THRUSH AIRCRAFT INC - MODEL S2R-G10
AIRPLANE MAINTENANCE MANUAL
the prop blade is parallel with the horizon
and the aircraft wings are generally level.
Zero the propeller protractor on the
propeller hub and take all measurements
at the blade station called out in the
propeller owner’s manual, or Figure 4-1.
Measure the flight idle and reverse blade
angles with the unfeathering pump
supplying steady oil pressure to the
propeller.
* NOTE *
The unfeathering pump draws oil
from the engine oil tank to actuate
the propeller. Bleed oil from the
prop is dumped into the reduction
gear box, not the engine oil tank. If
the unfeathering pump is operated
frequently or for prolonged periods,
it will pump the engine tank dry. If
you hear the pump suddenly
unload, cavitate or speed up, stop
the pump. You can pump the oil
out of the gearbox and back into the
oil tank by turning the propeller 50
revolutions by hand or by the
starter. It is not uncommon to
experience some oil loss overboard
from the vent.
4-10
DO NOT USE THE STARTER TO
RETURN OIL TO THE ENGINE
TANK IF THE PROPELLER IS IN
THE FEATHERED POSITION.
TURN THE PROPELLER BY
HAND ONLY
IN THE NORMAL
DIRECTION OF ROTATION.
The feathered, start lock and reverse blade
angles are preset by the propeller
manufacturer. The flight idle blade angle is
hydraulically controlled by the position of
the beta tube. Remove the locking bolt
and nut before attempting to turn the beta
tube. Turning the beta tube clockwise
(looking aft) will decrease the blade angle.
Counterclockwise movement will increase
the blade angle.
Checking and adjusting the flight idle blade
angle requires taking the blades off the
start locks to the feathered position. To
accomplish this, move the power lever to
the full reverse position and turn on the
feathering pump to move the blades off the
start locks. Retract the start locks with
your fingers and hole them in place with
modified clothespins. Turn off the
unfeathering pump and pull the emergency
cutoff lever. The blades will move under
spring pressure to the feather position. As
an alternate method, or, if hot engine is
required, start the engine in accordance
with normal start procedures. When ready
to shut down the engine, briefly pull the
power lever into reverse to release the
start locks and return to ground or flight
idle. Actuate the fuel shutoff switch with
the power lever in ground idle or flight idle.
The blades will feather under spring
pressure as the oil pressure decreases.
With the propeller protractor previously
zeroed on the propeller hub and with the
prop in the feathered position, move to the
face of the blade to be measured. Be sure
that the power lever is in the flight idle
position and the prop pitch servo valve is
pinned at 40º with a 1/8” diameter drill bit
or rigging pin. Verify the proper feathered
angle at this time.
WARNING
If the propeller installation is new or if the
beta tube has been removed or disturbed,
screw the beta tube into the prop until it is
¼ inch inside its housing.
Have an assistant turn on the unfeathering
pump. When the blades move off the
feathered stop to the flight idle angle,
check the blade angle at the proper blade
station. Adjust the beta tube accordingly to
achieve 4.5 degrees plus or minus 0.2
degrees blade angle on a hot engine. If
the engine is cold, the cold setting will be
about 1 degree lower. For example, if 4.5
degrees is required, set a cold engine at
3.5 degrees. Check the blade angle again
Page Effective: 03/26/2010
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