Chapter 12 - Direct Reading Magnetic Compass Flashcards
Purpose of Direct Reading Magnetic Compass in an airline?
Standby instrument
What is the task of a Direct Reading Compass?
indicate direction on the surface of the Earth, relative to Magnetic North.
What is the fluid in a direct reading magnetic compass?
Damping fluid
How do we balance a Direct reading mag compass?
compensating magnet
What is the serviceability check of a Direct Reading mag compass?
- Glass clean
- No discoloration of the fluid
- No bubbles visible
- Indications within 5° of known heading, e.g. runway heading
The compass sensing magnets must lie as nearly as possible in the …… plane during normal straight and level flight.
horizontal
Where does the NORTH SEEKING end of a direct reading magnetic compass point?
Magnetic North Pole
What are the three major limitations of a direct reading magnetic compass?
- Turning and acceleration errors due to dip.
- Closeness to sources of deviation (electric lights, electric motors and ferrous metal).
- The instrument is self-contained. It is not possible to take a magnetic heading and input it into other equipment.
What is magnetic dip?
Acceleration and turning errors only occur where the vertical component (Z) in the earth’s field is large.
What are the turning principles?
Heading increase?
Heading decrease?
Compared to the compass card
Heading increase – compass card anticlockwise
Heading decrease – compass card clockwise
What are acceleration errors with a direct reading mag compass?
acceleration on a heading of west in the northern hemisphere causes the compass card to rotate anticlockwise indicating an apparent turn to the north, or nearer pole.
NH: Acceleration North Deceleration South (ANDS)
SH: North Deceleration South Acceleration (NDSA)
What causes acceleration errors on a direct reading magnetic compass?
Caused by inertia acting on a magnet with residual dip.
What does the size of the acceleration error depend on in a direct reading magnetic compass?
aircraft heading, acceleration, latitude and design of the magnet system.
What are the size of acceleration errors on a direct reading magnetic compass on a east/west or north/south heading?
Acceleration / deceleration errors are MAX on East and West Headings (M) and ZERO on North and South Headings (M).
What is the apparent turn due to acceleration errors in the northern and southern hemisphere on a direct reading magnetic compass?
Apparant turn North in the Northern hemisphere.
Apparent turn south in the southern hemisphere.
What is DEAP (Dip) of a direct reading magnetic compass?
DEAP (dip): Deceleration toward Equator / Acceleration toward Poles
In the northern hemisphere, during a take-off run in a westerly direction, a direct reading magnetic compass indicates:
An apparent turn to the north.
In the southern hemisphere, during deceleration following a landing in a northerly direction, a direct reading magnetic compass indicates:
No apparent turn.
When are turning errors of a direct reading magnetic compass max and min?
MAX when turning through North and South and ZERO when turning through East and West.
The Plane Pushes the Pivot near the Pole
Southern Hemisphere
What is lag through the turn?
moment set up by the turn causes an anti-clockwise rotation of the compass card causing its reading to lag in the turn.
How is turning error of a direct reading magnetic compass further magnified?
The error will be further magnified by liquid swirl – think viscosity.
Because of a turning errors of a direct reading magnetic compass is it over or under reading?
because the reading is lagging behind the aircraft, we call this under-reading.
Therefore, if we wish to roll out of our turn on a magnetic heading of 315 ̊, we will need to roll out when our compass reads, say, 335 ̊ or apparently early.
When turning away from the nearer pole the your direct reading magnetic compass will…? Due to turning error
Your compass will lead in the turn
Turning error
Turning away from the pole in the SH, the damping fluid will, increase or decrease the error of your direct reading magnetic compass?
Decrease, as compass is trying to lead in the turn.
Is the heading indicated on the compass leading the aircraft, over or under reading?
over-reading if leading the aircraft heading
What is compass sluggish and lively?
sluggish - under reading in the turn
lively - leading, over reading in the turn
What is UNOS and ONUS
Northern Hemisphere - U N O S - Under-reads turning through North, Over reads turning through South
Southern Hemisphere - O N U S – Over-reads turning through North, Under-reads turning through South
Timed turns are a solution for?
Turning errors on the direct reading magnetic compass
what causes turning errors?
Dip of the compass
The effect of the turning error of a direct reading magnetic compass increases when?
The magnetic latitude increases
