The degree of stabilizer deflection needed for equilibrium is most directly related to which parameter?

• A. CG position
• B. Tail surface area
• C. Fuselage length
• D. Engine thrust

Answer: (A)

The moment balance about the center of gravity is what sets trim. The stabilizer deflection controls the tail lift, and the tail’s ability to create the necessary moment depends on the distance between the CG and the tail (the lever arm). That distance is determined by the CG position, so where the CG sits directly dictates how much tail lift—and thus how much stabilizer deflection—is needed to achieve equilibrium. If the CG moves forward, the lever arm to the tail changes in a way that often requires less tail lift to trim; if the CG moves aft, more tail lift (and more deflection) is needed. Tail area or thrust affect how much lift or moment the tail can produce, but the primary factor that determines the required deflection is the CG location.