A main rotor helicopter or rotor system is a combination of some rotary wings ( rotor blades ) and the control system that generates an aerodynamic lift style that supports helicopter weight, and a push against aerodynamic drag on the forward flight. Each main rotor is mounted on a vertical pole above the helicopter, compared to the helicopter tail rotor, which connects through a combination of drive shaft (s) and gearbox along the tail boom. Pitch knives are usually controlled by a swashplate that is connected to a helicopter flight control. Helicopter is one example of rotary wing (rotorcraft). This name is derived from the Greek word helix , helic-, which means spiral; and pteron means wing.
Video Helicopter rotor
History and development
The use of rotor for vertical flight has been around since 400 BC in the form of bamboo helicopters, ancient Chinese toys. The bamboo-copter spins by rolling the stick attached to the rotor. Spinning creates lift, and flying toys when released. Ge Hong's philosopher Baopuzi (Master Who Embraces Simplicity), written around 317, describes the apocryphal use of a possible rotor on the plane: "Some have made flying cars [feiche ??] with wood from the inside of the tree jujube, using an ox skin (rope) tied back to the propeller to set the engine moving. "Leonardo da Vinci designed a machine known as an" air screw "with a rotor based on a water screw. Polymath Russia Mikhail Lomonosov develops rotor based on Chinese toys. Christian de Launoy, the French naturalist, made his rotor from turkey. Sir George Cayley, inspired by Chinese toys in his childhood, created several vertical flight engines with rotor made of lead sheet. Alphonse PÃÆ' Â © naud later developed a coaxial rotor helicopter model toy in 1870, backed by a rubber band. One of these toys, given as a gift by their father, will inspire the Wright brothers to pursue the dream of flying.
Prior to the development of the helicopter energized in the mid-20th century, autonomous pioneer Juan de la Cierva examined and developed many rotor basics. De la Cierva is credited with the successful development of a fully articulated, multi-blade articulated rotor system. This system, in its modified form, is the basis of most multi-blade rotor helicopter systems.
The first successful attempt in the design of a single lift rotor helicopter using a four-blade main rotor, designed by Soviet aviation engineers Boris N. Yuriev and Alexei M. Cheremukhin, both worked at the Tsentralniy Aerogidrodinamicheskiy Institute (TsAGI, Central Aerohydrodynamic Institute) near Moscow in the early 1930s. Their 1-EA TsAGI helicopter was capable of flying in low-altitude testing in 1931-32, with Cheremukhin flying as high as 605 meters (1,985 feet) by mid-August 1932.
In the 1930s, Arthur Young improved the stability of the two-rotor system blades by introducing the stabilizer bar. This system is used in several models of Bell and Hiller helicopters. Hiller system variants using an airfoiled paddle on the fly's end have been used in many of the earliest designs of the remote control model helicopters, from the 1970s to the 21st century.
In the late 1940s, the manufacture of helicopter rotors was a work that inspired John T. Parsons to be a pioneer of numerical control (NC). NC and CNC turn out to be an important new technology that then affects all the machinery industries.
Maps Helicopter rotor
Design
Overview
The rotor helicopter is powered by a machine, through transmission, to a rotating pole. The pole is a cylindrical metal shaft extending upward from - and transmitted by - transmission. At the top of the pole is an attachment point for a rotor blade called a hub. The rotor blades are then attached to the hub, and the hub can have 10-20 times the drag of the knife. The main rotor system is classified according to how the main vane is mounted and moves relative to the main rotor hub. There are three basic classifications: non-stop, staggered, and fully articulated, although some modern rotor systems use a combination of these classifications. A rotor is a finely tuned spinning mass, and different fine adjustments reduce vibrations at different airspeed. The rotor is designed to operate on fixed RPMs (within a narrow range of a few percent), but some experimental aircraft use variable speed rotors.
Unlike the small diameter fan used on a turbofan jet engine, the main rotor on the helicopter has a large diameter that allows it to accelerate large air volumes. This allows lower downwash speed for the given amount of drive. Because it is more efficient at low speeds to accelerate large quantities of air with a small degree of small amounts of air at a large rate, low disk loading (thrust per disk area) greatly improves the energy efficiency of aircraft, and this reduces fuel use and allows a reasonable range. The efficiency of hover ("service figure") of a typical helicopter is about 60%. The length of the three inner rotor blades contributes very little to lift because of its low air velocity.
Parts and functions
Simple rotor from Robinson R22 shows (from above):
- The following is driven by the connecting rod from the swashplate rotating part.
- Pitch hinges, allowing twisted propellers about the axis extending from the root of the blade to the tip of the blade.
- Hinge hinges, allowing one blade to rise vertically while the other falls vertically. This movement occurs whenever there is translational translation wind, or in response to a cyclic control input.
- Cut links and balancers, bringing the main shaft rotation down the swashplate
- Rubber covers protect moving and non-moving shafts
- Swashplate, cyclic and collective pitch transmissions to blade (topmost spin)
- Three non-rotating control bars transmit pitch information to the bottom swashplate
- Main mast leading to the main gearbox
Swash Plate
The control varies the pitch of the main rotor blades cyclically throughout the rotation. The pilot uses this to control the direction of the rotor thrust vector, which defines the portion of the rotor disc in which the maximum thrust develops. The collective pitch varies the magnitude of the rotor drive by increasing or decreasing the thrust of the entire disc rotor at the same time. This pitch blade variation is controlled by tilting, raising, or lowering the swash plate with flight controls. Most helicopters maintain a constant rotor speed (RPM) during flight, leaving the angle of the blade as the only way to adjust the thrust of the rotor.
The swash plate is two disks or concentric plates. A rotating plate with a pole, connected with a blank link, while the other does not rotate. Rotating plates are also connected to individual knives through pitch links and trumpets. No spin plates connected to links manipulated by pilot control - in particular, collective and cyclic controls. The swash plate can be shifted vertically and tilted. By sliding and tilting, the non-rotating plates control the rotating plate, which in turn controls each pitch blade.
Articulated fully
Juan de la Cierva developed a fully articulate rotor for autogyro. The design base enables the development of successful helicopters. In a fully articulated rotor system, each rotor blade is attached to the rotor hub through a series of hinges that allow the blades to move independently of the others. This rotor system usually has three or more blades. The propellers are left to flap, feather, and lead or are left independently of each other. The horizontal hinges, called flapping hinges , allow the blades to move up and down. This movement is called flapping and is designed to compensate for the adoptive uncertainty. The hinging hinges may lie at varying distances from the rotor hub, and there may be more than one hinge. A vertical hinge, called a lead-lag hing or hinge drag , allows the blade to move back and forth. This movement is called lead-lag, drag, or hunt. Dampers are usually used to prevent excessive back and forth movement around the drag hinges. The purpose of the drag hinges and dampers is to offset the acceleration and deceleration caused by the Coriolis effect. The next model shifts from using traditional bearings to elastomeric pads. Elastomeric pads are naturally unsafe and their wear is gradual and visible. The metal-to-metal contact of the older bearings and lubrication requirements is eliminated in this design. The third hinge in a fully articulated system is called the feather hinge on the fur axis. This hinge is responsible for changing the pitch of the rotor that is turned on through the pilot input to Collective or Cyclic. A fully articulated system variation is the "soft-in-plane" rotor system. This type of rotor can be found on several aircraft manufactured by Bell Helicopter, such as OH-58D Kiowa Warrior. This system is similar to a type that is fully articulated in every blade having the ability to lead/lag and hunt independently from other blades. The difference between a fully articulated system and a soft-in-plane system is that the soft-in-plane system uses a composite yoke. This yoke is attached to the pole and runs through the grip of the blade between the blade and the sliding bearing inside the grip. This blow moves several movements of one blade to the other bar, usually the opposite bar. Although this is not fully articulated, flight characteristics are very similar and time and maintenance costs are reduced.
Aircraft
- AgustaWestland AW109
- Hughes TH-55 Osage
- MD Helicopters MD 500
- Sikorsky S-300
Rigid
The term "rigid rotor" usually refers to an endless rotor system with blades that are flexibly attached to the hub. Irv Culver of Lockheed developed one of the first rigid rotor, which was tested and developed on a series of helicopters in the 1960s and 1970s. In a rigid rotor system, each blade flaps and drags around the flexible part of the root. The rigid rotor system is mechanically simpler than the fully articulated rotor system. The load from the flapping and leading/lag styles is accommodated through a flexible rotor blade, not through a hinge. By stretching, the propeller itself offset the style that previously required a harsh hinge. The result is a rotor system that has less lag in the control response because large hub moments are usually generated. The rigid rotor system thereby eliminates the danger of the crashing pole attached to the trained rotor.
Aircraft
- MBB Bo 105
- Eurocopter EC135
- HAL Dhruv/HAL Rudra
- HAL Light Combat Helicopter
- Sikorsky S-97 Raider
Semirigid
The semirigid rotor can also be referred to as a seesaw rotor or a seesaw. This system usually consists of two blades that meet just below the hinge or common baseball hinges on the rotor shaft. This allows the knife to flap together in the opposite movement like a seesaw. The rolling of the blades under these hobbled hinges, combined with a sufficient dihedral or conical angle on the blade, minimizes the variation within the radius of each center of the blade from the rotation axis as the rotor rotates, which in turn reduces the pressure on the propellers from lead and lag strength caused by Coriolis effect. Secondary flapping hinges can also be provided to provide enough flexibility to minimize bouncing. Feathering is achieved by a hairy hinge on the blade root, which allows a change in the pitch angle of the blade.
Flybar (stabilizer bar)
A number of engineers, including Arthur M. Young in the U.S. and aeromodeler radio control Dieter SchlÃÆ'¼ter in Germany, found that flight stability for helicopters can be achieved with a stabilizer bar, or flybar. Flybar has a weight or oar (or both to add stability to smaller helicopters) at each end to maintain a constant rotational plane. Through mechanical connection, the stable rotation of the bars mixes with the swashplate movement to dampen the internal (steering) and external (wind) forces on the rotor. This facilitates the pilot to maintain control of the aircraft. Stanley Hiller arrives at the same method to improve stability by adding a short fat airfoil, or paddle, at each end. However, the "Rotormatic" Hill system also delivers cyclic control inputs to the main rotor as a kind of control rotor, and the paddle provides additional stability by dampening the effects of external forces on the rotor.
The Lockheed rotor system uses gyro control, similar in principle to the Bell stabilizer bar, but is designed for hand stability and rapid control response of irregular rotor systems.
In a fly-by-wire helicopter or RC model, a microcontroller with gyroscope sensor and Venturi sensor can replace the stabilizer. This flybar-less design has the advantage of easy reconfiguration and fewer mechanical components.
Planes
- Bell 47
- Bell 206/OH-58
- Bell UH-1 Iroquois
- Robinson R22
Combination
Modern rotor systems may use the combined principle of the above mentioned rotor systems. Some hub rotors incorporate flexible hubs, allowing for bending of blades (flexing) without the need for cushioning or hinges. This system, called "bending", is usually constructed from composite materials. Elastomeric pads can also be used instead of conventional roller bearings. The elastomeric pads are constructed of rubber type material and provide limited movement that is perfect for helicopter applications. Flexible and elastomered bearings do not require lubrication and, therefore, require less maintenance. They also absorb vibrations, which means less fatigue and longer service life for helicopter components.
Aircraft
- Bell 407
- Bell 430
- Eurocopter AS350
Rotor Configuration
Most helicopters have a single main rotor but require a separate rotor to overcome the torque. This is achieved through a variable antiterque-pitch rotor or tail rotor. This is a design that Igor Sikorsky completed for his VS-300 helicopter, and it has become a recognized convention for helicopter design, although the design varies. When viewed from above, most of the helicopter rotors rotate counter-clockwise; French and Russian helicopter rotors rotate clockwise.
Single main rotor
With one main rotor helicopter, the creation of torque as a rotating rotor engine creates a torque effect that causes the helicopter body to rotate in the opposite direction of the rotor. To eliminate this effect, some sort of antitorque control should be used with sufficient power margins available to allow the helicopter to retain its post and provide yaw control. The three most commonly used controls today are tail rotor, Eurocopter Fenestron (also called fantail ), and MD Helicopters' NOTAR .
Tailboat
The tail rotor is a smaller rotor mounted so that it rotates vertically or almost vertically at the tail end of a traditional single rotor helicopter. The position and distance of the rotor tail from the center of gravity allow it to develop the opposite thrust of the main rotation of the rotor to counteract the torque effect made by the main rotor. The tail rotor is simpler than the main rotor because it requires only a collective change on the pitch for various impulses. The tail vane plates are adjusted by the pilot via an anti-torque pedal, which also provides directional control by allowing the pilot to rotate the helicopter around the vertical axis, thus changing the direction of the directed plane.
Distributed fan
Fenestron and FANTAIL are trademarks for discharge fan mounted at the end of the helicopter tail boom and used instead of the tail rotor. The ducted fan has between eight and eighteen blades arranged with irregular distances so that noise is distributed at different frequencies. This housing is integral to the skin of the aircraft and allows high rotation speed; Therefore, the dispensing fan can have a smaller size than the conventional tail rotor.
Fenestron was used for the first time in the late 1960s on a second experimental model of SA 340 from SA and produced on the later model AÃÆ' Â © rospatiale SA 341 Gazelle. In addition to Eurocopter and its predecessors, the tailed fan tail rotor was also used in the aborted military helicopter project, the RAH-66 Comanche belonging to the US Army, as FANTAIL.
NOTAR
NOTAR, the acronym for NO TA il R author , is a helicopter anti-torque system that removes the use of the tail rotor on a helicopter. Although the concept needs time to be fixed, the NOTAR system is simple in theory and gives antitrites in the same way as developing a lift wing using Coand? effect. The variable closed pitch fan at the rear of the fuselage immediately advances from the tail boom and is driven by the main rotor transmission. To provide a sideways force to counter the clockwise torque generated by the main rotor which rotates counter-clockwise (as seen from above the main rotor), the variable-pitch fan forces low air pressure through two slots on the right side of the tailboom, causing downwash from the main rotor to embracing the tailboom, generating the lift and thus the antitorque size is proportional to the amount of airflow from the rotorwash. This is coupled with a direct jet thruster that also provides yaw direction control, with the presence of fixed surface empennage near the tail end, incorporating a vertical stabilizer.
The development of the NOTAR system dates back to 1975 when engineers at Hughes Helicopters began to work on concept development. In December 1981, Hughes flew OH-6A equipped with NOTAR for the first time. The more modified prototype demonstrator first flew in March 1986 and successfully completed the advanced flight test program, validating the system for future applications in helicopter design. There are currently three production helicopters that incorporate NOTAR designs, all manufactured by MD Helicopters. This antitorque design also improves security by eliminating the possibility of personnel walking into the tail rotor.
Its predecessor (s) is in the form of a British Cierva W.9 helicopter, a 1940s aircraft that uses a cooling fan from its piston engine to push the air through a nozzle built into the tailboom to eliminate the rotor-torque.
Tip jets
The main rotor can be driven by a jet tip. Such systems may be supported by the high-pressure air provided by the compressor. Air may or may not be mixed with fuel and burned in ram-jet, jet-pulse, or rocket. Although this method is simple and eliminates the torque reaction, the prototype has been built less fuel-efficient than the conventional helicopter. Except for the jet tip driven by unburned pressurized air, the extremely high noise level is the single most important reason why the jet powered rotor tip does not gain wide acceptance. However, research on noise suppression is ongoing and can help make this system feasible.
There are several examples of jet powered rotorcraft tips. The Percival P.74 is less powerful and can not fly. The Hiller YH-32 Hornet has good lift ability but performs poorly on the contrary. Other aircraft use an additional thrust for translational flight so that the tip jet can be turned off when the rotor is rotated. Experimental Fairey Jet Gyrodyne, 48-seat Fairey Rotodyne passenger prototype and gyroplanes compound McDonnell XV-1 fly well using this method. Perhaps the most unusual design of this type is the Rotary ATV Rocket Rotary, which was originally planned to take off using a rocket-tipped rotor. France Sud-Ouest Djinn uses unburned compressed air to drive the rotor, which minimizes noise and helps it to be the only jet driven by the rotor to enter production. Hughes XH-17 has a jet-driven rotor tip, which remains the largest rotor ever mounted to a helicopter.
Dual rotor (inhibitor)
Counterrotating rotor is a rotorcraft configuration with a pair or more of large horizontal rotors that rotate in opposite directions to counteract the effect of torque on an aircraft independent of the antiterque rotor tail. This allows the aircraft to apply forces that will propel the tail rotor to the main rotor, increasing lift capacity. In particular, three common configurations use the effects of restraint on rotorcraft. Tandem rotor are two rotor - one mounted behind the other. Coaxial rotor are two rotor mounted one above the other on the same axis. Rotor intermeshing are two rotor mounted adjacent to each other at an angle sufficient to allow the intermesh rotor above the top of the plane. Another configuration - found on tiltrotors and some early helicopters - is called a transverse rotor, where a pair of rotor is mounted on each end of a wing or outrigger structure.
Tandem
Tandem rotor are two main horizontal rotor assemblies mounted one behind the other. The rotor tandem attains a pitch change of attitude to accelerate and slow down the helicopter through a process called cyclic pitch. To advance and accelerate, the two rotors increase the pitch at the rear and reduce the pitch on the front (cyclic) keeps the same torque on both rotor, flying to the side is achieved by increasing the pitch on one side and reducing the pitch on the other. The yaw control develops through the opposite cyclic pitch in each rotor. To rotate right, the front rotor tilts to the right and the rear rotor tilts to the left. To turn left, the front rotor tilts to the left and the rear rotor tilts to the right. All rotor power contributes to lifting, and it is easier to handle changes in the center of gravity forward. However, it requires the cost of two large rotors rather than the more common one large main rotor and a much smaller tail rotor. Boeing CH-47 Chinook is the most common tandem rotor helicopter.
Coaxial
The coaxial rotor is a pair of rotor mounted one above the other on the same axis and rotates in the opposite direction. The advantage of the coaxial rotor is that, in forward flight, the lift provided by the forward portion of each rotor compensates for the other half of the retreat, eliminating one of the main effects of the asymmetry of lift: the retreating blade stall. However, other design considerations interfere with the coaxial rotor. There is an increased mechanical complexity of the rotor system because it requires a connection and a swashplate for two rotor systems. Also, since the rotor must rotate in the opposite direction, the pole is more complicated, and the control relationship for pitch change to the upper rotor system must pass through the lower rotor system.
Intermeshing
The rotor intermeshing on the helicopter is a set of two rotating rotors in opposite directions with each mast rotor mounted on the helicopter with a slight angle to the other so that the intermesh blades do not collide. This configuration is sometimes referred to as a synchropter. Rotor intermeshing has high stability and strong lifting ability. This arrangement was pioneered in Nazi Germany in 1939 with Flettner's successful Flettner Fl 265 design, and was then placed in limited production as a successful Flettner Fl 282 hummingbird, used by the German Kriegsmarine in small numbers (24 airframes) produced) as an experimental light anti-submarine war helicopter. During the Cold War, an American company, Kaman Aircraft, produced HH-43 Huskie for USAF's fire and rescue missions. The latest Kaman model, Kaman K-MAX, is a special sky crane design.
Transverse
The transverse rotor is mounted on the end of the wing or outrigger perpendicular to the body of the plane. Similar to tandem rotor and rotor intermeshing, the transverse rotor also uses a differential collective pitch. But like the rotor intermeshing, the transverse rotor uses the concept for a change in the rotorcraft roll attitude. This configuration was found on the first two decent helicopters, Focke-Wulf Fw 61 and Focke-Achgelis Fa 223, as well as the world's largest ever built helicopter, Mil Mi-12. This is also a configuration found on tiltrotors such as Bell-Boeing V-22 Osprey and AgustaWestland AW609.
Quadcopter
A quadcopter has four rotor in the "X" configuration set as front-left, front-right, left-back, and right-back. The rotor to the left and right is in a transverse configuration while the front and back are in a tandem configuration.
The main attraction of quadcopters is their mechanical simplicity, because the quadcopter uses electric motors and fixed-pitch rotors have only four moving parts. Pitch, yaw, and bank can be done by changing the relative lift of different rotor pairs without changing the total lift.
Blade design
Long helicopter blades, narrow airfoils with high aspect ratio, shapes that minimize drag from the tip of vortices (see the glider wings for comparison). They generally contain a washing rate that reduces lift power generated at the tip, where the fastest airflow and vortex generation will be a significant problem. The rotor blades are made of various materials, including aluminum, composite structures, and steel or titanium, with abrasion protector along the front edge.
The Rotorcraft knife is traditionally passive; However, some helicopters include active components on their swords. Kaman K-MAX uses trailing edge flaps for blade pitch control and Hiller YH-32 Hornet is supported by ramjets mounted on the blade end. In 2010, research into active blade control via trailing edge flaps was underway. The tips of some blade helicopters can be specially designed to reduce turbulence and noise and provide more efficient flight. An example of such a tip is the BERP rotor tip made during the British Experimental Rotor Program.
Two family of airfoil
- airfoil symmetric
- asymmetric airfoil
The symmetrical bar is very stable, which helps keep the blades and flight control loads to a minimum. This stability is achieved by keeping the center of pressure almost unchanged when the angle of attack changes. The pressure center is an imaginary point on the chord line where the resultant all aerodynamic forces are considered to be concentrated. Today, designers use thinner airfoils and obtain the necessary stiffness by using composite materials.
In addition, some airfoils are asymmetrical in design, which means the top and bottom surfaces do not have the same camber. Normally this airfoil will not be stable, but this can be corrected by bending the trailing edge to produce the same characteristics with symmetrical airfoils. This is called "reflex." Using this type of blade rotor allows the rotor system to operate at higher forward speeds. One reason the asymmetric rotor blade is unstable is the center of the pressure changing with the change of angle of attack. When the center of the pressure lifting force is behind the pivot point on the rotor blade, it tends to cause the rotor plate to overturn. As the angle of attack increases, the pressure center moves forward. If moving in front of the pivot point, the rotor disc pitch decreases. Since the angle of the rotor blades keeps changing during each rotation cycle, the propeller tends to flap, feather, lead, and lag to a greater extent.
Limits and dangers
Helicopters with staggered rotor - eg a two-blade system on Bell, Robinson and others - should not experience low conditions because such a rotor system does not control the posture of the fuselage. This may result in a fuselage with an attitude assumption controlled by the momentum and impulse of the tail rotor causing the tail boom to bypass the main-end rotor plane or produce a root of the blade that contacts the main rotor drive shaft, causing the blade to separate from the hub (crashing pole).
Abrasion in sandy environment
When operating in sandy environments, the sand that hit the moving rotor blades erodes the surface. This can damage the rotor and cause serious and costly maintenance problems.
The abrasion strip on the helicopter blades is made of metal, often titanium or nickel, which is very hard, but less loud than sand. When the helicopter flies low to the ground in the desert environment, the sand that attacks the rotor blades can cause erosion. At night, the sand that crashes into the metal abrasion strip causes the corona or halo to be visible around the rotor blades. This effect is caused by the eroded pyrophoric oxidation of particles, and by triboluminescence where impact with sand particles produces photoluminesce.
Fighter photographer and journalist Michael Yon observes his impact while accompanying US troops in Afghanistan. When he discovered that the effect had no name he created the name "Kopp-Etchells Effect" after two soldiers killed in war, one American and one English.
References
External links
- Rotor Analysis - Blade Elements of Momentum Theory
- Picture Gallery near Rotorhead Helicopters
- "Helicopter Airplane". US Patent 2,368,698, for the discovery of flies, by Arthur Young
Source of the article : Wikipedia
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