Final answer:
Vmc refers to the minimum control speed with a critical engine inoperative, and an aft CG is used for determining Vmc because it results in a less stable condition, requiring more rudder force to maintain control.
Step-by-step explanation:
The term Vmc, which stands for minimum control speed with the critical engine inoperative, is an essential concept in aviation. When determining Vmc, it is important to consider the aircraft's center of gravity (CG) because the placement of the CG can significantly affect aircraft stability and control. An aft CG is used for determining Vmc because it results in the least stable condition whereby the arm of the rudder effectiveness is reduced, and more rudder force is required to overcome the yawing moment caused by the inoperative engine. Consequently, the speed at which the rudder can no longer maintain yaw control, which defines Vmc, is higher. Setting the aft CG for the Vmc determination ensures that the pilot can maintain control at all certified CG positions under the worst-case scenario.