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Instrument Flying Handbook
Flight Instruments
Basic Aviation Magnetic Compass

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Instrument Flying
Handbook

Preface

Table of Contents

Chapter 1. Human Factors
Chapter 2. Aerodynamic Factors
Chapter 3. Flight Instruments
Chapter 4. Section I
Airplane Attitude Instrument
Flying
Using Analog Instrumentation
Chapter 4. Section II
Airplane Attitude Instrument
Flying
Using an Electronic Flight
Display

Chapter 5. Section I
Airplane Basic
Flight Maneuvers
Using Analog Instrumentation
Chapter 5. Section II
Airplane Basic
Flight Maneuvers
Using an Electronic Flight
Display

Chapter 6. Helicopter
Attitude Instrument Flying

Chapter 7. Navigation Systems
Chapter 8. The National
Airspace System

Chapter 9. The Air Traffic
Control System

Chapter 10. IFR Flight
Chapter 11. Emergency
Operations

The Effects of Acceleration Error.
Figure 3-21. The Effects of Acceleration Error.

When an aircraft is flying on a heading of south and begins
a turn toward cast, the Earth's magnetic field pulls on the
end of the magnet that rotates the card toward east, the same
direction the turn is being made, if the turn is made from south
toward west, the magnetic pull starts the card rotating toward
west again, in the same direction the turn is being made. The
rule for this error is: When starting a turn from a southerly
heading, the compass indication leads the turn.

In acceleration error, the dip-correction weight causes the end
of the float and card marked N (the south-seeking end) to be
heavier than the opposite end. When the aircraft is flying at
a constant speed on a heading of east or west, the float and
card is level. The effects of magnetic dip and the weight are
approximately equal. If the aircraft accelerates on a heading
of east [Figure 3-21], the inertia of the weight holds its end of
the float back and the card rotates toward north. As soon as the
speed of the aircraft stabilizes, the card swings back to its east
indication. If, while flying on this easterly heading, the aircraft
decelerates, the inertia causes the weight to move ahead and the
card rotates toward south until the speed again stabilizes.

When flying on a heading of west, the same things happen.
Inertia from acceleration causes the weight to lag, and the
card rotates toward north. When the aircraft decelerates on a
heading of west, inertia causes the weight to move ahead and
the card rotates toward south,

Oscillation is a combination of all of the other errors, and it
results in the compass card swinging back and forth around
the heading being flown. When setting the gyroscopic
heading indicator to agree with the magnetic compass, use
the average indication between the swings.

The Vertical Card Magnetic Compass
The floating magnet type of compass not only has all the
errors just described, but also lends itself to confused reading.
It is easy to begin atom in the wrong direction because its card
appear's backward. East is on what the pilot would expect to he
the west side. The vertical card magnetic compass eliminates
some of the errors and confusion. The dial of this compass
is graduated with letters representing the cardinal directions,
numbers every 30°, and marks every 5°. The dial is rotated by
a set of gears from the shaft-mounted magnet, and the nose
of the symbolic airplane on the instrument glass represents
the lubber line for reading the heading of the aircraft from
the dial. Eddy currents induced into an aluminum-damping
cup damp oscillation of the magnet. [Figure 3-22]

The Flux Gate Compass System
As mentioned earlier, the lines of flux in the Earth's magnetic
field have two basic characteristics: a magnet aligns with
these lines, and an electrical current is induced, or generated,
in any wire crossed by them.

 

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