B - Directional Gyro Indicator (31-05-18) Flashcards
How does a Directional Gyro Indicator work?
A free gyro is tied to the aircraft in pitch and roll with a nozzle pillar, wedge plate or mercury micro switch.
in a turn the gyro is free to drift about the yawing axis and the amount of drift is measured with its starting position (north) as a reference
How does an air driven gyro eliminate topple?
When the gyro begins to topple, the air that causes the gyro to spin in the first place either:
with a nozzle pilar hits the gyro at an angle which creates a torque force which precesses, which re erects the gyro.
or
With a wedge plate the air coming out of the gyro case hit the plate and more air will be directed one way that the other. This causes a torque force which re erects the gyro.
What is a caging mechanism?
A gear system with a knob that allows the user to push to cage the gyro and then rotate it until it is in the correct heading.
How often must an airdriven gyro system be re-synced?
Every 10 mins
When must an airdriven gyro system be resynced?
every 10 minutes
after heavy manoeuvring (anything beyond 55deg pitch or roll)
What are the manoeuvre limits of an electric driven DG?
up to 85deg pitch or roll.
What errors are associated with a DGI?
- Gimballing error
torque forces created in pitch or roll, precessing causing a small change in indicated heading
- Random wander
manufacturing defects
- Apparent wander
ER & transport wander
What is a latitude nut?
an adjustable nut that acts like a bob weight, creating a precession force that counters ER.
If an aircraft is travelling to the North/South Pole from the equator, what will happen to the DGI indication?
The gyro will progressively drift more and more to the east, indicating an apparent turn to the west.
What does the rate of transport wander depend on?
The direction of travel
The latitude (higher latitude = greater transport variation)
Ground speed
How do you calculate transport wander?
The same way you calculate EC
chlong x sin(mean(lat))
What are the components of total drift?
Total drift = Random drift + ER - LN correction + transport wander
