What do vortex generators help prevent during flight?

Vortex generators are small aerodynamic devices typically mounted on the wings and control surfaces of an aircraft. Their primary function is to enhance airflow over the wings, effectively managing the boundary layer of air. By generating controlled vortices, these devices help maintain attached airflow over the wing's surface, which can significantly reduce the chances of shock-induced separation.

Shock-induced separation occurs when the airflow over the wing is disrupted, especially at high speeds. This results in a loss of lift and can lead to a stall, compromising the aircraft's performance and control. By keeping the boundary layer attached to the wing, vortex generators can delay the onset of shock-induced separation, thereby improving the aircraft's stability and performance during critical phases of flight, especially at high speeds.

Other options like excessive drag, stall at high speeds, and wingtip vortices may relate to the overall aerodynamic characteristics of an aircraft but do not directly address the specific preventative role that vortex generators play with respect to shock-induced separation. Thus, while those issues can be influenced by various design elements and operational factors, the primary and most direct function of vortex generators relates to preventing shock-induced separation.