How is wing loading expressed in SI units?

Wing loading is a critical parameter in aerodynamics that describes the distribution of an aircraft's weight over its wing area, and it is expressed in units of force per unit area.

The correct expression for wing loading in SI units is in Newtons per square meter (N/m²). This is because wing loading is calculated by dividing the total weight of the aircraft (in Newtons, which is the force due to gravity acting on the mass) by the wing area (in square meters). Thus, the resulting units reflect the pressure or loading experienced by the wings, which is fundamental to understanding how an aircraft will perform in terms of lift and handling characteristics.

Other choices such as kilograms per square meter (kg/m²) and Pascals (Pa) do not accurately reflect the forces involved; kg/m² would describe a mass distribution rather than a loading force, and Pascals, while a measure of pressure, incorporates a unit of force based on the mass of the object, which does not directly align with the way wing loading is defined. Kilograms per cubic meter (kg/m³) describes a density instead, and is irrelevant in the context of wing loading.