At approximately what angle of attack does airflow over a wing's upper surface become turbulent?

Airflow over a wing's upper surface becomes turbulent when the angle of attack (AoA) increases beyond a certain threshold, which is typically around 15 to 20 degrees for many airfoil designs. As the angle of attack rises, the flow tends to separate from the wing surface, resulting in the transition from a smooth, laminar flow to turbulent flow. This transition has significant implications for lift and drag; turbulent flow can maintain attached flow at higher angles of attack than laminar flow, thereby delaying stall.

Choosing the range of 15 to 20 degrees reflects an understanding of the aerodynamic characteristics of wings and how they behave as conditions change. While lower angle ranges may experience different flow dynamics, they do not typically lead to turbulent flow over the upper surface as consistently as the higher range defined here. The critical angle where turbulence begins is vital for pilots to understand when managing aircraft performance, especially during maneuvering or approach phases of flight.