In airfoil analysis using XFOIL, Ncrit (critical amplification factor) is a key parameter that controls the transition from laminar to turbulent flow over the airfoil surface by modeling the growth of Tollmien-Schlichting waves via linear instability. It represents the logarithm of the amplification factor of the most-amplified frequency that triggers transition, and its value is chosen based on the ambient disturbance level in the operating environment. A higher Ncrit value indicates a less sensitive flow, promoting laminar flow over a larger portion of the airfoil, while a lower value indicates a more sensitive flow, leading to earlier transition to turbulence. Typical Ncrit values range from 12–14 for high-performance sailplanes where laminar flow is desired, 9 for average wind tunnel conditions (the default in XFOIL), and 4–8 for dirty or highly turbulent environments.