Girl

There are many other stories with girls as protagonists in the Shōjo style of manga, which is targeted to girls as an audience. For this reason, good pilotage demands operation within safe flight regimes and avoiding hazardous conditions. Most of the animated films of Hayao Miyazaki feature a young girl as the hero, as in Majo no takkyūbin (Kiki's Delivery Service). Each of these conditions is potentially fatal and recovery might not be possible. In Japanese manga and anime, girls are often protagonists. The following is a list of some of the potential hazards:. Franco-Belgian comics with girls in a central role include Isabelle (by Will) and Sophie (by Jidéhem). For helicopters the hazards are particularly acute since they are flying at relatively low altitude, with little time to react to a sudden event.

The most famous Flemish comic strip is Spike and Suzy (Suske and Wiske), about the adventures of a boy and a girl (each about 10 years old); it was translated from Flemish into French and English. As with any moving vehicle, operation outside of safe regimes could result in loss of control, structural damage, or fatality. In the Peanuts series (by Charles Schulz), girl characters include Peppermint Patty, Lucy van Pelt, and Sally Brown. The whirling rotor blades of a helicopter can cause large charges to build up on the airframe, large enough to cause injury to shipboard personnel should they touch any part of the helicopter as it approaches the deck. In superhero comic books, an early girl character was Etta Candy, one of Wonder Woman's sidekicks. A secondary purpose of the haul-down device is to equalize electrostatic potential between the helicopter and ship. There have been many American comic books and comic strips featuring a girl as the main character, such as Little Lulu, Little Orphan Annie, Girl Genius, and Amelia Rules. Navy implementation of this device, based on Beartrap, is called the "RAST" system (for Recovery Assist, Secure and Traverse) and is an integral part of the LAMPS MK III (SH-60B) weapons system.

Books which have both boy and girl protagonists tend to focus on the boys, but important girl characters appear in Knight's Castle, The Lion, the Witch and the Wardrobe, The Book of Three, and the Harry Potter series (by Book 6, Harry Potter's social circle includes 1 boy and 2 girls, although newcomer Ginny still isn't let into secrets like Ron and Hermione are). The U.S. Children's books about girls include Little House on the Prairie, Eloise, Pippi Longstocking, Dragonsong, and A Wrinkle in Time. This device was pioneered by the Royal Canadian Navy and was called "Beartrap". European fairy tales include some memorable stories about girls, including Goldilocks and the Three Bears; Hans Christian Andersen's The Little Match Girl, The Little Mermaid, and The Princess and the Pea; the Brothers Grimm's Little Red Riding Hood; and others. Tension is maintained on the cable as the helicopter descends, assisting the pilot with accurate positioning of the aircraft on the deck; once on deck locking beams close on the probe, locking the aircraft to the flight deck. Most early children's stories focused on boys, with the notable exception of Alice's Adventures in Wonderland, by Lewis Carroll, whose photographs of little girls are part of the history of photographic art.
. Shipboard landing for some helicopters is assisted though use of a haul-down device that involves attachment of a cable to a probe on the bottom of the aircraft prior to landing.

Other novels include Harper Lee's To Kill a Mockingbird, which has a young girl as protagonist; and Vladimir Nabokov's Lolita, about a girl subjected to sexual abuse. In the Royal Navy, landing on is usually achieved by lining up slightly astern and on the port quarter, as the ship steams into the wind and the aircraft captain slides across and over the deck. Examples include Jane Eyre, who suffers ill treatment; and Natasha in War and Peace, who is sentimentalized. Navy it is commonly and properly referred to as the flight deck. Many novels begin with the childhood of their heroine. In the U.S. As in art, portrayals of girls in literature can reflect the social norms of the time at which they were written. A helicopter deck (or helo deck) is a helicopter pad on the deck of a ship, usually located on the stern and always clear of obstacles that would prove hazardous to a helicopter landing.

Only Sappho's poetry includes love poems addressed to girls. Some also use mechanical feedback systems to sense and counter vibration. Ancient Greek classical art and literature paid scant attention to female children, though there are many poems about boys. Most also have vibration dampers for height and pitch. Egyptian murals included sympathetic portraits of young girls of royal descent. To reduce vibration, all helicopters have rotor adjustments for height and pitch. Portrayals of girls may reflect their standing in the artists' culture, and a brief overview of different views of girls in different art periods gives a sense of girls' roles in societies around the world and at different points in time. An unadjusted helicopter can easily vibrate so much that it will shake itself apart.

The slang word "gal", as in "Buffalo gals won't you come out tonight", is a variant pronunciation of girl. Helicopters vibrate. The word girl has many synonyms, including "belle", "chick", "doll", "gal", "lass" or "lassie", "maiden", and "miss". 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. While outsiders might use "girl" or "girly" as a pejorative to refer to a gay male, within the gay community it is used as a term of endearment. Urban communities have often expressed great dislike of noisy aircraft, and police and passenger helicopters can be unpopular. Calling a male a girl often serves as a provocation to fight (see fighting words). During the closing years of the 20th century designers began working on helicopter noise reduction.

The more insulting "girly-boy", which originated in 1589 as "girle-boy", is used to indicate a weak or "sissy" male. There are several reasons why a helicopter cannot fly as fast as a fixed wing aircraft. Using the word "girl" to refer to a male is usually meant as insulting, such as "You throw like a girl". The current record is around 400 km/h set by the Westland Lynx. The term "young woman" is sometimes used in the period between childhood and full adulthood. The single most obvious limitation of the helicopter is its slow speed. In modern usage, "girl" is properly restricted to mean a human female who has not reached adulthood, and some would restrict the usage to prepubescent girls. While fixed-wing aircraft are generally designed so pilots sit on the left side of the aircraft, freeing up their right hand for dealing with radios, engine controls, and the like, helicopters are generally designed so pilots sit on the right side of the aircraft so they can keep their right hand (usually the strong hand) on the cyclic at all times, leaving the radios and engine controls for their left hand (usually the weaker hand).

There is a parallel objection to use of the word "boy" to describe a male over the age of puberty. Small helicopters can be so unstable that it may be impossible for the pilot to ever let go of the cyclic while in flight. With the rise of feminism, the use of "girl" applied to any adult female became offensive to many, especially given the fact that the word was so often used to indicate low social status, low morals, weakness, or homosexuality. Changing collective will also cause a change in torque, which will require the pilot to adjust the foot pedals. But social shifts generally permit only the female gender group themselves to use such terminology without giving offence. Increasing collective will reduce rotor RPM, requiring an increase in throttle to maintain constant rotor RPM. Adult women will sometimes refer to themselves as "girls", as in "We're having a girls' night out" or "It's a girl thing". Moving the cyclic forward causes the helicopter to move forward, but will also cause a reduction in lift, which will require extra collective for more lift.

A woman of a certain age might be called a girl to suggest that she looked younger than she was, or a group of women might speak of themselves as "us girls", though all were well over the age of maidenhood. Adjusting one flight control on a helicopter almost always has an effect that requires an adjustment of the other controls. In America today, the word "girl" is often used as an intended compliment or used humorously. Hovering a helicopter has been compared to balancing yourself while standing on a large beach ball. In England, the word "girl" was also used as a euphemism for "prostitute", as for example by Richard Steele in The Spectator. When a hovering helicopter is nudged in one direction by a gust of wind, it will tend to continue in that direction, and the pilot must adjust the cyclic to correct the motion. In England, a "girl" was often a serving girl, while in America a "girl" was often a sweetheart or "girlfriend", for example, in the lyrics of the popular song "The Girl I Left Behind Me". Simply hovering requires continuous, active corrections from the pilot.

By the 1700s, there was a difference in some uses of the word between England and the Americas. In contrast, helicopters are very unstable. Note the parallel shift in the meaning of the word "maid". Many small, fixed wing aircraft are stable enough that a pilot can let go of the controls while looking at a map or dealing with a radio, and the plane will generally stay on course. In 1668, in his Diary, Samuel Pepys uses the word to mean a female servant of any age: "girl" = "serving girl". If a gust of wind or a nudge to one of the controls causes a fixed wing aircraft to pitch, roll, or yaw, the aerodynamic design of the aircraft will tend to correct the motion, and the aircraft will return to its original attitude. Within little more than a century, however, the word began to take on implications of social class. Fixed wing aircraft are usually inherently stable.

There are manuscripts dating from 1530 in which the word "girl" is used to mean "maiden" (also originally applied to both genders), or any unmarried human female. It took inventors many years to recognize precession, and to learn how to arrange the cyclic's control system to overcome it. Like many other words that originally were not gender specific, "girl" gradually came to be used primarily and then exclusively for one gender. The helicopter's control linkages rotate the pitching forces 90 degrees backwards against the rotor spin, to push on the sides of the rotor rather than its front and back. A male child was called a "Knave girl"; a female child was called a "gay girl". For example, forward motion requires less lift at the front of the disk and more lift at the rear of the disk, so the pilot pushes the cyclic forward. While there is no general agreement about the etymology of "girl", it is found in manuscripts dating from 1290 with the meaning "a child" (of either gender). So control forces on the rotor are rotated 90 degrees before the desired motion.

The Anglo-Saxon word gyrela = "ornament" may have given rise to the modern pronunciation of "girl", if the change in meaning can be explained. This is called "gyroscopic precession". The word "girl" first appears during the Middle Ages. This is because when one tries to tilt a spinning object (like a rotor), it moves at right angles to the direction of the force. Relatively few girls become engineers, though in the USA, more do become doctors. A very peculiar feature of the cyclic is that the lift is made to occur 90 degrees of rotation before the direction of tilt. However, their choices afterwards in postsecondary school are often very different and lead them to less socially recognized professions. (see Height-velocity diagram).

Several studies, such as the Programme for International Student Assessment of the OECD, have shown that, in developed countries, girls usually obtain better scores than boys do in secondary schools in Literature and Language, boys on the other hand tend to score higher in mathematics. Autorotation can allow a pilot to make an emergency landing if the engine failure occurs while the helicopter is traveling high enough or fast enough. This conflict is often called nature versus nurture. A transmission connects the main rotor to the tail rotor so that all flight controls are available after engine failure. Some feminists deny this, but many feminists agree that both biology and upbringing have an influence on gender roles, with the question being the relative importance of each. This technique is known as autorotation. The biological viewpoint of gender roles is not that all gender distinctions result from biology, but rather that biology has an influence. The main rotor acts like a "windmill" and turns.

Due to the influence of (among others) Simone de Beauvoir's feminist works and Michel Foucault's reflections on sexuality, the idea that gender was unrelated to sex gained ground during the 1980s, especially in sociology and cultural anthropology. Helicopters are powered aircraft, but they can still fly without power by using the momentum in the rotors and using downward motion to force air through the rotors. On the other hand, feminists have argued that gender roles are the result of stereotypes and socialization rather than any innate biological differences. On a helicopter, this can happen in any of three ways. Simon Baron-Cohen, a Cambridge University professor of psychology and psychiatry, argues that "the female brain is predominantly hard-wired for empathy, while the male brain is predominantly hard-wired for understanding and building systems.". This condition is called aerodynamic stall. For example, the need to take care of offspring may have limited the females' freedom to hunt and to assume positions of power. If the angle of attack of any wing, including rotor blades, is too high, the airflow above the wing separates causing instant loss of lift and increase in drag.

The idea that differences in gender roles originate in differences in biology originates from 19th-century anthropology; more recently, sociobiology and evolutionary psychology have turned to this problem to explain those differences by treating them as evolutionary adaptations to a lifestyle of Paleolithic hunter-gatherer societies. And the angle of attack is decreased on the advancing blade to produce less lift, compensating for the faster airspeed over the blade. The reasons for this perceived difference in the behavior of girls and boys are a controversial topic in both public debate and the sciences. The angle of attack is increased on the retreating blade to produce more lift, compensating for the slower airspeed over the blade. Girls, as a group, may be perceived as being more docile than boys, and as being less capable of rational decision making and more governed by emotional responses. To compensate for the added lift on the advancing blade and the decreased lift on the retreating blade, the angle of attack of the blades is regulated as the blade spins around the helicopter. Sometimes boys are presumed to be more responsible than girls, except in the cases of caring for younger children, which is sometimes thought to be instinctual in girls. As the blade swings to the other side of the helicopter, it moves at rotor tip speed minus aircraft speed and is called the retreating blade.

Girls are less often encouraged to pursue sports, with the exception of those that might be considered "feminine," such as figure skating or gymnastics; or those considered "gender-neutral," such as tennis.^[1] They may be prevented from participating in many of the same activities that boys participate in at the same age, as a matter of protecting them from perceived outside dangers, such as boys and men, or anything that may cause physical injury. As a helicopter moves forward, the rotor blades on one side move at rotor tip speed plus the aircraft speed and is called the advancing blade. Girls have traditionally been associated with playing with dolls and toy cooking and cleaning equipment, while boys have been associated with toys and games that require more physical activity or simulated violence, such as toy trucks, balls, and toy guns. If the pilot pushes the cyclic forward, then the helicopter tilts forward, and the rotor produces a thrust in the forward direction. In almost all cultures, girls have been socialized into gender roles. This causes the helicopter to tilt in the same direction as the cyclic. This disparity is targeted to end under the Millennium Development Goals and has closed substantially since 1990.^ . When it is tilted, the links give a pitch-up at some azimuthal angle and a pitch-down at the opposite angle, hence creating a sinusoidal variation in blade angle of attack.

65%). When the swashplate is not tilted, the blades are all at the collective angle. 74% for boys) or secondary education (59% vs. The rotating section rotates with the rotor and is connected to blade pitch horns through pitch links, one link for each blade. Although the International Covenant on Economic, Social and Cultural Rights specifies that "primary education shall be compulsory and available free to all", girls are slightly less likely to be enrolled as students in primary (70% enrollment vs. The cyclic controls the angle of the stationary section of the swashplate, which in turn controls the angle of the rotating section of the swashplate. From birth, girls are a slight minority due to both natural factors (the human sex ratio has been observed since the 1700s as approximately 1,050 boys for every 1,000 girls) and due to sex selection on the part of parents. The cyclic is similar to a joystick and is usually positioned in front of the pilot.

UNICEF, 2004) aged 18 or under in the world, for a total of more than one billion living girls. This variation in lift causes the rotor disk to tilt, and the helicopter to move during hover flight or change attitude in forward flight. There are 2.18 billion people (est. The cyclic changes the pitch of the blades cyclically, causing the lift to vary across the plane of the rotor disk. . Turbine engined helicopters, and some piston helicopters, use servo-feedback loop in their engine controls to maintain rotor RPM and relieves the pilot of routine responsibility for that task. Images of girls in art, literature, and popular culture often demonstrate assumptions about gender roles. The pilot manipulates the throttle to maintain rotor RPM and therefore regulates the effect of drag on the rotor system.

An ongoing debate about the influences of nature versus nurture in shaping the behavior of girls and boys raises questions about whether the roles played by girls are the result of inborn differences or socialization. In many piston-powered helicopters, the pilot must manage the engine and rotor RPM. Historically, girls faced discrimination and limitations on the roles they were expected to play in their societies, and the United Nations targeted discrimination in schooling to end by 2010. In general, RPM must be maintained within a tight tolerance, usually a few percent. Usage in the sense of (romantic) "sweetheart" arose in the 17th century. If the RPM is too high, damage to the main rotor hub from excessive forces could result. Subsequently, it was extended to refer also to mature but unmarried young women since the 1530s. If the RPM is too low, rapid descent with power, known as settling with power could result.

During the 14th century its sense was narrowed to specifically female children. Helicopter rotors are designed to operate at a specific RPM. The English word from 1290 designated a child of either sex. RPM control is critical to proper operation for several reasons. The age at which a female person transitions from girl to woman varies in different societies, typically the transition from adolescence to maturity is taken to occur in the late teens. The throttle control is a twist grip on the collective control. A girl is a young female human, as opposed to a boy, a young male human. The throttle controls the absolute power produced by the engine that is connected to the rotor by a transmission.

Simultaneously increasing the collective and adding power with the throttle causes a helicopter to rise. The collective control is usually a lever at the pilot's left side, near his leg. When the angle of attack is increased, the blade produces more lift. The collective pitch control lever controls the collective pitch, or angle of attack, of the helicopter blades altogether, that is, equally throughout the 360 degree plane-of-rotation of the main rotor system.

Helicopters maneuver with three flight controls besides the pedals. More lift at the rear of the rotary wing will cause the aircraft to pitch forward, an increase on the left will cause a roll to the right and so on. For pitch (tilting forward and back) or roll (tilting sideways) the angle of attack of the main rotor blades is altered or cycled during the rotation creating a differential of lift at different points of the rotary wing. Yaw controls are usually operated with anti-torque pedals, on the floor in the same place as a fixed-wing aircraft's rudder pedals.

Dual-rotor helicopters have a differential between the two rotor transmissions that can be adjusted by an electric or hydraulic motor to transmit differential torque and thus turn the helicopter. Varying the pitch of the tail rotor alters the sideways thrust produced. For rotation about the vertical axis (yaw) the anti-torque system is used. In a helicopter, however, there often isn't enough airspeed for this method to be practical.

In a fixed-wing aircraft, this is easy: small movable surfaces are adjusted to change the aircraft's shape so that the air rushing past pushes it in the desired direction. Useful flight requires that an aircraft be controlled in all three dimensions (see flight dynamics). Although this method is simple and eliminates precession, development of such helicopters ceased soon, because their extreme noise levels preclude both military and civilian use. The most unusual design is the roto-rocket principle, where the single main rotor draws power not from the shaft, but from its own wingtip jet nozzles, which are either pressurized from a fuselage-mounted gas turbine or have their own pulsejet combustion chambers.

The NOTAR system was developed in the United States and is used exclusively by McDonnel Douglas Helicopters, or MD Helicopters. The NOTAR eliminates the tail rotor by conducting high-velocity air through the tail boom. A recent development in helicopter technology is the NOTAR system, which stands for NO TAil Rotor. V-22 Osprey tilting rotorcraft is similar, although its nacelles can be rotated, and shares some of the inherent technical problems of a cross system.

The U.S. The world's largest ever helicopter, the Soviet Mil-V-12 prototype, was a cross of two Mil Mi-6 turbine-rotor units built onto a modified Antonov cargo plane. The 1930s German FW-61 helicopter was built to such design. Such helicopters are rare, because structural integrity of the wings is difficult to maintain against the amplified resonance of far off-board rotor-turbine units.

In the cross system, the rotary wing aircraft resembles a traditional fixed-wing airplane, with the two main rotors mounted at the extremities of its wings. These were placed at the corners of an equilateral triangle and all turned the same direction. A helicopter built by Juan de la Cierva had three main rotors. The main drawback of a waggon is limited agility in air and the need for a highly trained crew, as the large main rotors have long outreach beyond the fuselage and may easily hit nearby obstacles (in 2001, a South Korean army CH-47 Chinook crashed onto a bridge for that reason while being shown live on TV).

The rotors and turbines are located very high on top of the fuselage, making them less sensitive to damage and dirt. Waggon helicopters are practical for military logistical purposes, because entry and unloading is easily facilitated via the unobstructed front and rear ramps. A prime example is the Boeing CH-47 Chinook, that can carry 14 tons of payload. examples), the two main rotors are located at the front and rear extremity of a long, boxy fuselage that resembles a railway wagon.

In the flying-waggon or tandem rotor system (sometimes called "flying banana" for the peculiar shape of early U.S. Kamans have high stability and powerful lifting capability, thus the latest Kaman V-Max model is a dedicated sky crane design, used for construction works. During the Cold War the American Kaman company started to produce similar helicopters for USAF firefighting purposes. The contra-rotating rotors are located on top of the fuselage, close to each other.

The Kaman system of intermeshing rotors, which was developed in Nazi Germany for a small anti-submarine warfare helicopter, features two main rotors on separate, obliquely mounted axles. Another example is the Kamov Ka-26, a successful crop duster aircraft. Co-axial helicopters in flight are highly resistant to side-winds, which makes them suitable for shipboard use, even without a rope-pulley landing system. The co-axial design, where rotors are mounted on top of each other at the top of the fuselage and share a common main axle complex, was first built by Theodore von Karman and Asbóth Oszkár in 1918 and later became the hallmark of soviet Kamov design bureau (see for example the Kamov Ka-50 "Hokum").

These methods introduce even more mechanical complexity to the design and are usually relegated to specialized helicopter types. All of these systems are designed for the same purpose: the torques from each rotor have opposite signs, so the net effect on the vehicle is negligable. Such designs use two rotors which turn in opposite directions, or contra-rotate. There are alternatives to Sikorsky's layout, which save the weight of a tail boom and rotor.

In extreme cases, such as that of the Mil Mi-24, the wings are large enough to obstruct airflow down from the rotors, making the helicopter all but unable to hover. They are also used as external mounts for weapons. Many military helicopters, especially attack types, have short wings called stub wings to add lift during forward motion. Another reason for the angled vertical stabilizer is to make it possible to stage a successful high-speed, run-on landing, in case of the tail rotor failure or damage.

This is commonly known as slip-streaming and can make hovering turns difficult on windy days. At high speeds, it is possible for the vertical stabilizer to counteract the entire torque, leaving more power available for forward flight. To reduce this waste during cruise, the vertical stabilizer is often angled to produce a force which helps counter the main rotor torque. A tail rotor typically uses about 5 to 6% of the engine's power, and this power does not help the helicopter produce lift or forward motion.

The amount of power required to prevent a helicopter from spinning is significant. Notars adjust thrust by opening and closing a sliding circular cover near the end of the tail boom. Other helicopters use a NOTAR (an acronym meaning no tail rotor) design: they blow air through a long slot along the tail boom, utilizing the Coanda effect to produce forces to counter the torque. It is less efficient but the advantages are that less noise is generated, it's safer for people that may walk near it and there is less chance of the blades being damaged by objects because it's shrouded, unlike the traditional tail rotor.

The fenestron rotor system on the model EC120 helicopter uses a shaft driven system and gearbox to turn the fan. If the tail rotor is shrouded (i.e., a fan embedded in the vertical tail) it is called a fenestron. AH-64 Apache).
Sometimes the blades of a tail rotor are not separated by the same angle, but laid out in an X-shape, which is supposed to reduce the noise levels for military use (e.g.

The world's fastest helicopter, the Westland Lynx can perform aerobatic loops and rolls with this conventional rotor system. Almost all civilian helicopters have the main rotor and tail rotor system. The Mil Mi-26 can lift 27 metric tons, the Robinson R22 has a crew of two and a gross weight of 1300 lbs (590 kg). The world's largest and smallest series-produced helicopters follow this principle.

When the thrust from the tail rotor is sufficient to cancel out the torque from the main rotor, the helicopter will not rotate around the main rotor shaft. This rotor creates thrust which is in the opposite direction from the torque generated by the main rotor. At low speeds, the most common way to counteract this torque is to have a smaller vertical propeller mounted at the rear of the aircraft called a tail rotor. It is as follows: turning the rotor generates lift but it also applies a reverse torque to the vehicle, which would spin the helicopter fuselage in the opposite direction to the rotor.

The most common design is the Sikorsky-layout, which is used by approximately 95% of all helicopters manufactured to date. There are several possible design layouts for arranging a helicopter's rotors. The helicopter's rotor can simply be regarded as rotating wings, from where the military appellation of "rotary wing aircraft" originates. A helicopter makes use of the same principle, except that instead of moving the entire aircraft, only the wings themselves are moved in a circular motion.

However, the more the lift of the airfoil, the more drag that is caused. This pressure difference integrated over the airfoil area causes a net lift. Thus, by causing the air to flow faster over the top surface than the bottom, the airfoil causes a pressure difference directed upward. The higher the speed of a fluid, the lower the dynamic pressure (as opposed to static pressure) on the surface.

The longer path that the fluid (in this case air) must travel across the top surface equates to a higher speed. In conventional aircraft, the wing profile (called airfoil) is designed to have a shape where the bottom surface has a shorter path than the top surface. Turboshaft engines are the preferred powerplant for all but the smallest and least expensive helicopters today. 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.

Improvements in fuels and engines during the first half of the 20th century were a critical factor in helicopter development. Igor Sikorsky is reported to have delayed his own helicopter research until suitable engines were commercially available. This is largely due to higher engine power density requirements when compared with fixed wing aircraft.
Reliable helicopters capable of stable hover flight were developed decades after fixed wing aircraft.

The Bell 47 designed by Arthur Young became the first helicopter to be licensed (in March 1946) for certified civilian use in the United States and two decades later the Bell 206 became the most succesful commercial helicopter ever built with more hours and set (and broken) more industry records than any other aircraft in the world. Mass production of the military version of the Sikorsky XR-4 began in May 1942 for the United States Army. Models such the Flettner FL 282 Kolibri were use in the Mediterranean Sea. Nazi Germany used the helicopter in combat during WWII in little numbers.

The German Focke-Wulf Fw 61 first flew with limited control achieving vertical and forward flight in 1934. A flight of the first fully controllable helicopter was demonstrated by Raúl Pateras de Pescara 1916 in Buenos Aires, Argentina. Developers such as Jan Bahyl, Oszkár Asbóth, Louis Breguet, Paul Cornu, Emile Berliner, Ogneslav Kostovic Stepanovic and Igor Sikorsky pioneered this type of aircraft, with Juan de la Cierva introducing the first practical autogiro in 1923 that was to be the basis for the modern helicopter. The first somewhat practical idea of a human carrying helicopter was first conceived by Leonardo da Vinci around 1490, but it was not until after the invention of the powered aeroplane in the 20th century that actual models were produced.

"Pao Phu Tau" was a 4th century book in China that described some of the ideas in a rotary wing aircraft. This toy eventually made its way to Europe via trade and has been depicted in a 1463 European painting. Since around 400 BC the Chinese had a flying top that was used as a children's toy. Speed and range limitations also constrain commercial applications.

For these reasons, helicopters are not economically viable for commercial transportation. The costs are due to inherent mechanical complexity and greater power requirements for a given gross weight. Helicopters suffer from significantly higher operating and maintenance costs compared with fixed wing aircraft. Unmanned helicopters are used in industrial and military applications in areas deemed dangerous for manned flight.

Helicopters have many uses, both military and civil, including troop transportation, infantry support, firefighting, shipboard operations, business transportation, casualty evacuation (including MEDEVAC, and air/sea/mountain rescue), police and civilian surveillance, carrying goods (some helicopters can carry slung loads, accommodating awkwardly shaped items), or as a mount for still, film or television cameras. . However these other configurations have considerably more cruise speed than a helicopter (270 km/h for a helicopter, 460 km/h for a tiltrotor, 900+ km/h for a vectored thrust airplane), giving each their place in the operational spectrum. Compared to other vertical lift aircraft like Tiltrotors (V-22 Osprey for example) and Vectored Thrust airplanes (AV-8 Harrier for example), helicopters are very efficient, carrying more than twice the payload, consuming less fuel in hover and costing considerably less to buy and operate.

Subject only to refuelling facilities and load/altitude limitations, a helicopter can travel to any location, and land anywhere with enough space (a diameter of length 1.5 times the rotor disk). The compensating advantage is maneuverability: helicopters can hover in place, reverse, and above all take off and land vertically. Compared to conventional fixed-wing aircraft, helicopters are much more complex, more expensive to buy and operate, relatively slow, have shorter range and restricted payload. The first stable, single-rotor, fully-controllable helicopter to enter large full-scale production was made by Igor Sikorsky in 1942.

The engine-driven helicopter was invented by the Slovak inventor Jan Bahyl. The word helicopter is derived from the Greek words helix (spiral) and pteron (wing). Helicopters are classified as rotary-wing aircraft to distinguish them from conventional fixed-wing aircraft. A helicopter is an aircraft which is lifted and propelled by one or more horizontal rotors (propellers).

Vortex ring state, a problem the V-22 Osprey was associated with. Operating within the shaded area of the height-velocity diagram. Low-G condition. Ground resonance.

Settling with power. Retreating blade stall. If this ring is augmented by terrain, wind, rain, or sea spray, the helicopter can lose enough lift to experience settling with power and hit the ground. In these, the downward wind from the rotor causes a circular vortex to form around the rotor.

Helicopters are susceptible to potentially disastrous vortex ring effects. Low or negative-G situations encountered in a semi-rigid system will result in blade flapping down until it hits the tail boom or other airframe structure, followed by rotor separation, causing a crash. Rotorhead design is a limiting factor on many helicopters. The adjustment is either by adjusting the angle of attack of the blades, or by engine-powered vacuum devices that suck air into the blades, adjusting the lift.

In most such designs, the lift is varied cyclically and according to the speed of the helicopter. Fully rigid rotors exist and create very responsive helicopters. The blades are made from composites which can bend without breaking. In some designs the hub is rigid.

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. Conversely, the retreating blade flaps down, develops a higher angle of attack, and generates more lift. In consequence, 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, thus producing less lift than a rigid blade would. Because the advancing blade has higher airspeed than the retreating blade, a perfectly rigid blade would generate more lift on that side and tip the aircraft over.

Most rotors are not rigid. It is theoretically possible to have spiralling rotors, similar in principle to variable-pitch swept wings, which could exceed the speed of sound, but no presently known materials are light enough, strong enough, and flexible enough to construct them. It is possible for this blade to exceed the speed of sound, and thus produce vastly increased drag and vibration. The airspeed of the forward-going rotor blade is much higher than that of the helicopter itself.

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. When the helicopter is at rest, the outer tips of the rotor travel at a speed determined by the length of the blade and the RPM. Unique to helicopters is vertical ring vortex which is when a helicopter in a hover or decent comes into contact with its own down wash causing imense turbulence and complete loss of lift. Any low rotor RPM flight condition accompanied by increasing collective pitch application will cause aerodynamic stall.

This is called retreating blade stall. With a low enough relative airspeed and a high enough angle of attack, aerodynamic stall is inevitable. As helicopter speeds increase, the retreating blade experiences lower relative airspeeds and the controls compensate with higher angle of attack. As helicopter speed increases, the advancing blades approach the speed of sound and generate shock waves that disrupt the airflow over the blade causing loss of lift.