Gyroscopic Instruments Questions and Answers

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 first. Precession rate is \( T/I\omega \), so a larger angular momentum means less unwanted movement for the same disturbing torque.

Designers therefore make the rotor as heavy and as fast as the bearings allow, and concentrate its mass at the rim where it contributes most to the moment of inertia. The same relation explains why a rotor running down drifts progressively faster.

Answer: B

Correct answer: 1 and 2 only

The first two are correct: rigidity in space is the axis holding its direction absent a torque, and precession appears 90 degrees from the applied force in the direction of rotor rotation.

The third inverts the relation. Precession rate is \( T/I\omega \), so it is inversely proportional to angular momentum - which is the whole reason a fast heavy rotor makes a good reference and a slowing one does not.

Answer: C

Correct answer: 1 and 2 only

The first two are correct: bearing friction applies a torque and produces genuine movement, and earth rotation produces apparent drift of \( 15\sin\phi \).

The third misclassifies transport wander. It is apparent: the spin axis holds its direction in space while the direction of local north changes as the aircraft moves over the earth. The test is whether a torque acts on the gyro, and none does here.

Answer: D

Correct answer: 1 and 2 only

The first two describe the instrument correctly: the spin axis is vertical with gimbal freedom in pitch and roll, and the erection system applies small torques that precess the axis back towards the vertical.

The third is false, and follows from the second. The erection sensor finds the vertical pendulously, so it responds to the resultant of gravity and any acceleration - which is precisely the source of acceleration and turn errors.

Answer: A

Correct answer: 1 and 2 only

The first two are correct: a standard rate turn is 3 degrees per second, giving a full circle in two minutes, and the turn coordinator's canted gimbal makes it respond to roll rate as the turn is entered.

The third misassigns the ball, which shows whether the turn is balanced - slipping, skidding or coordinated - and says nothing about its rate. Rate comes from the gyroscopic needle or miniature aircraft beside it.

Answer: B

Correct answer: A-1, B-2, C-3, D-4

Each instrument answers a different question. The attitude indicator gives pitch and roll relative to the horizon; the directional gyro holds a heading against a reference set from the compass.

The turn coordinator gives rate of turn, with roll rate showing on entry because of its canted gimbal. The slip indicator shows whether the turn is balanced. Three are gyroscopic and one is a ball in a tube - which is the distinction worth carrying through this topic.

Answer: C

Correct answer: A-1, B-2, C-3, D-4

The four divide into two real causes and two apparent ones. Bearing friction and rotor imbalance both apply torques, so the axis genuinely moves - real drift, unpredictable and correctable only by realignment.

Earth rotation and change of longitude both leave the axis fixed while the reference frame turns - apparent drift, computable from latitude and track and therefore compensable by design. Sorting the list into real and apparent first settles the matching.

Answer: D

Correct answer: A-1, B-2, C-3, D-4

Each technology has its characteristic weakness. An air-driven gyro fails gradually as the pump or filter degrades, and the instrument stays plausible while becoming wrong - the most dangerous kind of failure.

An electric spinning mass has no pump but still has bearings, so wear produces real drift. A ring laser gyro suffers lock-in at low rates, requiring dither. A fibre optic gyro is sensitive to temperature variation along the coil, which must be compensated.

Answer: A

Correct answer: A-1, B-2, C-3, D-4

The four terms cover the property, the response, the failure and the correction. Rigidity is the axis staying fixed absent a torque; precession is the motion at 90 degrees when a torque is applied.

Toppling is the axis tumbling when the gimbal limits are exceeded, after which the reference is lost. Erection is the system that torques the axis gently back towards the vertical, correcting drift - and it is the source of the acceleration and turn errors, since it finds the vertical pendulously.

Answer: B

Correct answer: The slip and skid indicator

The slip indicator is a ball in a curved liquid-filled tube. It has no rotor, no gimbals and no power supply - it settles along the resultant of gravity and centrifugal force by simple mechanics.

The other three all contain gyroscopes: a vertical-axis gyro in the attitude indicator, a horizontal-axis one in the directional gyro, and a canted rate gyro in the turn coordinator. The ball shares a case with the last of these, which is the source of the confusion.