text: A stable configuration is desirable not only in sailing, but in aircraft design as well.  Aircraft design therefore borrowed the term center of pressure.  And like a sail, a rigid non-symmetrical airfoil not only produces lift, but a moment.
  The center of pressure of an aircraft is the point where all of the aerodynamic pressure field may be represented by a single force vector with no moment.  A similar idea is the aerodynamic center which is the point on an airfoil where the pitching moment produced by the aerodynamic forces is constant with angle of attack.
  The aerodynamic center plays an important role in analysis of the longitudinal static stability of all flying machines.  It is desirable that when the pitch angle and angle of attack of an aircraft are disturbed (by, for example wind shear/vertical gust) that the aircraft returns to its original trimmed pitch angle and angle of attack without a pilot or autopilot changing the control surface deflection. For an aircraft to return towards its trimmed attitude, without input from a pilot or autopilot, it must have positive longitudinal static stability.