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pronounced and the range
236 Canadian Professional Pilot Studies
indicated by the needle is less
and more difficult to read. Any
given power setting has only
one pitch attitude where altitude
and airspeed are constant.
· Vertical Speed Indicator (VSI). A
secondary pitch instrument,
which should be used with the
altimeter. Don't forget that it
will give a brief reverse
indication if abrupt control
movements are used.
Bank
· Artificial Horizon (Attitude
Indicator). Also the most
important bank instrument, for
similar reasons to pitch.
· Heading Indicator. An indirect
instrument, because if you
change heading, pitch must be
involved somewhere.
· Turn Coordinator. As it shows a
rate of turn (3° per second for
rate 1), it is an indirect
indication of bank.
Power
Not strictly in the traditional T, but
you have to check them anyway.
· Engine RPM. Direct indication
of power. Turbines rotate so
fast that the numbers are too
large to make sense of, so
percentages are used instead
(that is, 100% means full
power). In a helicopter, the
engine and rotor RPM needles
usually sit on top of each other
in the same instrument,
although they can be separate.
In powered flight, the needles
are joined; in autorotation, they
are split. Both conditions have a
range outside which the rotor
needle should not go. A turbine
helicopter will also have a
smaller gauge showing "gas
producer" RPM.
· The Manifold Pressure gauge
shows pressure inside the inlet
manifold, measured in inches.
The theory is that the higher the
pressure, the more the amount
of fuel/air mixture potentially
available. The equivalent of the
manifold pressure gauge in a
turbine helicopter is the
torquemeter, expressed as a
percentage. Although 100% is
the usual maximum, it may
often be increased for a few
seconds (see the flight manual).
When the engine is running,
MAP is below atmospheric
because of the pressure drop
across the throttle plate
(butterfly valve). As the throttle
is closed, the pressure drop will
increase, and MAP will fall.
When the engine is stopped, the
MAP will be atmospheric.
You keep MAP constant with
altitude by opening the throttle.
Power will increase because
exhaust back pressure falls,
improving scavenging.
· The Cylinder Head Temperature
(CHT) gauge shows you the
temperature of a selected
cylinder in a piston engine, but
not necessarily the hottest (it's
usually a rear one in a
horizontally opposed engine).
Operating an engine at a higher
than intended temperature will
cause loss of power, excessive
oil consumption and damage to
the cylinders.
Instruments 237
· Knowing the Exhaust Gas
Temperature (EGT) is useful
when leaning mixtures. The
probe is in the exhaust
manifold.
· Airspeed Indicator. A secondary
power instrument, as it changes
in relation to power application.
· Angle of Attack Indicator. This is
usually a vane or a probe fitted
flush with the side of the
aircraft to detect relative air
flow, and therefore an
indication of the angle of attack.
It is a basis for the stall warning
system and helps to verify the
aircraft attitude and speed.
Pitot-Static System
This consists of a series of pipes
through which air flows to feed
three common instruments on your
panel, the altimeter, airspeed indicator
and vertical speed indicator. The Mach
indicator will also be included, if you
have one, but this may not be part of
an exam question.
The system itself starts with a pitot
tube (pronounced pee-toe) connected
to the airspeed indicator (see below),
to measure dynamic pressure, and a
static line connected to all three (or
four), to measure the static pressure, so
called because it remains relatively
static (it's actually the normal
barometric pressure that decreases
with height). The static lines are
connected to static ports or static vents
on the side of the machine, at right
angles to the relative airflow. They
may or may not be heated.
Information from the static ports
may also be fed to non-flight
systems, such as Mach warning,
autopilots, flight directors and
recorders, and pressurisation,
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