Description And Operation; Propeller And Beta Feedback Mechanism - Thrush Aircraft S2RHG-T65 TURBO THRUSH Maintenance Manual

Table of Contents

THRUSH AIRCRAFT, INC – MODEL S2RHG-T65 TURBO THRUSH

Perform the engine ground test and checks. (Refer to procedures outlined later

in this section and Pratt & Whitney Maintenance Manual.)

Prior to engine run-up, ensure the engine air inlet plenums are

free of foreign objects.

This section describes the function of the following:

- Propeller and Beta Feedback Mechanism

- Constant Speed Unit (CSU)

- Propeller Over speed Governor

- Engine Power and Propeller Controls (FCU)

- Propeller Speed Select and Feathering Control

- Propeller Settings

The Fuel Control Unit (FCU) is not included, as it is covered in

the Engine Maintenance Manual

PROPELLER AND BETA FEEDBACK MECHANISM

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 (See Figure 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

Effective: 05/05/04

AIRCRAFT MAINTENANCE MANUAL

** CAUTION **

PROPELLER