Airspeed and Mach Number Indicator
The airspeed and mach number indicator (fig. 7-8)
displays the speed of the aircraft in relation to the air in
which it is flying. In some instances, the speed of an
aircraft is shown in Mach numbers. The Mach number
of any moving body is its speed compared to the speed
of sound in the surrounding medium (local speed). For
example, if an aircraft is flying at a speed equal to
one-half the local speed of sound, it is flying at Mach
0.5. If it moves at twice the local speed of sound, its
speed is at Mach 2.
The rate-of-climb indicator (fig. 7-9) shows the rate
at which an aircraft is climbing or descending. The case
of a climb indicator is airtight except for a small
connection through a restricted passage to the static
line. Changes in atmospheric pressure move the
operating mechanism that displays the rate of change.
This change occurs only when the aircraft is ascending
or descending. When the aircraft ceases to climb or
dive, the airflow through the metering units equalizes
and the pointer returns to zero.
PRESSURE INDICATING GAUGES
Electrical signals from a pressure transmitter
activate a variety of aircraft instrument systems.
Electrically activated instruments are usually in the
form of small voltmeters with calibrated dials. These
dials are calibrated to display a variety of conditions
such as oil pressure, fuel pressure, and hydraulic
Oil Pressure Indicator
Oil pressure instruments (fig. 7-10) show the
pressure of the oil. Drops in oil pressure (below normal
conditions) signal possible engine failure caused by
lack of oil.
Fuel Pressure Indicator
The fuel pressure indicator provides a check on the
operation of the fuel system. It shows if fuel is being
supplied steadily under the correct operating pressure.
Hydraulic Pressure Indicator
The pressures of hydraulic systems vary for
different models of aircraft. In most pressure systems,
Figure 7-10.Oil pressure indicator.
Figure 7-9.Rate-of-climb indicator.
INDEX ADJUSTING KNOB
MACH LIMIT INDEX
Figure 7-8.Airspeed and Mach number indicator.