Longitudinal Control and Trim Questions and Answers

Answer: C

Correct answer: High control power, very low hinge moment

The table's own columns give the answer: very high control power alongside feel described as too light without a tab. Those two facts together are the problem.

Deflecting the whole surface changes its angle of attack directly, so a small movement produces a large pitching moment, while the surface is closely balanced about its pivot and generates little hinge moment. The stick force per g would be below what certification allows, and a pilot could reach a high load factor almost inadvertently. The anti-servo tab restores the force.

Answer: D

Correct answer: The rearward movement of the aerodynamic centre

Mach tuck and the reversal of speed stability are the same phenomenon described twice. As shock waves form, the lift distribution moves rearward and the aerodynamic centre shifts aft, so the same lift acts further behind the centre of gravity and produces a nose-down moment.

Because the moment grows with Mach number, the aeroplane that accelerates gets a further nose-down input rather than a restoring one - the speed stability reverses. One cause, two symptoms, and one countermeasure in the Mach trim system.

Answer: A

Correct answer: Each reproduces a different aspect of feel

Natural feel on a manual control combines several dependencies, and each component reproduces one of them. The q-feel unit supplies the variation with dynamic pressure, so the column stiffens with speed. The centring spring gives force proportional to displacement, so the stick returns and resists movement from neutral.

The bob weight gives force proportional to normal acceleration, which is what produces stick force per g. None substitutes for another, so they are a set rather than alternatives, and redundancy is not the reason for having three.

Answer: B

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the second is the mechanism. The forward centre of gravity limit is a control limit, not a stability one: forward loading makes the aeroplane more stable, not less, and the difficulty is finding elevator travel.

The flare at forward centre of gravity demands the largest tail download at the lowest speed of the approach, with ground effect adding a nose-down moment on top. The limit is placed where enough elevator travel remains after trim, manoeuvre and gusts have been allowed for.

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the second explains why the system is necessary. As the aerodynamic centre moves aft with shock formation, the nose-down moment grows with Mach number.

The consequence is a reversal of speed stability: an aeroplane that accelerates receives a further nose-down input instead of a restoring one, so the divergence feeds itself. Certification requires the stick to move and the force to build in the conventional sense with speed, and the Mach trim system supplies compensating trim automatically to preserve that.

Answer: D

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the second is the reason for the first. A stabilator's control power is high because deflecting the whole surface changes its angle of attack directly, while its hinge moment is small because it is closely balanced about the pivot.

The combination gives a stick force per g below what certification permits - a pilot could overstress the aeroplane with very little effort. The anti-servo tab deflects with the surface to oppose its motion, deliberately degrading an over-light control to an acceptable one.

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the second is why the feel must vary. Real hinge moments go with dynamic pressure and therefore with the square of airspeed, so a manual control naturally stiffens as the aeroplane goes faster.

A hydraulic actuator isolates the pilot from that entirely, so the artificial system must reproduce it. A q-feel unit senses dynamic pressure and generates force accordingly; feel that did not vary with speed would make the control equally light at 400 knots as at 150, inviting gross overcontrol.

Answer: B

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the second identifies the additional mechanism. The thrust line's offset from the centre of gravity produces a couple, but on a propeller aeroplane it is not the whole story.

The slipstream raises the dynamic pressure at the tailplane and alters the downwash reaching it, so the tail load changes with power independently of the thrust line. The effect is largest at low speed, where the slipstream velocity is a substantial fraction of the free stream - which is why a go-around demands prompt retrimming.

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the second is how the protection works. The foreplane is sized and set so it reaches its stalling angle before the main wing.

When it does, its lift falls, the nose drops and the angle of attack reduces automatically, so the aeroplane cannot be held beyond that point whatever the pilot does with the stick. The main wing never stalls, and the classic wing drop is avoided. It is a designed-in limit rather than a warning device, which is what distinguishes it from a stick pusher.

Answer: D

Correct answer: A is false but R is true

The reason is correct: trimming is exactly what lets the pilot release the column and have the aeroplane hold the chosen speed.

But that is achieved by zeroing the force, not the deflection. A trim tab or a movement of the tailplane balances the aerodynamic hinge moment, and the elevator generally remains deflected several degrees, carrying the download that balances the wing's pitching moment. A true reason paired with a false assertion, so each must be judged separately before they are compared.