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Helicopters Reference – The Billion Dollar Site
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Helicopters Reference
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Content derived from Wikipedia article on Helicopters
Helicopters are classified as rotary-wing aircraft to distinguish them from conventional fixed-wing aircraft. The word helicopter is derived from the Greek words helix (spiral) and pteron (wing). The first single-rotor, fully controllable helicopter to enter large full-scale production was made by Igor Sikorsky in 1942.
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 compensating advantage is maneuverability: helicopters can hover in place, reverse, and above all take off and land vertically. Subject only to refueling facilities and load/altitude limitations, a helicopter can travel to any location, and land anywhere with enough space (approximately twice the area of the rotor disk).
Compared to other vertical lift aircraft like tiltrotors (V-22 Osprey for example) and vectored thrust airplanes (also known as VT-OL jets, standing for Vertical Take-Off & Landing) (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. 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).
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Contents
1 History 2 Generating lift 2.1 Conventional layout 2.2 Alternative layouts 3 Controlling flight 4 Stability 5 Limitations 6 Landing 6.1 On a ship 7 Hazards of helicopter flight 8 Helicopter models and identification 9 See also 10 References
History
Since 400 BC the Chinese had a bamboo flying top that was used as a children's toy. This toy eventually made its way to Europe and has been depicted in a 1463 European painting. Pao Phu Tau (抱朴子) was a 4th century book in China that described some of the ideas in a rotary wing aircraft. The first semi-practical idea of a human carrying helicopter was first conceived by Leonardo da Vinci around 1490.
The word "helicopter" (hélicoptčre) was coined in 1861 by Gustave de Ponton d'Amécourt, a french inventor who demonstrated a small steam-powered model.
But it was not until after the invention of the powered airplane in the 20th century that actual helicopters were produced. Developers such as Jan Bahyl, Oszkár Asbóth, Louis Breguet, Paul Cornu,Traian Vuia, 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.
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A flight of the first fully controllable helicopter was demonstrated by Raúl Pateras de Pescara 1916 in Buenos Aires, Argentina.
In 1922, Albert Gillis von Baumhauer, a Dutch aeronautical engineer, started studying the possibilities of VTOL rotor craft. His first prototype 'flew' ('hopped' and hovered really) on September 24, 1925, with Dutch Army-Air arm Captain Floris Albert van Heijst at the cyclic and collective (both are Von Baumhauer inventions). Patents were granted Von Baumhauer by the British ministry of aviation January 31st, 1927, under number 265,272.
In 1931, Soviet aeronautical engineers Boris Yuriev and Alexei Cheremukhin began experiments with the TsAGI 1-EA helicopter, also a single lifting rotor helicopter, with forward and aft anti-torque rotors. It reached an altitude of 605 meters (1,984 ft) on August 14, 1932 with Cheremukhin at the controls.
The German Focke-Wulf FW-61 was the first production fully controllable helicopter and had its first flight in 1936. The FW-61 broke all world records in 1937. Nazi Germany used the helicopter in combat during World War II in small numbers. Models such the Flettner FL 282 Kolibri were used in the Mediterranean Sea.
Mass production of the military version of the Sikorsky XR-4 began in May 1942 for the United States Army and was used over Burma for rescue duties.[1] It was also used by the Royal Air Force, the first British military unit to be equipped with helicopters being the Helicopter Training School, formed in January 1945 at RAF Andover with nine Sikorsky R-4B Hoverfly I helicopters.
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. Two decades later the Bell 206 became the most successful commercial helicopter ever built with more hours and has set more industry records than any other aircraft in the world.
Reliable helicopters capable of stable hover flight were developed decades after fixed wing aircraft. This is largely due to higher engine power density requirements when compared with fixed wing aircraft. Igor Sikorsky is reported to have delayed his own helicopter research until suitable engines were commercially available. Improvements in fuels and engines during the first half of the 20th century were a critical factor in helicopter development. 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. Turboshaft engines are the preferred powerplant for all but the smallest and least expensive helicopters today.
Generating lift
The eight-bladed fenestron of the Eurocopter EC120BIn conventional aircraft, the wing profile (called airfoil) is designed to deflect air efficiently downward. This downward deflection causes an opposite lifting force on the wing (described by Newton's third law) and a lower pressure on the upper surface, higher pressure on the lower surface. This pressure difference integrated over the airfoil area causes a net lift. However, the more the lift of the airfoil, the more drag that is caused (induced drag by creating wingtip vortices). 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. The helicopter's rotor can simply be regarded as rotating wings, from where the military name of "rotary wing aircraft" originates.
Conventional layout
The major components of a Sikorsky-layout helicopter anatomy.There are several possible layouts for arranging a helicopter's rotors. The most common design is the Sikorsky-layout, which is used by approximately 95% of all helicopters manufactured. 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 if no counter-acting force was applied. 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. This rotor creates thrust which is in the opposite direction from the torque generated by the main rotor. 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.
The world's largest and smallest series-produced helicopters follow this Sikorsky layout. The Mil Mi-26 can lift 27 metric tons, the Robinson R22 has a crew of two and a gross weight of 1300 lb (590 kg). Almost all civilian helicopters have the main rotor and tail rotor system.
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. AH-64 Apache). The primary reason is to make the arrangement of the pitch controls simpler. If the tail rotor is shrouded (i.e., a fan embedded in the vertical tail) it is called a fenestron. The fenestron rotor system on the model EC120 helicopter uses a shaft driven system and gearbox to turn the fan. It is less efficient but the advantages are that less noise is generated, it is safer for people that may walk near it and there is less chance of the blades being damaged by objects because it is shrouded, unlike the traditional tail rotor.
The amount of power required to prevent a helicopter from spinning is significant. 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. To reduce this waste during cruise, the vertical stabilizer is often angled to produce a force which helps counter the main rotor torque. At high speeds, it is possible for the vertical stabilizer to counteract the entire torque, leaving more power available for forward flight. This is commonly known as slip-streaming and can make hovering turns difficult on windy days. 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.
Many military helicopters, especially attack types, have short wings called stub wings to add lift during forward motion. They are also used as external mounts for weapons. Depending on the design, wings can often degrade hovering performance as they partially obstruct the airflow created by the main rotor.
Alternative layouts
There are alternatives to Sikorsky's layout, which save the weight of a tail boom and rotor. Such designs use two main rotors which turn in opposite directions, or contra-rotate, so that the torques from each rotor cancel each other out. These methods introduce even more mechanical complexity to the design and are usually relegated to specialized helicopter types.
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"). 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. Another example is the Kamov Ka-26, a successful crop duster aircraft. See Coaxial rotor.
Bell 206B Jet Ranger III at Filton Airfield, Bristol, England. Used for electricity pylon patrols.The slightly different system of intermeshing rotors, also called a synchropter, which was developed in Nazi Germany for a small anti-submarine warfare helicopter, the Flettner Fl 282 Kolibri, features two main rotors on separate, obliquely mounted axles. The contra-rotating rotors are on top of the fuselage, close to each other. During the Cold War the American Kaman company started to produce similar helicopters for USAF firefighting purposes. Kamans have high stability and powerful lifting capability. The latest Kaman K-Max model is a dedicated sky crane design, used for construction works.
In the flying-wagon or tandem rotor system (sometimes called "flying banana" for the peculiar shape of early U.S. examples), the two main rotors are located at the front and rear extremity of a long, boxy fuselage that resembles a railway wagon. A prime example is the Boeing CH-47 Chinook, that can carry 14 tons of payload. Wagon helicopters are practical for military logistical purposes, because entry and unloading is easy via the unobstructed front and rear ramps. The rotors and turbines are located very high on top of the fuselage, making them less sensitive to damage and dirt. The main drawback of a tandem rotor 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 into a bridge for that reason while being shown live on TV.
A helicopter built by Juan de la Cierva had three main rotors. These were placed at the corners of an equilateral triangle and all turned the same direction.
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. 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. The 1930s German FW-61 helicopter was built to such design. 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 U.S. 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.
MD 600N (Helicopters of America)A recent development in helicopter technology is the NOTAR system, which stands for NO TAil Rotor. The NOTAR eliminates the tail rotor by conducting high-velocity air through the tail boom, using the Coandă effect to produce forces to counter the torque. NOTARs adjust thrust by opening and closing a sliding circular cover near the end of the tail boom. The NOTAR system was developed in the United States and is used exclusively by McDonnell Douglas Helicopters.
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. Although this method is simple and eliminates torque, the prototypes that have been built lack the efficiency of conventional helicopters.
Controlling flight
Controls of an Alouette IIIUseful flight requires that an aircraft be controlled in all three dimensions (see flight dynamics). 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. In a helicopter, however, there is often not enough speed for this method to be practical.
Enstrom (USA) 280FX Shark, an aerodynamically restyled F28 for the corporate market.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. This is also how the helicopter is maneuvered, ie. pitching forward causes forward flight.
For rotation about the vertical axis (yaw) the anti-torque system is used. Varying the pitch of the tail rotor alters the sideways thrust produced. Yaw controls are usually operated with anti-torque pedals, on the floor in the same place as a fixed-wing aircraft's rudder pedals.
Helicopters maneuver with three flight controls besides the pedals. 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. When the angle of attack is increased, the blade produces more lift. The collective control is usually a lever at the pilot's left side. Simultaneously increasing the collective and adding power with the throttle causes a helicopter to rise.
Dual rotor helicopters follow the same principles, but differentiate in the following ways:
Tandem rotor designs achieve yaw by applying opposite left and right cyclic to each rotor, effectively rolling both ends of the helicopter in opposite directions. To achieve pitch, opposite collective is applied to each rotor; decreasing the lift produced at one end, while increasing lift at the opposite end, effectively tilting the helicopter forward or back. Synchropters use a similar system to tandem rotor helicopters, but as the two rotors are side by side, they use opposite pitch for yaw, and opposite collective for roll. Co-axial designs achieve yaw by applying opposite collective to each rotor. This increases drag, and therefore torque, in one rotor, while decreasing the drag in the other. Since the rotors spin in opposite directions, the torque difference causes the helicopter to rotate.
Sikorsky S-92The throttle controls the absolute power produced by the engine that is connected to the rotor by a transmission. The throttle control is a twist grip on the collective control. RPM control is critical to proper operation for several reasons. Helicopter rotors are designed to operate at a specific RPM. However, for each weight and speed there would be an ideal RPM (design-rpm). In practice, a single (higher) RPM is used in order to minimize resonance design requirements and add a safety margin to rotor stall RPM. Usually only in autorotation are different RPMs used to increase rotor efficiency, which can be crucial in the case of an emergency without engine power.
If the RPM becomes too low, the rotor blades stall. This suddenly increases drag and slows the rotor down further. The centrifugal forces are then not able to straighten the rotor blades any more, excessive coning ("tuliping") develops and a catastrophic accident is certain.
If the RPM is too high, damage to the main rotor hub, power transmission and engine from excessive forces could result. In general, RPM must be maintained within a tight tolerance, usually a few percent. In many piston-powered helicopters, the pilot must manage the engine and rotor RPM. The pilot manipulates the throttle to maintain rotor RPM and therefore regulates the effect of drag on the rotor system. 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.
The cyclic (pitch control lever) changes the pitch of the blades cyclically, causing the lift to vary across the plane of the rotor disk. This variation in lift causes the rotor disk to tilt and the helicopter to move during hover flight or change attitude in forward flight. The cyclic is similar to a joystick and is usually positioned in front of the pilot. 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. The rotating section rotates with the rotor and is connected to blade pitch horns through pitch links, one link for each blade. When the swashplate is not tilted, the blades are all at the collective angle. 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. This causes the helicopter to tilt in the same direction as the cyclic. If the pilot pushes the cyclic forward, then the rotor disc tilts forward, and the rotor produces a thrust in the forward direction.
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. 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. 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. The angle of attack is increased on the retreating blade to produce more lift, compensating for the slower airspeed over the blade. And the angle of attack is decreased on the advancing blade to produce less lift, compensating for the faster airspeed over the blade.
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. This condition is called aerodynamic stall. On a helicopter, this can happen in any of four ways.
As helicopter speed increases, airflow over the advancing blades approaches the speed of sound and generates shock waves that disrupt the airflow over the blade causing loss of lift. As helicopter speeds increase, the retreating blade experiences lower relative airspeeds and the controls compensate with higher angle of attack. With a low enough relative airspeed and a high enough angle of attack, aerodynamic stall is inevitable. This is called retreating blade stall. See dissymetry of lift for a fuller treatment of cases 1 and 2 together in a single analysis. Any low rotor RPM flight condition accompanied by increasing collective pitch application will cause aerodynamic stall. Unique to helicopters is the vortex ring state (also known as settling with power) which is when a helicopter in a hover or descent comes into contact with its own down wash causing immense turbulence and loss of lift.
Ex-military Westland Scout AH.1 (XV134), now on the UK Civil Register.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. The main rotor acts like a "windmill" and turns. This technique is known as autorotation. A transmission connects the main rotor to the tail rotor so that all flight controls are available after engine failure. 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. (see Height-velocity diagram).
Stability
Fixed wing aircraft are usually inherently stable. 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. 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 contrast, helicopters are very unstable. Simply hovering requires continuous, active corrections from the pilot. 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. Hovering a helicopter has been compared to balancing yourself while standing on a large beach ball.
Adjusting one flight control on a helicopter almost always has an effect that requires an adjustment of the other controls. 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. Increasing collective will reduce rotor RPM, requiring an increase in throttle to maintain constant rotor RPM. Changing collective will also cause a change in torque, which will require the pilot to adjust the foot pedals.
Small helicopters can be so unstable that it may be impossible for the pilot to ever let go of the cyclic while in flight. 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).
Limitations
The single most obvious limitation of the helicopter is its slow speed. There are several reasons why a helicopter cannot fly as fast as a fixed wing aircraft.
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. 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. The airspeed of the forward-going rotor blade is much higher than that of the helicopter itself. It is possible for this blade to exceed the speed of sound, and thus produce vastly increased drag and vibration. 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. Most rotors are not rigid. 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. To counter this dissymmetry of lift, 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. Conversely, the retreating blade flaps down, develops a higher angle of attack, and generates more lift. 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. For this reason, the maximum safe forward speed of a helicopter is given a design rating called VNE, Velocity, Never Exceed. In some designs the hub is rigid. The blades are made from composites which can bend without breaking. Fully rigid rotors exist and create very responsive helicopters. In most such designs, the lift is varied cyclically and according to the speed of the helicopter. 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.
The Bristol Type 192 Belvedere (then taken on by Westland) twin rotor helicopter had a large cargo door and external hoist, and was used as personnel/paratroop transport, casualty evacuation, and for lifting large loads. The Belvedere had a production run of only 26 and went into RAF service in 1961.Rotorhead design is a limiting factor on many helicopters. 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. Helicopters are susceptible to potentially disastrous vortex ring effects. In these, the downward wind from the rotor causes a circular vortex to form around the rotor. 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. During the closing years of the 20th century designers began working on helicopter noise reduction. Urban communities have often expressed great dislike of noisy aircraft, and police and passenger helicopters can be unpopular. 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.
Helicopters vibrate. An unadjusted helicopter can easily vibrate so much that it will shake itself apart. To reduce vibration, all helicopters have rotor adjustments for height and pitch. Most also have vibration dampers for height and pitch. Some also use mechanical feedback systems to sense and counter vibration. Usually the feedback system uses a mass as a "stable reference" and a linkage from the mass operates a flap to adjust the rotor's angle of attack to counter the vibration. Adjustment is difficult in part because measurement of the vibration is hard. The most common adjustment measurement system is to use a stroboscopic flash lamp, and observe painted markings or coloured reflectors on the underside of the rotor blades. The traditional low-tech system is to mount coloured chalk on the rotor tips, and see how they mark a linen sheet.
Landing
Helicopter in 2006 aviation exposition in Maloka Museum of Colombia
On a ship
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. In the U.S. Navy it is commonly and properly referred to as the flight deck. 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.
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. 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. This device was pioneered by the Royal Canadian Navy and was called "Beartrap". The U.S. 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.
A secondary purpose of the haul-down device is to equalize electrostatic potential between the helicopter and ship. 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. Coaxial rotor helicopters in flight are highly resistant to side-winds, which makes them suitable for shipboard use, even without a rope-pulley landing system.
Hazards of helicopter flight
As with any moving vehicle, operation outside of safe regimes could result in loss of control, structural damage, or fatality. 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 following is a list of some of the potential hazards for "conventional" helicopters:
Settling with power Retreating blade stall Ground resonance Low-G condition Operating within the shaded area of the height-velocity diagram Vortex ring state, a problem the V-22 Osprey was associated with.
Helicopter models and identification
In identifying helicopters during flight it is helpful to know that when viewed from below, the rotor of a French, Russian, or Soviet designed helicopter rotates counter-clockwise, whilst that of a helicopter built in Italy, the UK or the USA rotates clockwise.
Some companies, notably Schweizer Aircraft Corporation in the USA, are developing remotely-controlled variants of light helicopters for use in future battlefields. Rotomotion is currently selling a line of small (less than 50 kg) rotorcraft UAVs, including an all electric helicopter.
Hybrid types that combine features of helicopters and fixed wing designs include the gyrodyne such as the experimental Fairey Rotodyne of the 1950s, the compund helicopter (Lockheed AH-56 Cheyenne), and the tiltrotor (Bell Boeing Osprey. The latter is on order by the U.S. Marine Corps and will be the first mass produced tilt-rotor aircraft to enter service.
A helicopter should not be mistaken for an autogyro, which is a predecessor of the helicopter, that gains lift from an unpowered rotor.
Some common nicknames for helicopters are "copter", "chopper", "whirlybird", "windmill", "helo" (common U.S. Navy usage) or "paraffin Budgie" (the latter term being mostly used in the UK offshore oil industry).
Helicopters are useful for landing in tight spaces.
Many companies have helicopters for transport.
See also
Wikimedia Commons has media related to: HelicoptersCoaxial rotor Helicopter rotor Helicopter pilotage Helicopter flight controls Helicopter noise reduction Autorotation Aeronautical engineering Transverse Flow Effect Attack Helicopter Harold E. Thompson Gyrocopter Radio-controlled helicopter Gyrodynes and Heliplanes
References ^ http://www.helis.com/stories/burma45.php Thicknesse P, Jones A et al, Military Rotorcraft, 2nd edition, 2000, Brassey's World Military Technology series, Shirvenham UK, xvi + 160pp, ISBN 1-85753-325-9 Wragg D, Helicopters at War: A pictorial history, 1983, Robert Hale Ltd, London UK, 283pp, ISBN 0-7090-0858-9
End of Wikipedia content, http://en.wikipedia.org/wiki/Helicopter
Helicopter Pictures
A picture of a military helicopter from 1000 Pictures Two CV-22 Osprey helicopter-aircraft in formation flight, seen from behind right – from 1000 Pictures A US Department of Defense helicopter picture taken at Jalalabad, Afghanistan – from Air Cav A unique picture of Columbia CH-46 helicopter – from Globe Master
Content derived from Wikipedia article on Helicopter Rotor
A rotor is the rotating part of a helicopter which generates lift, either vertically in the case of a main rotor, or horizontally in the case of a tail rotor.
Contents
1 Rotor head design 2 Description of parts and their functions 3 History and development 3.1 Swash plate 3.2 Fully articulated rotors 3.3 Two bladed rotors 3.4 Tail Rotors 4 Blade design 5 Limitations and hazards 6 Why do helicopters not use ring-protected rotors?
Rotor head design
The rotor head is comprised of a robust hub with attachment points for the blades and mechanical linkages designed to control the pitch of the blades.
Description of parts and their functions
The simple rotor of a Robinson R22 showing (from the top):
The following are driven by the link rods from the rotating part of the swashplate. Pitch hinges, allowing the blades to 'twist', ie change pitch or roll. Teeter hinge, allowing one blade to rise while the other falls. Usually rise and fall is due to pitch or roll. There may be harmonics, it allows pitch and roll of the rotor to be independent of the fuselage, it disables negative G flights. Scissor link and counterweight, carries the main shaft rotation down to the upper swashplate Rubber covers protect moving and stationary shafts Swashplates, transmitting cyclic and collective pitch to the blades (the top one rotates) Three non-rotating control rods transmit pitch information to the lower swashplate Main mast leading down to main gearbox
History and development Prior to the development of powered helicopters in the mid 20th century, autogiro pioneer Juan de la Cierva researched and developed many of the fundamentals of the rotor. Cierva is credited with successful development of multi-bladed, fully articulated rotor systems. This type of system is widely used today in many multi-bladed helicopters.
In the 1930s, Arthur Young improved stability of two bladed rotor systems with the introduction of a stabilizer bar. This system was used in several Bell and Hiller helicopter models. It is also used in many remote control model helicopters.
Some modern military helicopters employ a rigid rotor design, in which flexible materials are used in place of hinges.
Swash plate
The pitch of main rotor blades is varied throughout its rotation in order to control the magnitude and direction of the thrust vector. Collective pitch is used to increase or decrease rotor thrust perpendicular to the axis of rotation. Collective pitch controls the magnitude of the thrust vector. Blade pitch is varied during rotation to effectively tilt the rotor disk and control the direction of the thrust vector. These blade pitch variations are controlled by the swash plate.
The swash plate is essentially comprised of two concentric disks or plates, one plate rotates with the blades while the other does not rotate. The rotating plate is connected to individual blades through pitch links and pitch horns. The non-rotating plate is connected to links which are manipulated by pilot controls, specifically, the collective and cyclic controls.
The swash plate can shift vertically and tilt to some degree. Through shifting and tilting, the non-rotating plate controls the rotating plate, which in turn controls the individual blade pitch.
Fully articulated rotors
During the development of the autogyro, Juan de la Cierva built scale models to test his designs. After promising results, he built full size models. Just prior to takeoff, his autogyro rolled unexpectedly and was destroyed. Believing this to have been caused by sudden wind gusts, Cierva rebuilt it only to suffer an almost identical accident. These setbacks caused Cierva to consider why his models flew successfully, while the full-sized aircraft did not.
Cierva realized that the advancing blade on one side created greater lift than on the retreating side. This is due to increased airspeed on the advancing side which creates a rolling force. The scale model was constructed with flexible materials, specifically rattan, so the rolling force was absorbed as the blades flapped and compensated for asymmetry of lift. Cierva concluded that the full size steel rotor hub was far too rigid and introduced flapping hinges at the rotor hub.
Flapping hinges solved the rolling problem, but introduced lateral hub stresses as the blade center of mass moved as the blades flapped (remember there is some coning). Due to conservation of angular momentum, the blades accelerate and decelerate as their center of mass moves inward and outward, like a twirling ice skater. Cierva added lag-lead, or delta hinges to reduce lateral stresses.
Two bladed rotors
Rotors with more than two blades have two dedicated connections, which make the inner swash plate turn. In two bladed rotor systems the blades take over this task.
Arthur Young found that stability could be increased significantly with the addition of a stabilizer bar perpendicular to the two blades. The stabilizer bar has weighted ends which cause it to stay relatively stable in the plane of rotation. The stabilizer bar is linked with the swash plate in such a manner as to reduce the pitch rate. Other names are Hiller panels, Hiller-system, Bell-Hiller-system, and flybar. In fly by wire helicopters or RC-models a computer with gyros and a venturi sensor can replace the stabilizer. This flybarless design has the advantage of easy reconfiguration from beginner, to 3d, to drag race.
The two blades can flap as a unit and therefore do not require lag-lead hinges (the whole rotor slows down an accelerates per turn). Two bladed systems require a single teetering hinge and two coning hinges to permit modest coning of the rotor disk as thrust is increased.
Tail Rotors
Tail rotors are generally simpler than main rotors since they require only thrust control. A simplified swash plate is used to control collective pitch. Two bladed tail rotors include a teetering hinge to compensate for dysymmetry of lift.
Blade design
The blades of a helicopter are long, narrow aerofoil cross-sections with a high aspect ratio, a shape which minimises drag from tip vortices (see the wings of a glider for comparison). They generally contain a degree of washout to reduce the lift generated at the tips, where the airflow is fastest and vortex generation would be a significant problem.
Limitations and hazards
Helicopters with semi-rigid rotors, for example the two-bladed design seen on Robinson and some other light helicopters, must not be subjected to a low-G spot. Otherwise their rotors may move beyond the normal limits in a condition known as mast humping which can cause the rotor droop stops to shear the mast and hence detach the whole system from the aircraft.
Why do helicopters not use ring-protected rotors?
There are serious dangers of rotor contact with a fixed object, the fuselage or people. Some people have asked if there is any reason that the rotors do not have some sort of ring fixed around the blades to protect them from contact-damage (or slicing someone in half)? Many radio-controlled model helicopters have this feature.
It has never been implemented in a full-size helicopter, even though blade strike accidents often have tragic consequences:
A ring would add a significant amount of mass, and hence rotor inertia, where it isn't wanted - at the blade tips A ring would prevent blades from flapping up and down as they face towards or away from the translational airflow A ring would prevent blades from leading and lagging, which is necessary on systems with more than two blades In order to provide a realistic degree of blade strike protection, such a ring would have to be massively strong and contribute a big weight penalty So, such a device would seriously impair the helicopter's ability to achieve powered flight and lead to very poor flight characteristics and fuel economy. The more practical approach, which is implemented in most places where helicopters are commonly used by the emergency services and private individuals, is to tightly regulate the locations where helicopters are allowed to take off and land, always ensuring that the avoidance of human and property damage is the highest priority.
Retrieved from http://en.wikipedia.org/wiki/Helicopter_rotor
End of Wikipedia content, http://en.wikipedia.org/wiki/Helicopter_rotor
Content derived from Wikipedia content on Helicopter Pilotage
Helicopter pilotage is the art of manipulating the flight controls of a helicopter in order to achieve controlled aerodynamic flight.
Contents
1 Flight controls 1.1 Cyclic 1.2 Collective 1.3 Anti-torque pedals 2 Flight conditions 2.1 Hovering 2.2 Forward flight 2.3 Hazards 3 See also
Flight controls
A typical helicopter has three separate flight control inputs. These are the cyclic, the collective, and the anti-torque pedals. Depending on the complexity of the helicopter, the cyclic and collective may be linked together by a so-called mixing unit, a mechanical or hydraulic device that combines the inputs from both and then sends along the "mixed" input to the control surfaces to achieve the desired result.
Cyclic
The cyclic stick is usually located in between the pilot's legs. The cyclic is so called, because it changes the pitch of the rotor blades cyclically, that is the pitch of a given blade will be different depending upon its position as it rotates about the rotor head. The result is to tilt the rotor disk in a particular direction, resulting in the helicopter moving in that direction.
Collective
The collective is usually located on the pilot's left side. The collective changes the pitch of the rotor blades collectively or all at the same time, regardless of their position. Therefore, if a collective input is made, all the blades change equally, and the result is the helicopter increasing or decreasing in altitude.
Anti-torque pedals
The anti-torque pedals are located in the same position as the rudder pedals in an airplane, and serve a similar purpose, namely to control the direction in which the nose of the aircraft is pointed. Application of the pedal in a given direction changes the pitch of the tail rotor blades, increasing or reducing the thrust produced by the tail rotor and causing the nose to yaw in the direction of the applied pedal.
Flight conditions
There are two basic flight conditions which may be considered for a helicopter. These are hovering and forward flight.
Hovering
Hovering is the most challenging part of flying a helicopter. This is because that while in a hover, a helicopter generates its own gusty air which acts against the fuselage and flight control surfaces. The end result is constant control inputs and corrections by the pilot to keep the helicopter where he wants it. However, despite the actual complexity of the act itself, the control inputs themselves in a hover are quite simple. The cyclic is used to eliminate drift in the horizontal plane, that is to control forward and back, right and left. The collective is used to maintain altitude. The pedals are used to control nose direction or heading. It is the interaction of these controls that makes hovering so difficult, since you cannot change one without having to change the other two, which will then require even more changes in a never-ending cycle of correction after correction.
Forward flight
For the purposes of this article, we will consider forward flight to be flight at airspeeds in excess of 40 KIAS, as it is at this airspeed at which most pitot-static airspeed systems become reliable. In forward flight a helicopter's flight controls behave more like that in a fixed-wing aircraft. Displacing the cyclic forward will cause the nose to pitch down, with a resultant increase in airspeed and loss of altitude. Aft cyclic will cause the nose to pitch up, slowing the helicopter and causing it to climb. The collective now becomes analogous to the throttle in an airplane. Increasing collective(power) while maintaining a constant airspeed will induce a climb while decreasing collective will cause a descent. Coordinating these two inputs, down collective + aft cyclic or up collective + forward cyclic, will result in airspeed changes while maintaining a constant altitude. The pedals serve the same function in both a helicopter and an airplane, and that is to maintain balanced flight. This is done by applying a pedal input in whichever direction is necessary to center the balance ball.
Hazards
Retreating blade stall Settling with power Ground resonance Vortex Ring
See also
Anatomy of a helicopter Helicopter flight controls Helicopter rotor Aeronautical engineering
Retrieved from http://en.wikipedia.org/wiki/Helicopter_pilotage
End of Wikipedia content, http://en.wikipedia.org/wiki/Helicopter_pilotage
Content derived from Wikipedia article on Helicopter Flight Controls
Flight regimes
Helicopters can operate in several flight regimes.
Forward flight is when airspeed is greater than 15 mph, which is about the point of effective translational lift (ETL). At ETL, less engine power is required until about 40 mph airspeed when power requirements increase again.
Hover in ground effect is when the helicopter is flying within a half main rotor diameter above the ground and less than about 15 mph airspeed (ETL). This requires a significant amount of power, much more than in forward flight, but less then hover out of ground effect.
Hover out of ground effect is similar to hover in ground effect, but the altitude is greater than a half main rotor diameter. This requires the greatest amount of engine power and is also the most dangerous flight condition.
Autorotation is a descent with no engine power used. The engine can still be running, but a one-way freewheel disengages the engine from the transmission. Autorotation is used for emergency landing or high speed descent.
The following mnemonics are used to recall changes necessary for speed-up and for slowing:
Speed-Up: "L.L.F. Lift, Left, Forward" - Lift Collective, Left Pedal and Forward Cyclic. Slow-Down: "R.R.A. Reduce, Right, Aft" - Reduce (drop) Collective, Right Pedal and Aft Cyclic. Note that left pedal is applied with increased collective for counterclockwise rotating main rotor (advancing from pilots right to left). This is common in most helicopters built in Italy, the UK, or the United States. For clockwise rotating main rotors (French, Russian, or Soviet designed helicopters), right pedal is applied with increased collective.
The following is a table of helicopter flight controls.
Name Directly controls Primary effect Secondary effect Used in forward flight Used in hover flight Cyclic lateral Varies main rotor blade pitch fore/aft Tilts main rotor disk laterally via the swashplate Increase descent rate To turn the aircraft To move sideways Cyclic longitudinal Varies main rotor blade pitch left/right Tilts main rotor disk longitudinally via the swashplate Increase descent rate Control attitude To move forwards/backwards Collective Collective angle of attack for the rotor main blades via the swashplate Increase/decrease vertical thrust vector Increase/decrease torque and engine RPM To adjust vertical speed To adjust skid height/vertical speed Pedals Collective pitch supplied to tail rotor blades Yaw rate Increase/decrease torque and engine RPM (less than collective) Adjust slip angle Control yaw rate/heading
See also
Helicopter Pilotage Anatomy of a helicopter Helicopter rotor Aeronautical engineering Retrieved from http://en.wikipedia.org/wiki/Helicopter_flight_controls
End of Wikipedia content, http://en.wikipedia.org/wiki/Helicopter_flight_controls
Content derived from Wikipedia article on Attack Helicopter
A Russian Mil Mi-24 attack helicopter.An attack helicopter is a military helicopter armed for attacking targets on the ground such as enemy infantry, armored vehicles and structures, using autocannon and machine-gun fire, rockets, and precision guided missiles such as the Hellfire. Many attack helicopters are also capable of carrying air to air missiles, though mostly for purposes of self-defense. Today's attack helicopter has two main roles: first, to provide direct and accurate close air support for ground troops, and second, to destroy enemy armored concentrations behind enemy lines.
Contents
1 History 1.1 Algerian War 1.2 U.S. Army 1.3 Vietnam and the Gunship 1.4 Soviet Army 2 The Modern Attack Helicopter 3 Models 4 References 4.1 Uncited References
History
Algerian War
After the Korean War, a few farsighted military establishments began to examine the helicopter as a possible platform for use in ground attack. The French Army was one of the first military forces to modify and use helicopters in combat in a ground attack role during the Algerian War of 1954-62. In 1955, French field commanders placed infantry machine gunners in the stretcher panniers of their Bell 47 (Sioux H-13) casualty evacuation helicopters. The ad hoc gunships were used to reach FLN guerrilla positions on otherwise inaccessible mountain ridges and peaks, but were far too underpowered.
In 1956, the French Air Force experimented with arming the Sikorsky H-19 Chickasaw aka Sikorsky S-55, then being superceded in service by the more capable Piasecki CH-21 and Sikorsky CH-34 helicopters. The H-19 was originally fitted with two rocket launchers, and a 20-mm cannon, both mounted axially on the outside of the aircraft. Then, a 20-mm cannon, two 12.7-mm machine guns, and a 7.5-mm light machine gun were mounted to be fired from the cabin windows[1], but this load proved far too heavy, and even more lightly-armed H-19 gunships proved underpowered. Some Piasecki CH-21 helicopters were armed with fixed, forward-firing rockets and machine guns and a few even had racks for bombs, but the H-21 lacked the maneuverability and performance needed for offensive action. Most CH-21s in service were eventually fitted with a door-mounted 12.7- or 20-mm gun for self-defense only.
The Sikorsky CH-34 was also modified into a gunship by the French Navy: standard armament comprised a MG 151 20-mm cannon firing from the cabin door, two 12.7-mm machine guns firing from the cabin windows to port, plus racks for 37 mm or 68 mm rockets. While the CH-34 was effective in the ground attack role, official evaluations at the time indicated that the CH-21 was more likely to survive multiple hits by ground fire than was the CH-34; this was assumed to be a consequence of the location and construction of the CH-34's fuel tanks. Nevertheless, by the close of the Algerian War, attack helicopters such as the CH-34 were being used in synchronized operations with troop-carrying CH-21 helicopters in large-scale counterinsurgency operations.
U.S. Army
The U.S. Army began to employ helicopters built by Bell, Hiller, Sikorsky and Piasecki. At first, helicopters were used mainly as airborne ambulances, cargo carriers, and observation platforms, or as a rescue craft for picking up pilots downed in the sea or from otherwise inaccessible terrain. However, the U.S. and the United Kingdom soon began modifying existing helicopters as anti-submarine weapons (ASW) platforms, carrying depth bombs and Magnetic Anomaly Detector gear. After learning of French Army experiments, the U.S. Army modified Sikorsky and other larger helicopters with fixed and flexible-mount machine guns, rockets, and cannon. [verification needed]
Vietnam and the Gunship
Helicopters played an integral part in the U.S military's land and air operations.During the 1950s, with the increasing use of the helicopter for infantry transport, the U.S. saw a need for helicopters to be used as aerial artillery to provide fire suppression and ground support close to the battle. The first United States use of the attack helicopter in large-scale combat operations was during Vietnam. The U.S. Army took a UH-1 'Huey' and put machine guns and 2.75" Folding Fin Aerial Rockets (FFAR) on struts parallel with the fuselage. With its more powerful turbine engine, the Huey UH-1C gunship configuration worked well, and saw considerable combat service in Vietnam.
In the mid-1960s the U.S. Army concluded that a purpose-built gunship with more speed and firepower was required in the face of increasingly intense ground fire (often using heavy machine guns and anti-tank rockets) from Viet Cong and NVA troops. Based on this realization, and with the growing involvement in Vietnam, the U.S. Army developed the requirements for a dedicated attack helicopter, the Advanced Aerial Fire Support System (AAFSS). The aircraft would be able to hover out of ground effect (OGE) at 6000 feet (PA) and 95 degrees, with a 220 knot speed dash capability and carry a much larger payload of weapons. The aircraft design selected for this program in 1965, was the Lockheed AH-56 Cheyenne.[2]
However, the U.S. Army split its efforts between the acquisition of a dedicated attack helicopter, and the continued use of improvised interim aircraft (such as the UH-1B/C). So, that same year, a group of high-level officers met to evaluate several prototype versions of armed aircraft to determine which provided the most significant increase in capability to the UH-1B. The three highest-ranking aircraft out of the evaluation (Sikorsky S-61, Kaman UH-2, and Bell Huey Cobra) were selected to compete in flight trials conducted by the Aviation Test Activity. As a result, Bell's Huey Cobra was recommended to be the interim armed helicopter until the Cheyenne was fielded. On 13 April 1966, the U.S. Army awarded Bell Helicopter Company a production contract for 110 AH-1G Cobras.[2] The Cobra had a slender fuselage to make the aircraft a smaller target, increased armor protection, and greater speed.
In 1967, the first AH-1Gs were deployed to Vietnam, around the same time that the Cheyenne successfully completed its first flight and initial flight evaluations. And while, the Cheyenne program suffered setbacks over the next few years due to design issues (a result of discrepancies in requirement documents during the contract process), the Cobra was establishing itself as an effective aerial weapons platform, even despite its performance shortcomings when compared to the AH-56[2] and design issues of its own. By 1972, when the Cheyenne program was eventually cancelled to make way for the Advanced Attack Helicopter (AAH)[2], the interim "Snake" had built a solid reputation as an attack helicopter.
Soviet Army
During the 1960s, the Soviet Union, saw the same need for a ground attack helicopter. The Soviets equipped Mil Mi-8's in a similar configuration as the US Army's UH-1s. This attack helicopter was eventually developed into the famous Mi-24 Hind.
The Modern Attack Helicopter
During the late 70's the U.S. Army saw the need of more sophistication within the attack helicopter corps, allowing them to operate in all weather conditions. With that the Advanced Attack Helicopter program was started. From this program the Hughes YAH-64 came out as the winner. The Russians, watching US aircraft development, saw the need of a more advanced helicopter also. Military officials asked Kamov and Mil to submit designs. The Ka-50 officially won the competition, but Mil decided to continue development of the Mil-28 that they had originally submitted.
The 1990's could be seen as the coming-of-age for the U.S. attack helicopter. The AH-64 Apache was used extensively during Operation Desert Storm with great success. Apaches fired the first shots of the war, destroying enemy early warning radar and SAM sites with their Hellfire missiles. They were later used successfully in both of their operational roles, to direct attack against enemy armor and as aerial artillery in support of ground troops. Hellfire and cannon attacks by Apache helicopters destroyed many enemy tanks and armored cars.
Today, the attack helicopter has been further refined, and the AH-64D Apache Longbow demonstrates many of the advanced technologies being considered for deployment on future gunships. The Russians are currently deploying the Ka-50, and Mi-28, though these attack aircraft are not linked into a command and control system at a level comparable to current U.S. equipment. Many students of ground attack helicopter warfare feel that this is a requirement of today's modern armies, since attack helicopters are being increasingly incorporated as part of a linked support element system by most of the armies of the world.
In the last 20 years USSOCOM has been developing the armed special forces gunship, using the MH-60. These helicopters are to be used as an attack element with Special Operators to do the clean up, or to deliver the operators and support them on the ground. They were used successfully (to the chagrin of CINC CENTCOM) during the Scud Hunt.
The US Army typically uses observation helicopters (such as the OH-58 and OH-6) in support of attack helicopter. But it is starting to fall out of favor as the gunships are getting as sophisticated or more than the observation helicopters deployed to support them.
Models
An Apache Helicopter of the U.S ArmyModern examples include:
AH-1 Cobra Mil Mi-24 AH-64 Apache Agusta A129 Mangusta Eurocopter Tiger Mil Mi-28 Havoc Kamov Ka-50 Kamov Ka-52 Alligator Denel Aviation AH-2 Rooivalk HAL Light Combat Helicopter (Under Development)
References
^ Tom Cooper (12 Nov 2003). Algerian War 1954-1962. Western and North African Database. Air Combat Information Group (www.acig.org). ^ a b c d Office of the Assistant Vice Chief of Staff of the Army (1973). "An Abridged History of the Army Attack Helicopter Program". Department of the Army.
Uncited References
Duke, R.A., Helicopter Operations in Algeria [Trans. French], Dept. of the Army (1959) France, Operations Research Group, Report of the Operations Research Mission on H-21 Helicopter (1957) Leuliette, Pierre, St. Michael and the Dragon: Memoirs of a Paratrooper, New York:Houghton Mifflin (1964) Riley, David, French Helicopter Operations in Algeria Marine Corps Gazette, February 1958, pp. 21-26. Shrader, Charles R. The First Helicopter War: Logistics and Mobility in Algeria, 1954-1962 Westport, CT: Praeger Publishers (1999) Spenser, Jay P., Whirlybirds: A History of the U.S. Helicopter Pioneers, Seattle, WA: University of Washington Press (1998) Retrieved from http://en.wikipedia.org/wiki/Attack_helicopter
End of Wikipedia content, http://en.wikipedia.org/wiki/Attack_Helicopter
Content derived from Wikipedia article on Radio Controlled Helicopters
Radio controlled (RC) helicopters are model aircraft which are unique from RC airplanes because of the differences in construction, aerodynamics, and flight training. Several basic designs of RC helicopters exist, some more maneuverable than others (such as helicopters with collective pitch). The more maneuverable designs are often harder to fly, but benefit from greater aerobatic capabilities.
Flight controls allow pilots to control the collective and throttle (usually linked together), the cyclic controls (pitch and roll), and the tail rotor (yaw). Controlling these in unison enables the helicopter to perform most of the maneuvers an aeroplane can do, and many that aeroplanes cannot do; in this manner, they are quite similar in operation to full-sized helicopters.
The various helicopter controls are effected by means of small servo motors. A piezoelectric gyroscope is typically used on the tail rotor (yaw) control to counter wind and torque reaction induced tail movement. This "gyro" does not apply a mechanical force, but rather, electronically adjusts the control signal to the tail rotor servo.
The engines used are typically methanol powered two stroke motors, however gasoline, jet turbine and increasingly electric motors are also used.
RC helicopters can range in price from as little as $30 to several thousands of dollars or more.
Contents
1 Types of R/C Helicopter 2 Electric 3 Glow 4 Turbine 5 Radio Mfgs 6 PCM 7 PPM 8 Construction 9 Competition 10 Commercial applications 11 References
Types of R/C Helicopter
Electric, Glow, Gas, Turbine.
Electric
Electric helicopters come in many different sizes, sometimes referred to as 300, 400 and 600 etc. This nomenclature originate from the practice applied to brushed motors of giving sizes based roughly on the length of the motor's can in millimetres divided by ten.
One of the smallest commercial electric helicopters made is the Picco Z sold at Radio Shack and on Ebay as well, costing about $50. The next smallest might be the Micron FP helicopter, another battery operated R/C helicopter.
Glow
Glow-plug engine powered helicopters come in different sizes, typically 30,50,60 and 90 size. These numbers originated from the size of glow-plug engine used in the different models (0.30 cu in, 0.50 cu in etc). The bigger and more powerful the engine, the larger the main rotor blade that it can turn and hence the bigger the aircraft overall.
Turbine
Turbine power plants are of 3 basic configurations as of 10/2006. These configurations each utilize a single stage compressor wheel, combustion chamber, exhaust turbine wheel. The differences between the three are drive systems; belt, second turbine wheel (2 stage), or gear reduction. From that point on most helicopters are quite similar to 'regular' RC helicopters. They run on JetA, or K1 (Kerosene) and have a little oil mixed in the fuel. Turbines are rated in Kilowatts (KW) of power. Currently marketed turbine powerplants average 3-7 KW.
Radio Mfgs
Leading radio manufacturers are Spektrum, Futaba, JR,Hitec, Multiplex, Airtronics, Sanwa and Graupner in no particular order.
Small fixed-pitch helicopters need a 4 channel radio (throttle, elevator, aileron, rudder) while collective-pitch models need a minimum of 5 channels with 6 being most common (throttle, collective pitch, elevator, aileron, rudder and gyro gain).
Radio prices vary from $199-$3,000 USD.
PCM
Pulse Code Modulation. A scheme in which the commanded position for each servo is transmitted as an encoded number.
PPM
Pulse Position Modulation. A scheme in which the commanded position for each servo is transmitted as the position of a pulse edge with respect to a reference edge.
Construction
Construction is typically of plastic, glass reinforced plastic, aluminium or carbon fibre. Rotor blades are typically made of wood, fibreglass or carbon fibre. Models are typically purchased in kit form from one of about a dozen popular manufacturers and take 5 to 20 hours to completely assemble.
Construction of a scale helicopter will use all of the above materials, plus others, may take as many at 2500 hours to complete to the builders satisfaction. Many are scratch built from 3D mechanics. Scale (body) kits may be purchased to use with the mechanical portions to create a minature replica.
Competition
Aerobatic helicopter flying has historically been flown according to the Fédération Aéronautique Internationale rules, which for helicopters are labelled F3C. These include a predetermined routine of hovering and aerobatics.
An advanced form of RC helicopter flying is called 3D. During 3D flying, helicopters perform advanced aerobatics in a freestyle form. There are a number of 3D competitions around the world, two of the best known are the 3D Masters in the UK and the eXtreme Flight Championship (XFC) in the USA.
Scale competition is the competing with a minature replica of a real flying helicopter. In the USA there are local competitions, AMA Scale Helicopter Championships, and IRCHA scale competitions. Some of these models are so detailed as to be indiscernable from the real aircraft. Competition requires documentation of the full sized helicopter being modeled. It is not at all uncommon for a helicopter of this quality to have a value near $20,000 USD. Flying in a scale competition is centered around actual helicopter maneuvers, performed with proper speed, orientation, and consistency.
Commercial applications
Although RC helicopters are generally used by hobbyists for recreational purposes, they are sometimes used in applications such as aerial photography, filming, and remote observation or inspection. Some companies make RC helicopters specifically for these uses.
References
^ http://www.ezonemag.com/pages/faq/a414.shtml
Australian R/C Helicopters Online
Electric RC Helicopter
RC Precision Products
Retrieved from http://en.wikipedia.org/wiki/Radio-controlled_helicopter
End of Wikipedia content, http://en.wikipedia.org/wiki/Radio-controlled_helicopter
Helicopter Tidbits
B206, a helicopter manufactured by Bell Helicopter, is one of the more commonly used helicopters in the world today. There are about 6000 B 206 helicopters in the world today. A B206 costs, on an average, about $ 1.2 million (2007 data)
Other main makes of Bell Helicopters are B429. The B 429 caters primarily to emergency medical service industry
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