Gyroscopic Instruments Questions and Answers

Answer: C

Correct answer: False, it holds a direction but does not find one

A gyroscope has no north-seeking property. Nothing in it responds to the earth's magnetic field, and a simple directional gyro does not sense the earth's rotation either.

It is set to a heading read from the magnetic compass and holds that direction, accumulating real and apparent drift thereafter - which is why realignment is needed at intervals. Electrical drive changes the power source, not the physics. A gyrocompass does find north, but by a quite different mechanism.

Answer: D

Correct answer: Its rate rises as angular momentum increases

The relation is \( \Omega = T/I\omega \), so precession rate falls as angular momentum rises. That inverse dependence is why a fast heavy rotor makes a stable reference.

The other three statements are true: precession appears 90 degrees from the applied force, in the direction of rotor rotation, and its rate is proportional to the torque. The formula contains both dependencies, and the question tests whether the denominator is read correctly.

Answer: A

Correct answer: No, it is greatest at the poles and zero at the equator

Earth rate drift is \( 15\sin\phi \), so the sine takes it from zero at the equator to the full 15 degrees per hour at the poles.

The surface speed at the equator is indeed greatest, but that is irrelevant - what matters is the angle between the local vertical and the earth's rotation axis. At the equator they are perpendicular and rotation produces no apparent movement in azimuth; at the pole they coincide and the whole rate appears.

Answer: B

Correct answer: The turn coordinator

The turn coordinator is electrically driven in the conventional light aircraft arrangement, so it survives a vacuum failure.

That is the point of the split: the attitude indicator and directional gyro are both air-driven and go together, but the turn coordinator remains, giving a rate-of-turn reference for partial panel flight, alongside the pressure instruments which need no power at all. A single failure must not remove every attitude reference.

Answer: C

Correct answer: False, toppling is abrupt, drift gradual

Drift is a slow wander of the spin axis, from friction or from a rotating reference frame, measured in degrees per hour and corrected by realignment.

Toppling is a sudden loss of the reference when the gimbal limits are exceeded in an extreme attitude, after which the gyro tumbles and must be re-erected. The mechanisms differ, the timescales differ and the remedies differ - only the result, an unusable indication, is shared.

Answer: D

Correct answer: Wander caused by friction in the gimbal bearings

Friction applies a torque, so the spin axis genuinely moves. That is real drift - unpredictable, and removable only by realigning the instrument.

The other three are apparent: earth rate and both forms of transport wander leave the axis fixed in space while the direction of local north changes beneath it. Apparent drift can be computed from latitude and track, which is why latitude-compensated gyros can cancel it automatically.

Answer: A

Correct answer: No, the erection sensor mistakes acceleration for tilt

Rigidity does protect the rotor: the gyro itself is unmoved by acceleration. The error enters through the erection system.

That system finds the vertical by pendulous means, and a pendulum aligns with the resultant of gravity and any acceleration - which tilts aft when the aircraft accelerates. The erection then torques the gyro towards that false vertical, giving a nose-up indication. The gyro is rigid; its correction system is not.

Answer: B

Correct answer: Flying at a lower latitude

Latitude governs apparent drift, through the \( 15\sin\phi \) term, and has no bearing on real drift at all. Flying south does not make the bearings smoother.

The other three all attack the real causes: better rotor balance removes an unwanted torque, lower bearing friction removes another, and a higher rotor speed raises angular momentum so that any remaining torque produces less precession. Real drift is a matter of the instrument, not of where it is.

Answer: C

Correct answer: False, it indicates rate of turn, and roll rate on entry

The miniature aircraft is a rate display, not a bank display. Its canted gimbal makes it sense roll rate as the turn is entered and yaw rate once the turn is established.

Bank angle comes from the attitude indicator. The distinction matters in practice: the same rate of turn corresponds to quite different bank angles at different speeds, which is why a standard rate turn needs 25 degrees at 180 knots and far more at high speed. The ball, separately, shows balance.

Answer: D

Correct answer: It requires a spin-up period before use

A ring laser gyro has no rotor, so there is nothing to spin up and the instrument is available essentially immediately - one of its principal advantages over a mechanical gyro.

The other three are true: it has no bearings and therefore no friction drift, it suffers lock-in when the counter-rotating beams couple at low rates, and it is mechanically dithered to keep the rate outside that dead band.