Gyroscopic Instruments Questions and Answers

Answer: C

Correct answer: 4.5 degrees per second

Divide the heading change by the time:

\[ \frac{360}{80} = 4.5\ \mathrm{deg/s} \]

That is one and a half times the standard rate of 3 degrees per second, so the turn is steeper than the standard and would need a correspondingly greater bank angle. Comparing a computed rate against the 3 degree standard is the quickest way to judge whether a manoeuvre is conventional.

Answer: D

Correct answer: 14.6 degrees per hour

Both terms carry the same sine of latitude, so they can be added before it is applied:

\[ (15 + 4)\sin 50^\circ = 19 \times 0.766 = 14.56\ \mathrm{deg/h} \]

Increasing longitude means an easterly track, on which transport wander adds to earth rate; flying west it would subtract. That is why the sign of the longitude change matters, and why a gyro's drift depends on the direction of flight as well as the latitude.

Answer: A

Precession rate is inversely proportional to angular momentum, which is proportional to spin speed. Halving the speed therefore doubles the drift, which is why a failing vacuum pump makes an instrument progressively less trustworthy.

Answer: B

Correct answer: 120 degrees

At the standard rate of 3 degrees per second:

\[ 3 \times 40 = 120^\circ \]

The arithmetic is the basis of the timed turn, which is the procedure when the directional gyro or the compass has failed: hold a standard rate turn on the turn indicator for the calculated time and the heading change follows, without any heading reference at all.

Answer: C

Correct answer: Both Statement I and Statement II are correct

Both are true and the second explains the first. A gyroscope maintains whatever direction it is set to, but it has no means of finding north - nothing in it is sensitive to the earth's magnetic or rotational field in the way a compass or a north-seeking gyrocompass is.

It therefore starts from a heading given to it and accumulates real and apparent drift thereafter. Realignment against the magnetic compass, conventionally about every fifteen minutes, corrects both.

Answer: D

Correct answer: Both Statement I and Statement II are correct

Both are true and the second is the mechanism. The spin axis holds its direction in inertial space; what moves is the earth beneath it, and the aircraft over the earth.

An observer using local north as a reference therefore sees the axis appear to wander, though no torque has acted on it. The distinction matters practically: apparent drift is predictable from latitude and track and can be compensated by design, whereas real drift is random and can only be removed by realignment.

Answer: A

Correct answer: Both Statement I and Statement II are correct

Both are true and the second is the reason. The erection system senses the direction of the apparent vertical by pendulous means, and a pendulum responds to the resultant of gravity and any acceleration.

Under forward acceleration that resultant tilts aft, and the system erects the gyro towards it - producing a false nose-up indication just when the aircraft is accelerating for take-off. The effect is small and slow, since erection is deliberately weak, but it is enough to matter.

Answer: B

Correct answer: Both Statement I and Statement II are correct

Both are true and the second explains the first. Precession rate is \( T/I\omega \), so a larger angular momentum means less precession for the same disturbing torque.

Making the rotor heavy and fast therefore buys rigidity directly. The mass is concentrated at the rim to maximise the moment of inertia, and speed is pushed as high as the bearings allow - which is also why a gyro running down becomes rapidly less reliable as its momentum falls away.

Answer: C

Correct answer: Both Statement I and Statement II are correct

Both are true and the second is the reason for the first. The turn coordinator's gimbal axis is canted upwards, typically by about 30 degrees, so the gyro senses a component of roll rate as well as yaw rate.

The instrument therefore indicates as soon as the aircraft banks, before any appreciable turn has developed, which gives the pilot an earlier cue. A turn indicator with a horizontal gimbal responds to yaw rate alone and does not move until the turn begins.

Answer: D

Correct answer: Statement I is incorrect but Statement II is correct

The second statement is right: the ball settles along the resultant of gravity and the centrifugal force of the turn, which is why it sits centred in a balanced turn and slides towards the inside or outside when the turn is slipping or skidding.

The first is false. It is a simple ball in a curved glass tube filled with damping fluid - an inclinometer with no rotating part at all. It is mounted alongside a gyroscopic instrument, which is the source of the confusion.