Control Surface Hinge Moments Questions and Answers

Answer: C

Because the two problems are independent. Mass balance settles the flutter question by putting the surface's centre of gravity on the hinge; it does nothing whatever to the aerodynamic hinge moment, so the control can be flutter-free and still need forces no pilot could sustain. Conversely a beautifully light surface with its mass aft of the hinge is a flutter risk. That is why both kinds of balance appear on the same drawing and why confusing them is the most consequential error on this topic. Neither causes overbalance, which is a matter of area ahead of the hinge, and neither prevents trimming.

Answer: D

Friction adds a force that must be overcome before anything moves and that does not vary with deflection, so it raises the breakout force and masks the genuine gradient around neutral, leaving the pilot unable to feel small displacements and inclined to over-control. It is why friction limits appear in maintenance manuals alongside free-play limits. It has no effect on the aerodynamic moment at the surface. It tends to reduce rather than raise the flutter speed, by admitting free play as components wear. And it degrades rather than improves the speed gradient, since a constant force term carries no speed information at all.