What is the primary cause of rotation in a spin?

The primary cause of rotation in a spin is that one wing is stalled more than the other. When an aircraft maneuvers into a stall, a critical angle of attack is exceeded, leading the wings to lose lift. In a spin scenario, typically, one wing reaches this stall condition before the other, causing an imbalance in the lift and drag forces acting on the aircraft.

This differential stalling creates a significant yawing moment towards the stalled wing. The wing with higher lift will continue to generate some lift and drag, while the stalled wing will induce a downward and rearward movement. This yawing motion is what initiates the rotation around the aircraft's vertical axis, leading to the characteristic rotation of a spin.

The factors influencing spin behavior are crucial for pilots to understand, particularly in recovery procedures, as recognizing which wing is stalled is fundamental to regaining control of the aircraft.