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					Overview and general propeller operation.
The Cessna 350 Corvalis is equipped with the McCauley C444 constant speed propeller
(D3A36C444). This propeller was implemented in production during 2006. The Cessna
400 Corvalis TT is equipped with the McCauley C447 constant speed propeller
(D3A36C447) effective February 2010. Both of these propeller models are available as
an STC kit that can be installed on all 300/350/400 Corvalis aircraft. All 350/400 aircraft
are also delivered with a McCauley constant speed governor installed.

These aircraft were originally certified with a Hartzell constant speed propeller. The two
main differences between the McCauley and the Hartzell are that the McCauley utilizes a
single piece hub for added structural integrity (the Hartzell uses a split, 2 piece hub) and
the McCauley is filled with red-dyed oil for superior internal corrosion protection and
lubrication (the Hartzell is grease filled). The McCauley propeller was certified as “equal
to or better than” the performance of the Hartzell, so no changes are necessary to the
POH regarding performance and field length.

Cessna 350 Corvalis with a McCauley constant speed propeller.
          A constant speed propeller is defined as a single-acting unit in which hydraulic pressure
          works against the forces of springs and the natural centrifugal moment of the rotating
          blade to provide the correct pitch for engine load. Hydraulic pressure causes the blades to
          move toward high pitch (decreasing rpm).The springs and centrifugal moments urge
          blades toward low pitch (increasing rpm).

          The source of hydraulic pressure for operation is oil from the engine lubricating system,
          controlled by the engine driven governor. Pressure is supplied to the forward side of the
          propeller piston through the engine shaft flange. Increasing the engine speed will cause
          oil to be forced into the cylinder to move the piston with a corresponding increase in
          pitch. Conversely a decrease of engine speed will result in oil leaving the cylinder, with a
          decrease in pitch. Flow of oil through the governor and propeller does not interfere with
          engine lubrication.

          A complete reduction of hydraulic pressure in flight, either by a failure in the system
          causing loss of oil, or by manipulation of controls to require maximum rpm, will cause
          springs to automatically move the blades to low or minimum pitch position.

From                                       Governor
Pilot                                      Control
                                                                                       Propeller Blade
                                                                                       Pitch Range

                                                                                                 Oil Cavity

                                              Valve                                  Constant

                                                 Engine Flange
                         Oil to Sump

          Cutaway view of oil passages through a typical McCauley non-feathering, constant speed
          propeller and its governor.
Why Red Oil?

McCauley uses red-dyed lubricating oil in its C444 and C447 propellers. The oil is dyed
red to aid in troubleshooting to distinguish propeller oil from engine oil. The propeller oil
is completely independent of the engine oil. Engine oil and propeller oil are compatible
with one another. Any mixing of the two would have no harmful effects. It is not
necessary to “check the oil” between overhauls.

Commonly Referenced Field Service Information

The C444 and C447 propellers have no service issues, but below are a few general
service items that are commonly used by aircraft owner’s/operator’s.


Per SB137AD, McCauley recommends overhauls on its C444 and C447 to be carried out
every 2400 hours or 72 calendar months (whichever occurs first). Also included in
SB137AD is information about the necessary pre-service inspections of controllable pitch
propellers, along with other McCauley products, which have been in long-term storage.


SB227B discusses the correct installation procedures for McCauley constant speed
propellers and fixed pitch propellers. The proper torque for McCauley C444 and C447
propellers installed on their respective aircraft is 50-45 ft-lbs (lubricated torque only).


SB177B details the necessary and required inspection criteria for McCauley propellers
following a suspected lightning strike. If a lightning strike is suspected, the necessary
action steps are provided using this SB.


SL1995-4B discusses the proper techniques used to evaluate and repair typical wear and
tear experienced by propellers under normal usage. Specific instructions are given to aid
the mechanic in performing an acceptable repair.

NOTE: The above service information can be accessed at
 The website also contains much additional information including product information,
propeller educational materials, STC information, the McCauley Application Guide
(MAG), and information regarding technical training available at our Wichita, KS
training facility.

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