Governors/Control Systems | Constant Speed-Undampened & Dampened | Feathering Governors | Feathering Governor Options |
McCauley Governor General Reference Guide | General Calibration Procedures | General Facts About McCauley Governors |
Governor TroubleShooting

Governors/Control Systems

A governor is defined as a mechanical device which is used to sense the speed of a motive device and maintain its speed using mechanical feedback. McCauley uses this type of control system device to hydraulically control a propeller. In fact, McCauley has developed a full line of control system components to control the propeller on both single and twin reciprocating engine applications.

McCauley's control system family is divided into two major and distinct product groups. The first is constant speed governors which are designed to deliver engine oil to the propeller to increase pitch. The second is feathering governors which are designed to deliver engine oil to the propeller to decrease pitch.

Constant Speed-Undampened & Dampened
Constant speed governors were the original unit developed to maintain a constant speed on the propeller as the name implies. The single engine aircraft benefited a great deal from the development of the constant speed propeller. The governor uses oil from the engine to hydraulically maintain a set speed setting. The constant speed governing system decreased takeoff roll and improves climb rates and cruise speeds.

McCauley manufactures two different type styles of constant speed governors. The two types are defined as dampened and un-dampened. The basic undampened model is identified by the alphanumeric callout C290D3(X)/T(X). The dampened version is identical to undampened version except for the flyweight assembly. The basic dampened model is identified by the alphanumeric callout DC290(X)/T(X). The dampened version uses a spring loaded flyweight assembly designed to filter out unwanted vibrations that could interfere with the smooth operation of the pilot valve on certain makes and models of engines. Both dampened and undampened constant speed governors feature a retained flyweight assembly which insures smooth, even rotation, free from fluctuations.

Feathering Governors
Feathering governors were developed to maintain a constant speed on the feathering propeller as the name implies. The basic feathering governor model is identified by the alphanumeric callout of DCF290D(X)/T(X). Twin engine aircraft benefit from the safety of the use of the feathering propeller control system. The feathering governor uses oil from the engine to hydraulically maintain a given speed setting and allows the pilot to feather the propeller in the event of a loss of power or other engine problem. Feathering the propeller eliminates drag that would be caused by a wind-milling, non-feathered propeller. This gives the pilot the ability to fly the aircraft with one engine to the nearest airport for repairs.

Feathering Governor Options

Using the basic feathering governor (DCF) many options can be added to increase safety and comfort of the passengers. Some feathering governors have been designed to include the option of unfeathering. The basic unfeathering governor model is identified by the alphanumeric callout of DCFU290D(X)/T(X). The unfeathering option allows the pilot to unfeather the propeller if desired after it has already been feathered. The unfeathering systems includes a McCauley unfeathering accumulator which provides high pressure oil to the propeller to "push" the propellers blades out of the feathered position by using stored oil to move the propeller piston.

Synchrophasing governors use an electromagnet in the head of the governor to automatically adjust, or 'fine-tune" flyweight position to increase the speed of the slower propeller to match the speed of the faster propeller. This is referred to as "synchronizing" the propellers. The system often also incorporates a feature that allows the pilot to "phase" the propellers. Phasing is means of re-clocking the propellers blades on one propeller in relation tot the blades of the other. The ability to phase often allows the pilot to move much of the propeller vibration to unoccupied sections of the aircraft, thereby reducing the annoying "beat" of the propellers and providing additional comfort to the passengers.

Feathering, unfeathering and synchrophasing governors can be equipped with a tachometer pickup. A tach pickup takes it data directly from the flyweight assembly within the governor and transmits it to the aircraft avionics system. This information is used to create the engine/propeller RPM readout in the aircraft cockpit.

Features and Benefits
All McCauley constant speed and feathering governors are built to the same quality and reliable standards that the aircraft industry has come to expect. All exterior governor components are double-coated with anodize plating to insure protection from corrosion. The externally adjustable pressure relief valve is double sealed to eliminate unwanted external oil leaks. McCauley uses viton o-ring seals to insure a leak tight seal at high oil temperatures. Tight tolerance, balanced, retained flyweight assemblies insure smooth operation and quick response to changes in rpm. All McCauley governor designs are lightweight and compact, often providing a 25% weight reduction over the competition. Manufactured under very strict, ISO9000 certification standards, McCauley governors are compatible with all engine manufacturers utilizing an AND20010 mounting pad.

McCauley Governor General Reference Guide

The information in this guide is intended for general reference use only. The procedures explained in this guide may not be applicable for your installation. If any question exists regarding these procedures, contact McCauley Product Support at 1-800-621-7767.

Always consult the aircraft Type Certificate Data Sheet or owner/operator's handbook before modification to governor or installation

General Calibration Procedures
Following Installation of McCauley Constant Speed Governors

A. Perform Static Run-up: Lock aircraft brakes. Place cockpit propeller RPM lever in high RPM (takeoff) position. Advance throttle slowly to maximum permitted engine manifold pressure limits. Record propeller RPM. If local wind conditions are over 5 knots, repeat check with aircraft pointed in opposite direction and average the two numbers. As a general rule, propeller RPM should be 25-100 RPM below redline limit during the above check.

B. Perform Flight Test: During takeoff acceleration, record maximum propeller RPM. When sufficient altitude is reached, level out aircraft, leaving propeller control in full RPM position. Maintain this setting for three (3) to five (5) minutes while monitoring propeller RPM. Following this check, two conditions may exist which require adjustment:

1) If propeller RPM is exceeding redline limit, reduce it to redline using propeller control. Leaving propeller at this redline RPM setting, land aircraft and shutdown. Remove cowling and note position of control arm on governor. Adjust governor high RPM screw clockwise so it just touches stop on governor control arm; this will ensure that the correct arm position for governor redline RPM setting cannot be exceeded.

2) If propeller RPM is below redline limit with max RPM setting on the propeller cockpit control, note RPM and land. Remove engine cowling and adjust the governor high RPM screw counterclockwise to increase RPM.
Note that one full screw turn will cause an increase of approximately 25 RPM.
Perform another test flight to confirm adjustments were sufficient.

General Facts About McCauley Governors

Static Run-Up - What is Normal?

There has been some confusion in the field concerning propeller low blade angle setting, the governor setting and how it relates to static run-up and take-off RPM. As a general rule, engine redline RPM cannot be reached during a full power static run-up. Contrary to popular belief, the governor is not controlling the propeller at this time, the propeller is against its low pitch stop. Attempting to increase propeller static run-up RPM by adjusting the governor high RPM screw will have no effect and will probably result in a propeller overspeed during the take-off roll. On a single engine aircraft several considerations determine both the low and high blade angle settings. Normally 25 to 100 RPM below rated take-off RPM is desirable and acceptable during a static run-up. McCauley's practice is to set the low blade angle so that rated take-off RPM is not reached until the aircraft has reached some significant groundspeed during roll out. At this time, and only this time, the propeller is controlled by the governor. There are two advantages to this practice. First, the maximum static RPM can be used as a check on developed horsepower as with a fixed pitch propeller. Any loss of maximum power over time is readily apparent during a preflight check. Second, if the propeller remains in a flat pitch after take-off due to some malfunction, the higher angle low pitch setting will permit more thrust to be developed to fly the aircraft without overspeeding the engine.

Governor TroubleShooting

Propeller Surging or "Wandering"

Possible Causes: Excessive Transfer Bearing Leakage

Engines with excessive transfer bearing leakage can experience surging since the governor may not be able to get enough pressure to the propeller. This causes a delay in propeller responsiveness and by the time the propeller responds to earlier governor inputs, they have changed, resulting in propeller "wandering".

Solution - Perform a transfer bearing leakage test per engine manufacturer's instructions. If test indicates a high rate of leakage (even though it may still be on the high side of "acceptable" tolerance), this may be your cause. Install the suspect governor on a known "good" aircraft; if problem disappears, engine work may be indicated.

Malfunctioning Magnetos Dirty Engine Oil

Contaminants in dirty engine oil can cause blockage of close tolerance passages in governor, leading to erratic operation.

Solution - Timely engine oil changes, as often as every 30 hours, should eliminate this problem.

Excessive "Play" in Aircraft Propeller Control Linkage

Excessive "play" in the linkage between the governor and the cockpit control often leads to erratic operation. Specifically, if the propeller RPM is suddenly changing and holding a new setting on its own, this could indicate loose linkage.

Solution - Trace linkage and locate unsecured sections and tighten-up as needed. Please note that although linkage may appear to allow full governor control while the engine is off, it may not in the air. Engine vibration and "stretch" of the mount during operation can often aggravate the condition. Therefore, it is important the entire length of linkage be properly secured, even if the ends alone are tight.

Excessive Propeller Friction - (NOTE: This is rarely the cause of RPM malfunction.)

Propeller may be overly-resistant to pitch movement. This can be caused by either excessively tight shimming of the propeller blades, or internal corrosion or part failure, causing binding.

Solution - Check amount of blade "play" as defined below: A total lack of blade "shake" may indicate excessively tight blade shims. If this is suspected, have the propeller checked by a qualified FAA-approved propeller repairman. Note that this check and any needed correction can usually be performed with the propeller installed on the aircraft.


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