Product Code Database
A helicopter is a type of rotorcraft in which lift and thrust are supplied by horizontally spinning Helicopter rotor. This allows the helicopter to VTOL, 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 short take-off and landing (STOL) or short take-off and vertical landing (STOVL) aircraft cannot perform without a runway.
The Focke-Wulf Fw 61 was the first successful, practical, and fully controllable helicopter in 1936, while in 1942, the Sikorsky R-4 became the first helicopter to reach full-scale mass production. Starting in 1939 and through 1943, Igor Sikorsky worked on the development of the VS-300, which over four iterations, became the basis for modern helicopters with a single main rotor and a single tail rotor.
Although most earlier designs used more than one main rotor, the configuration of a single main rotor accompanied by a vertical anti-torque tail rotor (i.e. unicopter, not to be confused with the single-blade monocopter) has become the most common helicopter configuration. However, twin-rotor helicopters (bicopters), in either tandem rotors or transverse rotors configurations, are sometimes in use due to their greater payload capacity than the monorotor design, and coaxial rotors, tiltrotor and compound helicopters are also all flying today. Four-rotor helicopters () were pioneered as early as 1907 in France, and along with other types of , have been developed mainly for specialized applications such as commercial unmanned aerial vehicles (drones) due to the rapid expansion of drone racing and aerial photography markets in the early 21st century, as well as recently utilities such as artillery spotting, and suicide attacks.
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.
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 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:
Tip jet designs let the rotor push itself through the air and avoid generating torque.
Early helicopter designs utilized custom-built engines or 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 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 powered by a remote compressor are referred to as cold tip jets, while those powered by combustion exhaust are referred to as hot tip jets. An example of a cold jet helicopter is the Sud-Ouest Djinn, and an example of the hot tip jet helicopter is the YH-32 Hornet.
Some radio-controlled helicopters and smaller, helicopter-type unmanned aerial vehicles, use or motorcycle engines. Radio-controlled helicopters may also have that use fuels other than gasoline, such as nitromethane. Some turbine engines commonly used in helicopters can also use biodiesel instead of jet fuel. "Jay Leno's EcoJet Concept". businessweek.com, 2 November 2006. Retrieved 12 December 2010.Skinner, Tony. "Eurosatory 2010: Industry celebrates first helicopter biofuel flight". shephard.co.uk, 17 June 2010. Retrieved 12 December 2010.
There are also human-powered helicopters.
/ref> Helicopter Instructor's Handbook, FAA, 2014, ISBN 9781629141442, 1629141445Bailey, Norman (2014) 'Helicopter Pilot's Manual'' Crowood, ISBN 9781847979230, 1847979238
The drive shafts of helicopter engines are typically not aligned with the rotor shafts, so the transmission must translate the alignment of the drive shaft to match the shafts of the rotors. Many engine drive shafts are aligned horizontally, yet the main rotor shaft ("mast") is usually vertical, and the tail rotor shaft is often perpendicular to the engine's drive shaft. The transmission contains a series of gears, usually , that translate the alignment of the drive shaft to the alignment of the rotor shafts. Bevel Gear Fundamentals and Applications, Jan Klingelnberg, 2015, Springer Berlin Heidelberg, ISBN 9783662438930, 3662438933
The transmission also reduces the RPMs of the engine to the lower RPMs required by the rotors. The output drive shaft of the engine, before any gearing is applied, is typically between 3,000 and 50,000 RPM (Gas turbine typically have higher RPM than ). The main rotor typically rotates between 300 and 600 RPM. The tail rotor, if present, usually rotates between 1,000 and 5,000 RPM. (The RPMs of a given model of helicopter are usually fixed the RPM ranges listed above represent a variety of helicopter models). The transmission contains a series of to reduce the engine RPM to the rotor RPMs. Several types of reduction gears may be used, including bevel gears, , , and . Most transmissions contain several reduction gears: the engine itself may contain reduction gears (often spur gears) between the engine's internal shaft and the output drive shaft; the main rotor may have a reduction gear at its base (typically a planetary gear); and there may be reduction gears at the tail rotor, and on the shaft leading to the tail rotor.
The transmission often includes one or more , which permit the rotors to engage or disengage from the engine. A clutch is required so the engine can start up and gain speed before taking the load of the rotors. A clutch is also required in the case of engine failure: in that situation, the rotors must disengage from the engine so that the rotors can continue spinning and perform autorotation. Helicopter clutches are usually freewheel clutches relying on centrifugal forces ( are commonly used), but belt drive clutches are also used.
The cyclic control is usually located between the pilot's legs and is commonly called the cyclic stick or just cyclic or stick and moves forwards and backwards and side to side. On most helicopters, the cyclic is similar to a joystick. However, the Robinson R22, Robinson R44 and Robinson R66 have a unique teetering-bar cyclic control system and a few helicopters have a cyclic control that descends into the cockpit from overhead.
The cyclic is called the cyclic because it cyclically changes the pitch of the main rotor blades. In a forward flight state, as the blades rotate, the blade rotating forward will see higher speed and a corresponding increase in lift compared to the retreating blade. As such, the angle of attack of the forward rotating blade has to be lower than the retreating blade or the helicopter will roll to the retreating blade side. This happens cyclically as the blades rotate through a complete rotation leading to the naming of this control as the cyclic. The cyclic controls this differential angle.
The cyclic controls the tilt of the rotor. In hover, the cyclic controls motion of the helicopter over the ground. In flight, the cyclic controls the pitch and roll of the helicopter.
In a hover, if the pilot pushes the cyclic forward, the rotor disk tilts forward, and the rotor produces a thrust in the forward direction. If the pilot pushes the cyclic to the side, the rotor disk tilts to that side and produces thrust in that direction, causing the helicopter to move sideways.
Because of precession, the cyclic moves the swashplate 90 degrees before the desired main rotor tilt. This can be seen when the rotor is stopped. With the blades aligned fore/aft, moving the cyclic forward does not change the blade angle but moving the cyclic to the side will change the blade angle.
In flight, the cyclic acts like the stick in an airplane. Moving the cyclic forward pitches the nose down for more speed. Moving the cyclic aft lifts the nose to slow the aircraft. Moving the cyclic to the side rolls the helicopter in that direction which generally leads to turning in that direction, assuming coordinated flight.
The collective pitch control or collective is located on the left side of the pilot's seat with an adjustable friction control to prevent inadvertent movement freeing the pilot's left hand for other uses. The collective changes the pitch angle of all the main rotor blades collectively (i.e. all at the same time) and independently of their rotational position. Therefore, if an up collective input is made, all the blades increase angle of attack equally, and the result is additional lift (power) to the main rotor system which can increase helicopter speed or altitude. Lowering the collective results in less lift from the main rotor system.
A swashplate controls the collective and cyclic pitch of the main blades. The swashplate moves up and down, along the main shaft, to change the pitch of the blades. The stick is connected to the swash plate through the collective and cyclic systems allowing both systems to independently control the angle of the blades.
The anti-torque pedals are located in the same position as the rudder pedals in a fixed-wing aircraft, and serve a similar purpose, namely to control the flight dynamics or direction in which the nose of the aircraft is pointed. Application of the pedal in a given direction changes the pitch of the tail rotor blades, increasing or reducing the thrust produced by the tail rotor and causing the nose to yaw in the direction of the applied pedal. The pedals mechanically change the pitch of the tail rotor altering the amount of thrust produced. Helicopters do not exhibit adverse yaw as seen in airplanes and the pedals are not generally required when turning in forward flight. Use of the pedals is closely related to the collective in hover. For example, increasing collective increases aerodynamic drag on the main rotor system causing a yaw of the helicopter. The pedals are used to counter that yaw.
Both the cyclic and collective can have a wide variety of toggles and switches available to the pilot to control such things as aerodynamic trim, engine speed trim, radio and intercom, hook release, water release, etc. This allows the pilot to control these functions without removing their hands from the controls.
Helicopter rotors are designed to operate in a narrow range of RPM.Croucher, Phil. Professional helicopter pilot studies page 2-11. . Quote: Rotor "is constant in a helicopter".Johnson, Pam. Delta D2 page 44 Pacific Wings. Retrieved 2 January 2010 "Helicopters". Helicopter Vietnam. Retrieved: 16 February 2011.The UH-60 permits 95–101% rotor RPM UH-60 limits US Army Aviation. Retrieved 2 January 2010John M. Seddon, Simon Newman. Basic Helicopter Aerodynamics p. 216, 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. The throttle control is a motorcycle-style twist grip mounted on the collective control.
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 Heli-logging to lift trees out of terrain where vehicles cannot travel and where environmental concerns prohibit the building of roads.Day, Dwayne A. "Skycranes" . Centennial of Flight Commission. Retrieved 1 October 2008. These operations are referred to as longline because of the long, single sling line used to carry the load.Webster, L.F. The Wiley Dictionary of Civil Engineering and Construction. New York: Wiley, 1997. . In military service helicopters are often useful for delivery of outsized slung loads that would not fit inside ordinary cargo aircraft: artillery pieces, large machinery (field radars, communications gear, electrical generators), or pallets of bulk cargo. In military operations these payloads are often delivered to remote locations made inaccessible by mountainous or riverine terrain, or naval vessels at sea.
In electronic news gathering, helicopters have provided aerial views of some major news stories, and have been doing so, from the late 1960s. Helicopters have also been used in films, both in front and behind the camera.
The largest single non-combat helicopter operation in history was the disaster management operation following the 1986 Chernobyl nuclear disaster. Hundreds of pilots were involved in airdrop and observation missions, making dozens of sorties a day for several months.
"Helitack" is the use of helicopters to combat wildland fires.Butler, Bret W. et al. "Appendix A: Glossary: Fire Behavior Associated with the 1994 South Canyon Fire on Storm King Mountain, Colorado research paper". U.S. Dept. of Agriculture, Forest Service, September 1998. Retrieved 2 November 2008. The helicopters are used for aerial firefighting (water bombing) and may be fitted with tanks or carry helibuckets. Helibuckets, such as the Bambi bucket, are usually filled by submerging the bucket into lakes, rivers, reservoirs, or portable tanks. Tanks fitted onto helicopters are filled from a hose while the helicopter is on the ground or water is siphoned from lakes or reservoirs through a hanging snorkel as the helicopter hovers over the water source. Helitack helicopters are also used to deliver firefighters, who rappel down to inaccessible areas, and to resupply firefighters. Common firefighting helicopters include variants of the Bell 205 and the Erickson S-64 Aircrane helitanker.
Helicopters are used as 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.Kay, Marcia Hillary. " 40 Years Retrospective: It's Been a Wild Ride" Rotor & Wing, August 2007. Accessed: 8 June 2014. . 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 Police aviation to pursue suspects and patrol the skies. Since helicopters can achieve a unique aerial view, they are often used in conjunction with police on the ground to report on suspects' locations and movements. They are often mounted with lighting and heat-sensing equipment for night pursuits.
Military forces use attack helicopters to conduct aerial attacks on ground targets. Such helicopters are mounted with missile launchers and . 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 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 continue to operate. Various companies specialize in this type of operation.
NASA developed Ingenuity, a helicopter used to survey Mars (along with a rover). It began service in February 2021 and was retired due to sustained rotor blade damage in January 2024 after 73 sorties. As the Martian atmosphere is 100 times thinner than Earth's, its two blades spin at close to 3,000 revolutions a minute, approximately 10 times faster than that of a terrestrial helicopter.
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 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%.
Designs similar to the Chinese helicopter toy appeared in some Renaissance paintings and other works.Donald F. Lach. (1977). Asia in the making of Europe. Volume II, A Century of Wonder . p. 403 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 2010Pilotfriend.com "Leonardo da Vinci's Helical Air Screw". 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 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 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. 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, a French inventor who demonstrated a small steam-powered model. While celebrated as an innovative use of a new metal, aluminum, the model never lifted off the ground. D'Amecourt's linguistic contribution would survive to eventually describe the vertical flight he had envisioned. Steam power was popular with other inventors as well. In 1877, the Italian engineer, inventor and aeronautical pioneer Enrico Forlanini developed an unmanned helicopter powered by a steam engine. It rose to a height of , where it remained for 20 seconds, after a vertical take-off from a park in Milan. Milan has dedicated its city airport to Enrico Forlanini, also named Linate Airport, as well as the nearby park, the Parco Forlanini. Emmanuel Dieuaide's steam-powered design featured counter-rotating rotors powered through a hose from a boiler on the ground. In 1887 Parisian inventor, Gustave Trouvé, built and flew a tethered electric model helicopter.
In July 1901, the maiden flight of Hermann Ganswindt's helicopter took place in Berlin-Schöneberg; this was probably the first heavier-than-air motor-driven flight carrying humans. A movie covering the event was taken by Max Skladanowsky, but it remains lost film.
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.Bryan, George S. Edison: the Man and His Work. New York: Garden City Publishers, 1926. p. 249 Ján Bahýľ, a Slovaks 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 . "Pioneers – 1900/1930". Helicopter History Site. Retrieved: 3 May 2007 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.Dowd, George L. "Flops of famous inventors". Popular Science, December 1930
That same year, fellow French inventor Paul Cornu designed and built the Cornu helicopter which used two counter-rotating rotors driven by a Antoinette engine. On 13 November 1907, it lifted its inventor to and remained aloft for 20 seconds. Even though this flight did not surpass the flight of the Gyroplane No. 1, it was reported to be the first truly free flight with a pilot.Leishman, J. Gordon, Technical Fellow of AHS International. "Paper". 64th Annual Forum of the American Helicopter Society International, on the aerodynamic capability of Cornu's design, arguing that the aircraft lacked the power and rotor loading to lift free of the ground in manned flight. Cornu's helicopter completed a few more flights and achieved a height of nearly , but it proved to be unstable and was abandoned.
In 1909, J. Newton Williams of Derby, Connecticut, and Emile Berliner 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 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.Taylor, Michael J. H. Jane's Encyclopedia of Aviation, p. 348. London: Studio Editions, 1989.
During World War I, Austria-Hungary developed the PKZ, an experimental helicopter prototype, with two aircraft built.
In March 1923 Time magazine reported Thomas Edison sent George de Bothezat a congratulations for a successful helicopter test flight. Edison wrote, "So far as I know, you have produced the first successful helicopter." The helicopter was tested at McCook 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 quadcopter ." 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. "Helicopter Development in the Early Twentieth Century" . 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. The JAviator Quadrotor – Rainer K. L. Trummer, University of Salzburg, Austria, 2010, p. 21
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,Relly Victoria Petrescu and Florian Ioon Petrescu The Aviation History, p. 74. USA, 2013, . 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 extractAlex de Voogt. The Transmission of Helicopter Technology, 1920-1939: Exchanges with von Baumhauer. Int. j. for the history of eng. & tech., Vol. 83 No. 1, January 2013, 119–40. web extract Patents were granted to von Baumhauer for his cyclic and collective controls by the British ministry of aviation on 31January 1927, under patent number 265,272.
In 1927, Engelbert Zaschka from Germany built a helicopter, equipped with two rotors, in which a gyroscope 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. "Asboth Helicopter". The Evening Post (New Zealand), 27 April 1935. Retrieved: 12 December 2010.
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.
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 kilometres per hour (27.8 mph). The aircraft was destroyed in 1943 by an Allied airstrike at Villacoublay airport.Day, Dwayne A. " Jacques Bréguet—Gyroplane-Laboratoire ". Paragraph 10. Centennial of Flight. Retrieved 24 September 2015.
During World War II, Nazi Germany 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's own pioneering Fl 265—was used in the Baltic Sea, Mediterranean, and Aegean Sea Seas. The Focke-Achgelis Fa 223 Drache, like the Fw 61, used two transverse rotors, and was the largest rotorcraft of the war. Extensive bombing by the Allied forces prevented Germany from producing helicopters in large quantities during the war.
In the United States, Russian-born engineer Igor Sikorsky 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-1Francillon 1997 in 1941. Meanwhile, Sikorsky settled on a simpler, single-rotor design, the VS-300 of 1939, which turned out to be the first practical single lifting-rotor helicopter design. After experimenting with configurations to counteract the torque produced by the single main rotor, Sikorsky settled on a single, smaller rotor mounted on the tail boom.
Developed from the VS-300, Sikorsky's R-4 of 1942 was the first large-scale mass-produced helicopter, with a production order for 100 aircraft. The R-4 was the only Allied helicopter to serve in World War II, used primarily for search and rescue (by the USAAF 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 hired Arthur Young to help build a helicopter using Young's two-blade teetering rotor design, which used a weighted stabilizer bar placed at a 90° angle to the rotor blades. The subsequent Model 30 helicopter of 1943 showed the design's simplicity and ease of use. The Model 30 was developed into the Bell 47 of 1945, which became the first helicopter certified for civilian use in the United States (March 1946). Produced in several countries, the Bell 47 was the most popular helicopter model for nearly 30 years.
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.
At the same time, the advancing blade creates more lift traveling forward, the retreating blade produces less lift. If the aircraft were to accelerate to the air speed that the blade tips are spinning, the retreating blade passes through air moving at the same speed of the blade and produces no lift at all, resulting in very high torque stresses on the central shaft that can tip down the retreating-blade side of the vehicle, and cause a loss of control. Dual counter-rotating blades prevent this situation due to having two advancing and two retreating blades with balanced forces.
Because the advancing blade has higher airspeed than the retreating blade and generates a dissymmetry of lift, rotor blades are designed to "flap" – lift and twist in such a way that the advancing blade flaps up and develops a smaller angle of attack. Conversely, the retreating blade flaps down, develops a higher angle of attack, and generates more lift. At high speeds, the force on the rotors is such that they "flap" excessively, and the retreating blade can reach too high an angle and stall. For this reason, the maximum safe forward airspeed of a helicopter is given a design rating called VNE, velocity, never exceed. Rotorcraft Flying Handbook 2007, pp. 3–7. 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.
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. Loss of Tail Rotor Effectiveness , Dynamic Flight Inc. Accessed 11 May 2016.
When the trailing vortices colliding with the tail rotor are rotating in the same direction, this causes a loss of thrust from the tail rotor. When the trailing vortices rotate in the opposite direction of the tail rotor, thrust is increased. Use of the foot pedals is required to adjust the tail rotor's angle of attack, to compensate for these instabilities.
These issues are due to the exposed tail rotor cutting through open air around the rear of the vehicle. This issue disappears when the tail is instead ducted, using an internal impeller enclosed in the tail and a jet of high pressure air sideways out of the tail, as the main rotor vortices can not impact the operation of an internal impeller.
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.
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 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.
| + Deadliest helicopter crashes by death toll | ||||
| 127 | ||||
| Mil Mi-8 | Shot down by Sandinistan rebels while carrying 88 people. All 84 passengers were killed and all four crew members survived. | 84 | ||
| 73 | ||||
| Mil Mi-8 | Shot down by Georgian forces in Abkhazia using SA-14 MANPADs, despite heavy escort. Three crew and 58 passengers, composed of mainly Russian refugees. | 61 | ||
| Mil Mi-8 | Shot down when transporting 60 refugees from eastern Abkhazia; all on board were killed. | 60 | ||
| 54 | ||||
| 8 January 1968 | United States | Sikorsky CH-53A Sea Stallion, USMC | Crash near Đông Hà Combat Base in South Vietnam. All five crew and 41 passengers were killed. | 46 |
| 11 July 1972 | United States | Sikorsky CH-53D Sea Stallion, USMC | Shot down by missile near Quảng Trị in South Vietnam. Six U.S. Marines and 50 Vietnamese Marines on board. Three U.S. Marines and 43 Vietnamese Marines were killed. | 46 |
| 46 | ||||
| Boeing 234LR Chinook | 45 | |||
| 44 | ||||
| 41 | ||||
| CH-47 Chinook | Shootdown, Afghanistan|38 | |||
| 18 August 1971 | United States | CH-47 Chinook, U.S. Army | Crash near Pegnitz, then located in West Germany. All four crew and 33 passengers were killed. | 37 |
| 31 | ||||
|
|
