What is the function of applying battery power before folding the tail?

Applying battery power before folding the tail plays a crucial role in indexing the tail rotor, which prevents it from free spinning. When the aircraft is powered on, the tail rotor systems can engage, allowing for controlled movement and positioning. This indexing helps ensure that the rotor blades are correctly aligned and secured in a designated position when the tail is folded, mitigating the risk of damage during ground operations.

It is important to prevent the tail rotor from free spinning, as this could lead to unintended movements or potential damage to the rotor system, which is critical for the aircraft's stability and control. By engaging the battery power, the necessary systems are activated, ensuring a safe and efficient procedure when folding the tail.