What happens during excessive flapping in a helicopter's rotor system?

Excessive flapping in a helicopter's rotor system refers to the abnormal movement of the rotor blades up and down, which can occur due to a variety of aerodynamic reasons or pilot inputs. When flapping becomes excessive, the rotor blades can indeed move in such a way that they come into contact with the mast at the hub of the rotor system. This can lead to structural damage and potentially catastrophic failure of the rotor system.

While excessive flapping might cause disturbances in lift and handling characteristics, the primary concern is the physical contact between the blades and the mast. This contact is not just a minor issue; it can result in immediate mechanical failure.

On the other hand, decreased lift leading to stall, rapid altitude gain, or automatic stabilization are not accurate descriptions of the direct consequences of excessive flapping. Flapping does not inherently result in a stall or a stable flight condition; rather, it is a significant aerodynamic problem that requires correction to avoid damage and maintain safe flight operations.