For an aircraft with a conventional aft tail, shifting the center of gravity ($X_{cg}$) aftward towards the aerodynamic center of the wing-body combination:

(A) Increases static longitudinal stability margin

(B) Decreases static longitudinal stability margin

(C) Has no effect on static margin

(D) Inverts directional stability

Answer Key:

B

### Solution: Static margin is defined as $\frac{X_{np} - X_{cg}}{\bar{c}}$. Moving $X_{cg}$ aft (closer to or behind $X_{np}$) decreases the static margin. Correct: B.

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