Propeller Owner's Manual
136
DESCRIPTION AND OPERATION
61-00-36
Page 2-13
Rev. 2 Feb/17
Centrifugal locks built into the beta lockout assembly are
RPM sensitive such that they will engage a groove in
the hub barrel at RPMs above 900 RPM to prevent axial
moment in the barrel of the hub. At an RPM below
900 RPM the centrifugal locks will retract into the body of
the low pitch stop unit and permit axial movement in the
barrel of the hub for beta range operation.
For fixed wing amphibian aircraft this requires that the
aircraft is landed with minimum forward movement to
permit the engine to be idled down to an RPM below 900
RPM to permit release of the centrifugal locks and allow
linear movement of the beta lockout assembly below low
pitch into beta range.
A lighter than air vehicle, such as a blimp, will also need to
idle the engine below 900 RPM to facilitate movement of
blade pitch from low pitch into beta range.
(5) Before selecting beta range for maneuvering (low positive
blade pitch and reverse blade pitch) the governor must
be set by the pilot to a maximum RPM selection. It is
important to understand that all operation in the beta range
must be at an RPM less than the maximum governor RPM
selection. In this manner the governor interprets all beta
range operation as an underspeed and will continue to
supply maximum oil pressure to the pressure control unit
in an effort to decrease blade angle for RPM increase in a
positive thrust constant speed situation.
If the RPM is allowed to exceed the governor maximum
RPM selection then the governor will interpret this as an
overspeed and will immediately drain oil to force a sudden
and unexpected blade angle increase. This will cause
a sudden and powerful positive thrust that could cause
damage to the aircraft during manual pilot control during
maneuvering.
The supply of maximum oil pressure (270 to 300 PSI)
to the pressure control unit is required to maintain pilot
control of propeller blade angle in beta range (between low
pitch and maximum reverse blade angle) for maneuvering.
A minimum pressure of 270 PSI from the governor is
required to reach maximum reverse pitch. Refer to
Figure 2-3.
