Control Surface Hinge Moments Questions and Answers

Answer: A

A bigger surface aft of the hinge produces more lift and therefore more control power and a larger hinge moment together, which is the trade that makes balancing necessary in the first place. Getting more effectiveness for less force requires balance rather than size. Lowering both would follow from a smaller surface. Nothing here leaves them unchanged, since both scale with the area and chord aft of the hinge line.

Answer: B

Multiplying through:

\[ \begin{aligned} H &= -0.12 \times 4500 \times 0.8 \times 0.30 \\ &= -130 \ \mathrm{N\,m} \end{aligned} \]

so about -130 newton metres per aileron, and both must be overcome together in a roll, which is why aileron forces dominate the stick force in a manual system. -432 omits the chord. -65 halves the result. -13 slips a decade. Doubling the speed would take each aileron past 500 newton metres, which is the practical reason for spoilers on fast aeroplanes.

Answer: C

Force scales with the square of the speed ratio:

\[ \begin{aligned} \left(\frac{250}{150}\right)^{2} &= 2.78 \\ F &= 90 \times 2.78 = 250 \ \mathrm{N} \end{aligned} \]

so about 250 newtons, which is beyond sustained one-handed effort. 150 N assumes a linear dependence. 90 N assumes none. 540 N would follow from a cube law. The calculation is the clearest possible argument for balance devices or power assistance as design speeds rise.

Answer: D

A gust lock holds the surfaces still on the ground, where wind can slam them against their stops and damage the hinges or the control run. It is removed before flight, and interlocks or checklists exist precisely because taking off with one fitted has caused accidents. Flutter is an in-flight phenomenon addressed by mass balance and stiffness. Trim settings and actuator runaways are handled by other means entirely.

Answer: A

Elevator angle per g is set by the manoeuvre margin, the stick-fixed counterpart of stick force per g, and it is a purely aerodynamic and geometric quantity. The hinge derivative with incidence affects the force the pilot feels, not the angle required. Tab authority concerns trimming. The flutter speed is a structural dynamics limit unconnected to the steady manoeuvre balance.

Answer: B

Both statements are true and the reason is the mechanism. An undersized jack will stall against the air load exactly when the pilot most needs authority, so the estimate must cover the corner cases and not merely the cruise. That is also why hinge moment measurement continues in the tunnel long after the decision to fit powered controls, and why load cases for the actuator are among the outputs of a control surface design.

Answer: C

In a shielded arrangement the horn sits behind the fixed surface, which smooths the flow reaching it and makes the balance less sensitive to incidence. An unshielded horn projects clear of the fixed surface and is more effective but rougher in its behaviour. A sealed chamber describes the internal balance. Horns often do carry balance weights as well, but that is a convenient coincidence rather than the definition.

Answer: D

Because the tab must generate an aerodynamic moment to move the main surface, its authority falls with dynamic pressure and the response is poor at low speed - exactly where a large aeroplane needs crisp control, on approach and in the flare. Stick forces are light, which is the system's virtue. Flutter is managed by balance as on any surface. Trim remains available through a separate tab or through the tab's own datum.

Answer: A

The coefficient grows in magnitude to 10 degrees and then falls again, so the gradient has reversed sign somewhere beyond it - the signature of incipient overbalance, and a finding that would send the surface back for less balance area. Calling it well behaved ignores the reversal. Mass balance cannot be inferred from aerodynamic data. And there is nothing implausible about the numbers: this is precisely the behaviour an over-balanced nose produces at large deflection.

Answer: B

More set-back gives lighter forces but brings the surface closer to overbalance, particularly at large deflection and high incidence, so the trade is force level against margin from a reversal. Flutter is set by mass and stiffness rather than by hinge position in this sense. Trim authority is a tab matter. Gearing and area are both design variables but are not the pair that set-back itself trades between.