Stallwinkel

Stallwinkel is a term used in aerodynamics to denote the angle of attack at which a lifting surface, such as an airfoil or wing, reaches the critical point at which lift begins to decline due to flow separation, causing a stall. The concept is closely tied to the critical angle of attack, which is the specific angle where the transition from attached to separated flow occurs.

The exact stallwinkel depends on several factors, including airfoil geometry (camber, thickness), surface roughness, Reynolds number, Mach number, wing planform, and any high-lift devices such as flaps or slats. For a clean, subsonic airfoil, typical stallwinkles lie roughly in the range of about 12 to 18 degrees, but values can be lower for highly cambered sections or rough surfaces, and higher for certain thin, advanced airfoils. The presence of flaps, slats, winglets, or other devices can alter the stallwinkel and the stall characteristics, often shifting the stall to a different part of the flight envelope.

Mechanism: as the angle of attack increases, lift rises until the boundary layer separates on the upper surface, leading to a rapid loss of lift and a large increase in drag. This flow separation is the defining feature of stall. Recovery involves reducing the angle of attack to reattach the flow, sometimes assisted by specific pilot inputs and, in some aircraft, by deliberate stall-breaking procedures.

In flight operations, stallwinkel is a key design and training consideration, with indicators such as stall warning systems and angle-of-attack sensors used to prevent inadvertent stalls. Some configurations, like certain T-tail designs or highly swept wings, can be prone to deep stall, requiring particular recovery procedures.