From RC Helicopter Wiki
The tail rotor is a smaller, vertically mounted rotor attached to the end of the tail boom, whose purpose is to provide control the helicopter's yaw, including counteracting the torque reaction of the main rotor. The tail rotor usually takes one of two forms:
- A fixed pitch rotor driven by an electric motor, with the thrust varied by controlling the rotor speed via an electronic speed controller.
- A variable pitch rotor constructed from two blade grips, a tail rotor hub, and a tail pitch slider which allows the blade pitch (and therefore the thrust of the rotor) to be controlled via a servo. Power is supplied to the tail rotor from the main motor either by a shaft or a tail belt
The ESC or tail pitch servo is controlled indirectly via a gyro; this fine tunes the rudder commands you send from the transmitter to allow for changes in anti-torque demand coming from side winds, fluctuations in head speed, and other transient variables.
The tail rotor is traditionally mounted on the side of the boom towards which the boom would move (from torque reaction from the main rotor) if the tail rotor were to fail (LTE). The tail rotor turns so that the blades come up towards the front of the aircraft, thus making best use of the downwash from the main rotor.
With a variable pitch tail rotor, it is usually best if the pitch slider controls the tail blade pitch on the leading edge of the tail blades. This will in general give a much more useful pitch range, with more '"positive" (clockwise turning) pitch than "negative", which is what you want. Often it is best to set the tail servo centre position to provide enough positive pitch to offset the torque reaction; this can be determined by adjusting the tail setup in rate mode.
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