Helicopter

a helicopter (particularly in Switzerland also: Helicopter, shortened: Heli coil, too griech. hélix, gene. hélikos „turn, spiral “and pterón „wings “; English. ) an airplane and an aircraft are more helicopter, by one orseveral motor propelled rotary wings lift and propulsion receives.

The rotary wings, rotor mentioned, work like turning bearing areas, therefore helicopter belongs also to the rotary-wing aircraft, in contrast to the rigid wing airplanes. They are further VTOL aircraft, can thus vertically start andland. To helicopters are not counted:Autogyro, hybrid and VTOL - airplanes.

Sikorsky S-61 Seaking der Dänischen Marine.
Sikorsky S-61 Seaking of the Danish navy.

Table of contents

function

the rotary rotor blades producing opposite the airstream a dynamic lift. As is the case for the rigid bearing areas of an airplane this depends on their profile and angles of incidence. With the floating helicopter the incident-flow velocity corresponds to the peripheral speed; if it moves itself, it increases angledependently maximally by the airspeed.

A collective blade control working at the same time at all sheets changes the lift and causes thereby a rise orSink. It is steered by the raising or lowering of the swash plate in the rotor head. This rotates the rotor blades at the blade roots over a linkage running along with the rotor and changes thereby their angle of incidence.

The cyclic blade control again serves for the controlthe lateral movement, i.e. of forward of, sideways or backward flight over the main rotor. Here the Blattanstellung is changed during the circulation around the rotor axis (cyclic), as the swash plate is bent. During the forward flight thereby the angle of incidence of the sheets becomesdependent on the angle of rotation so changed that the rotor level leans forward, the air flow to the rear, and such a thrust develops forward.

From the aerodynamics of the rotor blade asymmetrical forces result on pre and backward-moving sheets, those with the forward flightby impact and drag hinges at the rotor head to be caught must. Newer constructions get along without these joints, by rotor head and - sheets from materials are designed, which can take up the dynamic forces, without developing fatigue fractures. This hingeless rotor head became for the first time with Bo-105 by sheets from glass-fiber reinforced plastic (GRP) and a solid rotor head from titanium realized, with the EC 135 developed (campless rotor head) and are continued to use today with most current models.

yaw moment reconciliation

With the exception of the tip jet the rotor is always shifted by a drive in the trunk in turn, and thus a torque (yaw moment) develops at the rotor axis, which causes an opposite turn of the trunk. In order to avoid this, givesit several possibilities:

A system with double rotor likes at first sight as the more efficient constructionappear, then in practice however the tail rotor configuration became generally accepted. A cause are the lower building and maintenance costs of rotor head and transmission, the aufwändigsten and most sensitive building groups of a helicopter.

There are tail rotors in remarkswith two to five sheets. In order to reduce the noise, partly four-leaf rotors are used in X-form. A particularly quiet variant is the Fenestron, an encased propeller in the tail arm with up to 18 sheets.

Usually is those Number of revolutions of the tail rotor over a fixed connection with that of the main rotor coupled, the drive is made then from the main gear box by waves and bellcranks. The thrust for the controlling of the yaw axis is regulated over the angle of incidence of the tail rotor blades, according to the same principlelike the collective adjustment of the main rotor.

During the forward flight with many helicopters the tail rotor is relieved, as the incident flow of the vertical stabilizer compensates the yaw moment. The end plates have in addition an easy skew to the side, dependent on the direction of rotation of the main rotor.

Should the drive fail, can helicopters nevertheless still land. They change then into a descending flight, whereby the unsolicited rotor is held now by the air flow in turn - an autorotation as with the autogiro. A yaw moment reconciliation is not necessary therebysuch a landing is therefore also in case of failure the tail rotor possible, for example with break of the drive shaft or the whole tail arm. Briefly before putting on now the pitch and thus the lift are increased, over with the kinetic energy of theTo make possible rotor uniquely soft putting on. The loss of the control around the vertical axis and the necessity to meet the correct moment exactly makes this maneuver however always risky.

flight performances

Geschwindigkeitsüberlagerung am vor- und rücklaufenden Blatt.
speed overlay to pre and backward-moving sheet.

Helicopterdo not reach in principle the flight performances of rigid wing airplanes:

The maximum speed lies usually between 200 and 300 km/h, some combat helicopters reaches 340 km/h. The speeds - record is with 400,87 km/h and became at the 11. August 1986 with Westland Lynx obtains.

The maximum speed is limited thereby by the aerodynamics of the rotor blades: In each case after in front current sheet has a higher speed than running to the rear opposite from the front flowing against air - to the rotating speed the speed adds itself of theHelicopter. Reached now the forward-moving sheet in the external area supersonic speed, it comes to flow separation. For the pilot this expresses itself for example in strong oscillations, which can make control of the helicopter impossible.

Usually the speed becomesa helicopter however by the backward-moving rotor blade limits: Here the combination of high angle of incidence ( cyclic adjustment, s.o.) and small flow rate leads during the return to flow separation and thus lift decrement. Many helicopters tilt therefore first toward to the backward-moving rotor blade, before thatforward-moving sheet into the supersonic range arrives.

Also the ceiling is limited and normally is about 5,000 meters, whereby individual models up to 9,000 reach meters. The elevator record of 13.716 m (45,000 ft) became in May 2005 of Didier Delsalle alsoa Eurocopter AS 350 optimized on it set up.

The fuel consumption of a helicopter is during same additional load generally clearly over that of a bearing area airplane.

The advantage of a helicopter however is in the ability, in air stands to remain (hovering flightto fly, also Hover) backwards and sideways to turn as well as in the slow flight around the vertical axis (yaw axis). Further a helicopter can start perpendicularly and land (VTOL) and necessarily therefore no starting or runway,separate only even place of sufficient diameter.

history of the development

Igor Sikorski in its VS-300 of 1941.

Already Leonardo da Vinci had end 15. Century sketches of a helicopter made, but only in 20. Century succeeded the technicalConversion of this idea. Pioneers of the helicopter development were Étienne Oehmichen, Juan de la Cierva, Louis Bréguet, Henrich Focke and Igor Sikorski:

At the 11. November 1922 brought Étienne Oehmichen for the first time its Oehmichen No.2 into air, to that probablyfirst reliably flying, man-basic VTOL aircraft.

With the development of its autogiro Juan de la Cierva 1923 substantial solutions arrive at the stabilization of the rotor of a rotary-wing aircraft, so the flapping hinges.

In the early 30's built Louis Bréguet and Rene Dorand alsothe Gyroplane Laboratoire the first longer time stably flying helicopter. It had a coaxial rotor and held starting from June 1935 all international records for helicopters.

The Focke Wulf L.G. 61, which used a tandem configuration, took over 1937 the top position. Both helicopters were unique pieces.

The first models built in series were 1941 the Focke Achgelis company 223 in Germany, and 1944 the Sikorsky R4 “Hoverfly” in the USA, which like its predecessor Sikorsky VS-300 was equipped with tail rotor.

1955 prepared the French company Sud aviation its helicopter Alouette II with for 250 a KW-Turboméca-Artouste-shaft turbine out and built thereby the first helicopter with gas turbine drive.

A further technical milestone was the German Boelkow Bo 105, the 1961 as the first helicopter a hingeless rotor head as well as GRP- Rotor blades began (for the first time with the Kamow the Ka-26 were used). The Eurocopter EC 135 begins as current successors far improved form of this building method.

Mil Mi-12, world largest helicopter.

1968 ever started with the Soviet Mil Mi-12 the largestbuilt helicopters, a crosswise arranged tandem building method with a takeoff weight of 105 t and a pay load of 40 t.

Starting from 1983 developed with the RAH-66 Comanche a combat helicopter with Stealth - for technology, its manufacturing however briefly before reaching the operational readiness 2004 one stopped.

In November 2003 flies for the first time Boeing X-50, whose rotor is determined with the forward flight and then as additional bearing area serves. As is the case for other VTOL - concepts are to be achieved thereby opposite pure rotary-wing aircraft better flight performances.

Control

Steuerknüppel eines Helikopters.
control stick of a helicopter.

A helicopter is conceptionally an unstable aircraft, i.e., it has constantly the tendency to tilt or turn in or other direction.

The pilot must intercept these movements by continuous tax inputs, forwardseverything at the hovering flight or low speed. Above approx. A helicopter behaves and is accordingly simple 60 knots similarly as an airplane to steer.

For the controlling of the helicopter the pilot (differently than right in the rigid wing airplane usually sitting) needs bothHands and feet. With the left hand it controls the collective blade control (English over a lever. Pitch) and thus the lift. In order to prevent with the ascent the waste of the rotor speed, also engine performance and thus the produced become Torque increases, manually or automatically. With the right hand the pilot controls the cyclic blade control, i.e. the inclination of the swash plate and thus the movement over the control stick around along and transverse axis.

At the soil are two foot pedals, alsothose one steers the tail rotor and thus the movement around the yaw axis, thus the right anti-clockwise turn.

accidents

Hughes AH-64 Apache der US Army, abgestürzt 1999 in Albanien.
Hughes AH-64 Apache of US Army, fallen 1999 in Albania.

Compared to fixed-wing aircraft helicopters exhibit a clearly higher accident frequency:Between 1980 and 1998 the Federal Agency for flight accident investigation (BFU) registered 54 accidents with six dead ones with helicopters statistically per one million takeoff, with fixed-wing aircraft of only ten accidents with 1,6 dead ones. The accident causes are thereby proportionately more frequently in the human failure (over80 %).

This higher probability of accident can be explained by the way of application: Emergency services and military cannot determine a place of work before. So the contact can be due by obstacles (like antennas, Stromleitungen) with deep overflights/flyovers to the fact that the pilot the areafor the first time flies over. Employments in the high mountains, like load transport and mountain rescue, can bring again by the smaller atmospheric pressure and descending winds the drive to the power limit. With its loss then the conditions for an autorotation are - landing frequently bad.

Admits becamelast the accident of a CH-53GS to 21.12.2002, with which sieved German soldiers came into Afghanistan around the life, when they fell after an investigation flight near the airport Kabul, under a drive damage, whereupon parts of the flight control were damaged. It actedaround the up to then heaviest misfortune with international missions of the German Federal Armed Forces.

ways of application

the enterprise of a modern helicopter is clearly more expensive compared with a fixed-wing aircraft with comparable additional load. Arise nevertheless due to its ability, on unprepared areastart and to land to be able, a set of additional operational areas, distinguishable into civilian and military.

civilian use

helicopter in the air rescue mission.

The most frequent use in Central Europe is the range air rescue with the Rettungshubschrauber, about which it alone inGermany over 50 bases gives. Further specializations represent intensive transport helicopters, region rescue helicopters, emergency surgeon employment helicopters and mountain emergency service . Also at the police and at the fire-brigade helicopters became an important supporting factor. The use of transport helicopters places, approximately with offshore construction works, an important element of logistics. In the high mountains the transport of building material and construction units is often important for lack of suitable Landwege for the establishment of alpine mechanisms.

Model helicopter constantly developed gotten increasingly meaning, there the technology and thatPilot its hobby also in interiors to exercise can. Remote controlled helicopter drones became so reliable in service that with the production aircraft manned by aerial photos for commercial purposes and for surveying employments in place of are consulted.

military use

US combat helicopter AH-1WSuper Cobra.

Typical military operational areas are antitank defense by specialized combat helicopters, like the Eurocopter tiger, the Hughes AH-64 or the Mil Mi-24, the far artillery observation, CSAR (Combat search and Rescue, dt. Searches/saving in combat) the air defenseand employments within the navy for the antisubmarine chase, sea-clearing-up and sea-rescue (SAR - search and Rescue).

In order to reduce costs, further multi-purpose helicopters assigned, which are convertible for external loads or the armed infantry support apart from the troop transport also, so that Sikorsky UH-60. Further operational areas are electronic warfare by disturbance of hostile radio signals or VIP - transportation.

helicopter technology

further details to building method and technology of helicopters are in these articles:

Variants of the building method to torque reconciliation
tail rotor configuration - Tandem configuration - coaxial rotor - Flettner Doppelrotor - tip jet
used aircraft construction ways
autogyro - aerogyro - Wandelflugzeug - VTOL aircraft - VTOL
rotor
rotor head - swash plate - flapping hinge - drag hinge - rotor blade
lift and propulsion
hovering flight - forward flight
landing device
helicopter engine

Important helicopter manufacturers

French Aérospatiale Alouette II (SA 315B-Lama BJ 1969) as camera helicopters.
Sikorsky S-61 Seaking of the German navy.

see also


work on []

Literature

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