Propeller; Description And Operation; Propeller And Beta Feedback Mechanism - Thrush Aircraft S2R–T660 Maintenance Manual

DESCRIPTION AND OPERATION

This section describes the function of the following:

− Propeller and Beta Feedback Mechanism

− Constant Speed Unit (CSU)
− Propeller Overspeed Governor
− Engine Power and Propeller Controls (FCU)
− Propeller Speed Select and Feathering Control
− Propeller Settings
The propeller has five blades mounted on a hollow hub in the front end of which is a servo-piston
that moves forward under servo-oil pressure or rearward under feather return spring pressure. (Ref.
Fig. 4-1) There are five links from the servo-piston. One goes to each blade root, and these links
transmit forward motion of the servo-piston to the blade roots and pivot the blades in the decrease
pitch direction. When servo-piston pressure is relieved, the servo-piston moves rearward under
feather return spring pressure and pivots the blades in the increase pitch direction. This action is
assisted by centrifugal force of the counterweight on each blade root.
Servo-oil is supplied from the constant speed unit (CSU). It flows through oil passages in the engine
reduction gear case through a transfer tube between the reduction gear case and propeller oil
transfer housing; then via the propeller oil transfer housing, the engine shaft, the hollow hub, and
the internal oil ports in the servo-piston. Refer to Figure 4-1.
The beta feedback mechanism has three low pitch stop rods (Fig. 4-1) that are screwed into the
propeller feedback ring (Fig. 4-1). These three rods slide fore and aft in small bushings mounted in a
flange integral with the hollow hub.
Near the forward end of each low stop rod is a beta nut (Fig. 4-1). Ahead of these is the ring rod
end (Fig. 4-1) which steadies the low stop rods. As the servo-piston moves forward, it picks up on
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THRUSH AIRCRAFT INC - T660 TURBO THRUSH
AIRCRAFT MAINTENANCE MANUAL

PROPELLER

*NOTE*
The Fuel Control Unit (FCU) is not included as
it is covered in the Engine Maintenance Manual
PROPELLER AND BETA FEEDBACK MECHANISM
Effective: 12/17/03