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helicopter

hélicoptèreἕλιξπτερόν

History

Early design

抱朴子 "Master who Embraces Simplicity") reportedly describes some of the ideas inherent to rotary wing aircraft.[12]

Designs similar to the Chinese helicopter toy appeared in Renaissance paintings and other works.[13] In the 18th and early 19th centuries Western scientists developed flying machines based on the Chinese toy.[14]

It was not until the early 1480s, when 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.[15][16] As scientific knowledge increased and became more accepted, people continued to pursue the idea of vertical flight.

In July 1754, Russian Mikhail Lomonosov had developed a small coaxial modeled after the Chinese top but powered by a wound-up spring device[14] 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[14] 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.[15] 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.[17]

In 1861, the word "helicopter" was coined by Gustave de Ponton d'Amécourt, a French inventor who demonstrated a small steam-powered model. While celebrated as an innovative use of a new metal, aluminum, the model never lifted off the ground. D'Amecourt's linguistic contribution would survive to eventually describe the vertical flight he had envisioned. Steam power was popular with other inventors as well. In 1878 the Italian Enrico Forlanini's unmanned vehicle, also powered by a steam engine, rose to a height of 12 meters (40 ft), 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.[15] In 1887 Parisian inventor, Gustave Trouvé, built and flew a tethered electric model helicopter.[citation needed]

First flights

Early development

Autogyro

Birth of an industry

Turbine age

Uses

  • A United States Navy Sikorsky HO3S-1 in action during the Korean War (1950-1953)

  • A Sikorsky S-64 Skycrane lifting a prefab house

  • An AgustaWestland Apache attack helicopter

  • A Harbin Z-19 reconnaissance-attack helicopter

  • A Bell 205 dropping water onto a fire

  • An HH-65 Dolphin demonstrating hoist rescue capability

  • A Spanish Maritime Safety Agency AW139SAR rescue helicopter

  • A Sikorsky S-76C+ air ambulance

  • A Eurocopter EC145 of the Swiss Air-Rescue (REGA)

  • A Ukrainian Naval Aviation Ka-27 preparing for take off from the USS Taylor

  • Search and rescue training in Estonia with a Mil Mi-8

  • An Aerospatiale Ecureuil AS 355N Twin (EC-JMK) of the General Directorate of Traffic, Moaña, Spain

Other uses of helicopters include:

  • Aerial photography
  • Motion picture photography
  • Electronic news gathering
  • Reflection seismology
  • Search and rescue
  • Tourism and recreation
  • Transport

Design features

Rotor system

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. The rotor blades are attached to 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 features

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 drive the tail rotor to be applied to the main rotors, increasing the aircraft's 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.
  • Coaxial rotors are two counter-rotating rotors mounted one above the other with the same axis.
  • Intermeshing rotors are two counter-rotating rotors mounted close to each other at a sufficient angle to let the rotors intermesh over the top of the aircraft without colliding.
  • Transverse rotors are pair of counter-rotating rotors mounted at each end of the wings or outrigger structures. They are found on tiltrotors and some earlier helicopters.
  • Quadcopters have four rotors often with parallel axes (sometimes rotating in the same direction with tilted axes) which are commonly used on model aircraft.

Engines

Flight controls

Flight

Hover

Transition from hover to forward flight

Forward flight

Safety

Maximum speed limit

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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.

Noise

Vibration

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 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

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

Hazards

As with any moving vehicle, unsafe operation could result in loss of control, structural damage, or loss of life. The following is a list of some of the potential hazards for helicopters:

  • Settling with power is when the aircraft has insufficient power to arrest its descent. This hazard can develop into Vortex ring state if not corrected early.[79]
  • 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.[79] 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.[80]
  • 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, or "rotor droop", 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.[81]
  • 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 helicopters[82]

Deadliest crashes

Deadliest helicopter crashes, sorted by death toll
Date/Year Operator Vehicle Event and location Death toll
2002 Russian Mil Mi-26 Shot down over Chechnya 127
1997 Israel two Sikorsky CH-53 Sea Stallions Collision over Israel 73
14 December 1992 Russia (Russian Army) Mil Mi-8 Shot down by Georgian forces in Abkhazia using SA-14 MANPADs, despite heavy escort 61: three crew, 58 passengers composed of mainly Russian refugees.[83]
4 October 1993 Georgia Mi-8 Shot down by Russian forces when transporting 60 refugees from eastern Abkhazia; all on board were killed.[83] 60
10 May 1977 Israel CH-53 Crash near Yitav in the Jordan Valley 54
11 September 1982 United States Boeing CH-47 Chinook, U.S. Army Crash at an air show in Mannheim, Germany 46[84]
1986 British International Helicopters Boeing 234LR Chinook Crash in the Shetland Islands 45
1992 Azerbaijan Mil Mi-8 Shootdown 44
2009 Pakistan (Pakistan Army) Mil Mi-17 Crash 41
2011 United States CH-47 Chinook Shootdown, Afghanistan 38[85]
26 January 2005 United States Sikorsky CH-53E Super Stallion, USMC Crash near Ar Rutbah, Iraq 31[86]

World records

See also

References

Notes

Footnotes

Bibliography

External links

Wikimedia Commons has media related to Helicopters.
Look up helicopter in Wiktionary, the free dictionary.
  • "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
  • Russian-language video about the Cheremukhin/Yuriev TsAGI 1-EA pioneer helicopter

Source: https://en.wikipedia.org/wiki/Helicopter






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