Which speed is primarily used after all obstacles have been cleared during a climb?

The best rate-of-climb speed (V_Y) is the speed primarily used after all obstacles have been cleared during a climb because it allows the helicopter to gain altitude in the most efficient manner.

When a helicopter has successfully traversed any nearby obstacles and is in a clean climbing attitude, transitioning to V_Y ensures that the helicopter will climb at the maximum possible rate. This speed is designed for optimizing vertical performance and is crucial in situations where height gain is a priority, such as when the helicopter is clear of hazards or when altitude needs to be quickly regained.

In contrast, the best angle-of-climb speed (V_X) is useful during the initial phase of the climb when clearance from obstacles is critical; it maximizes altitude gain over a specific horizontal distance. Stall speed is the minimum speed at which the helicopter can maintain controlled flight and is not directly related to climbing efficiently after obstacles. Minimum safe speed refers to a speed that ensures a sufficient margin above stall under various conditions and does not specifically optimize climb performance. Therefore, V_Y is the most appropriate speed for achieving effective ascent after obstacle clearance.