The moment per unit span about the aerodynamic center () is a measure of the twisting or rotational effect experienced by an airfoil or wing section due to aerodynamic forces. It quantifies the moment (torque) exerted around a specified axis per unit span length of the wing or airfoil. The concept of is fundamental in aerodynamics and plays a crucial role in understanding the stability and control characteristics of aircraft and other aerodynamic configurations. The aerodynamic center is a specific point on an airfoil or wing where changes in angle of attack (AoA) do not result in changes in pitching moment. In other words, the remains relatively constant as the angle of attack changes. This property is important for maintaining longitudinal stability of an aircraft.
- M’ac is the moment per unit span about the aerodynamic center
- is the dynamic pressure of the freestream airflow.
- is the wing area or the reference area of the airfoil (perpendicular to the flow direction).
- c is the chord length
- is the aerodynamic moment coefficient about the aerodynamic center