The point of the longitudinal axis, at which the resulting wind force F1
appears to attack is called the centre of pressure CPW of the wind force,
which, for spin-stabilized bullets is located ahead of the CG. As the flow
field varies, the location of the CPW varies as a function of the Mach
number. Due to the non-coincidence of the CG and the CPW, a moment is associated
with the wind force. This moment MWis called
overturning moment or yawing moment (see figure ).
For spin-stabilized projectiles MWtends to increase
the yaw angle and destabilizes the bullet. In the absence of spin, the
moment would cause the bullet to tumble.