Airplane & Systems Descriptions - Cessna 17273274 Pilot Operating Handbook

CESSNA
MODEL 172N
position. Spring clips will hold the valve open. After draining, use a
suitable tool to snap the valve into the extended (closed) position and
remove the drain hose.
IGNITION-STARTER SYSTEM
Engine ignition is provided by an engine-driven dual magneto, 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 magne­
tos 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 clock­
wise, OFF , R, L, BOTH, and ST ART. 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 energized and the
starter will crank the engine. When the switch is released, it will automati­
cally return to the BOTH position.
AIR INDUCTION SYSTEM
The engine air induction system receives ram air through an intake in
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 airbox. After passing
through the airbox, induction air enters the inlet in the carburetor which is
under the engine, and is then ducted to the engine cylinders through intake
manifold tubes. In the event carburetor ice is encountered or the intake
filter becomes blocked, alternate heated air can be obtained from a shroud
around an exhaust riser through a duct to a valve, in the airbox, operated
by the carburetor heat control on the instrument panel. Heated air from the
shroud is obtained from an unfiltered outside source.Use of full carburetor
heat at full throttle will result in a loss of approximately 100 to 225 RPM.
EXHAUST SYSTEM
Exhaust gas from each cylinder passes through riser assemblies to a
muffler and tailpipe. The muffler is constructed with a shroud around the
outside which forms a heating chamber for cabin heater air.
CARBURETOR AND PRIMING SYSTEM
The engine is equipped with an up-draft, float-type, fixed jet carburetor
1 July 1979
AIRPLANE & SYSTEMS DESCRIPTIONS
SECTION 7
7-19