Yawing during turns

Question

This is a question about aeronautics. Does an airplane yaw while it is turning?

Answer 1

Does an airplane yaw while it is turning?

Not always.

A turn is a curvature in the flight path.

Imagine we initiate a bank to the left in a sailplane, without touching the rudder.

As the aircraft rolls left, the nose will swing (yaw) to the right due to adverse yaw, and the yaw string will deflect to the right.

As the left bank angle increases, in most (but not all) gliders at some point the lateral force from the banked wing will overcome the opposing sideforce from the airflow hitting the side of the fuselage, and the flight path will start curving to the left.

As the left bank continues to increase, at some point the aircraft's inherent "weathervane stability" will act to prevent the sideslip angle (i.e. the yaw string deflection angle) from becoming any larger. If the sideslip angle (i.e. the yaw string deflection angle) is not increasing, and the flight path is curving to the left, the aircraft must also now be yawing to the left, not to the right.

At some instant in time before the sideslip angle stopped increasing, it must have been the case that the sideslip angle was still increasing, but at a rate that exactly matched the increasing rate of leftwards curvature in the flight path. At that moment in time, the aircraft's heading must have been momentarily constant. At that moment in time, the aircraft was yawing neither to the right nor to the left. So at that moment in time, the aircraft was turning without yawing.

A simpler (but less often-seen, except at airshows) case of turning without yawing is a 90-degree-banked "knife edge" turn, with the pilot holding top rudder so that the airflow strikes the earthward side of the fuselage and supports the aircraft's weight. Some yaw rotation was involved in establishing the "knife-edge" attitude, but once it is established, the aircraft can fly around in circles indefinitely without any rotation about the yaw axis.