In flight mechanics, the “boundary layer” refers to a thin layer of air adjacent to the surface of an aircraft’s wings or other aerodynamic surfaces. This layer of air experiences significant velocity changes and develops due to the interaction of the airflow with the solid surface.
BFL = 0.2387 * (W/S) * (T0 / ρ) * CLt0 * (T/W) * t0
Where: BFL = Balanced Field Length (runway length required for takeoff) W/S = Wing Loading (aircraft weight divided by wing area) T0 = Static Thrust at sea level ρ = Air density at sea level CLt0 = Lift Coefficient at takeoff T/W = Thrust-to-Weight Ratio t0 = Time interval between decision speed (V1) and takeoff speed (Vr)