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Instrument Flying Handbook
Flight Instruments
Gyroscopic Instruments

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Instrument Flying


Table of Contents

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

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

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

Steel vanes sliding in a steel housing need to be lubricated,
but vanes made of a special formulation of carbon sliding
inside carbon housing provide their own lubrication in a
microscopic amount as they wear.

Pressure Indicating Systems

Figure 3-29 is a diagram of the instrument pneumatic
system of a twin-engine general aviation airplane. Two dry
air pumps are used with filters in their inlet to filter out any
contaminants that could damage the fragile carbon vanes in
the pump. The discharge air from the pump flows through
a regulator, where excess air is bled off to maintain the
pressure in the system at the desired level. The regulated air
then flows through inline filters to remove any contamination
that could have been picked up from the pump, and from
there into a manifold check valve. if either engine should
become inoperative or either pump should fail, the check
valve isolates the inoperative system and the instruments are
driven by air from the operating system. After the air passes
through the instruments and drives [lie gyros, it is exhausted
from the case. The gyro pressure gauge measures the pressure
drop across the instruments.

Electrical Systems
Many general aviation aircraft that use pneumatic attitude
indicators use electric rate indicators and/or the reverse. Some
instruments identify their power source on their dial, but it
is extremely important that pilots consult the POWAFM to
determine the power source of all instruments to know what
action to take in the event of an instrument failure. Direct
current (D.C.) electrical instruments are available in 14- or
28-volt models, depending upon the electrical system in
the aircraft. AC. is used lo operate some attitude gyros and
autopilots. Aircraft with only D.C. electrical systems can use
AC instruments via installation of a solid-state DC to AC.
inverter, which changes 14 or 28 volts DC into three-phase
115-volt, 400-Hz AC.

Gyroscopic Instruments

Attitude Indicators
The first attitude instrument (Al) was originally referred to as
an artificial horizon, later as a gyro horizon; now it is more
properly called an attitude indicator. It's operating mechanism
is a small brass wheel with a vertical spin axis, spun at a high
speed by either a stream of air impinging on buckets cut into
its periphery, or by an electric motor. The gyro is mounted in
a double gimbal, which allows the aircraft to pitch and roll
about the gyro as it remains fixed in space.

Twin-Engine Instrument Pressure System
Figure 3-29. Twin-Engine Instrument Pressure System Using a Carbon Vane Dry Type Air Pump.