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
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.
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.
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.