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Questions and Answers
What is the primary function of direct-reading compasses on light aircraft?
What is the primary function of direct-reading compasses on light aircraft?
- To indicate altitude
- To serve as the primary heading reference (correct)
- To provide a standby reference
- To indicate airspeed
What is the material used to make the compass card or dial?
What is the material used to make the compass card or dial?
- Magnetic metal
- Lightweight alloy or plastic (correct)
- Cobalt steel
- Iridium-tipped
What is the purpose of the sapphire cup in the suspension?
What is the purpose of the sapphire cup in the suspension?
- To amplify the compass signal
- To magnify the compass reading
- To increase the magnetic field
- To reduce pivot friction (correct)
What is the material used to make the magnet in the magnet system?
What is the material used to make the magnet in the magnet system?
What is the function of the float assembly in a direct-reading compass?
What is the function of the float assembly in a direct-reading compass?
What is the characteristic of the pivot in the suspension?
What is the characteristic of the pivot in the suspension?
What is the primary cause of soft iron magnetism in an aircraft?
What is the primary cause of soft iron magnetism in an aircraft?
When is the error caused by soft iron magnetism the greatest?
When is the error caused by soft iron magnetism the greatest?
How many coefficients of deviation are required to quantify the effects of hard and soft iron magnetism?
How many coefficients of deviation are required to quantify the effects of hard and soft iron magnetism?
What is the shape of the error caused by soft iron magnetism?
What is the shape of the error caused by soft iron magnetism?
Which coefficients of deviation are relevant to practical compass compensation?
Which coefficients of deviation are relevant to practical compass compensation?
What is the reason for not inducing errors in compass readings when the aircraft is heading north or south?
What is the reason for not inducing errors in compass readings when the aircraft is heading north or south?
What does Coefficient A refer to?
What does Coefficient A refer to?
On which headings does Coefficient B error have an effect?
On which headings does Coefficient B error have an effect?
What is the purpose of the compensator magnets located in the lateral axis across the aircraft?
What is the purpose of the compensator magnets located in the lateral axis across the aircraft?
When does lateral magnetism not modify the magnetic meridian?
When does lateral magnetism not modify the magnetic meridian?
What is the orientation of the imaginary magnet in Coefficient B?
What is the orientation of the imaginary magnet in Coefficient B?
Which Coefficient refers to deviation produced by an imaginary magnet lying along the aircraft’s lateral axis?
Which Coefficient refers to deviation produced by an imaginary magnet lying along the aircraft’s lateral axis?
What happens to the card's magnet assembly when the aircraft accelerates?
What happens to the card's magnet assembly when the aircraft accelerates?
What is the primary factor that determines the extent and direction of acceleration error?
What is the primary factor that determines the extent and direction of acceleration error?
In which direction does the magnet system rotate when an aircraft in the southern hemisphere on an easterly heading increases its speed?
In which direction does the magnet system rotate when an aircraft in the southern hemisphere on an easterly heading increases its speed?
What happens to the magnet system when an aircraft decelerates in the southern hemisphere on an easterly heading?
What happens to the magnet system when an aircraft decelerates in the southern hemisphere on an easterly heading?
In which hemisphere is the acceleration error a mirror image of that produced in the other hemisphere?
In which hemisphere is the acceleration error a mirror image of that produced in the other hemisphere?
When does acceleration error occur?
When does acceleration error occur?
What is the purpose of an electronic compass calibrator?
What is the purpose of an electronic compass calibrator?
How is a datum compass used to determine magnetic heading?
How is a datum compass used to determine magnetic heading?
What role does a remote compass serve in the aircraft?
What role does a remote compass serve in the aircraft?
Which statement is true about the inertial navigation system?
Which statement is true about the inertial navigation system?
What does a landing compass or datum compass operator do while using the compass?
What does a landing compass or datum compass operator do while using the compass?
Why do complex aircraft operated by large organizations have access to electronic compass calibrator systems?
Why do complex aircraft operated by large organizations have access to electronic compass calibrator systems?
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Study Notes
Direct-Reading Compass Function
- Primary function: Indicate aircraft heading relative to magnetic north.
Compass Components and Materials
- Compass card/dial: Typically made of lightweight, durable plastic or acrylic.
- Sapphire cup suspension: Sapphire cup reduces friction and provides smooth, accurate movement.
- Magnet system: Magnet is usually made of high-coercivity Alnico (aluminum, nickel, and cobalt).
- Float assembly: Keeps the compass card level and accurate at different angles.
- Pivot: The pivot in the suspension should be frictionless for precise readings.
Soft Iron Magnetism
- Primary cause: Aircraft's metallic components becoming magnetized by the Earth's magnetic field.
- Greatest error: When the aircraft's heading aligns with the magnetic field lines.
- Quantifying magnetic effects: Deviation coefficients (A, B, C, D, E) represent hard and soft iron magnetism's influence.
- Soft iron magnetism error shape: Typically elliptical.
- Practical compensation: Coefficients A, B, C, D, and E are used to quantify soft iron magnetism for accurate compass operation.
- No error north/south: When the aircraft is heading north or south, the magnetic forces acting on the compass cancel out, resulting in no deviation.
Deviation Coefficients
- Coefficient A: (Hard iron magnetism): Affects the compass reading on all headings.
- Coefficient B: (Hard iron magnetism): Has an effect on headings east and west, causing a greater deviation.
- Lateral axis compensator magnets: Located laterally (across the plane) to counter hard iron magnetism.
- Lateral magnetism no effect: When the aircraft is heading north or south, the lateral magnetism doesn't influence the magnetic meridian.
- Coefficient B imaginary magnet: Orientation is horizontal, passing through the center of the compass.
- Coefficient D: Magnetic deviation produced by an imaginary magnet lying along the aircraft's lateral axis.
Acceleration Error
- Magnet system acceleration: When the aircraft accelerates, the compass card's magnet system aligns with the force of acceleration.
- Acceleration error magnitude: Determined by the rate of acceleration, aircraft heading, and hemisphere.
- Southern Hemisphere acceleration error: The magnet system rotates clockwise when an aircraft traveling eastwards accelerates.
- Southern Hemisphere deceleration error: The magnet system rotates counterclockwise when an aircraft traveling eastwards decelerates.
- Acceleration error mirror image: Northern and Southern hemispheres have mirror image acceleration errors.
- Acceleration error occurrence: Happens during acceleration, deceleration, or when the aircraft is on turning maneuvers.
Other Compass-Related Concepts
- Electronic compass calibrator: Used to calibrate electronic compasses and eliminate deviations.
- Datum compass: Provides a reference heading used to verify other compass readings.
- Remote compass: A compass located in another part of the aircraft, transmitted to the pilot's display.
- Inertial navigation system (INS): Primary function is navigation without external reference. It is not dependent on magnetic fields.
- Landing compass operator: Uses the landing (datum) compass to determine the aircraft's magnetic heading.
- Electronic compass calibrator in large organizations: Crucial for ensuring precise compass readings in complex aircraft.
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