Tail rotor
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The tail rotor of a helicopter is mounted on the tail of a traditional single-rotor helicopter, close to perpendicular to the main rotor. It is primarily used in order to counteract the yaw motion and the torque that a rapidly turning disk naturally produces.
[edit] Design variations
There are two major variations to traditional tail rotor design concerning the placement of the tail rotor and the surrounding structure. Some companies such as Eurocopter enclose the rotor within a fantail assembly. Such design - called fenestron - protects the tail rotor from foreign object damage better than the traditional outer mounted design but complicates the design of the tailcone to account for the enclosed mechanisms.
[edit] New developments
In some more recent helicopter designs, the tail rotor has been mounted tangential to the furthest back point of the top rotor. That is to say that it looks much like an old propeller plane, only at the back of the helicopter instead of the front of a wing. In these new designs the rotor spins in a direction opposite to the top rotor (i.e. counter-clockwise if the rotor spins clockwise and vise-versa). This in effect, cancels the spin and has the added benefit of producing forward thrust.[citation needed]
Most, if not all, dual-rotary helicopters do not use tail rotors, instead, the design of the two main rotors is such that they spin in the opposite directions of each other, thus each cancels out the torque and yaw produced by the other. This has been researched in the past and has been incorporated into some European designs.
Sikorsky Aircraft, a UTC subisidiary is currently researching the merger of these two concepts with a dual rotor helicopter with a a rear rotor to provide additional forward thrust and a respective increase in speed and operating range. First flight of a prototype aircraft, the X-2 Demonstrator is expected to be accomplished by the end of 2006
