Too much weight too far forward will make it difficult to raise the nose; too far aft, and it may be more difficult to recover from a stall. And, like a playground see-saw, a weight exerts more force the farther it is from the fulcrum—so baggage placed in the rear seat may be fine, for instance, when the same bag would cause the airplane to be out of balance in the rear baggage compartment. The center of gravity envelope (below) shows the range of weights and moments (weight times the arm, its distance from a pre-defined starting point) that are permissible for a given airplane. Calculating weight and balance is a skill that will pay dividends when you graduate from the training environment and start planning trips in the real world: friends, suitcases, and all.
Center of gravity. The mass center of an aircraft—the point where it would balance if you suspended it. This is usually expressed in inches from a reference datum.
Datum. A point from which moment arms are measured. Points forward of the datum have negative arms; points aft are positive. In this case, the datum is at the firewall.
Arm. The horizontal distance from the reference datum to an item’s center of gravity.
Moment. A force causing something to rotate, equal to an item’s weight times its arm.