The ability to control yaw and counter the main rotor’s torque comes from a tail rotor mounted on the tail boom that spins in a plane perpendicular to the main rotor’s plane. By adjusting the thrust of this tail rotor with the anti-torque pedals, the pilot can push the helicopter’s tail left or right, causing the fuselage to rotate around its vertical axis. This anti-torque action is essential because the spinning main rotor tends to force the fuselage to rotate in the opposite direction. The tail rotor provides the necessary counter-torque and yaw control. The other options don’t fit this role: the main rotor is the lift-producing rotor and doesn’t primarily control yaw; an auxiliary rotor isn’t the standard anti-torque device in a typical single-rotor helicopter; and a rudder system isn’t used to provide primary anti-torque in this configuration.

The main idea is that a turn coordinator shows how fast the helicopter is turning around the vertical axis—that is, the yaw rate. The gyro is mounted at a tilt so it responds to yaw and, to some extent, roll, but the information you rely on from this instrument is the rate at which your heading is changing as you turn left or right. It helps you judge how quickly you’re changing direction and ensures you fly coordinated turns. It does not give you a direct reading of pitch rate or your current heading; those come from other instruments.

The ability to control where and how much lift the rotor produces as each blade passes around the hub is essential for directing the helicopter. Changing the blade pitch differently at various azimuths—so one part of the rotor disc produces more lift while another produces less—tilts the rotor thrust and steers the aircraft. This cyclic variation of blade pitch is what’s described by cyclic feathering. It directly describes altering pitch as the blade rotates to change lift and drag around the disk, enabling forward, backward, or lateral movement. Delta hinge refers to a mechanical hinge feature that affects flap or feather motion, not the deliberate, azimuth-dependent pitch change used for steering. Coning is the outward bowing of blades due to centrifugal forces at speed, not a control method. The Coriolis effect involves inertial forces in a rotating frame and is a secondary effect, not the primary mechanism used to vary lift and drag with azimuth.

Rolling about the longitudinal axis happens when you move the cyclic to the left or right. That lateral cyclic input tilts the rotor disk in the same direction, so the helicopter banks toward that side. As the rotor disk tilts, one side of lift increases while the other decreases, causing the fuselage to roll (bank) in the direction of the input. This is why the movement described is called roll. For context, pitch is a different motion—rotation about the lateral axis—caused by forward or backward cyclic to tilt the rotor disk nose-up or nose-down. The agonic line is unrelated here, as it’s a magnetic-reference concept, and an airfoil is simply a lifting surface, not a motion about an axis.