During which flight condition do vertical fin vortex generators assist?

Vertical fin vortex generators are designed to improve the airflow characteristics around the vertical stabilizer and the rudder, particularly during conditions where airflow may become disrupted, such as during extreme angles of yaw. In this scenario, they create small vortices that energize the boundary layer on the vertical stabilizer. This helps maintain control authority and reduces the risk of adverse yaw or loss of control, which is critical when the aircraft is subjected to significant lateral forces that might lead to a stall in the vertical fin's effective performance.

The other flight conditions, such as steep climbs, level flight, or rapid descents, do not typically present the same critical need for vortex management as conditions with extreme yaw angles do. In steep climbs, airflow remains fairly consistent; in level flight, aerodynamic efficiency is balanced; and during rapid descents, the aircraft is primarily focused on maintaining vertical speed rather than lateral stability. Therefore, the role of vortex generators is most crucial during extreme angles of yaw when maintaining control becomes challenging.