Cessna 172N - Page 128

SECTION
7
AIRPLANE
&
SYSTEMS DESCRIPTIONS
CESSNA
MODEL
172N
Iong
range
system
(see
figure 7-6). Both
systems
consist
of two
vented
fuel tanks
(one
in
each wing), a
four-position selector valve,
fuel
strainer,
manual
primer,
and
carburetor.
Refer to figure 7-5 for
fuel
quantity
data
for both
systems.
FueI
flows
by
gravity
from
the
two
wing
tanks
to a four-position selec-
tor
valve,
labeled
BOTH,
RIGHT,
LEFT, and
OFF.
With
the
selector
valve in
either
the
BOTH,
LEFT,
or
RIGHT
position,
fuel
flows through
a
strainer
to the carburetor.
From
the
carburetor,
mixed
fuel
and
air
flows
to the
cylinders through
intake
manifold tubes.
The
manual
primer
draws
its fuel
from the fuel
strainer
and
injects
it
into
the
cylinder
intake
ports.
FueI system
venting is essential
to
system
operation.
Blockage of
the
system
will
result
in
decreasing
fuel
flow
and eventual
engine
stoppage.
Venting
is accomplished by
an
interconnecting line from
the
right
fuel tank
to the
left tank.
The left fuel
tank is vented
overboard
through a
vent
line,
equipped
with a
check valve,
which
protrudes
from the bottom
surface of
the left
wing
near
the
wing strut.
The
right
fuel
tank
filler cap is also
vented.
Fuel
quantity
is
measured
by
two
float-type fuel
quantity
transmit-
ters
(one
in
each tank)
and indicated by
two
electrically-operated
fuel
quantity
indicators
on the left
side
of
the instrument
panel.
An empty
tank is
indicated
by
a red
line
and
the letter
E.
When
an
indicator
shows
an empty
tank,
approximately 1.5
gallons
remain
in
a standard
tank,
and 2
gallons
remain
in a long
range
tank as unusable
fuel. The
indicators
cannot
be relied
upon for accurate readings during skids,
slips,
or
unusual
attitudes.
The fuel
selector valve
should be in
the
BOTH
position
for takeoff,
climb,
Ianding, and maneuvers
that involve
prolonged
slips
or
skids.
Op-
eration
from
either
LEFT or RIGHT
tank
is
reserved
for cruising
flight.
NOTE
When
the
fuel selector
valve
handle
is
in
the BOTH
po-
sition in cruising flight,
unequal fuel flow from
each
tank may
occur
if the
wings
are
not
maintained
exactly
level.
Resulting
wing heaviness
can
be alleviated
gradually
by turning the
selector
valve
handle to
the
tank
in the
"heavy"
wing.
NOTE
It is not
practical
to
measure the
time
required to con-
sume
all
of the fuel
in one
tank,
and,
after
switching
to
the opposite
tank,
expect
an
equal duration from
the
remaining
fuel. The
airspace in
both
fuel
tanks
is
inter-
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