For an aircraft to be simultaneously statically stable in pitch and trimmable at positive lift (C_L > 0), the pitching moment curve must satisfy:

(A) C_{m0} > 0 and dC_m / dC_L < 0

(B) C_{m0} < 0 and dC_m / dC_L < 0

(C) C_{m0} > 0 and dC_m / dC_L > 0

(D) C_{m0} = 0 and dC_m / dC_L = 0

Answer Key:

A

### Solution: Static stability requires dC_m / dC_L < 0 (negative slope). To trim at C_m = 0 with positive lift (C_{L,trim} = -C_{m0} / (dC_m/dC_L) > 0), the zero-lift pitching moment C_{m0} must be strictly positive. Correct: A.

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