The rotor disc tilts in the direction that pressure is applied to the cyclic pitch control. If the cyclic is moved forward, the rotor disc tilts forward; if the cyclic is moved aft, the disc tilts aft, and so on. Because the rotor disc acts like a gyro, the mechanical linkages for the cyclic control rods are rigged in such a way that they decrease the pitch angle of the rotor blade approximately 90° before it reaches the direction of cyclic displacement, and increase the pitch angle of the rotor blade approximately 90° after it passes the direction of displacement. An increase in pitch angle increases angle of attack; a decrease in pitch angle decreases angle of attack. For example, if the cyclic is moved forward, the angle of attack decreases as the rotor blade passes the right side of the helicopter and increases on the left side. This results in maximum downward deflection of the rotor blade in front of the helicopter and maximum upward deflection behind it, causing the rotor disc to tilt forward. Besides counteracting torque of the main rotor, the tail rotor is also used to control the heading of the helicopter while hovering or when making hovering turns. Hovering turns are commonly referred to as “pedal turns.” In forward flight, the antitorque pedals are not used to control the heading of the helicopter, except during por- tions of crosswind takeoffs and approaches. Instead they are used to compensate for torque to put the helicopter in longitudinal trim so that coordinated flight can be main- tained. The cyclic control is used to change heading by making a turn to the desired direction. The thrust of the tail rotor depends on the pitch angle of the tail rotor blades. This pitch angle can be positive, neg- ative, or zero. A positive pitch angle tends to move the tail to the right. A negative pitch angle moves the tail to the left, while no thrust is produced with a zero pitch angle. The antitorque pedals, located on the cabin floor by the pilot’s feet, control the pitch, and therefore the thrust, of the tail rotor blades. [Figure 4-5] . The main purpose of the tail rotor is to counteract the torque effect of the main rotor. Since torque varies with changes in power, the tail rotor thrust must also be varied. The pedals are connected to the pitch change mechanism on the tail rotor gearbox and allow the pitch angle on the tail rotor blades to be increased or decreased. With the right pedal moved forward of the neutral posi- tion, the tail rotor either has a negative pitch angle or a small positive pitch angle. The farther it is forward, the larger the negative pitch angle. The nearer it is to neu- tral, the more positive the pitch angle, and somewhere in between, it has a zero pitch angle. As the left pedal is moved forward of the neutral position, the positive pitch angle of the tail rotor increases until it becomes maxi- mum with full forward displacement of the left pedal. If the tail rotor has a negative pitch angle, tail rotor thrust is working in the same direction as the torque of the main rotor. With a small positive pitch angle, the tail rotor does not produce sufficient thrust to overcome the torque effect of the main rotor during cruise flight. Therefore, if the right pedal is displaced forward of neutral during cruising flight, the tail rotor thrust does not overcome the torque effect, and the nose yaws to the right. [Figure 4-6] With the antitorque pedals in the neutral position, the tail rotor has a medium positive pitch angle. In medium pos- itive pitch, the tail rotor thrust approximately equals the torque of the main rotor during cruise flight, so the heli- copter maintains a constant heading in level flight. 4-3 Figure 4-6. Tail rotor pitch angle and thrust in relation to pedal positions during cruising flight. Figure 4-5. Antitorque pedals compensate for changes in torque and control heading in a hover. Tail Moves Tail Moves Negative or LowGLYPH<.notdef> Positive Pitch MediumGLYPH<.notdef> Positive Pitch High PositiveGLYPH<.notdef> Pitch ANTITORQUE PEDALS HEADING CONTROL