Figure 6.12 illustrates the effect of moving the aircraft center of gravity aft (to the rear). From (6.10), moving the center of gravity aft (increasing ) increases the magnitude of the (destabilizing) wing term and decreases lt and Vh, so that the aircraft becomes less stable. The location of the center of gravity which would cause the airplane to have neutral static longitudinal stability is called the neutral point.
Figure 6.14 Effect on Trim Diagram of Moving the Center of Gravity Aft
) increases the magnitude of the (destabilizing) 
= 0, so an approximate expression for the location of the neutral point can be developed by setting (6.10) 
(6.17)