The solidity ratio in aerodynamics is a parameter that describes the fraction of an aircraft’s wing area that is occupied by its lifting surfaces, such as wings and flaps. It is used to characterize the openness or “solidity” of the wing.
Formula: The solidity ratio (S) is defined as the ratio of the total wing area (A_wing) to the planform area (A_planform) of the wing. The formula is as follows:
The solidity ratio is a dimensionless quantity, which means it has no specific SI unit. It is simply a ratio of areas and is expressed as a pure number without units.