You cannot spread or fold blades over how many knots?

The correct answer specifies that you cannot spread or fold the blades in winds over 45 knots. This is important for the safety and structural integrity of the rotor blades. At such wind speeds, there is a substantial risk of damage to the blades, as well as potential injury to personnel involved in the operation. The design and material properties of the rotor blades are tested for specific conditions, and exceeding the threshold can lead to excessive stress on the blades.

In practice, this limitation ensures that the blades remain stable and secure while on the ground. The operational procedures in aviation include strict adherence to these wind limitations to mitigate risks during ground handling and maintenance. Understanding and following this rule helps to prevent incidents related to rotor blade handling during high wind conditions.