Piper Navajo PA-31 Service Manual page 469

PIPER NAVAJO SERVICE MANUAL
8-19. ADJUSTMENT OF LOW PITCH BLADE ANGLE AND STOP
NOTE
Both types of propellers referred to, come from the factory with the
low pitch stop adjusted for proper blade angle. If, however this
adjustment has been disturbed, the procedure given below is used
for obtaining blade angle, but applies only to the propeller without
the feather assist spring. There is no way to check the low pitch blade
angle of the propeller, with the spring Kit installed, in the field. This
is due to the internal spring producing a force near to that of the air
change in the standard propeller which can and has to be released to
make this adjustment. The spring supplies constant pressure to the
blades making it very difficult to rotate the blades to a point where
the low pitch stop is contacted. Therefore, if the blade angle on a
spring propeller is suspected to be wrong it should be referred back
to the Hartzell Factory or Certified Repair Shop.
a.
The propeller comes from the factory with the low pitch stop adjusted for proper blade angle. If,
however, this adjustment has been disturbed, the following procedure is given for obtaining blade angle:
1. The blade angle (refer to Table VIII-I) is determined by placing a propeller protractor on the
face side of the propeller at the 30 inch station as measured from the hub centerline. The blade must be
horizontal.
2. The low pitch stop adjustment is made by a screw in the nose of the propeller cylinder.
Rotating the screw clockwise increases the low pitch and reduces the static RPM by about 100 RPM for
each half turn or vice verse.
CAUTION
Before adjusting the low pitch stop screw, the air pressure should
be dropped to zero. Unless this is done, it is possible to unscrew
the low stop far enough to disengage the threads, allowing the air
pressure to blow the stop screw out with great force. To insure the
complete discharge of all air pressure within the dome, place the
propeller CONTROL in the feather detent. There should be at
least four of the twenty threads of the stop screw engaged.
b. After the low pitch stop has been adjusted for proper blade angle, torque the low stop adjust nut
to 30 foot-pounds. The governor should then be adjusted to obtain maximum rated engine RPM during
take-off and climb.
c. In order to test whether the governor or the propeller low stop is limiting the static RPM, the
operator can run the engine up on the ground. With the throttle wide open, increase RPM slowly with the
RPM control. If the propeller low stop is limiting the RPM, the RPM will stabilize before the RPM control
reaches the limit of its travel. If the RPM increases continuously during the entire movement of the RPM
control, the governor is limiting the static RPM and not the propeller low stop.
8-20. BLADE TRACK. Blade track is the ability of one blade tip to follow the other, while rotating, in
almost exactly the same place. Excessive difference in blade track - more than .062 inch - may be an
indication of bent blades or improper propeller installation. Check blade track as follows:
Reissued: 10/12/79
POWER PLANT
2H19