Gyroscopic Instruments Questions and Answers

Answer: C

Correct answer: Only three

The first three pair each error with its cause: acceleration error from the erection sensor mistaking acceleration for tilt, turn error from centrifugal force acting on the same sensor, and earth rate drift from the earth rotating beneath a space-fixed axis.

The fourth misdescribes toppling, which is the gyro reaching a gimbal limit - typically in an extreme attitude - after which the reference is lost and must be re-erected. Friction produces slow drift, not toppling.

Answer: D

Correct answer: Only three

The first three describe their devices correctly: the ring laser gyro senses the frequency difference between counter-rotating beams, the fibre optic gyro the phase shift around a coil, and a rate integrating gyro gives an output proportional to the angle turned through.

The fourth is wrong. A flux valve senses the earth's magnetic field to provide a north reference for a gyro-stabilised compass system - a magnetic device with no rotation sensing and no precession involved.

Answer: A

The other three all depend on a spinning rotor for their indication. The ball is a purely mechanical device responding to the resultant of gravity and centrifugal force, and it merely shares a case with the turn instrument.

Answer: B

Correct answer: Friction in the gimbal bearings

Bearing friction applies a torque to the gyro, so the spin axis genuinely moves. That is real drift, and it is unpredictable.

The other three all produce apparent drift, where the axis holds its direction and the reference frame turns beneath it: the earth's rotation gives \( 15\sin\phi \), and movement in longitude or latitude changes the direction of local north relative to a space-fixed axis. Apparent drift can be computed and compensated; real drift cannot.

Answer: C

Correct answer: Air-driven spinning mass gyro

A spinning mass gyro has a rotor turning in bearings, driven here by an air stream - moving parts throughout, with the wear, spin-up time and friction drift that follow.

The other three sense rotation without any rotor: ring laser and fibre optic gyros use the Sagnac effect on counter-propagating light, and a MEMS rate sensor uses a vibrating structure on a silicon chip. Solid state devices are available instantly and drift far less, which is why they displaced the spinning mass.

Answer: D

Correct answer: Lock-in at low rotation rates

Lock-in belongs to the ring laser gyro, where the two counter-rotating beams couple together and cease to show a frequency difference below a threshold rate - which is why such gyros are mechanically dithered.

The other three are genuine attitude indicator errors: acceleration error and turn error from the pendulous erection system responding to the resultant of gravity and acceleration, and slow drift from bearing friction. A mechanical gyro has no beams to lock.

Answer: A

Correct answer: Electric gyros are immune to precession

Precession is a property of any gyroscope, whatever drives it. An electric gyro obeys \( \Omega = T/I\omega \) exactly as an air-driven one does.

The other three are genuine reasons: vacuum systems weaken with altitude as the air thins, splitting the drive between vacuum and electrical power means one failure cannot remove every attitude reference, and a pump failing gradually degrades the indication while it still looks plausible - the most dangerous kind of failure.

Answer: B

The pendulous erection sensor is displaced rearward by the acceleration and reads it as a tilt, so the erection system precesses the gyro. The error clears once the acceleration ceases, which is why the indicator is cross-checked during the roll.

Answer: C

A gyro holds a direction but does not find one, so drift accumulates until the instrument is realigned. A steady growth points at drift rather than at a discrete failure, which would show as a sudden step or a wandering indication.

Answer: D

The pitot-static instruments are unaffected and the electrically driven turn coordinator continues to work. Splitting the drive between vacuum and electrical power exists precisely so that one failure cannot remove every attitude reference.