Sliding angle

In figure (a) the aircraft flies forming a zero sliding angle, in the figure (b) wink to have a positive sliding angle. the circular arrow shows the necessary moment for directional stability. Credits: NASA.

The slip angle, slip angle or slip angle is the angle that forms the axis of the ship (axle system of the airplane body) with respect to the relative direction of the wind. It is also known as the angle β (beta), which is positive when the relative direction of the wind is to the right of the axis of the plane.

Do not confuse with yaw angle.

The angle β and the angle of attack (or angle alpha) represent the Euler angles of the wind axes (or aerodynamic axes), relative to the body axes, fixed to the airplane.

wiki