Gyros & Heading Instruments

C. all of the above are correct

A directional gyro suffers transport wander, earth-rate drift, errors from banking and pitching, and mechanical imperfections: all four.

B. 2 and 4

Rigidity in space (it holds its axis fixed) and precession (an applied force acts 90 deg on in the direction of spin). Mass, radius and rpm only set how rigid it is.

The question was recalled without its options; these options were written to it.

B. 1 degree of freedom

The gyro of a turn indicator is a rate gyro with one degree of freedom (a single gimbal, spring-restrained).

B. The movement of the spin axis 90 deg in the direction of rotation from the point where a force is applied

Precession is the movement of the spin axis, 90 degrees in the direction of rotation from the point where a force is applied. Holding a fixed direction is rigidity.

The question was recalled without its options; these options were written to it.

C. the horizontal plane

Drift is the wander of the gyro spin axis in the horizontal plane (topple is in the vertical plane).

C. the flux valve

A slaved gyro compass (remote indicating compass) is kept aligned to magnetic north by the flux valve.

A. directional gyro

DGI = 2 DOF, horizontal axis. Turn indicator = 1 DOF, horizontal axis. Artificial horizon = 2 DOF, vertical axis.

The question was recalled without its options; these options were written to it.

B. to compensate for earth rate error

The latitude nut on a directional gyro is set to the local latitude so that it can apply the correction for earth-rate drift.

B. turn to right and too much bank

Needle shows a right turn; the ball is on the inside of the turn (right), so the aircraft is slipping - too much bank for the rate of turn.

A. nose up and correct angle of bank

Turning errors of the classic AH: after 90 deg - bank under-read, false climb; after 180 deg - bank correct, false climb; after 270 deg - bank over-read, false climb; after 360 deg - all correct.

The question was recalled without its options; these options were written to it.

B. turning right with not enough bank

Needle right = right turn; ball on the outside (left) = skidding = not enough bank.

C. 1, 2

Rate of turn = g tan(bank) / TAS: it depends on bank angle and speed, not on weight.

C. Needle right and ball left.

Taxiing a right turn: needle right, ball left (outside).

B. contains its own gyro and has an independent (standby battery) power supply, and runs all the time

It is a separate, self-contained instrument with its own gyro and an independent power source, running continuously so it is already erect and reliable when the main attitude display fails.

The question was recalled without its options; these options were written to it.

B. two degrees of freedom, vertical axis

The AH needs freedom in pitch and roll and a vertical spin axis held to the earth vertical (earth gyro). DGI: 2 DOF, horizontal axis. Turn indicator: 1 DOF, horizontal axis.

The question was recalled without its options; these options were written to it.

B. Left turn with too little bank.

The needle shows a left turn; the ball is displaced to the right (outside the turn) - skidding, which means too little bank for that rate of turn.

B. rate of turn decreases and radius increases

Rate of turn = g tan(bank) / V and radius = V^2 / (g tan bank). At fixed bank, faster means slower turn rate and a much larger radius.

The question was recalled without its options; these options were written to it.

A. needle left, ball right

The gyro senses the turn (needle left). With no bank on the ground the ball is thrown to the outside of the turn - right.

The question was recalled without its options; these options were written to it.

C. It senses the earth's magnetic field rather than it seeks, so it is more sensitive

A remote indicating compass senses the field (flux valve) rather than seeking it, so it is more sensitive.

A. one degree of freedom

A rate gyro has one gimbal and is spring-restrained: it is free about one axis only and measures rate of turn by its precession. Displacement gyros (DGI, artificial horizon) have two.

A. turn indicator

A rate gyro with one degree of freedom and a horizontal spin axis is the turn indicator.

A. vertical axis

Turning in the horizontal plane means rotating about a vertical axis - which is exactly what upsets a DGI's heading.

The question was recalled without its options; these options were written to it.

A. 3.5 deg/h increasing

Parked, so there is no transport wander; the apparent wander (earth rate) is -15 sin 50 = -11.5 deg/h. Observed = real + apparent: -8 = real - 11.5, so the real wander is +3.5 deg/h (the gyro itself is drifting to increase the reading).

B. topple

Wander in the horizontal plane = drift; in the vertical plane = topple. Each can be real (friction, imbalance) or apparent (earth rate, transport across the earth).

The question was recalled without its options; these options were written to it.

A. More mass at periphery and high RPM

Rigidity rises with the mass of the rotor, the radius at which the mass is placed and its spin speed: more mass at the periphery and high RPM.

B. lock the gyro (and erect it quickly), preventing damage or toppling during manoeuvres beyond its limits

Caging locks the gimbals in a fixed position - used to re-erect a toppled gyro or to protect it in aerobatics.

The question was recalled without its options; these options were written to it.

A. 40 seconds

Rate 1 = 3 deg/s (2 min for 360); rate 2 = 6 deg/s (1 min); rate 3 = 9 deg/s: 360 / 9 = 40 s.

The question was recalled without its options; these options were written to it.

A. Needle right , ball left

Taxiing in a right turn the turn needle goes right and the ball (centrifugal force) goes left.

B. change of heading rate of the aircraft

Rate of turn is the rate of change of heading.

B. horizontal-axis tied gyro

A tied gyro is held to a reference other than the earth's vertical (the DGI is tied to the aircraft's yaw axis/horizontal). An earth gyro is controlled by gravity - the artificial horizon, vertical spin axis.

The question was recalled without its options; these options were written to it.

A. 15 deg per hour

360 deg in about 24 h = 15 deg/h (1 deg every 4 minutes). A gyro sees the vertical component of it, 15 sin lat deg/h, as apparent wander.

A. two degrees of freedom and a vertical axis

A gyro that senses pitch and roll (artificial horizon) has two degrees of freedom and a vertical spin axis.

A. (i) a lower (ii) higher rigidity is not required

A rate gyro runs slower than others because the high rigidity of a fast gyro is not required.

B. an apparent tilt of the spin axis in the vertical plane caused by the earth's rotation and movement over the earth - not by any torque

The gyro stays fixed in space while the earth turns beneath it, so its axis appears to tilt (topple) relative to the local vertical.

The question was recalled without its options; these options were written to it.

A. 30 seconds

The shortest way is left through 90 deg (050 -> 320). At 3 deg/s: 90 / 3 = 30 s.

The question was recalled without its options; these options were written to it.

A. the turn coordinator (bank) with the ASI, altimeter and VSI (pitch)

Partial panel: the turn coordinator/turn needle and DGI give bank and turn; pitch is read from the airspeed, altimeter and VSI trend.

A. 55° in roll and pitch

A typical air-driven directional gyro topples beyond about 55 deg of roll or pitch.

D. 84 minutes.

The Schuler period is 84 minutes.

A. aircraft symbol (needle) left, ball centred

Coordinated = no slip or skid, so the ball stays in the middle; the symbol/needle shows the direction and rate of turn. Ball to the inside of the turn = slipping (too much bank); to the outside = skidding (too little bank).

A. Bank

Gimballing error arises when the aircraft banks or pitches and the gyro gimbals are no longer orthogonal.

C. On the periphery and with a high rotation speed

Mass concentrated at the rim and a high spin speed give the greatest rigidity.

A. the inner gimbal is pivoted laterally inside the outer gimbal, which is pivoted longitudinally inside the case

Inner gimbal on the lateral (pitch) axis, outer gimbal on the longitudinal (roll) axis: the rotor stays vertical while the aircraft pitches and rolls round it.

The question was recalled without its options; these options were written to it.

A. causes the directional gyro to precess to align with the magnetic heading

The flux valve signal is compared with the gyro position; any error drives the torque motor, which precesses the gyro slowly until it agrees with the magnetic heading (slaving).

The question was recalled without its options; these options were written to it.

A. a false climb (with a right-wing-down error)

Acceleration acts on the pendulous erection system and the bottom-heavy rotor housing: the classic AH shows nose up and right wing down. Deceleration gives the opposite. Electric horizons with a clockwise rotor give opposite errors.

The question was recalled without its options; these options were written to it.

B. too much nose up and bank too low

At 90 deg of turn the classic AH under-reads the bank and shows a false climb (nose up). Errors cancel after a full 360.

The question was recalled without its options; these options were written to it.

A. asymmetrical friction at the spin axis bearings and imbalance

Real wander comes from the gyro itself - bearing friction and imbalance produce torques that precess it. Earth rotation and transport give APPARENT wander.

The question was recalled without its options; these options were written to it.

C. Needle central and ball to the right.

Right rudder holds the yaw and the wings are banked a few degrees towards the live (right) engine to remove sideslip. The fin side force is then balanced by that bank, so the ball sits about half a width towards the live engine (right), while the needle stays central because the aircraft is not turning.

B. decrease

The latitude correction is set for 56 N; further south the earth rate is smaller, so the fixed correction over-corrects and the DGI reading creeps up. Holding the reading constant, the pilot is actually turning left - the true heading decreases.

B. has one degree of freedom and is spring-restrained, measuring rate of turn

A rate gyro has one gimbal restrained by a spring; the precession torque in a turn is balanced by the spring, so the deflection measures rate of turn. A DGI is a free (displacement) gyro with two gimbals showing heading.