What determines the angle of attack at which an airplane stalls?

The angle of attack at which an airplane stalls is primarily determined by the design of the wing. This design encompasses various factors such as the shape, profile, and structure of the wing, which fundamentally affect the airflow over it. The stall angle is a crucial characteristic defined by the wing's aerodynamic properties, which include the maximum angle of attack that can be sustained before airflow separates from the wing's surface, resulting in a loss of lift.

While the weight of the aircraft can influence the flight dynamics and may affect the overall performance of the airplane, it does not alter the inherent aerodynamic properties of the wing itself, including the stall angle. Similarly, different types of airfoils can impact how a wing behaves at various angles of attack, but the essential stall angle is rooted in the wing's design specifics rather than merely the type of airfoil.

Weather conditions play a role in how the aircraft reacts to various flying situations but do not fundamentally change the angle of attack at which an airfoil will stall. Thus, the design of the wing is the definitive factor in determining the angle of attack at which stalling occurs.