Sikorsky settled on for his
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 ...
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 (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 The Coandă effect ( or ) is the tendency of a fluid jet to stay attached to a convex surface. ''Merriam-Webster'' describes it as "the tendency of a jet of fluid emerging from an orifice to follow an adjacent flat or curved surface and to ent ...
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 Transverse rotor aircraft have two large horizontal rotor assemblies mounted side by side. Single-rotor helicopters (unicopters) need an additional tail rotor or tail exhaust to neutralize the reactional angular momentum produced by the mai ...
are pair of counter-rotating rotors transversely mounted at the ends of fixed wings or outrigger structures. Now used on tiltrotors, some early model helicopters had used them. * Coaxial rotors are two counter-rotating rotors mounted one above the other with the same axis. *
Intermeshing rotors Intermeshing rotors on a helicopter are a set of two rotors turning in opposite directions, with each rotor mast mounted with a slight angle to the other, in a transversely symmetrical manner, so that the blades intermesh without colliding. T ...
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. * Multirotors make use of three or more rotors. Specific terms are also used depending on the exact amount of rotors, such as tricopter, quadcopter, 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 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 The Hiller YH-32 Hornet (company designation HJ-1) was an American ultralight helicopter built by Hiller Aircraft in the early 1950s. It was a small and unique design because it was powered by two Hiller 8RJ2B ramjet engines mounted on the rotor ...
. Some
radio-controlled helicopter A radio-controlled helicopter (also '' RC helicopter'') is model aircraft which is distinct from a RC airplane because of the differences in construction, aerodynamics, and flight training. Several basic designs of RC helicopters exist, of w ...
s and smaller, helicopter-type unmanned aerial vehicles, use electric motors or motorcycle engines. Radio-controlled helicopters may also have
piston engine A reciprocating engine, also often known as a piston engine, is typically a heat engine that uses one or more reciprocating pistons to convert high temperature and high pressure into a rotating motion. This article describes the common featu ...
s that use fuels other than gasoline, such as nitromethane. Some turbine engines commonly used in helicopters can also use biodiesel instead of jet fuel. There are also human-powered helicopters.


Flight controls

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 and Robinson R44 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 A helicopter pilot manipulates the helicopter flight controls to achieve and maintain controlled aerodynamic flight. Changes to the aircraft flight control system transmit mechanically to the rotor, producing aerodynamic effects on the rotor bla ...
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 A swashplate, also known as slant disk, was invented by Anthony Michell in 1917. It 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 c ...
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 In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is m ...
. 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 Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines. Standards ISO 80000-3:2019 defines a unit of rotation as the dimensionl ...
.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 John Wiley & Sons, Inc., commonly known as Wiley (), is an American multinational publishing company founded in 1807 that focuses on academic publishing and instructional materials. The company produces books, journals, and encyclopedias, in p ...
'', 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 A twistgrip is a handle that can be twisted to operate a control. It is commonly found as a motorcycle's right handlebar grip to control the throttle, but is sometimes found elsewhere, such as on a bicycle as a gearshift A gear stick (rarely s ...
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 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 The Lockheed AH-56 Cheyenne was an attack helicopter developed by Lockheed for the United States Army. It rose from the Army's Advanced Aerial Fire Support System (AAFSS) program to field the service's first dedicated attack helicopter. Lock ...
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 and the transition between the two.


Hover

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 Heading can refer to: * Heading (metalworking), a process which incorporates the extruding and upsetting processes * Headline, text at the top of a newspaper article * Heading (navigation), the direction a person or vehicle is facing, usually si ...
. 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 Translational lift is improved rotor efficiency resulting from directional flight in a helicopter. Translation is the conversion from the hover to forward flight. As undisturbed air enters the rotor system horizontally, turbulence and vortices creat ...
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.


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 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 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, 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 tes ...
and media, 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. 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 and observation missions, making dozens of sorties a day for several months. " Helitack" is the use of helicopters to combat
wildland fires A wildfire, forest fire, bushfire, wildland fire or rural fire is an unplanned, uncontrolled and unpredictable fire in an area of Combustibility and flammability, combustible vegetation. Depending on the type of vegetation present, a wildfire ...
.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 Abseiling ( ; ), also known as rappelling ( ; ), is the controlled descent of a steep slope, such as a rock face, by moving down a rope. When abseiling the person descending controls their own movement down the rope, in contrast to low ...
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 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", 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, 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. Military forces use
attack helicopter An attack helicopter is an armed helicopter with the primary role of an attack aircraft, with the offensive capability of engaging ground targets such as enemy infantry, military vehicles and fortifications. Due to their heavy armament they ...
s to conduct aerial attacks on ground targets. Such helicopters are mounted with missile launchers and miniguns. 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 Air assault is the movement of ground-based military forces by vertical take-off and landing (VTOL) aircraft—such as the helicopter—to seize and hold key terrain which has not been fully secured, and to directly engage enemy forces behind e ...
".
Unmanned aerial systems An unmanned aerial vehicle (UAV), commonly known as a drone, is an aircraft without any human pilot, crew, or passengers on board. UAVs are a component of an unmanned aircraft system (UAS), which includes adding a ground-based controlle ...
(UAS) helicopter systems of varying sizes are developed by companies for military reconnaissance 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 c ...
duties. Naval forces also use helicopters equipped with dipping sonar 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 platform An oil platform (or oil rig, offshore platform, oil production platform, and similar terms) is a large structure with facilities to extract and process petroleum and natural gas that lie in rock formations beneath the seabed. Many oil platfor ...
s continue to operate. Various companies specialize in this type of operation. NASA is developing the
Mars Helicopter ''Ingenuity,'' nicknamed ''Ginny,'' is a small robotic helicopter operating on Mars as part of NASA's Mars 2020 mission along with the ''Perseverance'' rover, which landed with ''Ingenuity'' attached to its underside on February 18, 2021. T ...
, 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, 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 Airbus Helicopters SAS (formerly Eurocopter Group) is the helicopter manufacturer, helicopter manufacturing division of Airbus. It is the largest in the industry in terms of revenues and turbine helicopter deliveries. Its head office is located ...
with $1.87 billion for 369 rotorcraft,
Leonardo Helicopters AgustaWestland was an Anglo-Italian helicopter design and manufacturing company, which was a wholly owned subsidiary of Finmeccanica (now known as Leonardo). It was formed in July 2000 as an Anglo-Italian multinational company, when Finmeccanica ...
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 with 7.7%,
Sikorsky Aircraft Sikorsky Aircraft is an American aircraft manufacturer based in Stratford, Connecticut. It was established by aviation pioneer Igor Sikorsky in 1923 and was among the first companies to manufacture helicopters for civilian and military use. Pre ...
with 7.2%,
MD Helicopters MD Helicopters, LLC. (formerly McDonnell Douglas Helicopter Systems) is an American aerospace manufacturer. It produces light utility helicopters for commercial and military use. The company was a subsidiary of Hughes Aircraft until 1984, when Mc ...
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 The Bell 206 is a family of two-bladed, single- and twin-engined helicopters, manufactured by Bell Helicopter at its Mirabel, Quebec, plant. Originally developed as the Bell YOH-4 for the United States Army's Light Observation Helicopter progra ...
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, 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 book ''
Baopuzi The ''Baopuzi'' () is a literary work written by Ge Hong (also transliterated as Ko Hung) (), 283–343, a scholar during the turbulent Jin dynasty. ''Baopuzi'' is divided into two main sections, the esoteric ''Neipian'' () "Inner Chapters" an ...
'' by
Ge Hong Ge Hong (; b. 283 – d. 343 or 364), courtesy name Zhichuan (稚川), was a Chinese linguist, Taoist practitioner, philosopher, physician, politician, and writer during the Eastern Jin dynasty. He was the author of '' Essays on Chinese Characte ...
( "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 Mikhail Vasilyevich Lomonosov (; russian: Михаил (Михайло) Васильевич Ломоносов, p=mʲɪxɐˈil vɐˈsʲilʲjɪvʲɪtɕ , a=Ru-Mikhail Vasilyevich Lomonosov.ogg; – ) was a Russian Empire, Russian polymath, s ...
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. It was powered by a spring, and was suggested as a method to lift
meteorological Meteorology is a branch of the atmospheric sciences (which include atmospheric chemistry and physics) with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did not ...
instruments. In 1783, Christian de Launoy, 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 The French Academy of Sciences (French: ''Académie des sciences'') is a learned society, founded in 1666 by Louis XIV of France, Louis XIV at the suggestion of Jean-Baptiste Colbert, to encourage and protect the spirit of French Scientific me ...
. 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 to pursue the dream of flight. In 1861, the word "helicopter" was coined by
Gustave de Ponton d'Amécourt Gustav, Gustaf or Gustave may refer to: *Gustav (name), a male given name of Old Swedish origin Art, entertainment, and media * ''Primeval'' (film), a 2007 American horror film * ''Gustav'' (film series), a Hungarian series of animated short cart ...
, 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'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, built and flew a tethered electric model helicopter. In July 1901, the maiden flight of
Hermann Ganswindt Hermann Ganswindt (12 June 1856, Voigtshof bei Seeburg, East Prussia – 25 October 1934) was a German inventor and spaceflight scientist, whose inventions (such as the dirigible, the helicopter, and the internal combustion engine) are thou ...
'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, but it remains
lost Lost may refer to getting lost, or to: Geography *Lost, Aberdeenshire, a hamlet in Scotland * Lake Okeechobee Scenic Trail, or LOST, a hiking and cycling trail in Florida, US History *Abbreviation of lost work, any work which is known to have bee ...
. In 1885, Thomas Edison was given US$1,000 (equivalent to $ today) by
James Gordon Bennett, Jr. James Gordon Bennett Jr. (May 10, 1841May 14, 1918) was publisher of the '' New York Herald'', founded by his father, James Gordon Bennett Sr. (1795–1872), who emigrated from Scotland. He was generally known as Gordon Bennett to distinguish hi ...
, 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 Ján Bahýľ (25 May 1856 – 13 March 1916) was a Slovak inventor and engineer. He specialised in military science, military construction, and engineering. Flying machines were a particular interest of his. In 1895, he was granted a patent ...
, 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 Louis Charles Breguet (2 January 1880 in Paris – 4 May 1955 in Saint-Germain-en-Laye, Île-de-France) was a French aircraft designer and builder, one of the early aviation pioneers. Biography Louis Charles Breguet was the grandson of L ...
, 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. That same year, fellow French inventor
Paul Cornu Paul Cornu (; June 15, 1881 – 6 June 1944) was a French engineer. Life Paul Cornu, of Romanian origins, was born in Glos la Ferrière, France and was one of thirteen children. At a young age, he helped his father in his transports company. H ...
designed and built the
Cornu helicopter The Cornu helicopter was an experimental helicopter built in France, and is widely credited with the first free flight of a rotary-wing aircraft when it took to the air on 13 November 1907. Built by bicycle-maker Paul Cornu, it was an open-frame ...
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, 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 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 whic ...
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, 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. 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'' 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 Étienne Edmond Œhmichen (; 15 October 1884, in Châlons-sur-Marne Châlons-en-Champagne – 10 July 1955, in Paris) was a French engineer and helicopter designer. Biography Œhmichen studied at École Centrale Paris. He patented the first ...
set the first helicopter world record recognized by the ''
Fédération Aéronautique Internationale The (; FAI; en, World Air Sports Federation) 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 maintai ...
'' (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 Albert Gillis von Baumhauer (Heerenveen, October 1891 – Alder, Washington, Alder, Washington (state), State of Washington, 18 March 1939) was a Dutch aviation pioneer notable for his design of the first Dutch helicopter and the related invention ...
, 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 A helicopter pilot manipulates the helicopter flight controls to achieve and maintain controlled aerodynamic flight. Changes to the aircraft flight control system transmit mechanically to the rotor, producing aerodynamic effects on the rotor bla ...
.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 Engelbert Zaschka (September 1, 1895 in Freiburg im Breisgau, Germany – June 26, 1955 in Freiburg im Breisgau, Germany) was a German chief engineer, chief designer and inventor. Zaschka is one of the first German helicopter pioneers and he is a ...
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 and angular velocity. It is a spinning wheel or disc in which the axis of rota ...
was used to increase stability and serves as an energy accumulator for a
gliding Gliding is a recreational activity and competitive air sport in which pilots fly unpowered aircraft known as gliders or sailplanes using naturally occurring currents of rising air in the atmosphere to remain airborne. The word ''soaring'' is al ...
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 General Corradino D'Ascanio (1 February 1891 in Popoli, Pescara – 6 August 1981 in Pisa) was an Italian aeronautical engineer. D'Ascanio designed the first production helicopter, for Agusta, and designed the first motor scooter for Ferdin ...
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 in Murcia, Spain – 9 December 1936 in Croydon, United Kingdom) was a Spanish civil engineer, pilot and a self taught aeronautical engineer. His most famous accomplish ...
invented the autogyro 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 The Asturian miners' strike of 1934 was a major strike action undertaken by regional miners against the 1933 Spanish general election, which redistributed political power from the leftists to conservatives in the Second Spanish Republic. The str ...
, 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 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 Nicolas Florine, born Nikolay Florin (19 July 1891 (Batumi, Georgia, Russian Empire) – 21 January 1972 (Brussels, Belgium)), was a Russian born engineer who settled in Belgium. He built the first tandem rotor helicopter in 1927 - a flying sc ...
, a Russian engineer, built the first twin tandem rotor machine to perform a free flight. It flew in
Sint-Genesius-Rode Sint-Genesius-Rode (; french: Rhode-Saint-Genèse, ) is a municipality located in Flanders, one of three regions of Belgium, in the province of Flemish Brabant. The municipality comprises the town of Sint-Genesius-Rode only, and lies between Brus ...
, at the ''Laboratoire Aérotechnique de Belgique'' (now
von Karman Institute The von Karman Institute for Fluid Dynamics (VKI) is a non-profit educational and scientific organization which specializes in three specific fields: aeronautics and aerospace, environment and applied fluid dynamics, turbomachinery and propulsi ...
) 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 (; FAI; en, World Air Sports Federation) 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 maintai ...
''. 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 kilometers per hour (27.8 mph). The aircraft was destroyed in 1943 by an
Allied An alliance is a relationship among people, groups, or states that have joined together for mutual benefit or to achieve some common purpose, whether or not explicit agreement has been worked out among them. Members of an alliance are called ...
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, fighters, heavy bombers, ground attack aircraft, attack helicopters and drones. The offic ...
at Villacoublay airport.


American single-rotor beginnings

American inventor
Arthur M. Young Arthur Middleton Young (November 3, 1905 – May 30, 1995) was an American inventor, helicopter pioneer, cosmologist, philosopher, astrologer, and author. Young was the designer of Bell Helicopter's first helicopter, the Model 30, and inventor ...
started work on model helicopters in 1928 using converted electric hover motors to drive the rotor head. Young invented the
stabilizer bar An anti-roll bar (roll bar, anti-sway bar, sway bar, stabilizer bar) is a part of many automobile suspensions that helps reduce the body roll of a vehicle during fast cornering or over road irregularities. It connects opposite (left/right) wheels ...
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 The Bell 30 was the prototype for the first commercial helicopter, and the first helicopter built by the Bell Aircraft Company. Designed by Arthur M. Young, the type served as a demonstration testbed for the successful Bell 47. Development Youn ...
, later succeeded by the Bell 47.


Birth of an industry

Heinrich Focke 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 Scotti ...
, which according to
Frank Kingston Smith Sr. Frank Kingston Smith Sr. (1919-2003) was a criminal attorney in Philadelphia, Pennsylvania, but is best known as the author of several books and articles on aviation. His first book, ''Week-end Pilot'', helped to bring the joys of flying to the a ...
, 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, 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 used helicopters in small numbers for observation, transport, and medical evacuation. The Flettner Fl 282 ''Kolibri''
synchropter Intermeshing rotors on a helicopter are a set of two rotors turning in opposite directions, with each rotor mast mounted with a slight angle to the other, in a transversely symmetrical manner, so that the blades intermesh without colliding. T ...
—using the same basic configuration as Anton Flettner'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 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 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 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
1st Air Commando Group 001, O01, or OO1 may refer to: *1 (number), a number, a numeral *001, fictional British agent, see 00 Agent *001, former emergency telephone number for the Norwegian fire brigade (until 1986) *AM-RB 001, the code-name for the Aston Martin Valkyrie ...
) 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 hired Arthur Young to help build a helicopter using Young's two-blade
teetering 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 aerod ...
design, which used a weighted
stabilizer bar An anti-roll bar (roll bar, anti-sway bar, sway bar, stabilizer bar) is a part of many automobile suspensions that helps reduce the body roll of a vehicle during fast cornering or over road irregularities. It connects opposite (left/right) wheels ...
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, 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 Charles Huron Kaman ( ; June 15, 1919 – January 31, 2011) was an American aeronautical engineer, businessman, inventor, and philanthropist, known for his work in rotary-wing flight
modified his
K-225 K225 or K-225 may refer to: * K-225 (Kansas highway), a former state highway in Kansas *Kaman K-225, an American experimental helicopter *HMCS Kitchener (K225) HMCS ''Kitchener'' was a Royal Canadian Navy revised which took part in convoy es ...
synchropter Intermeshing rotors on a helicopter are a set of two rotors turning in opposite directions, with each rotor mast mounted with a slight angle to the other, in a transversely symmetrical manner, so that the blades intermesh without colliding. T ...
—a design for a twin-rotor helicopter concept first pioneered by Anton Flettner in 1939, with the aforementioned Fl 265 piston-engined design in Germany—with a new kind of engine, the turboshaft 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 from the merger of Sud-Est (SNCASE, or ''Société nationale des constructions aéronautiques du sud-est'') and Sud-Ouest (SNCASO or ''Société n ...
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 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 heliports and government action to constrain flight paths in national parks 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 reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is m ...
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 Pascal Chrétien (born 7 April 1968) is a French-Australian commercial helicopter pilot and engineer Engineers, as practitioners of engineering, are professionals who invent, design, analyze, build and test machines, complex systems, st ...
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 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 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 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 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


"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