Anti-Torque Configurations in Helicopters
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Anti-Torque Configurations in Helicopters

Anti-Torque Configurations in Helicopters
       Helicopters are interesting modes of transport aside from airplanes for one thing, they need not use runways or airports to be able to take off and land. But what make them more interesting is how they look strikingly sophisticated and out of this world. They have rotating main rotors in place of wings and have a secondary small rotor at the tail but in some designs the small tail rotor is omitted in place of two rotating main rotors.

As Newton’s 3rd Law of motion states, in every action, there is equal and opposite reaction, in helicopters, this law is best demonstrated by the main rotor as it is being driven by the engine to rotate and produce lift. As the lifting force pushes the whole helicopter airborne, the helicopter body (fuselage) rotates in the opposite direction of the rotation of the main rotor. Say the main rotor rotates clockwise, then the fuselage rotates counterclockwise. To counter this effect termed as “Torque” so comes tail rotors to provide the balance. Other designs don’t have tail rotors but were configurated in a way just to avoid them or cancel out the torque. This article has been written to shed light on the mechanics of helicopters and the underlying theories behind the existing designs.

Sikorsky with the VS-300

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Sikorsky UH-60 Blackhawk

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A Bell 222U helicopter

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Conventional Helicopters – This refer to existing designs based on the basic main rotor and tail rotor concept as shown by Igor Sikorsky in his first helicopter model, the VS-300 which eventually ushered the age of the rotary wing flight. Manufacturers may vary their design signature as to the direction of rotation of the main rotor, the number of rotor blades employed in the main and tail rotors but the physical appearance is almost the same. Manufacturers which have built helicopters based on this concept were Sikorsky, Bell Helicopters, Robinson and Westland.

An MD 520N same type with the one used in the Film "Speed" with Keanu Reeves

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Diagram Showing the Movement of Air through the NOTAR System

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NOTAR (No Tail Rotor) - This anti-torque system was developed and perfected by McDonnell Douglas Helicopter Systems way back in 1975. Utilizing the Coanda Effect as discovered by Romanian aerodynamics pioneer Henri Coanda, an inner fan inside the tailboom builds a high volume of low pressure air directed outside at the end of the tail boom through slots with vents for directional control. The first helicopter model with this anti-torque system was the MD 520N which was successfully flown in May 1990. This design has increased ground safety and the quietest of all certified helicopters by the FAA.

An SA-342 Gazelle of the French Army 

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An EC-130 B4 from a photograph taken by the author

Close Up of the Fenestron Tail Rotor

Fenestron – This design make use of the tail rotor system which is a form of ducted fan. The approach was perfected by Sud Aviation forerunner of the French company Aerospatiale which eventually changed its name to Eurocopter, the helicopter division of the aerospace company EADS (European Aeronautic Defence and Space Company). Early applications of this design was seen in the SA341/342 Gazelle. The helicopter platform which became the basis of the helicopter as seen in the TV series “Highwayman” which stars Sam Jones back in the late 80s. Eurocopter still employs the design in its present helicopter models like the EC-120,EC-130 and EC-135s.

A Russian Kamov Ka-27 Helix helicopter

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Coaxial Rotors – This configuration of helicopter was ventured by the Russian Kamov helicopter bureau founded by Nikolai IIyich Kamov who started building rotor winged aircraft in 1929. In this rotor design, two rotors were set one above the other but rotating in the opposite direction thus cancelling torque. This design actually minimizes the problems and hazards prevalent in conventional helicopters but has increased mechanical complexity owing to its rotor hub design.

A Kaman K-Max helicopter

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Intermeshing Rotors – Sometimes termed the synchropter, this configuration was first utilized in Germany by Anton Flettner in the use of small helicopters for anti-submarine warfare. The design is characterized by two rotor masts mounted near each other in slight angle with the blades intermeshing without colliding. The adoption of this design in the west was made by Charles Kaman in his early helicopter designs through his company, the Kaman Aircraft Corporation. The company produced the HH-43 Huskie helicopter which was utilized by the USAF, US Navy and US Marine Corps in the 1950s and 1970s. The company still produces helicopters with the design as seen in the latest model, the K-Max.

Rear View of a Boeing CH-47 Chinook being loaded in Afghanistan

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A CH-47 variant being utilized as an inflight simulator by NASA

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Tandem Rotors – The tandem rotor system is the signature of Boeing Helicopters. This system is characterized by large rotors mounted one behind the other as in Chinooks (CH-47). The history of this rotor design dates back as far as late 1940s to early 50s when the design was perfected by Frank Piasecki of Piasecki Helicopter Corporation. Then the company changed name to Vertol Aircraft Corporation before it was eventually bought by Boeing in 1960 becoming the Boeing -Vertol. In this configuration, the main rotors are set one behind the other and rotate in the opposite direction thus cancelling the torque effect thereby concentrating the power from the engines to generate lift unlike in conventional helicopters where a portion of power is diverted to counter the torque.

References:

http://en.wikipedia.org/wiki/NOTAR

http://en.wikipedia.org/wiki/Fenestron

http://en.wikipedia.org/wiki/Intermeshing_rotors

http://en.wikipedia.org/wiki/Tandem_rotors

http://en.wikipedia.org/wiki/Coaxial_rotors

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About deep blue:              

                I have played with plastic aircraft toys as a child and was just fortunate to sit in the cockpit of an airplane and eventually learning to fly one in my adult life. The trouble with our lives as humans is the irony of existence. Those with the eyes could barely see and those with the most adventurous life couldn’t write. You may have the most prolific ideas thought about but you lack the ingenuity to work it out. In my own humble way of recollecting bits of pieces which matters to me, I have this opportunity to write and this doesn’t mean to brag about what I knew but to share to you a fragment of reality I was able to realize through the looking glass, ironically, a broken one.

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Comments (6)

As always, well researched, well written, and very informative.

NICE STUFF,YOU TRULY DESERVE TO BE NUMBER ONE ON THIS CATEGORY

Another interesting and well-written piece in helicopters.

awesome I fell in love with your pics

A very interesting post kabayan. You really know your stuff. Re tweeted.

Even with little education in this area, you have managed to teach me a lot and make that so interesting as well.

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