Final answer:
In helicopters with a main rotor disk that spins counter-clockwise, the fastest airflow speed happens when each blade reaches the bottom position.
Step-by-step explanation:
In helicopters with a main rotor disk that spins counter-clockwise, the fastest airflow speed happens when each blade reaches the bottom position. The speed of airflow around a helicopter can vary depending on several factors, including the helicopter's design, size, weight, and the specific phase of flight.