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Low static RPM

Draker

Well Known Member
Finally got around to doing a max static RPM test prior to first flight of my -7A.

First of all, side topic: Tying down an -A model by the gear legs. Since the gear legs sweep back on the -A, you can't just tie strap around the gear leg near the fuselage mount because the strap would slip down the leg when engine power was applied. I was also not comfortable strapping near the wheels because that results in a very long torque arm to the center of force. So, I called up an absolute genius and he suggested since the legs also sweep outward, wrap a third strap tightly around both legs, below the main straps. That third strap will keep the main straps from slipping down. Perfect! Strapped down, chocked and full-brakes, the plane didn't go anywhere (or buck around or even move) during the test.

Anyway, results:

New Lycoming IO-360-M1B and Hartzell C2YF-1BFP constant speed prop. Prop knob full forward, mixture full rich. Slowly advanced throttle. RPM smoothly rose to 2790, then after around 2 seconds, abruptly dropped to 2330, and stayed there for the remainder of the test. MP took 14 seconds to reach 28.7 and remained between 28.7 and 28.9 through duration of test (LVK altitude 400ft). I did not try adjusting the prop cable or leaning the mixture. Ended the test at about 60 seconds to keep CHT from exceeding 350F.

[Visual plot attached to this post]

So, that's a bummer. I'm not going to take off on my first flight barely making cruise RPM. Here are some ideas I have:

  1. Tachometer error
    I'm using the screw-in mag reader that comes with the Garmin stuff. I wonder if mine has any error. Might have to verify with an independent measurement.
  2. Throttle control not hitting stop
    Pretty sure I checked this many times during the build and condition inspection. I did adjust the idle RPM, but that should not affect max RPM. MP is also ~29 so I don't think the throttle is the problem.
  3. Prop control not hitting stop on governor
    Same as above but it wouldn't hurt to check.
  4. Is the prop or the governor limiting RPM?
    I should have slowly pulled back the Prop knob during the test. That would have told me if the prop's stop was limiting RPM or if the governor was in charge. I'll do that next time.
  5. Governor high RPM screw (per MT's manual) or prop low pitch stop (Hartzell)
    This is where I'm starting to get cautious. These are supposed to come correctly adjusted from the factory, no? Hartzell also lists "stop adjustment" as corrective for overspeed but not underspeed.
  6. Governor oil pressure/passage problem
    This might be beyond my ability to troubleshoot.
  7. Incorrect test procedure
    Hartzell recommends: a. backing out the RPM stop on the governor one turn during the test, b. going full power with the prop control about 1" out, and then c. advancing the prop control in until RPM stabilizes. I didn't want to mess with the RPM stop on a brand new install (in case it was set correctly) so I did not use this procedure.

Anything else to try that I'm missing? I'm really hesitant to start messing around with factory-set stop screws.
 

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Governor

Finally got around to doing a max static RPM test prior to first flight of my -7A.

First of all, side topic: Tying down an -A model by the gear legs. Since the gear legs sweep back on the -A, you can't just tie strap around the gear leg near the fuselage mount because the strap would slip down the leg when engine power was applied. I was also not comfortable strapping near the wheels because that results in a very long torque arm to the center of force. So, I called up an absolute genius and he suggested since the legs also sweep outward, wrap a third strap tightly around both legs, below the main straps. That third strap will keep the main straps from slipping down. Perfect! Strapped down, chocked and full-brakes, the plane didn't go anywhere (or buck around or even move) during the test.

Anyway, results:

New Lycoming IO-360-M1B and Hartzell C2YF-1BFP constant speed prop. Prop knob full forward, mixture full rich. Slowly advanced throttle. RPM smoothly rose to 2790, then after around 2 seconds, abruptly dropped to 2330, and stayed there for the remainder of the test. MP took 14 seconds to reach 28.7 and remained between 28.7 and 28.9 through duration of test (LVK altitude 400ft). I did not try adjusting the prop cable or leaning the mixture. Ended the test at about 60 seconds to keep CHT from exceeding 350F.

[Visual plot attached to this post]

So, that's a bummer. I'm not going to take off on my first flight barely making cruise RPM. Here are some ideas I have:

  1. Tachometer error
    I'm using the screw-in mag reader that comes with the Garmin stuff. I wonder if mine has any error. Might have to verify with an independent measurement.
  2. Throttle control not hitting stop
    Pretty sure I checked this many times during the build and condition inspection. I did adjust the idle RPM, but that should not affect max RPM. MP is also ~29 so I don't think the throttle is the problem.
  3. Prop control not hitting stop on governor
    Same as above but it wouldn't hurt to check.
  4. Is the prop or the governor limiting RPM?
    I should have slowly pulled back the Prop knob during the test. That would have told me if the prop's stop was limiting RPM or if the governor was in charge. I'll do that next time.
  5. Governor high RPM screw (per MT's manual) or prop low pitch stop (Hartzell)
    This is where I'm starting to get cautious. These are supposed to come correctly adjusted from the factory, no? Hartzell also lists "stop adjustment" as corrective for overspeed but not underspeed.
  6. Governor oil pressure/passage problem
    This might be beyond my ability to troubleshoot.
  7. Incorrect test procedure
    Hartzell recommends: a. backing out the RPM stop on the governor one turn during the test, b. going full power with the prop control about 1" out, and then c. advancing the prop control in until RPM stabilizes. I didn't want to mess with the RPM stop on a brand new install (in case it was set correctly) so I did not use this procedure.

Anything else to try that I'm missing? I'm really hesitant to start messing around with factory-set stop screws.

You need to back out your prop governor stop screw and make sure you have enough control travel for the lever to firmly hit the stop at the full forward control setting. There is no magic about the factory screw stop setting on the governor.

Since your engine surged to 2790, the propeller hub fine pitch stop is not the issue. In fact, once you get the governor set to allow full RPM, you need to adjust the propeller hub fine-pitch stop to limit the static RPM to ~ 2650 RPM per the Hartzell manual.

Adjusting the governor stop screw will require 5 or 6 full turns (or more), based on your current RPM. If the screw won’t move that far without running out of threads, then it’s possible that you have the wrong propeller governor model for your engine/governor drive gear ratio.

Skylor
 
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That sucks Ryan. So stressful.
What governor are you using?
Did you ever cycle the prop before?
Did you take the plug out of the crankshaft?
 
That sucks Ryan. So stressful.
What governor are you using?
Did you ever cycle the prop before?
Did you take the plug out of the crankshaft?

All the above plus: My interpretation of the data:
1. You didn’t go thru a couple of prop cyclings at around 1800 rpm, to get oil into the hub.
2. The fixed stop in the hub needs adjusting, as suggested by someone else, to red line minus 50 or so rpm.
3. As the oil finally filled the dome, prop governor kicked in but was at 2300 rpm. You need to make sure the governor was actually against the stop, and, if so, adjust it to allow higher rpm.

Edit. I see this has all been suggested by other posters. I need to read more carefully.
 
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Great ideas so far.

That sucks Ryan. So stressful.
What governor are you using?
Did you ever cycle the prop before?
Did you take the plug out of the crankshaft?

MT governor. Don't have the model number with me here away from the hangar.

Yes, I have cycled the prop in the past. No, I did not do it on the day of this test.

Yes the plug is out of the crankshaft :)

All the above plus: My interpretation of the data:
1. You didn’t go thru a couple of prop cyclings at around 1800 rpm, to get oil into the hub.
2. The fixed stop in the hub needs adjusting, as suggested by someone else, to red line minus 50 or so rpm.
3. As the oil finally filled the dome, prop governor kicked in but was at 2300 rpm. You need to make sure the governor was actually against the stop, and, if so, adjust it to allow higher rpm.

Bob's explanation convincingly accounts for the RPM drop after the initial surge.

There is no magic about the factory screw stop setting on the governor.

This is what I was hoping to hear.

Since your engine surged to 2790, the propeller hub fine pitch stop is not the issue. In fact, once you get the governor set to allow full RPM, you need to adjust the propeller hub fine-pitch stop to limit the static RPM to ~ 2650 RPM per the Hartzell manual.

Let me see if I can understand the interplay between the prop governor stop and the fine pitch stop. Ideally, I need them both of them set to the same static RPM limit, right? Or, should the governor limit be set higher (or lower) than the fine pitch stop? MT's manual implies that in-flight maximum RPM may end up different than static maximum RPM.

Adjusting the governor stop screw will require 5 or 6 full turns (or more), based on your current RPM. If the screw won’t move that far without running out of threads, then it’s possible that you have the wrong propeller governor model for your engine/governor drive gear ratio.

According to MT's manual, one turn is approximately 25 RPM. So to get this up to 2650 RPM will require 13 full turns. I hope I have enough threads. If not, the actual lever would need to be moved to a different spot on the shaft. I don't think I'm qualified to attempt that.
 
Let me see if I can understand the interplay between the prop governor stop and the fine pitch stop. Ideally, I need them both of them set to the same static RPM limit, right? Or, should the governor limit be set higher (or lower) than the fine pitch stop? MT's manual implies that in-flight maximum RPM may end up different than static maximum RPM.
.

Adjust the governor stop to get 2700 rpm at full power. Then turn down the prop mechanical limit until the rpm in a full power static runup is a bit under redline. Most people leave it there. The rpm will rise up to redline as you pick up speed on takeoff. If you adjust it back above redline, you’ll never know exactly where it is. Here’s the trade off: If your governor ever fails in flight in the ‘no pressurized oil’ direction, the rpm will zoom over redline. If you reduce throttle, you’ll be able to fly at low speed with rpm at redline - if the mechanical stop is set properly. But if the mechanical stop has drifted to a higher rpm setting, you may find, following a governor problem, that you have to overspeed the prop just to get minimum flying speed.
 
If the governor arm is actually hitting the stop, I would be a bit concerned. I would not expect the governor to be that far off from the factory; Maybe 100 or so, but 400 off makes me think something else is going on. Are you sure the governor is correctly matted to the gear drive. Lycoming has two different gear drive ratios for the governor shaft (they seem all over the map on where each is used) and internal setting on the governor must be made to match that.

Larry
 
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If the governor arm is actually hitting the stop, I would be a bit concerned. I would not expect the governor to be that far off from the factory; Maybe 100 or so, but 400 off makes me think something else is going on. Are you sure the governor is correctly matted to the gear drive. Lycoming has two different gear drive ratios for the governor shaft (they seem all over the map on where each is used) and internal setting on the governor must be made to match that.

I'll look at that closely when I get back to the hangar this weekend. It was hitting the stop when I originally installed the engine and pull cable a long time ago, and I'm pretty sure I checked full cable range during the pre-airworthiness condition inspection. Definitely don't want to have to pull the governor (is it even possible to get it out with the engine installed?)
 
Adjust the governor stop to get 2700 rpm at full power. Then turn down the prop mechanical limit until the rpm in a full power static runup is a bit under redline. Most people leave it there. The rpm will rise up to redline as you pick up speed on takeoff. If you adjust it back above redline, you’ll never know exactly where it is. Here’s the trade off: If your governor ever fails in flight in the ‘no pressurized oil’ direction, the rpm will zoom over redline. If you reduce throttle, you’ll be able to fly at low speed with rpm at redline - if the mechanical stop is set properly. But if the mechanical stop has drifted to a higher rpm setting, you may find, following a governor problem, that you have to overspeed the prop just to get minimum flying speed.

The mechanical stop on the prop blades is generally only valid at static (zero airspeed). Once the aircraft starts to roll, the governor takes over and the blades are off the stop. This is why you will often feel and hear the "surge" early in the roll as the governor comes alive. Point being: Anything above liftoff speed and the governor dies, you are pretty much guaranteed an overspeed. Been there, done that, trashed the engine and prop.

Back to the OP: seems like your pitch stops are set, but the governor should not be in play at static. Its set wrong or is the wrong drive ratio.
 
Not that bad, but

Definitely don't want to have to pull the governor (is it even possible to get it out with the engine installed?)

Yes, it can be removed with engine installed. I did mine more than once in phase I.

On other items, it sounds like you have plenty of help.
 
Propeller Fine Pitch Stop

Adjust the governor stop to get 2700 rpm at full power. Then turn down the prop mechanical limit until the rpm in a full power static runup is a bit under redline. Most people leave it there. The rpm will rise up to redline as you pick up speed on takeoff. If you adjust it back above redline, you’ll never know exactly where it is. Here’s the trade off: If your governor ever fails in flight in the ‘no pressurized oil’ direction, the rpm will zoom over redline. If you reduce throttle, you’ll be able to fly at low speed with rpm at redline - if the mechanical stop is set properly. But if the mechanical stop has drifted to a higher rpm setting, you may find, following a governor problem, that you have to overspeed the prop just to get minimum flying speed.

Properly setting the fine pitch stop is also important for maximizing engine out glide performance in cases where the governor is not able to supply oil to the prop!

Skylor
 
I'll look at that closely when I get back to the hangar this weekend. It was hitting the stop when I originally installed the engine and pull cable a long time ago, and I'm pretty sure I checked full cable range during the pre-airworthiness condition inspection. Definitely don't want to have to pull the governor (is it even possible to get it out with the engine installed?)

If this is a new governor, take the serial number back to MT and ask them how it was configured. One of the configurations should be for the drive ratio. Then research your specific engine and determine it's gov drive ratio. I know the hartzel S series is configured internally, but it's possible that MT actually has different models for the different ratios. They usually test these on a bench at the specified drive ratio and set the stop int the neighborhood of 2700 engine RPM, I believe, and that is why I suspect a ration mis match.

Larry
 
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If this is a new governor, take the serial number back to MT and ask them how it was configured. One of the configurations should be for the drive ratio. Then research your specific engine and determine it's gov drive ratio. I know the hartzel S series is configured internally, but it's possible that MT actually has different models for the different ratios. They usually test these on a bench at the specified drive ratio and set the stop int the neighborhood of 2700 engine RPM, I believe, and that is why I suspect a ration mis match.
Larry

Looks like contacting MT might be a good step. Got a chance to check out the paperwork that shipped with the governor, and this is pretty suspicious: It makes reference to a max. RPM of 2343. I don't speak German so I'm not sure if this is the RPM the governor's max RPM was set to as-shipped or if it is the maximum expected for this model/configuration.

 
Looks like contacting MT might be a good step. Got a chance to check out the paperwork that shipped with the governor, and this is pretty suspicious: It makes reference to a max. RPM of 2343. I don't speak German so I'm not sure if this is the RPM the governor's max RPM was set to as-shipped or if it is the maximum expected for this model/configuration.


I have the same governor, with the same "Equipment Log-Sheet" with 2332 max RPM and 760 min RPM and can get 2700 no problem.
Prop Governor test stats.png
 
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Looks like contacting MT might be a good step. Got a chance to check out the paperwork that shipped with the governor, and this is pretty suspicious: It makes reference to a max. RPM of 2343. I don't speak German so I'm not sure if this is the RPM the governor's max RPM was set to as-shipped or if it is the maximum expected for this model/configuration.


Most governor mfg's list the tested gov RPM. You need to used the appropriate ratio for your engine to convert that to engine RPM.
 
Had some time to work on RPM today. Verified throttle and prop cables are going all the way to the mechanical stops. I managed to adjust the max RPM from 2330 to 2480 using the governor's max RPM adjustment screw. I backed it out 4 full turns, leaving about 3 threads left, and that only increased RPM by about 150, so it's pretty clear I'm not going to get to 2700 on the ground using the screw. My next step is making calls to Vans, Lycoming and MT to get their input.

MT's manual confirms that the lever itself can be repositioned on the control shaft but warns that it's an adjustment requiring a bit more advanced skill:

Repositioning of Lever on Control Shaft (see Figure 13)
If the desired rpm is not attainable by moving the adjustment screws, it will be necessary to relocate the position of the lever on the speeder spring control shaft. This process should be accomplished by an approved governor repair facility, using a test stand to complete the adjustments.​

The other thing I did not do yet is rule out tach error by directly measuring RPM with the sensor from a prop balancer. Maybe I'll do that next weekend.

Another question: Is max static RPM on the ground indicative of max RPM during the takeoff roll? For those of you who have done a similar static run-up with your IO-360 engines, did you achieve 2700?

Before (as shipped, max 2330 RPM)


After (2480)
 
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The other thing I did not do yet is rule out tach error by directly measuring RPM with the sensor from a prop balancer. Maybe I'll do that next weekend.

Another question: Is max static RPM on the ground indicative of max RPM during the takeoff roll? For those of you who have done a similar static run-up with your IO-360 engines, did you achieve 2700?

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Park in the dark with one of LVK’s sodium street lights close behind you, like over near the tower. Have a piece of white tape on the backside of the prop. As you adjust the rpm you should see the tape ‘strobe’, e.g., appear to move very slowly. Careful adjustment of the prop control should make the tape appear stationary. This is exactly 2400 rpm.

You should be able to find a power off spec for your blade angle (something like XX degrees measured yy inches from the center of the hub.) If this is too coarse you’ll never make 2700 rpm static regardless of the governor. Most operators will not see 2700 rpm in a static runup because after adjusting the governor to get 2700 static, they then adjust the mechanical stop (in the prop hub) until it starts to limit static rpm, to maybe 2670 or so. If it were I, I’d remove the governor fine pitch stop screw completely, and also the prop control rod end attach bolt (just to be sure you were really against the stop), and repeat the test, see what you get.
Off topic: I’m a bit concerned with the angle the rod end is at. Is the prop control rod attached in the location called for in the plans?

PS. I’m not familiar with this governor. But others I am familiar with have a method of coarse adjustment of max rpm, e.g., slotted mounting holes that allow you to loosen the screws, rotate the end plate, re-tighten. Or maybe the arm can be loosened and re-positioned?
 
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You should be able to find a power off spec for your blade angle (something like XX degrees measured yy inches from the center of the hub.) If this is too coarse you’ll never make 2700 rpm static regardless of the governor. Most operators will not see 2700 rpm in a static runup because after adjusting the governor to get 2700 static, they then adjust the mechanical stop (in the prop hub) until it starts to limit static rpm, to maybe 2670 or so. If it were I, I’d remove the governor fine pitch stop screw completely, and also the prop control rod end attach bolt (just to be sure you were really against the stop), and repeat the test, see what you get.

At this point I'm going to wait and hear what Vans/Lycoming have to say. Honestly I'm a little ticked--I feel like I paid a fortune for this engine and specifically bought a new one thinking it would work out of the box without much tweaking. Maybe most builders with new engines go through this, what do I know?

Off topic: I’m a bit concerned with the angle the rod end is at. Is the prop control rod attached in the location called for in the plans?

I had the same first reaction too, but it's installed per Vans plans:


PS. I’m not familiar with this governor. But others I am familiar with have a method of coarse adjustment of max rpm, e.g., slotted mounting holes that allow you to loosen the screws, rotate the end plate, re-tighten. Or maybe the arm can be loosened and re-positioned?

Yea, the manual does mention a governor shop can reposition the lever on the shaft if you end up needing more RPM. That would require pulling the governor, which I'm slowly starting to accept might be inevitable.
 
So I'm sure there a good answer to this but I can't help wondering why you have an MT governor with a Hartzell prop.

MT is the default governor shipped with the FWF kit and I had to have them swap it out for the Harzell governor since I have a Hartzell prop..
 
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bought a new one thinking it would work out of the box without much tweaking. Maybe most builders with new engines go through this, what do I know?

I bought a stock IO 540, Hatrzell prop, Hartzell governor, prop control cable, all from Vans. I had to adjust the governor screws in the slotted holes (previously mentioned), play with the prop control rigging to get stop to stop range. The mechanical prop stop came pre-adjusted to the right place.
 
Yes, I was able to get 2700 RPM during ground runs.

RPM during ground runs HB-YMM.png

To confirm the RPM, see if someone has a prop balancer you can borrow. Also, check your fuel flow numbers to see if they are above 15GPH.

I'm guessing MT/Van's/Hartzell will tell you to keep moving the stop screws. I had to adjust mine, but in the other direction - I got 2700 on the ground easily, but on my first flight, I realized that would overspeed, so I had to screw mine in fully.
 
So, the governor is set in the factory for 2330 RPMs. You get it and install it on your plane. Lets assume you have the .866:1 ratio that most of the wide deck 4 cylinders have. That would mean you should get 2690 RPM from that governor without touching it, assuming the cables are all installed and working correctly, pushing the lever all the way to the stop.

Before I took it apart and started changing things I would want to know why it was off 400 RPM on your installation. It is not likely the screw was moving around in the box.

I wend through this with a Hartzel S series. It was set up for a different ratio and I needed to convert. Hartzel told me that adapting this via the external speed adjustment WOULD get me the right max RPM, but woiuld mess up the designed minimum RPM. Instead, I needed to get inside the unit and make more involved changes so that the unit could deal with the different RPM range.

Larry
 
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Had some time to work on RPM today. Verified throttle and prop cables are going all the way to the mechanical stops. I managed to adjust the max RPM from 2330 to 2480 using the governor's max RPM adjustment screw. I backed it out 4 full turns, leaving about 3 threads left, and that only increased RPM by about 150, so it's pretty clear I'm not going to get to 2700 on the ground using the screw. My next step is making calls to Vans, Lycoming and MT to get their input.

MT's manual confirms that the lever itself can be repositioned on the control shaft but warns that it's an adjustment requiring a bit more advanced skill:

Repositioning of Lever on Control Shaft (see Figure 13)
If the desired rpm is not attainable by moving the adjustment screws, it will be necessary to relocate the position of the lever on the speeder spring control shaft. This process should be accomplished by an approved governor repair facility, using a test stand to complete the adjustments.​

The other thing I did not do yet is rule out tach error by directly measuring RPM with the sensor from a prop balancer. Maybe I'll do that next weekend.

Another question: Is max static RPM on the ground indicative of max RPM during the takeoff roll? For those of you who have done a similar static run-up with your IO-360 engines, did you achieve 2700?

Taking the governor off and sending to a shop won't help a lot, as they will set it to 2330 RPM just as MT did, as that SHOULD be 2700 engine RPM on many/most WD 4 cyl Lyc. Again, you need to confirm the ratio for your particular engine as there are three different ratios out there. If yours has the .947 ratio this all makes sense, as 2330 gov RPM should net around 2450 engine RPM.

2700 shouldn't be hard to achieve on the ground with a Hartzel CS prop IF the fine pitch is set far enough out. In my experience, that stop comes pretty loose from the factory and most have to dial it in a couple turns.

Larry
 
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Taking the governor off and sending to a shop won't help a lot, as they will set it to 2330 RPM just as MT did, as that SHOULD be 2700 engine RPM on many/most WD 4 cyl Lyc. Again, you need to confirm the ratio for your particular engine as there are three different ratios out there. If yours has the .947 ratio this all makes sense, as 2330 gov RPM should net around 2450 engine RPM.

2700 shouldn't be hard to achieve on the ground with a Hartzel CS prop IF the fine pitch is set far enough out. In my experience, that stop comes pretty loose from the factory and most have to dial it in a couple turns.

Larry

Larry, where can I read about how this ratio works? The usual searches didn't yield any good info yet. Is the ratio an attribute of the engine or the governor or both? The governor came pre-attached to the engine, shipped together by Lycoming. EDIT: This is incorrect. The governor came with Vans FF kit.
 
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Larry, where can I read about how this ratio works? The usual searches didn't yield any good info yet. Is the ratio an attribute of the engine or the governor or both? The governor came pre-attached to the engine, shipped together by Lycoming.

The ratio is set via the gearing in the engine. On the forward mount versions, it is taken off the camshaft. I believe a common gear is used on the cam and different transfer gears are used to get diff ratios. On the rear mounted variants is is based on the takeoff gear meshed with the lower right idler gear. It may be in the operators manual or may find it through some other method of searching. Sorry, but I don't know the specific location to find it. The prop governor then needs to be set for the gearing on the engine it is mated to in order to provide the correct gov RPM range.

The engine has a ratio of crank speed to gov drive speed. You have to provide this ratio to the gov maker and they set up the internals to give the typical desired performance that is matched to engine RPM. Most gov makers either have different versions for different ratios (often changeable in the guts) and desired engine RPM ranges OR they ask you for the gear ratio and set it up internally for you. In your case, according to the test sheet, they set it up for an .866:1 ratio. If you have an engine with an .866 ratio that governor should net something close to 2700 engine RPM out of the box. If not, they either set it up wrong (not likely given the test sheet) or something else is going on. Given the test data sheet, it is very suspicious that you are so far off and I would not just start cranking the screw until I knew why.

The Lyc O/H manual gives various pictures of the accy case gear arrangements and can learn more by reading that. The parts manual will list different gears for different variants if they existed.

What engine do you have?

It is also possible that for some reason the fine pitch stop has been cranked way in and the stops are preventing a fine enough pitch to get 2700 on the ground at a stand still. Is this a new prop? They usually come pretty fine and expect the installer to adjust them down. If this came off a different plane, all bets are off.

Larry
 
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The drive ratio for the IO360-M1B is listed in the I0-360 manual page (section 2-7) as 0.866:1. It was also what I ordered for my PCU-5000X which was within 50 RPM as delivered.
Mike
 
IO-360-M1B. So the rear mounted governor drive ratio should be 0.866. I'll want to verify with the manufacturers that's what the governor I got is configured for. It's a new engine, new governor, new prop (Hartzell). According to Lycoming's test log, they had it up to 2741 for 15 minutes.
 
In case anyone's curiously following this mystery, I got a chance to talk to both Vans and MT today. Summarizing their input here.

Vans suggestion was to go fly and note what I get during take-off (and presumably other phases of flight).

MT had a bit more to say. Their tech confirmed my governor is the correct model and gear ratio for my engine--It's 0.866 and matches what's expected from a IO-360-M1B. He is confident that they ship them with the stop set correctly for 2340 (2700 engine RPM). He agrees the governor is limiting static RPM due to the initial surge to 2790. The propeller is probably not adjusted too low. He could not explain why I am unable to achieve 2700 on the ground, even after adjusting the max rpm stop, but that as-shipped it should achieve 2700 when airborne. Final suggestion was to go fly and adjust later if needed.

This was not really satisfying. I'd be deliberately giving myself an unnecessarily high workload to take off with an unknown RPM while I'm also managing the "normal first flight risks" too. I ask myself would an A&P sign off on an annual knowing the engine is producing 85%-90% RPM static at full throttle?

My next plan is to find a local A&P and seek out more advice/opinion. And borrow a prop balancer (or do BobTurner's sodium lights trick) to optically verify RPM and rule out tach measurement error.

On the plus side, I'm learning more about constant speed props than I thought I would. Hopefully this saga helps others learn, too.


EDIT: All due respect to Vans. As the kit manufacturer, I value and respect their input strongly as the kit manufacturer. It's just that "fly on" is a lot scarier than "build on" and I feel from a risk management point of view, I need to keep gathering input.
 
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Hi Ryan, Have you done more ground tests where you cycled the prop a few times? Also, have you noted max RPM, moved the screw a few turns, and run the test again? This would at least tell you if it's the governor that's controlling the prop RPM.
 
Hi Ryan, Have you done more ground tests where you cycled the prop a few times? Also, have you noted max RPM, moved the screw a few turns, and run the test again? This would at least tell you if it's the governor that's controlling the prop RPM.

He stated that on the initial power up, the RPM goes well above 2700 then comes down. That would seem to imply that the pitch stop is set quite fine and the governor has the authority (i.e. plenty of oil volume and pressure) to pull the pitch way coarse from there. Still a mystery as to why it is 300-400 RPM off from where it was set before installation. Just can't think of a reason why that is, beyond some flaw in the governor or human error in the final setup phase at the gov maker. Tach error doesn't make much sense either. If the tach is low by 300 RPM, that would mean you hit 3090 actual RPM on the initial power application and I don't believe any of the hartzel props come from the factory with the fine pitch stop that far off. 100 RPM or so high is typical, but 400 high is not.

I would be absolutely certain that their is not something weird going on with the control linkage, such that air flow or vibration could be causing the gov arm to move when under full power.

Did you by chance pull the cover off the gov in order to re-clock the arm position? I know on the hartzel that if the cover comes off, a special procedure for hooking the spring to the arm is required to re-install it and the know how is not really out there. It is not just putting the cover back on. SOrry, but know nothing about the MT.

Larry
 
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Did you by chance pull the cover off the gov in order to re-clock the arm position? I know on the hartzel that if the cover comes off, a special procedure for hooking the spring to the arm is required to re-install it and the know how is not really out there. It is not just putting the cover back on. SOrry, but know nothing about the MT.
Larry

I did re-clock the governor head 180 degrees in order to line the lever up correctly with the pull cable. Per MT's manual, this involved: 1. removing the safety wire from the six screws, 2. loosening the screws, 3. rotating the head 180 degrees, 4. re-tighten and safety the screws. The entire head rotates, so no change to the arm's position on the spindle or the stops.

EDIT: I think I've figured it out. Thanks to Larry for pointing me back to the initial installation. My build log (and my memory) is not very detailed here. I installed the prop governor on the engine two years ago. So I went back through my pictures to confirm a few things, and noticed something that might be the smoking gun:

Before re-clocking:



After re-clocking:



Note the safety wire on the screw holding the arm to the spindle is different from before to after. I would have had no business adjusting the lever on the spindle during the process of re-clocking the head, and have no memory of doing so, but the evidence is there that I did. If I inadvertently repositioned the arm on the spindle incorrectly, that would entirely explain my symptoms. I'm going to operate under the assumption that the arm is not on the correct location on the spindle and give MT a call again. See if they can walk me through correcting.
 
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Looking at the data, and reviewing the parts manual, governor manual I am strongly suspicious of the governor being setup incorrectly, despite the values on the data sheet.

Here's what's interesting to me -- when Ryan took delivery of the engine, the governor was already installed. This was not the case for both of my engines from Van's/Lycoming and a third -M1B that we're working on; governor came in a separate box -- and they are all MT P-860-4's... Others may have had a different experience.

The fact that the engine RPM climbed above 2700 RPM at full throttle and then settled down (assuming without any control inputs) would imply that the Minimum Pitch adjustment in the hub is set correctly, and the governor is capable of driving the propeller back down to a lower RPM (albeit incorrect) -- and holding it.

The Lycoming part #68137, is the drive gear for all of their rear mounted prop governors and is .866:1. Front mounted is Lycoming part 77875 and
.895:1

Since you cannot swap 68137 and 77875 parts without also changing idler gears in the accy. case or nose, I suspect that the engine is configured correctly (68137) and the governor was intended for an -A1D6 or other higher drive ratio engine...

Or -- maybe Colonel Mustard did it, in the Conservatory, with the lead pipe...
 
See my last post above. I think I figured it out and it is user error.

Here's what's interesting to me -- when Ryan took delivery of the engine, the governor was already installed. This was not the case for both of my engines from Van's/Lycoming and a third -M1B that we're working on; governor came in a separate box -- and they are all MT P-860-4's... Others may have had a different experience.

After chatting with Vans, they corrected me. I got the governor in the Firewall Forward kit. It did not come with the engine.
 
If I inadvertently repositioned the arm on the spindle incorrectly, that would entirely explain my symptoms.

While I don't know the MT, from the look of the design, yes, you are correct that moving the arm on the shaft would throw off your settings and fully explains the symptoms.
 
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While I don't know the MT, from the look of the design, yes, you are correct that moving the arm on the shaft would throw off your settings and fully explains the symptoms.

>Doh!<

Yes, if you move the arm relative to the spline gear then all-bets-are-off...
 
>Doh!<

Yes, if you move the arm relative to the spline gear then all-bets-are-off...

Doh! is right. I don't know what madness would have possessed me to make an adjustment to that shaft, but it's undeniable that the safety wire is different from picture to picture, so conservatively I have to assume the arm is now at an unknown position on the shaft.
 
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Adjustment

Ryan,

Move the propellor control to the high RPM position (all in, arm against the stop). Remove the screw that clamps the arm to the spindle. Remove the arm from the spindle. Rotate the spindle in a bit -- see attached picture; this is an unmolested P-860-4 as received from Van's in the High RPM position -- note position of spindle.

Reassemble.
 

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Doh! is right. I don't know what madness would have prompted me to make an adjustment to that shaft, but it's undeniable that the safety wire is different from picture to picture, so conservatively I have to assume the arm is now at an unknown position on the shaft.

The PCU5000 is basically this exact same governor, and when I went to reclock mine, the first thought I had was that if I just take the arm off and move it to the new position, I wouldn't have to redo the safety wire on all 6 screws. Glad you found the issue, now you just have to do some trial and error to find the correct spline position for the arm. I know you posted the manual section that says you have to send it to a qualified repair facility to adjust the arm, but its a single set screw and a splined shaft on an experimental aircraft. You've already tested your prop's low pitch stop so you know that no matter what you adjust the governor to you'll be limited to 2790 RPM for now. Time to make one-spline-at-a-time adjustments until you can get in the set screw adjustment window at 2700 rpm.
 
The PCU5000 is basically this exact same governor, and when I went to reclock mine, the first thought I had was that if I just take the arm off and move it to the new position, I wouldn't have to redo the safety wire on all 6 screws. Glad you found the issue, now you just have to do some trial and error to find the correct spline position for the arm. I know you posted the manual section that says you have to send it to a qualified repair facility to adjust the arm, but its a single set screw and a splined shaft on an experimental aircraft. You've already tested your prop's low pitch stop so you know that no matter what you adjust the governor to you'll be limited to 2790 RPM for now. Time to make one-spline-at-a-time adjustments until you can get in the set screw adjustment window at 2700 rpm.

Based on my before and after RPM measurements and doing a little trigonometry, I can calculate that I need to rotate the shaft two splines clockwise (20 degrees, as there are 36 splines) in order to get back to 2700 RPM with the original adjustment screw position. The only things I am concerned about are 1. can I reach this with the governor installed on the engine and 2. the arm is spring loaded, so I won't want to pull it entirely off the shaft.
 
Doh! is right. I don't know what madness would have possessed me to make an adjustment to that shaft, but it's undeniable that the safety wire is different from picture to picture, so conservatively I have to assume the arm is now at an unknown position on the shaft.

When I was building I tried hard to keep a notebook, to record anything I did that wasn’t spelled out in the plans (wiring, engine, etc). At the time I often said to myself, “What a waste of time. You’ll never forget this.” Now, a decade later, I go back and look at the notebook, and say, “Did I really do that?” Or maybe it’s old age creeping in, but those notes are invaluable.
 
Based on your previous work (4 turns increased rpm by xx) you should be able to make a good estimate of how many degrees to move the arm. Make sure to mark the current position with a sharpee before loosening the screw.
And, when it’s finally working properly, don’t forget to go back and adjust the mechanical fine pitch stop on the nose of the prop until it just starts to limit full power static RPM.
 
Based on my before and after RPM measurements and doing a little trigonometry, I can calculate that I need to rotate the shaft two splines clockwise (20 degrees, as there are 36 splines) in order to get back to 2700 RPM with the original adjustment screw position. The only things I am concerned about are 1. can I reach this with the governor installed on the engine and 2. the arm is spring loaded, so I won't want to pull it entirely off the shaft.

I could reach mine to do the clocking and other adjustments with it installed, but I gave up and removed it to get the safety-wire back in. Also, since you're dealing with fine adjustments and getting the splines lined up, it's much easier to do with the governor on the bench.

Also, if you're comfortable with the peanut gallery, let me know when you're getting ready for first flight. Would love to fly over and watch.
 
….The only things I am concerned about are 1. can I reach this with the governor installed on the engine and 2. the arm is spring loaded, so I won't want to pull it entirely off the shaft.

I would not be surprised if totally removing the clamping screw still leaves some of the splines engaged, e.g, the arm will have to come off. But if you do this at the low tension end of the spring the force to put it back on shouldn’t be overwhelming.
 
I would not be surprised if totally removing the clamping screw still leaves some of the splines engaged, e.g, the arm will have to come off. But if you do this at the low tension end of the spring the force to put it back on shouldn’t be overwhelming.

MT had a great recommendation to use a pick to temporarily unhook the spring, so there is no tension on the arm while I'm adjusting it.
 
Ryan
Even though I have now built an RV7, I find that I read some VAF threads and don't have a clue what they're talking about. On your threads, with good photos and your very clear writing, I not only understand the situation but am totally drawn in to how something happened and what needs to be done to rectify it. Another thing I appreciate is that your stories don't leave us hanging; you let us know how things work out in the end.
Thanks for that,
 
Good ending to this one. I relocated the lever on the governor shaft and can now easily make full power. I've got it dialed to ~2670 at the moment. Plan to do some flying (keeping an eye on RPM) and adjust later as needed. Will also adjust down the prop pitch stop some time during phase 1.
 
Good ending to this one. I relocated the lever on the governor shaft and can now easily make full power. I've got it dialed to ~2670 at the moment. Plan to do some flying (keeping an eye on RPM) and adjust later as needed. Will also adjust down the prop pitch stop some time during phase 1.

Great news…we’ll done.
 
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