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CS Propeller Low RPM Setting?

Chachi7565

Chachi7565

Well Known Member
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I'm following the excellent thread on setting the low-pitch static stops to prevent overspeeding, and heading to the airport tomorrow to make that adjustment. I have a suspicion that my governor (an MT 860-4 on a Hartzell CS blended airfoil propeller) may not be configured exactly correctly for my aircraft - the maximum RPM adjustment screw is bottomed out, and right now, that sets max RPM at 2800 - too high! That concerns me, as it's not an easy fix (the MT Manual says moving the arm on the governor has to be done by a service center), but it also makes me wonder if the low end of my governor is similarly askew, and low RPM isn't something I've seen addressed here.

What is the lowest RPM that I should be able to set with my prop lever, and how do I check that this is set correctly - i.e. what flight profile?
 
Most likely not in flight, but at run up. If you wish to perform the run up at 1700 rpm, then to test the governor it will need to go as low as 1600 rpm, give or take.
 
Bottling out implies the screw is all the way in. Should be backing out the screw to lower the max rpm.
 
lr172 said:
Bottling out implies the screw is all the way in. Should be backing out the screw to lower the max rpm.
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I'm not sure I understand that.

Here's a picture of the adjustment screw on my governor - it's all the way in (bottomed out), and the RPM is set too high. In this picture, I flew the aircraft, set the RPM to 2700, and landed. You can see there's about 1/8" - 1/4" gap (blue arrow) between the adjustment screw and the control arm. So to set the proper maximum RPM, I need to move the screw to the current position of the control arm, correct? Which I can't do, because the screw can't go in any further. (red arrow)

That seems to align with the instructions in the MT Manual that say "Set maximal propeller RPM by turning the stop screw. One full turn clockwise will reduce RPM by approximately 25 RPM. One full turn counterclockwise will increase RPM by approximately 25 RPM."

Am I misunderstanding that?
 

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BobTurner said:
Most likely not in flight, but at run up. If you wish to perform the run up at 1700 rpm, then to test the governor it will need to go as low as 1600 rpm, give or take.
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Can you explain what you mean? When I do my run-up, my prop lever is all the way forward, and I use the throttle to bring the RPM to 1800, I check the magnetos, and then I check the function of the prop lever by cycling it to low RPM, and back to high three times - checking that the RPM, MAP, and Oil Pressure react accordingly.

Do you mean that if my governor were misadjusted too high on the low side, I simply wouldn't see the RPM drop when I do that?
 
Sorry about that. Wrote too quickly. Something is not right in the configuration to cause this issue IMO, so need to do some digging as to why. In the interim, put the stop nut on the other side of the post to get enough screw travel to make it work. Screw goe into the threads on post, then the nut. Get the screw where you want it, then hold with screwdriver as you tighten nut on other side of post. Could also replace with a longer screw or use a jam nut instead of that regular nut. That may get enough extra travel.

May want to get the model number of gov and be sure it's designed gear ratio matches your engine. Lyc's have two different ratios they use.
 
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Chachi7565 said:
Can you explain what you mean? When I do my run-up, my prop lever is all the way forward, and I use the throttle to bring the RPM to 1800, I check the magnetos, and then I check the function of the prop lever by cycling it to low RPM, and back to high three times - checking that the RPM, MAP, and Oil Pressure react accordingly.

Do you mean that if my governor were misadjusted too high on the low side, I simply wouldn't see the RPM drop when I do that?
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Yes, that’s exactly the problem some have reported with mis-adjusted (or wrong model) governors.
 
Chachi7565 said:
I'm not sure I understand that.

Here's a picture of the adjustment screw on my governor - it's all the way in (bottomed out), and the RPM is set too high. In this picture, I flew the aircraft, set the RPM to 2700, and landed. You can see there's about 1/8" - 1/4" gap (blue arrow) between the adjustment screw and the control arm. So to set the proper maximum RPM, I need to move the screw to the current position of the control arm, correct? Which I can't do, because the screw can't go in any further. (red arrow)

That seems to align with the instructions in the MT Manual that say "Set maximal propeller RPM by turning the stop screw. One full turn clockwise will reduce RPM by approximately 25 RPM. One full turn counterclockwise will increase RPM by approximately 25 RPM."

Am I misunderstanding that?
Click to expand...
Can you get a longer screw so it will hit the arm and then safety wire after your adjustment is made?
 
lr172 said:
Sorry about that. Wrote too quickly. Something is not right in the configuration to cause this issue IMO, so need to do some digging as to why. In the interim, put the stop nut on the other side of the post to get enough screw travel to make it work. Screw goe into the threads on post, then the nut. Get the screw where you want it, then hold with screwdriver as you tighten nut on other side of post. Could also replace with a longer screw or use a jam nut instead of that regular nut. That may get enough extra travel.

May want to get the model number of gov and be sure it's designed gear ratio matches your engine. Lyc's have two different ratios they use.
Click to expand...
I checked the model number of the governor vs. the type of engine I have, and it's correct - IO-360 and P-860-4 governor (I'm attaching the PDF of the governor-engine list here, if anyone else needs it).

Today, I set the low-pitch static stops on the propeller; they were set pretty high - it took 3 1/2 turns of the adjustment bolt to bring the RPM down to an appropriate setting.

I set the governor adjustment screw to where I think it needs to be, based on a previous flight where I set it to 2700 RPM in flight, and noted the position. Couple of comments:

- It's not possible to move the stop nut to the other side of the post - there isn't enough clearance from the spring to allow the nut to rotate.
- I didn't have a longer screw, so I couldn't use that.
- I removed the stop nut, adjusted the screw to the new position, using threadlocker and a safety cable to hold it in position, and put a torque stripe on it. (see picture)

I'll fly it tomorrow to see if this worked for dynamic RPM. If so, I'll probably leave it like this until the next condition inspection. If it didn't work, I see a trip to a prop specialist in my future - as others have commented, and per the MT manual, the governor arm would need to be moved, and that's not straightforward, as the splined shaft is spring-loaded.
 

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Chachi7565 said:
I checked the model number of the governor vs. the type of engine I have, and it's correct - IO-360 and P-860-4 governor (I'm attaching the PDF of the governor-engine list here, if anyone else needs it).

Today, I set the low-pitch static stops on the propeller; they were set pretty high - it took 2 1/2 turns of the adjustment bolt to bring the RPM down to an appropriate setting.

I set the governor adjustment screw to where I think it needs to be, based on a previous flight where I set it to 2700 RPM in flight, and noted the position. Couple of comments:

- It's not possible to move the stop nut to the other side of the post - there isn't enough clearance from the spring to allow the nut to rotate.
- I didn't have a longer screw, so I couldn't use that.
- I removed the stop nut, adjusted the screw to the new position, using threadlocker and a safety cable to hold it in position, and put a torque stripe on it. (see picture)

I'll fly it tomorrow to see if this worked for dynamic RPM. If so, I'll probably leave it like this until the next condition inspection. If it didn't work, I see a trip to a prop specialist in my future - as others have commented, and per the MT manual, the governor arm would need to be moved, and that's not straightforward, as the splined shaft is spring-loaded.
Click to expand...
In order to move the arm, you need the manual. There is usually a special procedure for winding up the spring. I took my hartzel apart. Its not difficult, just need to know the procedure.

Still odd. You can tell that is a factory screw and they should always set the target rpm somewhere near the middle of the screw travel. Makes me wonder if this was a custom setup.
 
lr172 said:
In order to move the arm, you need the manual. There is usually a special procedure for winding up the spring. I took my hartzel apart. Its not difficult, just need to know the procedure.

Still odd. You can tell that is a factory screw and they should always set the target rpm somewhere near the middle of the screw travel. Makes me wonder if this was a custom setup.
Click to expand...
I have the Operation and Installation manual for the MT Governor; it's not particularly helpful - I suspect there is a more detailed maintenance manual, because when you get to the point in troubleshooting that the arm needs to be moved, it just says "If the requested RPM can not be reached, the control lever must be repositioned. It is recommended to do this at authorized service station."

If anyone has a PDF of the MT maintenance manual and is willing to share I would much rather do this myself!

Agreed, it is odd, and a little frustrating. It shouldn't have been too custom a setup - it's a pretty vanilla RV-8A with the typical throttle quadrant, IO-360-B1B, and Hartzell blended airfoil CS propeller.

I agree completely - the target RPM should be with that screw about halfway out, so you have 50% travel in either direction to adjust for individualities.

I'm going to contact MT USA, but they don't open back up until the 5th of January.
 
Chachi7565 said:
I have the Operation and Installation manual for the MT Governor; it's not particularly helpful - I suspect there is a more detailed maintenance manual, because when you get to the point in troubleshooting that the arm needs to be moved, it just says "If the requested RPM can not be reached, the control lever must be repositioned. It is recommended to do this at authorized service station."

If anyone has a PDF of the MT maintenance manual and is willing to share I would much rather do this myself!

Agreed, it is odd, and a little frustrating. It shouldn't have been too custom a setup - it's a pretty vanilla RV-8A with the typical throttle quadrant, IO-360-B1B, and Hartzell blended airfoil CS propeller.

I agree completely - the target RPM should be with that screw about halfway out, so you have 50% travel in either direction to adjust for individualities.

I'm going to contact MT USA, but they don't open back up until the 5th of January.
Click to expand...
If you feel daring and are creative, you can come up with a Method, even vice grips, to hold the shaft from rotating when you remove / reinstall the arm. Yes, these things always have maintenance manuals. I was lucky and got hartzel to give me one.
 
Wrapping up this thread for now - until I chat with MT.
  • Setting the low-pitch static stops worked great, as advertised by Vic in his video.
    No issues with overspeeding or surging on takeoff.
  • Setting the RPM by removing the jam nut on the governor worked as well; I need to tweak it slightly (max is set to 2670, it should be 2700).
I'd still like to get the governor arm set to the middle of the adjustment range, so I'm going to ping MT to see if I can get the maintenance manual and make that adjustment. If I get the manual, I'll post it here.
 
OK, closing this out! I spoke with MT USA yesterday, they were very helpful. He said that as long as I'm getting the function I need - the maximum RPM is set correctly, and I'm able to cycle the propeller at 1800 RPM during my runup - then I don't need to move the arm on the splined shaft. That CAN be done, but it's not easy to do, especially while the governor is mounted on the aircraft, as you have to disconnect the spring. Also, the procedure for making that change is no longer in the operating manual; I guess it used to be and they took it out. They (MT) do not share the overhaul manuals except with their authorized service centers. So, since everything is working as it should, I will leave the governor arm where it is, until such time as I need other work to be done or the governor comes off for another reason. Thanks to everyone for your help; very glad to wrap this up!
 
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