Propeller Overspeed Governor; Engine Power And Propeller Controls (Fcu) - Thrush Aircraft S2RHG-T65 TURBO THRUSH Maintenance Manual

THRUSH AIRCRAFT, INC – MODEL S2RHG-T65 TURBO THRUSH
cruise. Normally in those configurations the blades are much coarser than
the angle at which the servo-piston picks up the beta nuts.
2. The second function of the beta control valve is to enable direct control of
the propeller blade angle in beta and reverse. After the hydraulic low pitch
stop is reached, finer blade angles through flat pitch to reverse can be
selected by the aircraft operator after landing. If the beta control valve is
opened again by rearward movement, the servo-oil flows to the propeller
and moves the blades to a finer angle. This can be continued to the
maximum reverse blade angle. The beta feedback mechanism will limit the
blade angle reached in beta or reverse to that desired by the aircraft
operator. It does this by reclosing the beta control valve.
E. Feathering
Feathering is accomplished by raising the override rod.
plunger up to dump the servo-oil from the propeller. The blades feather automatically
under the action of the counter-weights and feather springs.

PROPELLER OVERSPEED GOVERNOR

The propeller over speed governor is installed in parallel with the propeller governor and
mounted at the approximate 10 o'clock position on the front case of the reduction
gearbox. The governor is incorporated to control any propeller over speed condition by
immediately bypassing pressure oil from the propeller servo to the reduction gearbox
sump. The governor consists of conventional type flyweights mounted on a hollow-
splined shaft and driven by the accessory drive gear shaft. The hollow shaft embodies
ports, which are normally closed by a pilot valve installed in the shaft centerbore and
held in position by the governor speeder spring. The spring tension acts in opposition to
the centrifugal force of the rotating flyweights.
When a propeller over speed condition occurs, the increased centrifugal force sensed
by the governor flyweights overcomes the speeder spring tension and lifts the pilot valve
to bypass propeller servo oil back to the reduction gearbox sump via the governor
hollow drive shaft. This allows the combined forces of the blade counterweights and the
return springs to move the propeller blades toward a coarse pitch position, thereby
absorbing engine power and reducing propeller rpm. A solenoid-operated valve is
incorporated to facilitate functional testing of the over speed governor. When operated,
the valve resets the governor below its normal over speeds setting. (See over speed
governor check later in this section.)

ENGINE POWER AND PROPELLER CONTROLS (FCU)

The cockpit power lever is connected to the engine power lever (Fig. 4-3, #3). This
operates the cam follower pin as shown in Figure 4-3, #12.
Connected to the beta control cam (Fig. 4-3, #2) is the push-pull control cable which
runs forward on the engine to connect to the top end of the propeller reversing lever
(Fig.4-2, #2), via the fuel governor interconnection rod (Fig. 4-2, #14), and connects to
the fuel governor reset arm. Figure 4-2.
The FCU is operated by the FCU actuating lever (Fig. 4-3, #11), the FCU control rod
(Fig. 4-3, #6), and the FCU arm (Fig. 4-3, #10).
Effective: 05/05/04
AIRCRAFT MAINTENANCE MANUAL
This pulls the pilot valve
4-15