How does thrust produce pitching moment about the CG, and how does CG position affect that tendency?

• A. Forward CG reduces pitch-up tendency from thrust.
• B. Forward CG increases pitch-up tendency from thrust.
• C. CG position has no effect on thrust-induced pitching moment.
• D. Aft CG reduces nose-down tendencies from thrust.

Answer: (A)

The thing being tested is how a force applied away from the center of gravity can cause rotation around the CG, and how moving the CG changes how that rotation feels in flight. When thrust acts on an aircraft, the line of action is not exactly through the CG, so it creates a pitching moment equal to the thrust magnitude multiplied by the vertical offset between the thrust line and the CG. The direction of that moment depends on whether the thrust line is above or below the CG, but what matters here is how the overall aircraft stability responds.

If the CG is forward, the airplane is more statically stable: a disturbance that tends to rotate the nose up is resisted by the weight distribution that favors returning to level flight. In practice, this makes the thrust-induced tendency to pitch the nose up smaller, because the forward weight and aerodynamic forces provide a stronger restoring moment. So, with a forward CG, the same thrust impulse produces less nose-up rotation, reducing that tendency.

In short, the pitching effect of thrust about the CG depends on the vertical offset of the thrust line, and moving the CG forward tends to dampen the nose-up tendency caused by thrust.