Helicopter

Etymology

The word helicopter was invented by Gustave Ponton of Amécourt, starting from the Greek helikos (propeller) and pteron (wing). This term appeared for the first time on August 3rd 1861 in an patent application deposited in England, then on July 16th 1862 in the certificate of addition to patent 49.077 initially deposited on April 3rd, 1861 in France. This inventor built with Gabriel of Landelle a small prototype of steam engine helicopter, whose boiler was one of the first uses of aluminum.

History

Since the IV E already the men made fly of the toys. This type of helicopter is represented in a painting of the 4th century of the work entitled CAM Phu Tau (抱朴子). Léonard de Vinci in 1486 made a drawing which shows a flying machine with revolving wing. It is necessary to wait the 18th century to see a project. Large signification advance occurred in 1907, year of first true takeoff. In the Thirties, a named machine “gyroplane of laboratory” succeeds in flying to 100 km/h during one hour. The helicopter remains a still experimental machine until 1940.

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Since fourth century BC, the Chinese made fly of small toys on the principle of the helicopter to fascinate the children. Via the trade, one knows that this toy arrived until in Europe. Indeed, it appears in a painting of 1463. The book CAM Phu Tau of the 4th century also traces the outline of an aircraft with rotary wings.

In Europe, the first to be been interested in the concept of helicopter was the scientist Italy N Léonard de Vinci. One of its drawings, gone back to 1486, watch a flying machine with revolving wing, based on the principle of the Archimedes' screw. However, in the absence of knowledge in Aerodynamic and without adequate motorization, it will remain with the state of project.

It will be necessary to await the end of the 18th century so that a true projection occurs: in 1754 the Russian Lomonossov tests in front of a scientific learned assembly a complex model with two contrarotating coaxial rotors , mûs by a mechanism of clock industry, and shows the existence of a force of lift. The April 26th 1784, the French Launoy and Bienvenu make steal in front of the royal Académie of sciences a very simple small size mû by a mechanism of spring to arc. In 1877, another Italian, Enrico Forlanini manages to make steal a small helicopter to vapor. Ten years later the French Finds made take off a model equipped with an electric engine , whose food is obtained since the ground by ends wire of Cuivre. In 1905 the brothers Henri and Armand Dufaux make take off vertically a spark-ignition engine apparatus carrying its own energy as well as a load of 6 kg.

It is in 1907 that the first takeoff in the world of a helicopter would have succeeded, in Normandy with Coquainvilliers, close to Lisieux. This machine of 203 kilos is invented and controlled by Paul Cornu. For the first time, a machine was freed from the ground without dash with a man on board. This dated November 13rd, 1907 is quoted in all the stories of aviation, as being that of the first coasting flight of a helicopter with its pilot. Other significant tests of helicopters carrying a man are carried out the same year, by Louis Breguet and Charles Richet with Douai. It is also the time of the tests of Maurice Leger.

It is the historical rocker between models of small size and machines made to carry their pilot. Then the Danish Jens Christian Ellehammer in 1912, the Argentinian Raoul Pateras Pescara de Castelluccio, marquis de Pescara (1890 - 1966), and the French Etienne Oehmichen starting from 1920, succeed in flying better and better. The marquis Raoul Pateras Pescara in particular, is impassioned by aviation. All its apparatuses are genuine helicopters, to be equipped with two contrarotating coaxial rotors (the Larousse of 1922 illustrates the word helicopter with the photograph of Pescara of 1919 in Barcelona accompanied by the text: " Pescara" system;). To ensure displacements, the pilot has a handle with brush which it can incline in the direction that it wants to follow. He results a cyclic variation from it from the step of each blade to each rotation. Its helicopter 2F buckles the kilometer the January 16th 1924 in 10 minutes 33 seconds strongly shaken by gusts. A stronger gust made than to 850 m, the tail skid touched the ground; it obtained the world records of distance in the helicopter the April 18th 1924

In 1922 the Larousse illustrates the word helicopter by a photograph with the legend: " Pescara" system; and the n° 142 of May 18th, 1922 of Sciences and voyages , in an article of 4 pages of P. James entitled: “Will the Helicopter supplant the plane? ” shows that there is no ambiguity to characterize the various models of apparatuses. It locates in the same category: Pateras-pescara, Crocker-Hewitt, Petrozy and Karman, Douhéret etc and “there can be interest, especially when the helicopter is combined with an airplane, to use separated propellers with axis, solution adopted by Cornu, Bréguet, Lacoin, etc” He informs us on what is a helicopter compared to a plane and its history starts with the toys of Delannoy and Bienvenu, in 1784, Philip in 1842, Coson in 1854, Bright in 1859, Landelle in 1861, etc to enter during the time of the tests of helicopters in real size, it is necessary to be interested into 1906 for the first tests of the Leger (propellers 6,25 m in diameter ordered by an electrical motor which remained on the ground, to see diagram) in the high rooms of the oceanographical Musée of Monaco. It continues the history by photographs of Horned (1906), Lamé, the apparatus of Mr. Oemichen “a kind of helicopter, suspended under an airship”, the apparatus of study built to Douai in 1908 by Bréguet-Richet, the plane-helicopter of Decazes and Besancon of 1910. Pescara 2R comprising 4 photographs of detail and complete of the apparatus in flight in the hangar. In 1924, the Aérophile publishes for Pescara 2F, the following performances: January 16th, 1924, flight of 1160 m, in 8 mn 13 dryness and on January 29th, 1924, flight in closed circuit of 750 m, 10 mn 10 dryness. All the Pescara apparatuses answer the definition of the helicopter. Its aircraft are equipped with two contrarotating coaxial rotors. To ensure displacements, the pilot has a handle with brush which it can incline in the direction that it wants to follow. He results a cyclic variation from it from the step of each blade to each rotation. The rotors produce a dissymmetrical thrust which inclines the apparatus in the selected direction. A lever orders the total variation of the step of the rotors, making it possible the helicopter to vertically go up or go down. This innovation of the orders are found in the current apparatuses under the respective names of collective step and cyclic pitch control. A wheel located on the handle at brush varies differently the warping of the blades of each rotor, which generates a torque allow the turn on the spot. The 4S which evolves/moves in 1931 weighing 400 kg provided with an engine of 40 CV lays out in front of a disengageable propeller. The 4S can thus function in the helicopter or Autogiro.

The reviews of the Aérophile and the AERONAUTICS of the years 1919 to 1931 make it possible to follow appliance testings to revolving aerofoil. The 4S which evolves/moves in 1931 weighing 400 kg provided with an engine of 40 CV lays out in front of a disengageable propeller. The 4S can thus function in the helicopter or in Autogire.La description of the 4S is in AERONAUTICS n° 143 of April 1931. A diagram having its scale shows that the apparatus although lighter has same dimensions as the precedents.

There will be a 3F in 1925 whose power was changed to 280 CV. The Larousse of 1922 put at the honor the “Pescara system” by including the photograph of the apparatus of Barcelona in the definition of the word “helicopter”. Its apparatus, coming from Barcelona, transformed into 2R will be given in state in order to be exposed in 2007 with the Museum of the air and the space of Le Bourget. Standard helicopter PESCARA 2R includes/understands 2 propellers 6,4 m in diameter, with 6 pairs of 0,4 m broad blades, turning in opposite direction on vertical axes. The length of the nacelle is of 5 m and the height is approximately 3,2 Mr. the engine is a the Rhone of 160 ch.

Finally, Etienne Oehmichen covers one kilometer in closed circuit the May 4th 1924 with Arbouans (close to Montbeliard). Its apparatus is the n° 2 which is presented with four lifting propellers, four propellers of evolution, a tractive propeller. An article of 4 pages with photographs “the Helicopter will supplant it the plane” of P. James in the n° 142 of May 18th, 1922 of Sciences and voyages . The apparatus of Oehmichen is described as a kind of helicopter because it could not be classified by the author in the two categories of genuine helicopters. In 1927, an experimental study of the revolving aerofoils by the Engineer of Aeronautics Mr. Lapresle is published. Indeed the Laboratory Eiffel is charged by the Engineering service and Industrialist with Aeronautics during years 1924,1925 and 1926 to study by the test of models of aerofoils of autogiros, gyroptères and helicopters their behaviors. The collection of the tests was published in April 1927. One is reminded that they hear an operation in the relative helicopter that if the aerofoil must ensure it only lift and the translation.

The period 1919 to 1924 thus sees the successes of Etienne Oehmichen and Raul Pateras Pescara. Indeed, in 1924 France, held with this last, on April 18th the record of distance in the genuine helicopter recorded by the international aeronautical Fédération (FAI) and with Oehmichen, those of distance in closed circuit and altitude with a compound. Louis Breguet and Rene Dorand succeeded in making steal during the Thirties a very successful apparatus, “Gyroplane Laboratoire”, which reached 100 km/h and stole more than one hour. However, the helicopter will remain an experimental vehicle until the Années 1940.

Meanwhile, of many pioneers launched out in their turn in the adventure, of which the Germans Heinrich Focke in 1937, Anton Flettner in 1939 and the American of Russian origin Igor Sikorsky in 1939 with its VS-300.

Implementation the operational

Military uses

During the Second world war, the German were interested in this type of apparatuses. They reflect in particular at the point a light helicopter of recognition, the Flettner Fl 282 Kolibri, as well as a helicopter of dual-rotor transport, the Focke-Achgelis F 223 Drache. However, these apparatuses were used very little during the conflict.

The first true operational engagement of helicopters took place during the Guerre of Korea. It was then used primarily to evacuate casualties of difficult to reach positions quickly. It was also the case during the Guerre of Indo-China. During the War of Algeria, it will massively be used by the French army to quickly move small quotas on the spot of the engagements, thus getting an incomparable mobility to them; to also carry out many medical evacuations; some will be armed with gun, machine-guns and even with lance rockets (Sikorsky H-34) and missiles (South-Aviation Lark II).

In the same way, during the War of Vietnam, the the United States will make a systematic employment of it so much so that one will call this war “ the war of the helicopter ”. It is during this war that will be born the concept of combat helicopter with the Bell AH-1 Cobra. From now on, the helicopter is not used only any more for transport: equipped with Machine-gun S, guns, Rockets and Missile S, it brings an appreciable support to the troops on the ground and proves also frightening in the fight anti tank.

In fact, until the middle of the years 1950, the helicopters were propelled by spark-ignition engine (even principle that those equipping the cars) in star or line. It is necessary to await 1955 and the startup of the Alouette II of South-Aviation to see appearing the first production helicopter propelled by a Turbine. Profiting from a great flexibility and a strong power, this type of engine is particularly well adapted to the helicopters.

Civil uses

August 1st One calls civil activities all that is not expressly soldier. They thus include/understand, in addition to the private helicopters and the shipping companies of passengers or air work. Activities known as “parapublic” like the services:

of police force and gendarmerie,
of the SAMU or medical assistance emergency by helicopter,
of fire control (see also Planes bombers of water),
the civil security.

But also, acivities of the civil aviation:

of the transport of passengers on regular lines (like Nice-Monaco),
of transport to the request, and/or VIP (whose baptème of the air),
of transport off - Shore (activity specific good different from transport to the request),
of the lifting and the transport of load,
of agricultural spreading,
deposits of pilot of port (generally on ship for the acostage of the latter to the port),
of the school (to train pilots private and professional),
of the technical flights (survey land, electric statement (the apparatus must be then especially equipped for these statements),
of the flights of catches of sights (photographs, vidéos…).

Technical sides of construction

There exist several formulas of construction of helicopters. The first to patent a project which used it was the German Heinrich Focke is composed of two essential parts:

the principal Rotor, whose axis is vertical, ensures lift (the Portance coming from the number of revolutions and the incidence of the Pale S), the level flight in all the directions: vertical, longitudinal (front, back) and side. It also ensures the control of attitude in Tangage and Roulis of the helicopter
the Rotor of tail or anti-torque Rotor, usually called RAC by the pilots of helicopter, whose axis is appreciably horizontal. It prevents the helicopter from turning on him even when the principal rotor turns and makes it possible to ensure control in lace.

Here some other formulas of construction of helicopters:

with two rotors of lift out of tandem (one behind the other, their principal promoter was the American Frank Piasecki. This system in which the rotors turn in opposite direction makes it possible to cancel the counter torque of the rotor on the cell
with two coaxial rotors of lift (turning around the same axis) like the apparatuses of the Russian manufacturer Kamov
with rotors of lift known as " gearing " , whose rotation is synchronized so that their blades cross without being touched during rotation, as the machines of the German manufacturer Anton Flettner taken again by the American Kaman realizer of the K-max which from their design also make the saving in a anti-torque Rotor.

Principle of operation

The blades of the principal rotor are generally pulled by the engine by means of a gear-box, called by its accronyme BTP (Limps of Principal Transmission). This gear-box, paramount element of the helicopter, allows the transmission of the engine output towards the principal rotor, like worms the RAC. It is generally made up of several gears making it possible to reduce the number of revolutions of exit engine (several thousands of turns per minute for the turbine engines) and to transmit the power to the principal rotor (generally in the neighborhoods of 400 rpm). The BTP also comprises one or more free wheels, for désolidarider the rotor of the engine in the event of breakdown and to allow autorotation. However one also tried to use the force of reaction of exhaust fumes in end of the blades as on the Djinn.

They have an asymmetrical or symmetrical profile and act as rotation according to the same principle as the wing S of a Avion. Rotor turning always with velocity angular constant, it is variation of angle of Incidence of blades (angle formed between the cord of the blade and the relative Vent) which causes a modification of the behavior of the rotor, and consequently of the position of the Aéronef. To go up for example, it is necessary that the rotor has a movement to pull up. One thus modifies the Incidence of the blade so that the bearing pressure of this one is maximum in the passing in front of the apparatus, and minimal to the back of the apparatus. The incidence of the blade thus varies in a sinusoidal way by carrying out a turn rotor. This variation of incidence is obviously realizable in any direction. It is controlled by the pilot using the cyclic pitch stick (the equivalent of the " handle with balai" on plane. The other manner of controlling the incidence of the blades is carried out by means of pitch the general control (also called not collective ) held by the left hand of the pilot. This variation of incidence is identical on each one of the blades (general modification of the incidence - called or the Pas - blades) and makes it possible to control the general bearing pressure generated by the rotor.

The rotor of tail

Any rotation of the principal Rotor involves a counter torque which tends to make turn the cell around him and opposite direction (3 {{E}} law of Newton). To counter this undesirable effect, one places (for the helicopters with only one principal rotor), at the end of the beam of tail a secondary rotor smaller and turning in an appreciably vertical plan called anti-torque Rotor . The counter torque varying according to the incidence of the blades of the principal rotor (the wind resistance is all the more large as the angle which form this one with the blade chord increases), the force to be applied must it also be able to be regulated via the anti-torque rotor which is ordered by two pedals (the Palonnier ) located at the feet of the pilot. According to the direction in which the pilot operates the swing bar (depression of the left pedal or the right pedal) it increases the incidence blades of the RAC, which more will counter the couple of the principal rotor (“to draw” the tail), or it decreases this incidence and which will cause to let “spin” this one. The movement of Giration in Hovering is ordered using the swing bar. According to whether the principal rotor turns clockwise as on the helicopters of French design or in anti-clockwise direction (helicopters of American design or allemande before fusion with Aérospatiale to create Eurocopter), the anti-torque rotor will be located on a side or other of the beam of tail or its breath will be directed in a direction or the other, if it is embedded in a Fenestron .

The conventional anti-torque rotor can be replaced for questions of security by the system NOTAR (for NO TAil Rotor ) which carries out the same action through a Turbine pulled by the blowing driving of the air in the tail ejected by slits (McDonnell Douglas MD-520N). This solution has nevertheless the disadvantage of not reaching the effectiveness of a more traditional RAC of design. Another solution, in order to avoid the use of an anti-torque rotor, consists in placing a second principal rotor at the revolving rear contrary to the first and which against the couple of this one (Boeing CH-47 Chinook). A third possibility consists in using two rotors one above the other and also turning in opposite direction, called rotor countered rotary, each one cancelling the counter torque of the other (Kamov Ka-50) or two rotor contrarotating gearing located side-by-side on masts rotor in " V" as on the Flettner Fl 282 Kolibri or the K-max of Kaman.

To move the helicopter in a direction or another, one slightly rocks the component of bearing pressure of the principal rotor in the desired direction. The force of Lift, perpendicular to the plan formed by the rotor in rotation seen on side and before vertical, thus will be tilted and “will draw” the helicopter in the desired direction. This is obtained by increasing in a selective way the incidence of the blades: that which will have a larger incidence will have also a more important Portance and will tend to be raised compared to the others, causing by there the rotor tilt. For a given blade, during its rotation, its incidence thus will vary from an angle given at the beginning to increase then to return to this same value when the blade finishes a full rotation. Since with each turn the blades will know a modification of their incidence in a recurring way, one names these changes of state the cyclic variation and for this reason the order which causes these modifications is called cyclic pitch control and held by the right hand of the pilot (see cyclic Plateau). In complement, the force of lift thus inclined guard the same value and sees its vertical component, being used indeed for lift of the aircraft, to decrease what causes a depression of this one. This is compensated by slightly increasing the general incidence of the blades (left hand), action which will require also a correction of the level of the Palonnier.

The blades are moreover animated of two types of movements during a complete rotation of the rotor: the Beat (" flapping" in English in the vertical direction) and the Trailed ( lead/lag in English) in the horizontal direction. They are angular displacements of the current part of the blade compared to the foot of blade which is fixed at the level of the hub rotor. These movements must with the aerodynamic loads being exerted during the flight of advance: the dissymmetry of lift is the difference in bearing pressure which exists between the advancing half of the disc rotor and the moving back half. It comes owing to the fact that in the direction of the flight, the relative wind is added to the rotatory relative wind of the advancing blade and withdraws folding blade. The blade which passes the tail and which advances right-sided of the helicopter has a speed air which reaches its maximum on position 3 of the clock. When the blade continues, speed air is primarily reduced at the rotatory speed of the air on the nose of the apparatus. By leaving the nose, speed air decrease gradually to reach its minimum at 9 a.m. Speed air then increases gradually and again reaches rotatory speed while passing on the tail. (see photographs of the Shock absorber between the blades in the cyclic article Plate). To avoid a rupture of the blade at the points requested in inflection, this one is equipped with special articulations and obstinate or shock absorbers. The modern composite material blades are freed from these articulations. The first helicopter without articulations was the Bo 105 of Ludwig Bölkow.

It is useful to specify that it is possible to identify the origin of the helicopters in vol. Vu of top, the rotor of a helicopter of design French or Russian (as Soviet) turns in the direction of the needles of a watch (or schedule), while a helicopter built in Italy, to the United Kingdom, in Germany or to the United States turns in the contrary direction of the needles of a watch.

Principle of the flight of the helicopter

Physical aspects

As for the plane, the relative speed of the air and the aerofoil generates a mechanical action which makes it possible the machine to fly. One distinguishes two components from this aerodynamic action:

the Trailed which is resistance to advance. From its action on the rotor of the helicopter, it results a couple tending to make turn the apparatus around its axis, from where need for an anti-torque device.
the Bearing pressure which raises the apparatus.

: Animation

The control of an apparatus rests then on the management of this bearing pressure. Whereas on the planes, of the shutters allow to modify the bearing pressure of the wings to transfer to go up… on the helicopter, as on the wind S, the step and the slope of the blades are modified. However, there exists a difference. So on the plane one acts individually on each Gouverne, on the helicopter one controls the bearing pressure of a blade according to his position compared to the apparatus. It is the role of the cyclic Plateau, part principal of the control device of vol.

Hovering.

The rotor of the helicopter being involved at constant speed, vertical displacements of the helicopter are obtained by the only modification of the step of the blades. At this stage of the flight, the bearing pressure of the blades remains identical on a lathe of the rotor. There exists a position where the total bearing pressure is opposed exactly to the weight of the apparatus: the helicopter can remain motionless. If it is lower to him, the apparatus goes down. If it is higher, it goes up.

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