M20C prop governor adjustment screw

[M20 Ogler]

My C tries to reach >2800 rpm on takeoff if I don’t back the speed control out 3 or 4 turns. IA found the adjustment screw missing and replaced it, but it’s still over speeding. What max static rpm are people seeing their C set to? Also is it 1 turn clockwise per 100 rpm decrease?

[jetdriven]

25 rpm per turn.  it wont make 2700 static, the manual says fly for 5 mins and note RPM, then make changes.

[PT20J]

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.
 

[cliffy]

High density altitude will also adversely affect the static RPM 

Summer in Page and we see DAs of 7500' 

Engine only makes 75% of rated HP so the static RPM will be lower

[M20 Ogler]

So my RPM will reach 2700 (Red line) in a static run up. Then go over 2800 rpm on takeoff if I allow it. I wonder if this means my stops are set to much of a fine of a pitch, in addition to needing to adjust the set screw 

[PT20J]

12 minutes ago, M20 Ogler said:

So my RPM will reach 2700 (Red line) in a static run up. Then go over 2800 rpm on takeoff if I allow it. I wonder if this means my stops are set to much of a fine of a pitch, in addition to needing to adjust the set screw 

The first thing to do is to make sure that the tach is accurate. Then, if it doesn't go over redline when static, it's unlikely the stops are set incorrectly. It is normal for the prop to speed up as the airspeed increases during the takeoff roll, but the governor should kick in and prevent it from doing this if it is set correctly.

[M20 Ogler]

On 2/13/2023 at 7:57 PM, jetdriven said:

25 rpm per turn.  it wont make 2700 static, the manual says fly for 5 mins and note RPM, then make changes.

You mean 25 rpm per 360 degree turn?

[jetdriven]

Yes. 

[carusoam]

Setting the stops correctly is important…

If the Gov fails… the prop will probably land on the high rpm stop….

If that stop isn’t set correctly… the engine can easily overspeed…

Then as PIC… you quickly realize that controlling rpm with MP doesn’t work very well…. Lots of power reduction required to bring the rpm down…

If you need the power to stay aloft, and the power is causing an overspeed…

The follow-up overspeed maintenance requirements can be expensive….

 

PP thoughts only, not a mechanic… my M20C lost its Gov control when the shaft plug went awry…

Best regards,

-a-

[M20 Ogler]

IA recommend only one turn on adjustment screw.
 

Weather broke today for test flight. And governor now keeps the prop less than 30 or 40 rpm over 2700 now.

 

Maybe another 1/4 turn on the screw would nail it, IA thinks we should leave it be, he doesn’t want to over do it. 

[hammdo]

I used this to confirm my settings were correct:

https://www.aircraftspruce.com/catalog/topages/trutach.php

-Don

[Immelman]

Open up the Apple app store on your ipone/ipad, buy "Engine RPM". Something like $5. It listens via the microphone. Works pretty well! Agreed with the optical tach that hammdo mentioned (my IA loaned it to me).....  agreed exactly with the tachs in our modern cars. Used it to dial in 2700. Go slow on the adjustments. And FWIW the tach in my plane reads about 60 rpm off.

Edited March 4, 2023 by Immelman