For longitudinal trim (C_m = 0) with the center of gravity ahead of the aerodynamic center (stable aircraft), the horizontal tail must typically generate:

(A) A downward aerodynamic force (negative lift) to balance the nose-down wing-body pitching moment

(B) An upward aerodynamic force equal to half the total weight

(C) Zero aerodynamic force at all airspeeds

(D) Pure rolling moment only

Answer Key:

A

### Solution: Because the CG is forward of the wing aerodynamic center, wing lift produces a nose-down moment about the CG, which requires a downward tail load (negative lift) to achieve moment equilibrium. Correct: A.

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