Refer to figures.
Tail Rotors counteract the torque of the main rotor and provide directional control.
The more work an engine has to do, the more anti-torque force is required, and the more power is required to drive the tail rotor, which must balance the main rotor torque at full power with enough thrust left over for directional control.
Typically, it is driven by the engine in powered flight and by the main gearbox in autorotation.
The purposes of the tail rotor include:
Balancing the fuselage torque reaction and stopping it from spinning the other way;
Altering the heading in the hover;
Maintaining a balanced forward flight;
Stopping the fuselage rotating in autorotation, for which it needs to go into a negative pitch.
Generally, tail rotors are around a sixth of the size of main rotors, with similar tip speeds but different speeds than the driveshaft and intermediate gearbox to reduce vibrations and to vary the torque.
They have no cyclic variation. The blades all feather simultaneously when the pedals are moved, so they move collectively from a negative angle setting to a positive angle setting.
Specifically, the amount of pedal needed to maintain heading increases in the hover as density altitude increases because the tail rotor is less effective, while in straight and level flight, or above about 60 knots, the pedals can nearly be ignored.
To minimize unwanted flapping, Delta 3 is used. Also, tail rotors are not fitted with dragging hinges as the blades have a relatively high stiffness and can absorb the bending loads due to lead/lag
Finally, the tail rotor blades have involved in a similar fashion to main rotor blades.They originally were made of wood and now composite materials. The main load-carrying part of a conventional tail rotor blade is its D-spar leading edge.
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