Direct Reading Compass Quiz & Flashcards for Aircraft

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Questions and Answers

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?

Magnetic metal

Lightweight alloy or plastic (correct)

Cobalt steel

Iridium-tipped

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?

Cobalt steel Signup and view all the answers

What is the function of the float assembly in a direct-reading compass?

To stabilize the magnet system Signup and view all the answers

What is the characteristic of the pivot in the suspension?

It is tipped with iridium Signup and view all the answers

What is the primary cause of soft iron magnetism in an aircraft?

The Earth's magnetic field Signup and view all the answers

When is the error caused by soft iron magnetism the greatest?

When the aircraft is heading NE, SE, SW, or NW Signup and view all the answers

How many coefficients of deviation are required to quantify the effects of hard and soft iron magnetism?

5 Signup and view all the answers

What is the shape of the error caused by soft iron magnetism?

Two-cycle error Signup and view all the answers

Which coefficients of deviation are relevant to practical compass compensation?

A, B, and C Signup and view all the answers

What is the reason for not inducing errors in compass readings when the aircraft is heading north or south?

The Earth's magnetic field runs directly down through the fuselage Signup and view all the answers

What does Coefficient A refer to?

Installation error and corrected by rotating the compass or flux valve Signup and view all the answers

On which headings does Coefficient B error have an effect?

East-west headings Signup and view all the answers

What is the purpose of the compensator magnets located in the lateral axis across the aircraft?

To correct Coefficient B Signup and view all the answers

When does lateral magnetism not modify the magnetic meridian?

When flying east or west Signup and view all the answers

What is the orientation of the imaginary magnet in Coefficient B?

Along the fore and aft axis of the aircraft fuselage Signup and view all the answers

Which Coefficient refers to deviation produced by an imaginary magnet lying along the aircraft’s lateral axis?

Coefficient C Signup and view all the answers

What happens to the card's magnet assembly when the aircraft accelerates?

It rotates and aligns with the vertical component of the Earth's magnetic field Signup and view all the answers

What is the primary factor that determines the extent and direction of acceleration error?

The aircraft's heading and hemisphere Signup and view all the answers

In which direction does the magnet system rotate when an aircraft in the southern hemisphere on an easterly heading increases its speed?

Anticlockwise Signup and view all the answers

What happens to the magnet system when an aircraft decelerates in the southern hemisphere on an easterly heading?

It rotates in a clockwise direction Signup and view all the answers

In which hemisphere is the acceleration error a mirror image of that produced in the other hemisphere?

Southern hemisphere Signup and view all the answers

When does acceleration error occur?

During acceleration or deceleration Signup and view all the answers

What is the purpose of an electronic compass calibrator?

Alter the alignment of a magnetic field for checking on all headings Signup and view all the answers

How is a datum compass used to determine magnetic heading?

By sighting an external reference point on the aircraft Signup and view all the answers

What role does a remote compass serve in the aircraft?

Swing a standby compass Signup and view all the answers

Which statement is true about the inertial navigation system?

It helps in determining magnetic heading Signup and view all the answers

What does a landing compass or datum compass operator do while using the compass?

Take readings by sighting an external reference point on the aircraft Signup and view all the answers

Why do complex aircraft operated by large organizations have access to electronic compass calibrator systems?

To check alignment on all headings without moving the aircraft Signup and view all the answers

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.

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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Description

Learn about the two common types of direct reading compasses used in aircraft: the vertical panel mounted compass of American design and the suspended type of British design. Understand their construction and usage in different aircraft.

Types of Direct Reading Compasses in Aircraft

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