Before Takeoff - Cessna 172 Ownersmanual

throttle run-ups over loose gravel are especially harmful to propeller
tips. When take-offs must be made over a gravel surface, it is very im-
portant that the throttle be advanced slowly. This allows the airplane to
start rolling before high RPM is developed, and the gravel will be blown
back of the propeller rather than pulled into
it.
Wben unavoidable small
dents appear in the propeller blades, they should be immediately cor-
rected as described in Section 4 under propeller care.
BEFORE TAKE-OFF.
WARM UP.
Since the engine is closely cowled for efficient in-flight engine cool-
ing,
precautions should be taken to avoid overheating during prolonged
engine operation on the ground.
MAGNETO CHECK .
The magneto check should be made at 1600 RPM as follows: Move
the ignition switch first to "R" position, and note RPM. Next move the
switch back to "BOTH" position to clear the other set of plugs. Then
move the switch to the
"L"
position and note RPM. The difference be-
tween the two magnetos operated indi. v idually should not be more than
75 RPM.
HIGH RPM MAGNETO CHECKS.
If there is a doubt concerning the operation of the ignition system,
RPM checks at higher engine speeds will usually confirm whether a de-
ficiency exists. If a full thro~le run-up is necessary the engine should
run smoothly and turn approximately 2230 to 2330 RPM with the car-
buretor heat off.
An absence of RPM drop may be an indication of faulty grounding of
one side of the ignition system or should be cause for suspicion that the
magneto timing has been "bumped-up" and is set in advance of the set-
ting specified .
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TAKE-OFF.
POWER CHECK.
Since the use of full throttle is not recommended in the static run-up,
it
is important to check full-throttle engine operation early in the take-off
run. Any signs of rough engine operation or sluggish engine acceleration
is good cause for discontinuing the take-off. If this occurs, you are
j ustified in ma.king a thorough full-throttle , static run-up before another
take-off is attempted.
Prior to take-off from fields above 5000 ft. elevation, the mixture
should be leaned to give maximum RPM
in
a full-throttle , static run- up.
WING FLAP SETTINGS.
Normal and obstacle clearance take-offs are performed with wing
flaps up. The use of 10° flaps will shorten the ground run approximately
10%, but this advantage is lost in the climb to a 50- foot obstac le. There-
fore the use of 10° flap is reserved for minimum ground runs or for take-
off from soft or rough fields with no obstacles ahead.
If
10° of flaps are used in ground runs,
it
is preferable to leave them
extended rather than retract them in the climb to the obstacle. The ex-
ception to this rule would be in a high altitude take-off in hot weather
where climb would be marginal with flaps 10° (1st notch).
Flap deflections of 30 ° to 40° are not recommended at any time for
take-off.
PERFORMANCE CHARTS.
Consult the take-off chart in Section 5, for take-off distances under
various gross weight, altitude, and headwind conditions.
CROSSWIND TAKE-OFFS.
Take-offs into strong crosswinds normally are performed with the
minimum flap setting necessary for the field length, to minimize the
drift angle immediately after take-off. The airplane is accelerated to
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