Helicopters, aircraft with one or more power-driven horizontal propellers or rotors capable of vertical take-off and landing, moving in any direction or remaining stationary in the air. Other vertical flight processes include autogiros, convertiplanes and some configurations of V / STOL aircraft. Helicopter History
Vertical take-off, the transition to horizontal flight to the destination, the idea of vertical landing has been the inventor’s dream for centuries. This is the most logical form of flight, as it is in the middle of a large landing field located far from the city center, and the unavoidable travel usually required in conventional aircraft – the middle mode of cars, subways, and buses. But vertical flight is also the toughest challenge in flight, requiring more complex structures, power, and control than traditional fixed-wing aircraft. These difficulties, resolved by certain engineers and inventors for some time, made the progress of vertical flight seem slower than conventional flight because the first useful helicopter did not appear until the early 1940s.
An important feature of the history of vertical flight is the widespread human interest in the subject; the inventors of many countries have been challenged for many years and have achieved varying degrees of success. Vertical flight history at least as early as about 400 years; the history of the Chinese kites mentioned, the use of the rotor as the source of the elevator. The principle of using helicopters for toys – a rotating blade turned by pulling the rope – was known in the Middle Ages. In the second half of the 15th century, Leonardo da Vinci painted a helicopter, with a spiral propeller to get the lift. A toy helicopter, using a rotor made of bird feathers, was submitted to the French Academy in 1784 by two craftsmen, Launoy and Bienvenu; this toy predicts a more successful model created in 1870 by Alphonse Pénaud of France.
The first scientific account of the principles that led to successful helicopters came from Sir George Cali in 1843, and he was also regarded by many as the father of fixed-wing flying. Since then, many inventors have produced a true gene pool of helicopter ideas, almost entirely in the form of models or sketches. Many are technically dead ends, but others contribute part of the final solution. In 1907 there were two important steps forward. On 29 September, under the guidance of physicist and aviation pioneer Charles Richet, the brothers Paul and Jacques made a short flight on their Gyroplane 1, powered by a 45-hp engine. The gyroscope has a spider web frame and four sets of rotors. The airplane was lifted from the ground at a height of about 2 feet but was held without any control. Breguet continues to be a famous name for the French aviation community, and Louis returns to the success of the helicopter. Later, in November, their countryman Paul Cole, who was a bike manufacturer like the Wright Brothers, gained a free-flying duration of about 20 seconds, reaching foot-high heights of one-footed rotorcraft by 24 hp engine. Another person, like Breguet, will flirt with the helicopter, continue to use a fixed-wing aircraft to make his name, and then later returned to the challenge of vertical flight, is Igor Sikorsky, who did some unsuccessful experiments at about Same time.
The next 25 years are characterized by two major trends in vertical flight. One is the small success of the helicopter’s widespread success; the second is the autogiro (also spelling the autogyro) look and apparent success. Helicopter History Helicopter History Helicopter History
Helicopters have gained increasing success in many countries, and the following short-term review will highlight only those who eventually found themselves in successfully developed helicopters. In 1912, the Danish inventor Jacob Ellehammer in a helicopter short jump, characteristic reverse rotor and cyclical pitch control, the latter an important insight into the control problem. On December 18, 1922, a complex helicopter designed by George De Botzet for the US Army Air Force was under control of the ground for less than two minutes. In France, Argentine inventor Raúl Pateras Pescara designed several helicopters with cyclic pitch control in the 1920s and 1930s. If the engine failed, a straight-line distance record was designed, at 736 m (2,415) on 18 April 1924 foot). On May 4 of the same year, the French Étienne Oehmichen established a helicopter distance record by flying a kilometer-long circle. Helicopter History Helicopter History Helicopter History
In Spain the year before, January 9, 1923, Juan de la Cierva made the first successful flight autogiro. The operating principle of autogiro is different from that of helicopters. Its rotor is not energized but its lift is obtained by its mechanical rotation as the auto-rotation moves forward through the air. It has the advantage of relatively short take-off times and near vertical descent, and the success of Cierva’s autogiros and his competitors seems to have an impact on the future of helicopter development. The Autogiros quickly improved and manufactured in several countries, and seemed to fill such a useful niche as they temporarily shelter the helicopter. Ironically, however, the technology developed for the autogiro rotor head and rotor blades has made an important contribution to the development of successful helicopters, which makes autogiro obsolete.
In 1936, Germany adopted Focke Achgelis Fa 61, set foot on the forefront of helicopter development, it has two three-blade rotors mounted on the legs, by 160 horsepower radial engine power. The Fa 61 has a controllably recirculating pitch and sets a number of records, including a height of 11,243 feet and an off-road flight of 143 miles in 1938. In 1938, the German pilot Hanna Reitsch became the world’s first female helicopter pilot to fly Fa 61 within the German Halle in Berlin. It was a victory for technology and publicity. Germany continued its helicopter development during World War II and was the first to put a helicopter, Flettner Kolibri, on a large scale production.
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In the United States, after the success of many commercial spaceships, Igor Sikorsky turned his attention to the helicopter again, after a long period of development, in 1939 to 1941, he successfully tested a series of VS-300. Basically, a test aircraft designed for easy and quick modifications, the VS-300 is a small (weighs 1092 pounds), powered by a 65-horsepower Lacking engine. But it possesses the characteristics of most modern helicopters: a main three-blade rotor, collective tilt, and tail rotor. However, as a success of the VS-300, it also clearly shows the difficulties of all subsequent helicopters in the development process. Over the years, compared with conventional aircraft, helicopter power shortage, difficult to control, and to withstand higher dynamic stress, resulting in material and equipment failure. However, the VS-300 led to a long Sikorsky helicopter, which affected their development in a number of countries, including France, the UK, Germany, and Japan. Helicopter History Helicopter History Helicopter History
After the Second World War, the commercial use of helicopters developed rapidly in many roles, including fire, police work, crop spraying, mosquito control, medical evacuation, carrying mail and passengers. Helicopter History Helicopter History Helicopter History
The expanding market has brought more competitors to the field, each with different approaches to solving vertical flight problems. Under the leadership of Arthur Young, Bell Aircraft began its long history of vertical flight history, with a series of prototypes that resulted in the Bell 47, one of the most important helicopters ever built, in conjunction with articulated, gyro-stabilized, twin-blade rotors. Frank Piasecki created the Piasecki Helicopter Company; its design is characterized by the tandem rotor concept. The use of dual series rotors allows the helicopter to be increased to almost twice its previous size without the difficulty of producing very large rotor blades. In addition, the arrangement of the double rotors provides a large center of gravity range. The race is international and has made rapid progress in the Soviet Union, the United Kingdom, France, Italy and elsewhere.
To a greater extent than fixed-wing aircraft, the development of the helicopter by the engine power limit. Reciprocating engine heavy, noisy, low efficiency at high altitude. The first application of jet engine technology on helicopters was done in 1951 by Kaman Aircraft Corporation’s HTK-1, which had Kaman’s patented “synchro” configuration of an aerodynamically servo-controlled rotor (i.e., with intermeshing Of the paths of the side-by-side rotor blade strokes). Helicopter History Helicopter History Helicopter History
In conventional aircraft, jet engine power is mainly used to increase speed. In a helicopter, the thrust of the jet turbine must be captured by a gearbox that rotates the rotor. Jet engines have many advantages over helicopters – they are smaller and weigh less than piston engines with comparable power, have less vibration, and use cheaper fuels. France SNCA-S.E. 3130 Alouette II first flight on March 12, 1955, powered by the Turbomeca Artouste II turbine engine. It quickly became one of the most influential helicopters in the world and began a trend of jet-powered helicopters everywhere.
There are a large number of helicopter types on the market, ranging from small two-person private helicopters to large passenger-carrying vehicles capable of carrying large loads to remote areas. All of these people responded to the basic principles of flight, but because of the helicopter rotor and the unique nature of the control system, flying their technology is different. There are other types of vertical lift aircraft, the control and technology are usually a mixture of conventional aircraft and helicopters. They form a small part of the general map of the flight, but their importance is increasing.
Autogiro has been the most reasonable alternative to helicopters as a means of vertical flight over the years. Since the rotor is not powered, the automatic rotation does not need to resist the torque (the tendency of the aircraft to rotate in the opposite direction of the rotor), thus avoiding many control problems hindering the development of the helicopter. The rotor of the autogiro is designed so that the blades arranged at a low positive angle pitch are automatically rotated as long as the air flow remains through the rotor (rotation). As the automatic cycle advances through the air, the air flows upward through its rotor, producing lift. The control is achieved, in part, by a universal joint at the rotor head, which tilts the vanes resulting in a force pulling the autorotation in an inclined direction. The elevator and the rudder are held within the propeller slipstream for additional control. While the future of autogiro’s commercial development as the success of helicopters evaporates, the autogiros known as the “gyroscope” movement become very popular.
A power lift can change the thrust of the propulsion system in flight. They are characterized by a tight integration of the fuselage and propulsion system, which allows the propulsion system to affect the air dynamics of the fuselage. They include a variety of types; the most successful of which are vector jet, outer-wing, and outer-wing.
The most successful of all alternative helicopters is the most technically the most complex of a vector jets, the best example is Harrier, originally developed by Hawker aircraft, and matured by British Aerospace and McDonnell Douglas. In a vectoring nozzle, the nozzle is designed to rotate so that the thrust can be applied vertically for take-off and then moved to a horizontal position for normal flight.
In an outer-blown wing system, the exhaust gas from the jet engine is directed onto the upper surface of the airfoil (and in some cases over the outer surface of the foil region), the exhaust from the jet engine in the outer- Guide the large flap extension surface.
Other types of vertical take-off include aircraft. There are two types of V / STOL (vertical or short takeoff and landing) aircraft that can alternate between vertical takeoff and conventional horizontal flight. These are convertible rotorcraft and convertible aircraft.
The first group includes two types, the most important of which are tilt-rotor aircraft, such as the Bell / Boeing V-22, where the helicopter rotor is vertically tilted vertically and horizontally for normal flight. V-22 comes from more than thirty years of development, beginning with the Bell XV-3 in the early 1950s. It represents a configuration that provides the best prospects for inter-city air traffic, combining the practicality of helicopters with the speed of transport close to turboprops. The second type is a lesser-found composite helicopter having additional means for driving the rotor and using an additional power source and generating pneumatic lift.
The second group, with a propeller convertible aircraft, has four basic configurations. The first is the type of yaw thrust, where the large propeller applies thrust to the wing deflected into a wide arc. The second type is an inclined wing. In these aircraft, the wings are rotated to vertically point the pusher for take-off and landing and then adjusted for horizontal flight by bringing the wings to a normal angle of attack. The third is a tilted pipe in which the propeller shaded in the pipeline is rotated from one flight mode to another. The fourth is tilting the propeller, perhaps the least successful group. Curtiss-Wright built the X-100 test rig, which succeeded enough to allow the construction of a more advanced but unqualified X-19 prototype that collided during the test.
A number of attempts have been made to vertically elevate the craft from the ground using the power of the jet engine and then switch to forward flight, but in each case, the difficulties involved in recovery have inhibited the procedure. An early example, the Ryan X-13 Vertijet, was launched from a trailer bed erected vertically before takeoff. The aircraft successfully flew in both vertical and horizontal modes, including take-off and “tail” landings, but operational limitations on speed, range and payload were too great to progress. The Ryan XV-5A Vertifan uses a jet engine to drive the bridge of the nose and the horizontally mounted fan on the wing; it is nominally successful. Another type of fixed jet uses a separate jet engine battery, some dedicated to vertical flight, some dedicated to horizontal flight, but this expensive technology was eventually rejected.
Over time, there were many miscellaneous attempts in vertical flight. These include propeller driven tail fins, dust tray platforms, ground effect aircraft (hovercraft (TM)) and deflection jet thrust. In most cases, the advantages sought are offset by the difficulties encountered, and tilting rotors, vector jets, especially helicopters, remain the most successful means of vertical flight. Helicopter History Helicopter History Helicopter History
Flight and Operational Principles
Unlike fixed-wing aircraft, the main airfoil of a helicopter is a rotating blade assembly (rotor) mounted on top of its fuselage on a hinged shaft (mast) connected to the vehicle engine and flight controller. Compared with the aircraft, the helicopter tail some slender, rudder smaller; the rear is equipped with a small anti-twist rotor (tail rotor). The landing gear is sometimes made up of a pair of skids instead of wheel assemblies.
The fact that a helicopter gains its lift by rotating the airfoil (rotor) complicates its flight not only by the rotor but also up and down in vibratory motion and by horizontal or vertical motion Of the helicopter itself. Unlike conventional aircraft wings, helicopter rotor wings are usually symmetrical. The chord of the rotor, such as the chord of the wing, is the imaginary line drawn from the leading edge to the trailing edge of the airfoil.
The relative wind is the direction of the wind relative to the airfoil. In helicopters, the flight path of the rotor moves forward (to the nose of the helicopter) during its circular motion and then backward (to the helicopter) Tail). Relative winds are always considered parallel and opposite directions to the flight path. When considering helicopter flight, the relative wind may be affected by blade rotation, helicopter horizontal movement, rotor blade flutter and wind speed and wind direction. In flight, the relative wind is a combination of rotor blade rotation and helicopter motion.
Like the propeller, the rotor has a pitch angle which is the angle between the horizontal rotation plane of the rotor disc and the chord of the airfoil. The pilot uses the set and loop pitch control (see below) to change the pitch angle. In fixed-wing aircraft, the angle of attack (the angle of the wing relative to the wind) is important in determining lift. This is also the case in helicopters, where the angle of attack is the angle at which the wind encounters the chord of the rotor blade.
The angles of attack and pitch are two different conditions. Changing the pitch angle of the rotor blade changes its angle of attack and therefore its lift. A higher pitch angle (up to the stall point) will increase lift; a lower pitch angle will decrease it. The individual blades of the rotor have individually adjustable pitch angles.
The rotor speed also controls lift – the higher the rpm, the higher the lift. However, pilots often try to maintain a constant rotor speed and change the lift by changing the angle of attack. Helicopter History Helicopter History Helicopter History
As with fixed-wing aircraft, air density (the result of air temperature, humidity, and pressure) affects helicopter performance. The higher the density, the greater the lift; the lower the density, the smaller the resulting lift. As in fixed-wing aircraft, the change in lift also causes a change in resistance. As lift is increased by increasing the pitch angle and thus increasing the angle of attack, the drag will increase and slow down the rotor rpm. Additional power will then be required to maintain the desired rpm. Thus, when the helicopter is affected by lift, thrust, weight, and resistance, as with conventional aircraft, its flight mode causes additional effects.
In a helicopter, the total lift and thrust generated by the rotor are applied perpendicular to its plane of rotation. When the helicopter hovers in windless conditions, the rotor’s plane of rotation (the tip path plane) is parallel to the ground, and the sum of the weight and the resistance is precisely balanced by the sum of the thrust and lift. In vertical flight, the components of weight and drag are combined in a single vector directly guided; the components of lift and thrust are combined in a single vector directed directly. In order to achieve forward flight in a helicopter, the rotational plane of the rotor is tilted forward. (It should be understood that the rotor mast of the helicopter does not tilt, but each rotor blade in the plane of rotation has a varying pitch angle.) For the lateral flight, the plane of rotation of the rotor is inclined in the desired direction. For the backward flight, the plane of rotation of the rotor is inclined rearwardly.
Because the rotor is powered, there is an equal and opposite torque reaction that tends to rotate the fuselage in the opposite direction to the rotor. This torque is offset by the tail rotor (counter-torque rotor) at the end of the fuselage. Pilot Control The pedal controls the thrust of the tail rotor and sets the neutral torque as required.
Other forces acting on the helicopter have not been found in conventional aircraft. These include the gyroscopic precession effect of the rotor, i.e., the asymmetry of the lift produced by the forward motion of the helicopter, resulting in the forward blade having more lift and less backlash. This is because the advancing blade has a combined speed of the blade speed and the speed of the helicopter in forwarding flight and the reverse blade has a difference between the blade speed and the helicopter speed. This difference in speed results in a lift difference – the advancing blade moves faster, thus generating more lift. If uncontrolled, this will cause the helicopter to roll. However, lift difference is compensated for by blade swing and cyclic feathering (pitch angle change). Since the blade is attached to the rotor hub by means of a horizontal swing hinge that allows the blade to move in a vertical plane, the advancing blade flaps upwards to reduce its angle of attack while retracting the blade down the flap increases its angle of attack. This combination of effects balances lift. (The blades are also attached to the hub by a vertical hinge which allows each blade to move back and forth in the plane of rotation, the vertical hinge weakens vibration and absorbs the effect of acceleration or deceleration). In addition, in the forward flight, the position of the cyclic pitch control produces a similar effect, contributing to an improved equalization.
Other forces acting on the helicopter include conical, upward bending effects on the blades caused by centrifugal forces; Coriolis effect, acceleration or deceleration of the blades caused by vibratory motion bringing them closer (acceleration) or farther away ) Rotation axis; and drift, the tail rotor thrust of the moving helicopter hovering.
The helicopter has four controls: common pitch control, throttle control, anti-torque control and cyclic pitch control. Helicopter History Helicopter History Helicopter History
The collective pitch control is typically on the left hand of the pilot; it is a lever that moves up and down to change the pitch angle of the main rotor blade. Raise or lower the pitch control to increase or decrease the pitch angle on all blades in the same amount. An increase in the pitch angle will increase the angle of attack, resulting in an increase in lift and drag, and a decrease in the rotational speed of the rotor and the engine. An inversion occurs with a decrease in pitch angle.
Since it is necessary to keep the rotor rpm as constant as possible, the overall pitch control is associated with the throttle to automatically increase power when the pitch rod is raised and decrease as the pitch rod is lowered. Therefore, the total distance control as the height and power of the main control.
Throttle control is used in conjunction with common pitch control and is an integral part of its assembly. The throttle control is twisted to the outside to increase the rotor speed and to rotate inward to reduce the rotational speed.
The anti-torque control is a pedal connected to operate the pitch mechanism in the tail rotor gearbox. The change in pedal position changes the pitch angle of the tail rotor to counteract the torque. As the torque varies with each change in flight conditions, the driver needs to change the pedal position accordingly. Counter-regulation does not control flight direction. Helicopter History Helicopter History Helicopter History
As mentioned above, the lift/thrust force is always perpendicular to the plane of rotation of the rotor. The cyclic pitch control is a lever control on the right side of the pilot that controls the direction of flight by tilting the plane of rotation in the desired direction. The term loop derives the pitch change of each blade from a sequential manner so that it takes the flight path needed to implement the change of direction.
Helicopters and Aircraft Design and Construction Differences
The most direct and obvious difference in the construction of fixed-wing aircraft and helicopters is, of course, the latter using a rotor rather than an airfoil. However, there are many other key additions, including the use of the tail rotor to offset the torque. (Some helicopters use a “tailless” system in which low-pressure air is circulated through the tail truss to control the torque of the rotating main rotor). Less obvious is the addition of transmission systems, such as accessories for transmitting power from the engine to the rotor, tail rotor, clutches for engaging the engine and transmission with the rotor, and the mechanics of the rotor system itself.
The first helicopter was quite primitive, with sliding parts, not wheeled landing gear, open cockpit and unpaired fuselage. Helicopters are now fully equipped, such as aircraft, retractable landing gear and complete instrumentation and navigation equipment, and provide any equipment that may be needed to complete a specific task at hand. For example, some helicopters are flying ambulances, specially equipped with a complete set of intensive care accessories. Others act as electronic news gatherers with appropriate sensors and telecommunications equipment.
The design and operation of helicopters have gained the same advances from computers and composites as other aircraft, particularly in the design and construction of rotor blades. One of the more important improvements is the simplified flight control system in which a simple side-lever controller performs the functions of collective control, recirculation control and throttle control with the aid of a computer.
The helicopter design includes a number of optional rotor configurations, such as stopping the rotor used as a fixed wing for forwarding flight; a rotor folded in the direction of flow for fusion with the fuselage profile or stored in the fuselage profile And an X-shaped rotor which is rotated for take-off and landing but is fixed for lift in flight.
In summary, the concept of additional force on helicopters slowed its development, making it harder to control than fixed-wing aircraft and generally hampered its use. While it is generally considered more costly to operate than conventional fixed-wing aircraft, a true comparison of costs can not be made without assessing the additional advantages conferred by vertical flight capability. The popularity of helicopters indicates that users are willing to pay any additional cost to acquire this capability. In some applications – medical evacuation, the supply of oil rigs, the spread of certain agricultural agents, to name a few – it is irreplaceable. Helicopter History Helicopter History Helicopter History
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