The moment about the aerodynamic center (often denoted as M’,ac) is a measure of the aerodynamic torque or moment that is exerted on an airfoil or wing due to changes in the angle of attack. The aerodynamic center is a specific point on an airfoil or wing where the pitching moment remains relatively constant over a range of angle of attack variations. In other words, the moment about the aerodynamic center is relatively insensitive to changes in angle of attack. The moment about the aerodynamic center is crucial for understanding the stability and control characteristics of an aircraft. When an aircraft experiences changes in angle of attack, the aerodynamic forces can cause it to pitch (rotate) around its center of gravity. The moment about the aerodynamic center helps determine how stable or unstable this pitching behavior will be.Â
- M′ac: Moment about the aerodynamic center
- L′: Lift per unit span
- c: Chord length of the airfoil or wing
- x̄ac: Location of aerodynamic center
- c/4: Quarter-chord position along the chord
- M′c/4: Moment about the quarter-chord point