Cessna 172N - Page 139

CESSNA
MODEL
172N
SECTION
7
AIRPLANE
& SYSTEMS
DESCRIPTIONS
system consists
of a
vacuum
pump
mounted on the engine, a
vacuum
re-
lief
valve
and
vacuum system
air
filter on the
aft
side
of
the
firewall
be-
low the
instmment
panel,
and instruments
(including
a
suction
gage)
on
the
left
side
of the instmment
panel.
ATTITUDE
INDICATOR
The attitude
indicator
gives
a visual indication of flight attitude.
Bank
attitude is
presented
by a
pointer
at the top of
the indicator rela-
tive
to the
bank scale
which has index
marks at
10", 20o, 30o, 60o, and
90o either
side
of the center mark.
Pitch
and
roll attitudes
are
present-
ed by a miniature airplane in
relation
to the horizon bar.
A
knob at the
bottom
of
the instrument is
provided
for
in-flight adjustment
of the
miniature
airplane
to
the
horizon
bar for a more
accurate flight attitude
indication.
DIRECTIONAT
INDICATOR
A
directional
indicator displays airplane
heading on a
compass
card in
relation
to a fixed
simulated
airplane
image
and
index. The
indicator
will
precess
slightly
over a
period
of time.
Therefore,
the compass
card
should
be
set
in
accordance
with the magnetic
compass
just
prior
to takeoff, and
oc-
casionally re-adjusted on extended
flights.
A
knob on the
lower left
edge of
the
instmment
is used to
adjust
the compass
card
to correct
for
precession.
SUCTION
GAGE
The
suction
gage
is
located on the
left
side
of the
instnrment
panel
and indicates, in
inches
of
mercury, the amount of
suction
available
for
operation of
the attitude indicator and
directional
indicator. The
desired
suction
range
is 4.6 to 5.4 inches of
mercury. A
suction
reading
below
this
range may
indicate
a system
malfunction
or improper
adjustment,
and
in this case, the indicators
should
not be
considered
reliable.
STATL WARNING
SYSTEM
The
airplane is equipped
with
a
pneumatic-type
stall warning
sys-
tem
consisting
of an inlet in the leading
edge
of
the left wing,
an air-
operated horn
near the upper left corner
of the
windshield,
and
asso-
ciated
plumbing.
As the airplane approaches
a stall, the low
pressure
on
the upper surface
of
the wings
moves forward around
the
leading
edge
of the wings. This low
pressure
creates a
differential
pressure
in
the
stall warning
system
which
draws air through
the
warning horn,
resulting
in
an audible
warning
at 5 to 10 knots
above stall
in
all flight
conditions.
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