Gyroscopic Instruments Questions and Answers

Answer: C

Precession rate is inversely proportional to angular momentum, so the drift climbs steeply as speed decays. The instrument keeps producing a believable reading throughout, which is exactly what makes a failing vacuum pump dangerous.

Answer: D

Bank angle for a given rate of turn rises with true airspeed, so a fast aircraft would need an uncomfortably steep bank to hold 3 degrees a second. Halving the rate keeps the manoeuvre within a comfortable and controllable bank.

Answer: A

Each generation eliminated the dominant failure of the one before it, replacing it with a different and generally more manageable limitation. None of them is free of limitations, which is why the last column is never empty.

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 property that makes the first possible. A spinning rotor holds its axis fixed in inertial space, so the aircraft can move around it while the gyro provides an unchanging datum.

The gimbals let the airframe rotate without applying torque to the rotor, and the display reads the angles between them. Everything else in the instrument - erection, gimbal limits, drift compensation - exists to preserve or correct that basic reference.

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 the mechanism. As the rotor slows, angular momentum falls and precession rate for a given torque rises, so the instrument drifts increasingly fast.

The danger is that the display still looks like an attitude indicator: it moves smoothly and shows a plausible attitude, so a pilot may follow it into an unusual attitude. A gyro that has stopped shows an obviously wrong indication and is recognised at once, which is why a vacuum failure warning is fitted.

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 common cause of both errors. The erection system finds the vertical by pendulous means, and a pendulum aligns with the resultant of gravity and any applied acceleration.

Forward acceleration tilts that resultant aft, giving a false nose-up indication; a prolonged turn tilts it outward through centrifugal force, giving errors in bank and pitch. Erection is deliberately slow to limit both, which is why the errors are small and transient.

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 the reason for the restriction. The magnetic compass suffers turning error, worst on northerly and southerly headings, and acceleration error, worst on east and west - both arising from the magnet's dip and pendulous mounting.

Its indication is therefore trustworthy only in steady level unaccelerated flight, and that is when the directional gyro may be set from it. Aligning during a turn would transfer the compass's error into the gyro.

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 reason. The drift is \( 15\sin\phi \), and \( \sin 0 = 0 \).

Physically, at the equator the local vertical is perpendicular to the earth's rotation axis, so rotating about that axis produces no apparent movement of the gyro's direction in azimuth. The apparent drift grows with latitude and reaches the full 15 degrees per hour at the poles, where the vertical and the earth's axis coincide.

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 dither is needed. Below a threshold rotation rate the counter-propagating beams couple through backscatter and lock to a common frequency, so the gyro reads zero over a small dead band around zero rate.

Dithering oscillates the assembly rapidly through a small angle, keeping the instantaneous rate outside that band, and the known dither is subtracted from the output. It reintroduces one moving part to an otherwise solid state device.

Answer: D

Correct answer: A is false but R is true

The reason is correct: the ball settles along the resultant of gravity and the centrifugal force of the turn, which is why it centres in a balanced turn and slides towards the inside when slipping.

The assertion is false. It is a ball in a curved glass tube filled with damping fluid - an inclinometer with no rotating part whatever. It shares a case with the gyroscopic turn instrument, which is the only reason the two are confused.