the nonrotating section. The rotating section
REVIEW SUBSET NUMBER 9
consists of the blades, hub, spinner, and the dome
that houses the pitch changing mechanism. The
Q1. What are the two ranges of propeller
nonrotating section contains the pressure and
operation?
scavenge oil pumps, the governor control
mechanism, and the spinner afterbody. It is
a constant-speed, full-feathering, reversing
propeller, having the added features of pitchlock
Q2. What mode of operation is the synchro-
and a combination synchronizing and synchro-
phaser in when maintaining all propellers
phasing system.
at the same RPM?
Low-Pitch Stop Assembly
A mechanical stop assembly in the propeller
Q3. What unit provides a means of setting phase
dome limits low pitch blade angle to maintain a
relationships between the master and slave
minimum blade angle. When the power levers
propellers in the synchrophase system?
position is below 28 degrees, a cam operated
backup valve in the propeller housing collapses
the low-pitch stop levers. The blades move toward
the reverse position as directed by the power lever
Q4. The synchrophaser speed derivative circuit
beta schedule.
is used to dampen changes in
Beta Follow-up System
The beta follow-up system provides a variable
hydraulic low-pitch stop. At the FLIGHT IDLE
power lever position, the beta follow-up stop is
Q5. The slave propellers are prevented from
10-degree blade angle; the mechanical low-pitch
following an overspeed or underspeed
stop is 13 degrees. The purpose of the beta
master propeller by what synchrophaser
follow-up stop is to provide a secondary low-pitch
circuit?
stop. As the power lever moves toward the
TAKEOFF position and the blade angle increases,
the mechanical low-pitch stop remains at 13
degrees. The beta follow-up control programs the
PROPELLER CONTROL SYSTEM
hydraulic stop in relation to power lever position
to a maximum of 22.5 degrees of blade angle.
Learning Objective: Recognize operating
If a sudden engine failure occurs and the
principles and features of aircraft propeller
negative-torque system fails to operate, beta
control systems.
follow-up prevents excessive reduction in blade
angle and associated violent yawing.
The propeller control system is similar to
systems already discussed in this chapter. It is an
Negative Torque System
integral part of, or works with, the propeller
synchrophaser system and the propeller governing
system. The discussion that follows concerns
The negative torque system (NTS) protects
propeller pitchlock, the negative torque system,
the aircraft from excessive drag by limiting
the negative torque from the propeller to a
and feathering, unfeathering, and autofeathering
predetermined value range of -150 to -500 shaft
operations. You should refer to figure 5-24
horsepower. During a negative torque condition,
throughout this discussion of the components in
NTS provides a mechanical signal that overrides
and operation of the propeller control system.
the propeller governing action to increase blade
angle. When the propeller reaches a position
PROPELLER
where it is no longer developing negative torque,
The four-bladed propeller converts engine
the propeller governor regains control of the
shaft horsepower to thrust. The propeller consists
propeller. If the negative torque condition persists,
a cycling action continues from the mechanical
of two principal sections--the rotating section and
