If the air plane enters a climb without any
change in the cockpit controls, the airspeed
will decrease and the propeller will tend to
slow (Figure 7-31). The flyweights in the
propeller governor will slow down, because
of a loss in centrifugal force, and the pilot
valve will lower. This will allow more oil
pressure to the propeller pitch mechanism.
High oil pressure will result in a lower pitch.
This in tur n will cause an increase in pro-
peller r pm. The propeller will increase to
its original r pm setting, the flyweights will
then speed up, and the pilot valve will return
t o i t s e q u i l i b r i u m o r “ o n s p e e d ” p o s i t i o n ,
such as torque, interstage turbine tempera-
ture, compressor speed, and fuel flow, cor-
recting the held constant by changing the
p r o p e l l e r bl a d e a n g l e s . T h e c o c k p i t p r o -
peller lever adjusts where the equilibrium
or “onspeed” condition will occur. The pilot
can select any constant propeller r pm from
1 , 6 0 0 t o 1 , 9 0 0 r p m , h oweve r, 1 , 9 0 0 r p m
should be used for all operations.
KING AIR C90GTi/C90GTx
PILOT TRAINING MANUAL
7-32
FOR TRAINING PURPOSES ONLY
7
POWERPLANT
OIL
GOVERNOR
PUMP
REVERSE
LEVER
OVERSPEED
GOVERNOR
1976 RPM
NORMAL
TO
CASE
AUTOFEATHER
SOLENOID (N.C.)
LOW PITCH
(HIGH OIL PRESSURE)
TRANSFER
GLAND
BETA
VALVE
TO
CASE
PILOT
VALVE
PROP
LEVER
PRIMARY PROP GOVERNOR
1600 TO 1900 RPM
OVERSPEED
Figure 7-31. Propeller Underspeed Diagram
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