Propeller Owner’s Manual
139
DESCRIPTION AND OPERATION
61-00-39
Page 2-9
Rev. 17 Apr/20
B. Feathering and Reversing Propellers
HC-B(3,4,5)( )( )-3( ) Series (External Beta System)
Refer to Figure 2-3. The propellers described in this section
are constant speed, feathering and reversing. They use a
single oil supply from a governing device to hydraulically
actuate a change in blade angle. The propellers can have
three, four, or five blades, and they are used primarily on
Pratt and Whitney and Walter turbine engines.
Propeller blades and bearing assemblies are mounted on the
arms of a steel hub unit (Figure 2-2) and are held in place by
two-piece blade clamps. A cylinder is threaded onto the hub,
and a feathering spring assembly is installed in the cylinder.
A piston is placed over the cylinder and is connected by a
link arm to each blade clamp. Propeller blade angle change
is accomplished through the linear motion of the hydraulically
actuated piston that is transmitted to each blade through the
link arms and blade clamps.
While the propeller is operating, the following forces are
constantly present: 1) spring force, 2) counterweight
force, 3) centrifugal twisting moment of each blade, and
4) blade aerodynamic twisting forces. The spring and
counterweight forces attempt to rotate the blades to higher
blade angle, while the centrifugal twisting moment of each
blade is generally acting toward lower blade angle. Blade
aerodynamic twisting force is usually very small in relation
to the other forces and can attempt to increase or decrease
blade angle.