Helicopter
A helicopter is an aircraft that is lifted and propelled by one or more horizontal rotors, each rotor consisting of two or more rotor blades. Helicopters are classified as rotorcraft or rotary-wing aircraft to distinguish them from fixed-wing aircraft because the helicopter achieves lift with the rotor blades which rotate around a mast. The word '
helicopter' is adapted from the French hélicoptère, coined by Gustave de Ponton d'Amecourt in 1861, which originates from the Greek helix/helik- (ἕλικ-) = "spiral" or "turning" and pteron (πτερόν) = "wing".[1][2]
The primary advantage of a helicopter is from the rotor which provides lift without the aircraft needing to move forward, allowing the helicopter take off and lan
d vertically without a runway. For this reason, helicopters ar
e often used in congested or isolated areas where fixed-wing aircraft cannot take off or land. The lift from the rotor also allows the helicopter to hover in one area and more efficiently than other forms of vertical takeoff and landing (VTOL) aircraft, allowing it to accomplish tasks that fixed-
wing aircraft cannot perform.
Although helicopters were developed and built during the first half-century of flight, some even reaching limited production, it was not until 1942 that a helicopter designed by Igor Sikorsky reached full-scale production,[3] with 131 aircraft built.[4]
Even though most previous designs used more than on
e main rotor, it was the single main rotor with a
ntitorque tail rotor configuration of this design that would come to be recognized worldwide as the helicopter.
History
Since 400 BC,[5] Chinese children have played with bamboo flying toys.[6][7] A book written in 4th-century China, referred to as Pao Phu Tau (also Pao Phu Tzu or Bao Pu Zi, 抱朴子), is reported to describe some of the ideas inherent to rotary wing aircraft:
| “ | Someone asked the master about the principles of mounting to dangerous heights and traveling into the vast inane. The Master said, "Some have made flying cars with wood from the inner part of the jujube tree, using o x-leather [straps] fastened to returning blades so as to set the machine in motion ." | ” |
In the early 1480s, Leonardo da Vinci created a design for a machine that could be described as an "aerial screw". His notes suggested that he built small flying models, but there were no indications for any provision to stop the rotor from making the whole craft rotate.[10][11] As scientific knowledge increased and became more accepted, men continued to pursue the idea of vertical flight. Many of these later models and machi
nes would
more closely resemble the ancient bamboo flying top with spinning wings, rather than Da Vinci's screw.
In July 1754, Mikhail Lomonosov demonstrated a small coaxial rotor to the Russian Academy of Sciences. It was powered by a spring and suggested
as a method to lift meteorological instruments. In 1783, Christian de Launoy, and his mechanic, Bienvenu, made a model with a pair of counter-rotating rotors, using turkey's flight feathers as r
otor 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
, grew up to develop a model of feathers, similar to Launoy and Bienvenu, but powered by rubber bands. By the end of the century, he had progressed to using sh
eets 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 pur
sue the dream of flight.
In 1861, the word "helicopter" was coined by Gustave de Ponton d'Amé
court, 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 v
ertical
flight he had envisioned. Steam power was popular with other i
nventors as well. Enrico Forlanini's unmanned helicopter was also powered by a steam engine. It was the first of its type that rose to a height of 13 meters (43 ft), where it remained for some 20 seconds after a vertical take-off from a park in Milan, in 1877, and Emmanuel Dieuaide's steam-
powered design featured counter-rotating rotors powered through a hos
e from a boiler on the ground. Dandrieux's design had counter-ro
tating rotors and a 7.7-pound (3.5-kilogram) steam engine. It rose more than 40 feet (12 m) and flew for 20 seconds circa 1878.
In 1885, Thomas Edison was given US$1,000 by James Gordon Bennet t, Jr. , to conduct experiments towards developing flight. Edison built a helicopter an d used 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 he badly burned one of his workers. Edison reported that it would take a motor with a ratio of three to four pounds per horsepower produced to be su ccessful, based on his experiments. Ján Bahýľ, a Slovak inventor, adapted the internal combustion engine to power his helicopter model that reached a height of 0.5 meters (1.6 ft) in 1901. On 5 May 1905, his helicopter reached four meters (13 ft) in altitude and flew for over 1,500 meters (4,900 ft). In 1908, Edison patented his own design for a helicopter powered by a gasoline engine with box kites attached to a mast by cables for a rotor, but it never flew.First flights
In 1906, two French brothers, Jacques and Louis Breguet, began experimenting with airfoils for helicopters and in 1907, those experiments resulted in the Gyroplane No.1. Although there is some uncertainty about the dates, sometime between 14 August and 29 September 1907, the Gyroplane No. 1 lifted its pilot up into the air about two feet (0.6 m) f
or a minute. the Gyroplane No. 1 proved to be extremely unsteady an
d required a man at each corner of the airframe to hold it steady. Fo
r this reason, the flights of the Gyroplane No. 1 are considered to be the first manned flight of a helicopter, but not a free or untethered flight.
That same year, fellow French inventor Paul Cornu designed and built a Cornu helicopter that used two 20-foot (6 m) counter-rotating rotors driven by a 24-hp (18-kW) Antoinette engine. On 13 November 1907, it lifted its inventor to 1 foot (0.3 m) 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. Cornu's helicopter would complet
e a few more flights and achieve a height of nearly 6.5 feet (2 m), but it proved to be unstable and was abandoned.
Early development
In the early 1920s, Argentine Raúl Pateras Pescara, while worki
ng 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; and the rotor hub also could, allowing the aircraft lateral movement without a separate propeller to push or pull it. Pescara also demonstrate
d the principle of autorotation, by which helicopters safely land after engine failure; by January 1924, Pescara's helicopter No. 3 could fly for up ten minutes.
One of Pescara's contemporaries, Frenchman Etienne Oemichen, set the first helicopter world record recognized by the Fédération Aéronautique Internationale (FAI) on 14 April 1924, flying his helicopter 360 meters (1,181 ft). On 18 April 1924, Pescara beat Oemichen's record, flying for a distance of 736 meters (nearly a half mile) in 4 minutes an
d 11 seconds (about 8 mph, 13 km/h) maintaining a height of six feet (2 m). to be outdone, Oemichen reclaimed the world record on 4 May when he flew his No. 2 machine again for a 14-minute flight covering 5,550 feet (1.05 mi, 1.692 km) while climbing to a height of 50 feet (15 m).[16] Oemichen also set the 1 km closed-circuit record at 7 minutes 40 seconds.
Meanwhile, Juan de la Cierva was developing the first practical rotorcraft in Spain. In 1923, the aircraft that would become the basis for the modern helicopter rotor began to take shape in the form of an autogyro, Cierva's C.4.[17] Cierva had discovered aerodynamic and structural deficiencies in his early designs that could cause his autogy
ros to flip over after takeoff. The flapping hinges that Cierva designed for the C.4 allowed the rotor to develop lift equally on the left and right halves of the rotor disk. A crash in 1927 led to the development of a drag hinge to relieve further stress on the rotor from its flapping motion. two developments allowed for a stable rotor system, not only
in a hover, but in forward flight.
Albert Gillis von Baumhauer, a Dutch aeronautical engineer, began studying rotorcraft design in 1923. His first prototype "flew" ("hopped" and hovered in reality) on 24 September 1925, with Dutch Army-Air arm Captain Floris Albert van Heijst at the controls. The controls that Captain van Heijst used were Von Baumhauer's inventions, the cycl
ic and collective. Patents were granted to von Baumhauer for his cyclic and collective controls by the British ministry of aviation on 31 January 1927, under patent number 265,272.
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, a concept that was later adopted by other helicopter designers, including Bleeker and K
aman. 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).
At this same time, in the Soviet Union, the aeronautical engineers Boris N. Yuriev and Alexei M. Cheremukhin, working at TsAGI, constructed and flew the TsAGI 1-EA single rotor helicopter, which used an open tubing framework, a four blade main rot
or, and twin sets (one set of two each at the nose and tail) of 1.8 meters (6 ft) diameter anti-torque rotors. Powered by two M-2 powerplants, themselves up-rated Soviet copies of the Gnome Monosoupape rotary radial engine of World War I, the TsAGI 1-EA made several successful low altitude flights, and by 14 August 1932 Cheremukhin managed to get the 1-EA up to an unofficial altitude of 605 meters (1,985 ft), shat
tering d'Ascanio's earlier achievement. As the Soviet
Union was not yet a member of the FAI, however, Cheremukhin's record remained unrecognized.
Nicolas Florine, a Russian engineer, built the first twin tandem rotor machine to perform a free flight. It flew in Sint-Genesius-Rode, at the Laboratoire Aérotechnique de Belgique (now von Karman Institute) in April 1933 and attained an altitude of six meters (20 ft) 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 probably the most stable helicopter in existence.
The Bréguet-Dorand Gyroplane Laboratoire was built in 1933. 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 500-meter (1,600 ft) diameter. The next year, on 26 September 1936, Claisse set a height record of 158 meters (520 ft). And, finally, on 24 November 1936, he set a flight duration
record of one hour, two minutes and 5 seconds over a 44 kilometer (27 mi) closed circuit at 44.7 km/h (27.8 mph). The aircraft was destroyed in 1943 by an Allied airstrike at Villacoublay airport.
Birth of an industry
Despite the success of the Gyroplane Laboratoire, the Ge
rman Focke-Wulf Fw 61, first flown in 1936, would eclipse its accomplishments. The Fw 61 broke all of the helicopter world records in 1937, demonstrating a flight envelope that had only previously been achieved by the autogyro. In February 1938, Hanna Reitsch became the first female helicopter pilot, exhibiting the Fw 61 before cro
wds in the Deutschlandhalle.
Nazi Germany would use helicopters in small numbers during World War II for observation, transport, and medical evacuation. The Flettner Fl 282 Kolibri synchropter was used in the Mediterranean Sea, while the Focke Achgelis Fa 223 Dra
che was used in Europe. Extensive bombing by the Allied forces prevented Germany from producing any helicopters in large quantities durin
g the war.
In the United States, Igor Sikorsky and W. Lawrence LePage, were competing to produce the United States military's first helicopter. Prior to the war, LePage had received the patent rights to develop helicopters patterned after the Fw 61, and built the XR-1. Meanwhile, Sikorsky had settled on a simpler, single rotor design, the VS-300. Aft
er experimenting with configurations to counteract the torque produced by the single main rotor, he settled on a single, smaller rotor mounted vertically on the tailboom.
Developed from the VS-300, Sikorsky's R-4 became the first mass produced helicopter with a production order for 100 aircraft. The R-4 was th
e only Allied helicopter to see service in World War II, primarily being used for rescue in Burma, Alaska, and other areas with harsh terrain. Total production would reach 131 helicopters before the R-4 was replaced by other Sikorsky helicopters such as the R-5 and the R-6. In all, Sikorsky would produce over 400 helicopters before the
end of World War II.
As LePage and Sikorsky were building their helico
pters for the military, Bell Aircraft hired Arthur Young to help build a helicopter using Young's semi-rigid, teetering-blade rotor design, which used a weighted stabilizing bar. The subsequent Model 30 helicopter demonstrated the simplicity and ease of the design. The Model 30 was developed into the Bell 47, which became the first helicopter certificated for civilian use in the United States. Produced in several countries, the Bell 4
7 would become the most popular helicopter model for nearly 30 years.
Turbine age
In 1951, at the urging of his contacts at the Department of the Navy, Charles Kaman modified his K-225 helicopter with a new kind of engine, the turbosh
aft engine. This adaptation of the turbine engine provide
d a large amount of power to the helicopter with a lower weight penalty than piston engines, with their heavy engine blocks and auxiliary components. On 11 December 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 Alouette II that
would become the first helicopter to be produced with a turbine-engine.
Reliable helicopters capable of stable hover flight were developed decades after fixed-wing aircraft. This is largely due to higher engine power density requirements than fixed-wing aircraft. Improvements in fuels and engines during the first half of the 20th century were a critical factor in helicopter development. The availability of lightweight turboshaft 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 tod
ay.
Uses
Due to the operating characteristics of the helicopter
—its ability to takeoff and land vertically, and to hover for extended periods of time, as well as the aircraft's handling properties under low airspeed conditions—it has been chosen to conduct tasks that were previously not possible with other aircraft, or were time- or work-intensive to accomplish on the ground. Today, helicopter uses include transportation, construction, firefighting, search and rescue, and military uses.
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 ter
rain where vehicles cannot travel and where envir
onmental concerns prohibit the building of roads.[24] These operations are referred to as longline because of the long, single sling line used to carry the load.[25]
Helitack is the use of helicopters to combat wildlan
d fires.[26] The helicopters are used for aerial firefighting (or 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 firefi
ghters, who rappel down to inaccessible areas, and to resupply firefighters. Common firefighting helicopters include variants of the Bell 205 and the Erickson S-64 Aircrane helitanker.
Helicopters are used as air ambulances for em
ergency medical assistance in situations when an ambulance cannot easily or quickly reach the scene. Helicopters are also used when a patient needs to be transported between medical facilities and air transportation is the most practical method for the safety of the patient. Air ambulance helicopters are equipped to provide medical treatment to a patient while in flight. The use of helicopters as an air ambulance is often referred to as MEDEVAC, and patients are referred to as being "airlifted", or "medevaced"
.
Oil companies charter helicopters to move workers and parts quickly to remote drilling sites located out to sea or in remote locations. The speed over boats makes the high operating cost of helicopters cost effective to ensure that oil platforms continue to flow. Companies such as CHC Helicopter, Bristow Helicopters, and Air Logistics specialize in this type of operation.
Police departments and other law enforcement agencies use helicopters to pursue suspects. Since helicopters can achieve a unique aerial view, 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 atta
cks 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. Unmanned Aerial Systems (UAS) helicopter systems of varying sizes are being 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.
Other uses of helicopters include but are not limited to:
- Aerial photography
- Motion picture photography
- Electronic news gathering
- Search and Rescue
- Tourism or recreation
- Transport
Design features
Rotor system
The rotor system, or more simply rotor, is the r
otating part of a helicopter which generates lift
. A rotor system may be mounted horizontally as main rotors are, providing lift vertically, or it may be mounted vertically, such as a tail rotor, to provide lift horizontally as thrust to counteract torque effect. The rotor consists of a mast, hub and rotor blades.
The mast is a cylindrical metal shaft which ext
en
ds upwards from and is driven by the transmission. At the top of the mast is the attachment point for the rotor blades called the hub. The rotor blades are then attached to the hub by a number of different methods. Main rotor systems are classified according to how the main rotor blades are attached and move relative to the main rotor hub. There are three basic classifications: rigid, semirigid, or fully articulated, although some modern rotor systems use an engineered combination of these types.
Rigid
In a rigid rotor system, the blades, hub, and m
ast are rigid with respect to each other. The rigid rotor system is mechanically simpler than the fully articulated rotor system. There are no vertical or
horizontal hinges so the blades cannot flap or drag, but they can be feathered. Operating loads from flapping and lead/lag forces must be absorbed by bending rather than through hinges. By flexing, the blades themselves compensate for the forces which previously required rugge
d hinges. The result is a rotor system that has less lag in the control response, because the rotor has much less oscillation. The rigid rotor system also negates the danger of mast bumping inherent in semi-rigid rotors. The rigid rotor can also be ca
lled a hingeless rotor.
Semirigid
A semirigid rotor system allows for two different movements, flapping and feathering. This system is normally comprised of two blades, which are rigidly attached to the rotor hub. The hub is then attached to the rotor mast by a trunnion b
earing or teetering hinge and is free to tilt with respect to the main rotor shaft. This allows th
e blades to see-saw or flap together. As one blade flaps down, the other flaps up. Feathering is accomplished by the feathering hinge, which changes the pitch angle of the blade. Since there is no vertical drag hinge, lead-lag forces are absorbed through blade bending.
Helicopters with semi-rigid rotors are vulnerable to a condition known as mast bumping which can cause the rotor flap stops to shear the mast. M
ast bumping is normally encountered during low-G maneuvers, so it is written into the operator's handbook to avoid any low-G conditions.
Fully articulated
In a fully articulated rotor system, each rotor blade is attached to the rotor hub through a series of hinges, which allow the blade to move independently of the others. These rotor systems usually have three or more blades. The blades are allowed to flap, feather, and lead or lag independently of each other. The horizontal hinge,
called the flapping hinge, allows the blade to move up and down. This movement is called flapping and is designed to compensate for dissymmetry of lift. The flapping hinge may be locat
ed at varying distances from the rotor hub, and ther
e may be more than one hinge. The vertical hinge,
called the lead-lag or drag hinge, allows the blade to move back and forth. This movement is called lead-lag, dragging, or hunting. Dampers are usually used to prevent excess back and forth movement around the drag hinge. The purpose of the drag hinge and dampers is to compensate for the acceleration and deceleration caused by Coriolis Effect. Each blade can also be feathered, that is, rotated around its spanwise axis. Feathering the blade means changing the pitch a
ngle of the blade. By changing the pitch angle of the blades the thrust and direction of the main rotor disc can be controlled.
Combination
Modern rotor systems may use the combined principles of the rotor systems mentioned above. Some rotor hubs incorporate a flexible hub, which allows for blade bending (flexing) without the need for bearings or hinges. These systems, called "flextures", usually constructed from composite material. Elastomeric bearings may a
lso be used in place of conventional roller bearings. Elastomeric bearings are bearings constructed from a rubber type material and have limited movement that is perfectly suited for helicop
ter applications. Flextures and elastomeric bearings require no lubrication and, therefore, require less maintenance. They also absorb vibration, which means less fatigue and longer service life for the helicopter components.
Antitorque configura
tions
Most helicopters have a single main rotor, but torque created as the engine turns the rotor against its air drag causes the body of the helicopter to turn in the opposite direction to the rotor. To eliminate this effect, some sort of antitorque control
must be used. The design that Igor Sikorsky settled on for his VS-300 was a smaller rotor mounted vertically on the tail. The tail rotor pushes or pulls against the tail to count
er the torque effect, and has become the recognized convention for helicopter design. Some helicopters utilize alternate antitorque controls in place o
f the tail rotor, such as the ducted fan (called Fenestron or FANTAIL), and NOTAR. NOTAR provides antitorque similar to the way a wing develops lift, through the use of a Coandă effe
ct on the tailboom.
The use of two or more horizontal rotors t
urning in opposite directions is another configurat
ion used to counteract the effects of torque on the aircraft without relying on an antitorque tail rotor. This allows the power normally required to drive the tail rotor to be applied to the main rotors, increasing the aircraft's lifting capacity. Primarily, there are three common configurations that use the counterrotating effect to benefit the rotorcraft. Tandem rotors are two rotors with one mounted behind the other. Coaxial rotors are two rotors that are mounted one above the other with the same axis. Intermeshing rotors are two rotors that are mounted close to each other
at a sufficient angle to allow the rotors to intermesh over the top of the aircraft. Transverse rotors is another configuration found on tiltrotors and some earlier helicopters, where the pair of rotors are mounted at each end of the wings or outrigger structures. Tip jet designs per
mit the rotor to push itself through the air, and avoid generating torque.
posted by artical news @ 12:56 AM
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