After entering a spin, what maintains autorotation?

In a spin, autorotation is maintained primarily due to the difference in stall characteristics between the two wings. Specifically, the down-going wing experiences a higher angle of attack and is more stalled compared to the up-going wing. As the aircraft rotates, the down-going wing exits its stall later than the up-going wing, leading to a situation where the down-going wing generates less lift and more drag. This imbalance reinforces the rotation of the aircraft, resulting in continued autorotation.

In this scenario, as the aircraft enters a spin, the differential stall condition is crucial to understanding why the spin persists. The up-going wing, which is at a lower angle of attack, can produce some lift, but since it is not stalled as severely as the down-going wing, it is unable to counteract the rotational forces effectively. Thus, the more stalled condition of the down-going wing continues to promote the spin until corrective action is taken, such as applying opposite rudder inputs and reducing the angle of attack.

The other potential options do not accurately capture the dynamics within a spin. A scenario where both wings are equally stalled would not sustain the spin, as there would be no differential lift to perpetuate the autorotation. Similarly, while the tail of the aircraft can indeed