Cessna 172R - Ignition and Starter System; Air Induction System

SECTION
7
AIRPLANE
&
SYSTEMS
DESCRIPTION
CESSNA
MODEL
172R
IGNITION
AND
STARTER SYSTEM
|
Engine
ignition
is
provided
by
two
engine-driven
magnetos,
and
two
spark
plugs
in
each
cylinder.
The
right
magneto
fires
the
lower
right
and
upper
left
spark
plugs,
and the
left
magneto
fires
the
lower
left
and
upper
right
spark
plugs.
Normal
operation
is
conducted
with
|both
magnetos
due
to
the
more
complete
burning
of
the
fuel/air
mixture
with
dual
ignition.
|
Ignition
and
starter
operation
is controlled
by
a
rotary-type
switch
located
on
the
left
switch and
control
panel.
The switch is labeled
clockwise,
OFF,
R,
L,
BOTH,
and
START.
The
engine
should be
operated
on
both
magnetos
(BOTH position)
except
for
magneto
checks. The
R
and
L
positions
are
for
checking
purposes
and
emergency
use
only.
When the
switch
is
rotated
to
the
spring
loaded
START
position,
(with
the
master
switch
in
the
ON
position),
|the
starter
contactor
is
closed and the
starter,
now
energized,
will
crank the
engine.
When the
switch
is
released,
it
will
automatically
return to
the
BOTH
position.
AIR
INDUCTION
SYSTEM
The
engine
air
induction
system
receives
ram
air
through
an
intake
on
the
lower
front
portion
of
the
engine
cowling.
The
intake is
covered
by
an
air
filter
which
removes
dust
and other
foreign
matter
from
the
induction air.
Airflow
passing
through
the
filter
enters
an
air
box.
The
air box
has
a
spring-loaded
alternate
air
door.
If
the air
induction
filter
should
become
blocked,
suction
created
by
the
engine
will
open
the door
and
draw
unfiltered
air
from
inside the
lower
cowl
area.
An
open
alternate
air door
will
result
in
an
approximate
10%
power
loss
at
full
throttle.
After
passing through
the air
box,
induction air
enters
a
fuel/air
control unit under the
engine,
and
is then
ducted
to
the
engine
cylinders
through
intake
manifold
tubes.
7-22
Revision
4