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Prop cable travel too short for new governor?

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skirting_virga

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My 8A has been finished for 5 years and I'm not the original builder. In the process of overhauling the engine, I elected to replace the Woodward prop governor (which was unserviceable) with a PCU 5000X. Now that the overhauled engine is hanging on the plane, I'm going through the long, careful process to reconnect everything. The governor is rear-mounted, like so:
governor crop.jpg
Right away, I notice the bracket doesn't fit in the same orientation as it did with the Woodward. I'm not convinced the screw holes are perfectly aligned either, so I just stopped and ordered a new PCU 5000X bracket from Showplanes. In the process of trying to line it up, I checked the travel for sanity. The (Vans/green) prop cable has a travel of about 1-5/8" to 1-3/4". The Showplanes site states their bracket is for 2.25-2.50" cables. A quick measurement of the governor arm suggests it wants about 2.25" of travel for the full sweep.

I thought the prop lever was limiting cable travel, so I pulled the quadrant, did some math, and drilled a new hole. Reinstalled and no change. So the cable itself is limited to max ~1.75" of travel. Is this a known issue with this governor or do I have a bum cable?

If I could buy a new arm for the governor with a shorter-radius hole, it would be a quick fix. Given that the order form doesn't specify any different arms, I don't think one is likely to be available. Looks like the stock arm is 1.5" to the hole and 1.15" would yield the right ratio for this cable.
1762698323268.png

It seems like every time I get something done, two more problems pop up. It hasn't flown since Dec 2024 and at this rate it may not fly in 2025 at all. I am decidedly not interested in replacing the cable if I can avoid it. Much as I would like an upgrade/premium cable... removing it, measuring it, ordering it, paying for it, waiting for it, and then installing it with necessary safety wire and firestop was not on my list of things to do.
 
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Your pic doesn't include the bracket. Drilling a new hole closer to the pt of rotation, should increase arm travel for a given cable travel, so surprised you observed no change. However, it does matter how it is clocked. Did you insure that the arm passes through a point where the cable is at a 90* angle to the arm at the center of the travel range?
 
Surprising that shortening the radius didn't cure the problem. What if you drilled at 1.15" radius as you stated? Wouldn't that allow for the shorter cable travel? Is a new hole to close to another hole?
 
lr172 said:
Your pic doesn't include the bracket. Drilling a new hole closer to the pt of rotation, should increase arm travel for a given cable travel, so surprised you observed no change. However, it does matter how it is clocked. Did you insure that the arm passes through a point where the cable is at a 90* angle to the arm at the center of the travel range?
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The old bracket won't fit, so I ordered a new one. I think there's a slight difference in holes (and at a minimum the clocking of the holes) on the old Woodward vs. the new PCU 5000X. For reference, this is a pic of the old governor with the old bracket:
woodward gov arm.jpggovernor woodward 2.jpggovernor cable woodward side.jpg
EDIT: I added a couple more old pics of the old governor

I just want to clarify that I drilled the prop lever in the cockpit to give more throw to the cable, not the arm on the governor. I don't think it's safe to drill a new hole in the governor arm. I did this before I realized that the throw on the cable itself is limiting, not the radius of the hole on the lever.

Your point about clocking is an interesting one. I'll have to examine in more detail when the new bracket arrives. Hypothetically I might want the 90 degree point to be at the beginning of the travel, for the fewest number of degrees per mm of travel (or however you want to measure it). Fine control sensitivity approaching the fine pitch stop, which is where most operation is happening. Maybe kinematically this doesn't work...

sansoneservices said:
Surprising that shortening the radius didn't cure the problem. What if you drilled at 1.15" radius as you stated? Wouldn't that allow for the shorter cable travel? Is a new hole to close to another hole?
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I don't think I can safely drill the arm on the governor. If this is common procedure, I'd reconsider, but it sketches me out. I redrilled the arm on the prop lever to give more throw. Turns out that even with the cable unconnected to anything on both ends, the travel is max 1.75", which seems too low.

I'm not too upset about having drilled the prop lever in a different spot - at the very least this will give more sensitivity for changing the prop pitch regardless of what else is happening.
 
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skirting_virga said:
I don't think it's safe to drill a new hole in the governor arm. I did this before I realized that the throw on the cable itself is limiting, not the radius of the hole on the lever.
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Moving the hole on the quadrant lever only changes quad lever travel, not gov lever travel.

The drawing you posted shows two holes in the gov arm, so seems the designer has no issue with it and in fact accounted for it. The further hole is 1.5", but appears the closer hole is .72", well below the requirements you posted above and should easilly meet your goal. What am I missing here?
 
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lr172 said:
Moving the hole on the quadrant lever only changes quad lever travel, not gov lever travel.
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Right, but if the cable itself had more range, drilling a new hole on the cockpit prop lever, further out from the pivot, would absolutely change the range of travel. If this cable was capable of ~2.5" of movement (unconnected on either end), that new hole would 100% have solved my problem and this post would not exist.

lr172 said:
The drawing you posted shows two holes in the gov arm, so seems the designer has no issue with it and in fact accounted for it. The further hole is 1.5", but appears the closer hole is approx .75", well below the requirements you posted above. What am I missing here?
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That other "hole" is actually the stop pin on the arm that contacts the fine and coarse pitch stops. Somewhat visible here:

PCU5000X.jpg
 
skirting_virga said:
Right, but if the cable itself had more range, drilling a new hole on the cockpit prop lever, further out from the pivot, would absolutely change the range of travel. If this cable was capable of ~2.5" of movement (unconnected on either end), that new hole would 100% have solved my problem and this post would not exist.


That other "hole" is actually the stop pin on the arm that contacts the fine and coarse pitch stops. Somewhat visible here:

View attachment 101619
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Only options I see are a different cable, drill a new hole (though not sure you can get where you need to be and meet edge distance requirements) on the arm or accept not getting all the way to full coarse. You can ask the PCU folks how important it is to get all the way to that full coarse stop. Certainly not used in most flight regimes, but not my expertise.
 
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lr172 said:
Only options I see are a different cable, drill a new hole (though not sure you can get where you need to be and meet edge distance requirements) on the arm or accept not getting all the way to full coarse. You can ask the PCU folks how important it is to get all the way to that full coarse stop. Not my expertise.
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Lots of folks use the PCU and presume many do so with the Vans cable. Hopefully someone will explain how they do it.
 
lr172 said:
Only options I see are a different cable, drill a new hole (though not sure you can get where you need to be and meet edge distance requirements) on the arm or accept not getting all the way to full coarse. You can ask the PCU folks how important it is to get all the way to that full coarse stop. Not my expertise.
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I appreciate your input. I have been leaning towards not getting full coarse pitch if it comes to that.


This is me [mis]using Solidworks to illustrate the prop control lever travel I was trying to point out. But hey, I learned how to dimension arc length, so that's good.
1762703703906.png

lr172 said:
Lots of folks use the PCU and presume many do so with the Vans cable. Hopefully someone will explain how they do it.
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I was hoping someone who had built an 8/8A would weigh in because I assume the cables are model-specific.
 
skirting_virga said:
This is me [mis]using Solidworks to illustrate the prop control lever travel I was trying to point out. But hey, I learned how to dimension arc length, so that's good.
View attachment 101625
Click to expand...
So your model here shows that an arm length of 2.14" will deliver 1.75" of travel and the PCU arm length is 1.5", which should deliver a travel of well less than your available 1.75". How did you conclude that this won't work?
 
Invest in a new cable with the proper amount of travel. I too have a pcu5000. I also measured about 2.25” travel at the governor arm. I bought McFarland cables with the correct travel. Works great, stop to stop movement at the governor arm. Had to go back and find some old pic to remember what I measured.
 
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lr172 said:
So your model here shows that an arm length of 2.14" will deliver 1.75" of travel and the PCU arm length is 1.5", which should deliver a travel of well less than your available 1.75". How did you conclude that this won't work?
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I think I see the disconnect. The range of angles of the prop lever and the governor arm are not the same. I don't know what they are, but the governor has a shorter arm, and a longer angular travel, as far as I can tell. So assuming the prop lever throw is approximately 45 degrees, the governor arm might travel 85 degrees to go the same distance.

EDIT: since I already have a drawing, I can add to it to show this:

1762704818636.png
Ok, it's ~47 and ~86 degrees

For those just stumbling across this: I realize throw distance is better described as a chord line.
 
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skirting_virga said:
I think I see the disconnect. The range of angles of the prop lever and the governor arm are not the same. I don't know what they are, but the governor has a shorter arm, and a longer angular travel, as far as I can tell. So assuming the prop lever throw is approximately 45 degrees, the governor arm might travel 85 degrees to go the same distance.
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Ok, lets move away from the engineer's toys. I am nbot an engineer and things like cad scare me, as i don't fully understand them and therefore cannot correctly interpret the results.

put gov in a vice. measure from a fixed point the distance to the hole center. swing arm to opposite extreme and measure again. the difference is your throw requirement. Just be sure that measurement line you are using crosses the arm at center of travel at 90*.
 
lr172 said:
put gov in a vice. measure from a fixed point the distance to the hole center. swing arm to opposite extreme and measure again. the difference is your throw requirement. Just be sure that measurement line crosses the arm at center of travel at 90*.
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I did a slightly imperfect version of this already and got 2.25", which was my basis for attempting to increase lever/cable throw.

To do a better version I have to wait for the bracket to show up.
 
I like to have midway cable travel to be at 90° on the Governor arm. On my hartzell Governor I noticed a dead area on the low pitch end of the Governor travel. I eliminated some of that wasted cable travel as well
 
resrob66 said:
Invest in a new cable with the proper amount of travel. I too have a pcu5000. I also measured about 2.25” travel at the governor arm. I bought McFarland cables with the correct travel. Works great, stop to stop movement at the governor arm. Had to go back and find some old pic to remember what I measured.
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Out of curiosity, do you have the measurement/order for McFarland? What bracket did you use on the governor? What sort of throttle quadrant do you have?
 
I think your fix is just going to be to buy a cable with the right throw. I have that same governor and the one I ordered from vans works, but the sheath is blue, not green, so I'd guess either vans sold a different style back in the day or you have an aftermarket one.

FYI- even if you wanted to, I don't think you can drill a new hole on the governor arm and gain as much throw as you need without causing the cable end and teh big washer thats supposed to capture it in the end comes apart to conflict with the stops on the governor housing.
 
Desert Rat said:
I think your fix is just going to be to buy a cable with the right throw. I have that same governor and the one I ordered from vans works, but the sheath is blue, not green, so I'd guess either vans sold a different style back in the day or you have an aftermarket one.
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Honestly my fix is going to be setting it to hit the fine pitch stop and seeing how close to coarse it will go just to get the thing back in the air. There's only one edge case I can imagine needing full coarse pitch, and that assumes I run out of fuel (but not oil) and need to stretch my glide.

Trying to make this plane 100% optimal is a case of shipwright's disease. It will never fly again if I have to make everything perfect. I need safety within reason.

Desert Rat said:
FYI- even if you wanted to, I don't think you can drill a new hole on the governor arm and gain as much throw as you need without causing the cable end and teh big washer thats supposed to capture it in the end comes apart to conflict with the stops on the governor housing.
Click to expand...
I wasn't seriously considering it, but that's a good point.
 

PCU5000X Lever Arm Travel

Howdy Everyone. I am getting ready for first flight and am doing the static RPM checks. I was able to get static RPM up to 2580 - 2600 by adjusting the governor lever arm. (Ran out of travel on the low pitch stop adjustment screw.) I want to tweak it more but I noticed that when I pull the...
vansairforce.net

See post #9
 
Flyhud said:

PCU5000X Lever Arm Travel

Howdy Everyone. I am getting ready for first flight and am doing the static RPM checks. I was able to get static RPM up to 2580 - 2600 by adjusting the governor lever arm. (Ran out of travel on the low pitch stop adjustment screw.) I want to tweak it more but I noticed that when I pull the...
vansairforce.net

See post #9
Click to expand...
This sounds like it's my answer - thanks for finding that!
 
skirting_virga said:
Out of curiosity, do you have the measurement/order for McFarland? What bracket did you use on the governor? What sort of throttle quadrant do you have?
Click to expand...
Hi, I used the vans bracket. I have the 3 lever throttle quadrant, also had to drill another hole to get greater throw. Here’s a pic of my initial measurements for my cables. Double check your own numbers!
IMG_6596.jpeg
 
skirting_virga said:
This is amazing, thanks. I assume your governor is rear mount also. Which engine and fuel servo?
Click to expand...
Yes, rear mounted governor. Titan io370, silver hawk FI system. I made my own throttle cable bracket on the engine and am using the vans mixture bell crank. **I don’t want to lead you astray so double check your own measurements please.** I also had to “clock” the governor arm assembly. I believe the gov manual tells you how to do that, really simple process.
 
resrob66 said:
Yes, rear mounted governor. Titan io370, silver hawk FI system. I made my own throttle cable bracket on the engine and am using the vans mixture bell crank. **I don’t want to lead you astray so double check your own measurements please.**
Click to expand...
Oh, fully agree.
resrob66 said:
I also had to “clock” the governor arm assembly. I believe the gov manual tells you how to do that, really simple process.
Click to expand...
I read through it and it looks much more painless than I thought.
 
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