Last Updated 02 Sep 2020

Helicopter

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Helicopter Definition: A helicopter (or chopper, helo or whirlybird) is a type of rotorcraft in which lift and thrust are supplied by rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forwards, backwards, and laterally. These attributes allow helicopters to be used in congested or isolated areas where fixed-wing aircraft would usually not be able to take off or land.

The capability to hover efficiently for extended periods of time allows a helicopter to accomplish tasks that fixed-wing aircraft and other forms of vertical takeoff and landing aircraft cannot perform. The word helicopter is adapted from the French helicoptere, coined by Gustave de Ponton d'Amecourt in 1861, which originates from the Greek helix/helik-  = "twisted, curved" and pteron = "wing". Helicopters were developed and built during the first half-century of flight, with the Focke-Wulf Fw 61 being the first operational helicopter in 1936.

Some helicopters reached limited production, but it was not until 1942 that a helicopter designed by Igor Sikorsky reached full-scale production, with 131 aircraft built. Though most earlier designs used more than one main rotor, it is the single main rotor with anti-torque tail rotor configuration that has become the most common helicopter configuration. Tandem rotor helicopters are also in widespread use, due to their better payload capacity. Quad rotor helicopters and other types of multicomputer have been developed for specialized applications. 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 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 of people and cargo, military uses, construction, firefighting, search and rescue, tourism, medical transport, and aerial observation, among others.

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Sikorsky S-64 Sky crane lifting a prefab house Sikorsky S-76C+ air ambulance Bell 205 dropping water on fire HH-65 Dolphin demonstrating hoist rescue capability AgustaWestland Apache attack helicopter 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 logline because of the long, single sling line used to carry the load. The most grand-scale 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 wild land fires. 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 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 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 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 air ambulances is often referred to as MEDEVAC and patients are referred to as being "airlifted", or "medevaced". 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 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. 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. 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. Various companies specialize in this type of operation. Other uses of helicopters include, but are not limited to:

  • Aerial photography
  • Motion picture photography
  • Electronic news gathering
  • Reflection seismology
  • Search and Rescue
  • Tourism or recreation

Transport Design features Parts and functions The simple rotor of a Robinson R22 Robinson R44 rotor head The simple rotor of a Robinson R22 showing (from the top):

  • The following are driven by the link rods from the rotating part of the swash plate.
  • Pitch hinges, allowing the blades to twist about the axis extending from blade root to blade tip.
  • Teeter hinge, allowing one blade to rise vertically while the other falls vertically.
  • This motion occurs whenever translational relative wind is present, or in response to a cyclic control input.
  • Scissor link and counterweight, carries the main shaft rotation down to the upper swash plate
  • Rubber covers protect moving and stationary shafts
  • Swash plates, transmitting cyclic and collective pitch to the blades (the top one rotates)
  • Three non-rotating control rods transmit pitch information to the lower swash plate
  • Main mast leading down to main gearbox Safety Limitations HAL Dhruv performing aerobatics during the Royal International Air Tattoo in 2008.

Royal Australian Navy Squirrelhelicopters during a display at the 2008 Melbourne Grand Prix The main limitation of the helicopter is its low speed. 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 RPM. 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 velocity. 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, and thus produce vastly increased drag and vibration. 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. 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. During the closing years of the 20th century designers began working on helicopter noise reduction. Urban communities have often expressed great dislike of noisy aircraft, and police and passenger helicopters can be unpopular.

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. Helicopters also vibrate; an unadjusted helicopter can easily vibrate so much that it will shake itself apart. To reduce vibration, all helicopters have rotor adjustments for height and weight. Blade height is adjusted by changing the pitch of the blade. Weight is adjusted by adding or removing weights on the rotor head and/or at the blade end caps. Most also have vibration dampers for height and pitch. Some also use mechanical feedback systems to sense and counter vibration.

Usually the feedback system uses a mass as a "stable reference" and a linkage from the mass operates a flap to adjust the rotor's angle of attack to counter the vibration. Adjustment is 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.

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 being pain, numbness, loss of tactile discrimination and dexterity. Helicopter Types Legend for “Category of Engines”: P - Piston Engine T -Turbine Engine NOTE: This Chart is provided as a guide only.

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Helicopter. (2017, Apr 25). Retrieved from https://phdessay.com/helicopter/

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