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  #1  
Old 02-16-2020, 06:03 PM
jwilbur jwilbur is offline
 
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Location: Culpeper, VA
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Default Momentary RPM jump

Question for the experts.

I have 115 hours on my RV10. Hartzell Governor, stock IO540, Hartzel prop, and mags, all new when I installed them. Today I had prop set at 2300, 13 Inches MAP, 3000 feet level flight (~90 knots) just burning fuel for a while practising some stuff. Pushed MAP up to 20, climbed 500 feet or so. As I pushed to level off and accellerate, RPM jumped. The Dynon voice said, "over-speed." By the time I looked it was falling back through 2400 back to the set point of 2300. It happened again while I watched. It jumped to ~2600. Then back down. It settled back with another jump or two. I noticed nothing unusual with the engine or sounds or feel, so it might be just a wire. I've got Dynon hooked to the P-leads. Early test flights had RPM jumpy so I increased the resistance in the lines back then. Never had any issues in the last 100 hours.

Back to today's flight. I pulled power back to 15" to be safe and turned for home. No more troubles. Near the airport I moved some knobs around and in and out and things seemed to behave normally.

Some time back I know there were troubles with another governor where props suddenly went fine pitch and caused troubles. What I don't know is if there were symptoms leading to those events. I'll be pulling the cowl this week to look over the wires and cables and all. Hoping to get some advice from the experts here on what not-so-obvious thing I might be interested in looking for. Or any theories on what might have happened today.

Thanks,
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  #2  
Old 02-16-2020, 07:04 PM
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Russ McCutcheon Russ McCutcheon is offline
 
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What I can say is that if it had actually jumped from 2300 to 2600 you would very definitely have felt and heard that, since you say you did not detect any difference in the engine operation then you probably have an indication error.
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  #3  
Old 02-16-2020, 08:38 PM
jwilbur jwilbur is offline
 
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Quote:
Originally Posted by Russ McCutcheon View Post
What I can say is that if it had actually jumped from 2300 to 2600 you would very definitely have felt and heard that, since you say you did not detect any difference in the engine operation then you probably have an indication error.
For sure I would if it were sustained for any length of time. Not sure I would if it were a few hundred milliseconds. Also since I'm connected to the mags, could something like this indicate a problem brewing in a mag?

I'm going to check the logs. I'm guessing if there were a real RPM change there would probably be some other things like MAP that might have blipped, too.
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  #4  
Old 02-17-2020, 06:20 AM
rdrcrmatt rdrcrmatt is offline
 
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When we switched from a narrow-deck to a wide-deck on our RV-10, I asked a few people which governor to get (I still have the narrow deck 540 Hartzell governor for sale!), and it was recommended to get the PCU5000X because of similar issues that others have had with the Hartzell.
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  #5  
Old 02-17-2020, 08:02 AM
lr172 lr172 is online now
 
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Quote:
Originally Posted by Russ McCutcheon View Post
What I can say is that if it had actually jumped from 2300 to 2600 you would very definitely have felt and heard that, since you say you did not detect any difference in the engine operation then you probably have an indication error.
+1

You can't really miss hearing a 300-400 RPM change. I would be looking at the RPM sense wires and consider yet another increase in resistor size. Sensing the RPM from a P lead is challenging and most mfg's recommended to keep increasing resistor size until the RPM is reliable/stable.

Larry
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  #6  
Old 02-17-2020, 08:05 AM
lr172 lr172 is online now
 
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Quote:
Originally Posted by jwilbur View Post
For sure I would if it were sustained for any length of time. Not sure I would if it were a few hundred milliseconds. Also since I'm connected to the mags, could something like this indicate a problem brewing in a mag?

I'm going to check the logs. I'm guessing if there were a real RPM change there would probably be some other things like MAP that might have blipped, too.
I don't think the governor can change 400 RPM and then change back in a few hundred milliseconds. They don't react that fast. You get a sense for governor reaction time during your runup, if you cycle the prop. Regardless of the time, I still don't believe your ears would miss it. If your resistor is too small/large or have a bad connection on the P lead, you will not find other signs of problems in your logs. It is not likely indicative of a problem in the mag without other performance indicators. Though changes in the mag's E gap over time will change the current / energy out of the coil and that could push past the threshold of sensing the RPM in the EFIS. RPM is sensed by monitoring the spike that occurs on the coil's primary winding, as the field collapses. The nature of that spike will change as the charge energy fed to the coil changes and this can change with a change in E gap. E gap drifts as the points wear over time. A bad condensor can accelerate that wear.

Larry
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Last edited by lr172 : 02-17-2020 at 08:22 AM.
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  #7  
Old 02-17-2020, 08:53 AM
jwilbur jwilbur is offline
 
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Quote:
Originally Posted by lr172 View Post
I don't think the governor can change 400 RPM and then change back in a few hundred milliseconds. They don't react that fast. .... The nature of that spike will change as the charge energy fed to the coil changes and this can change with a change in E gap. E gap drifts as the points wear over time. A bad condensor can accelerate that wear.

Larry
Thank you, Larry. I appreciate the explanation of what's going on in the mag. If I find that I need more resistance that would indicate a change in the mag(s) since I have not had this problem in 2 years.

Regarding the governor. The prop is controlled through oil pressure. Is there anything in the oil system that could cause a momentary change in the prop pitch outside the control of the governor? For example, I had just finished a climb as the event occurred. The airplane had been nose high, gravity pulling oil away from the prop, etc. Point of information, I measured just over 6 quarts before the flight. Anything important about this information?

Let me emphasize that I believe this is almost certainly a deteriorating connection in the wires between the mags and the Dynon or maybe a resistor or a ground connection. ... But I like to consider whatever other alternatives there may be and to take the opportunity to learn what more I can about my systems ... and avoid expectation bias if I can.
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  #8  
Old 02-17-2020, 09:16 AM
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vlittle vlittle is offline
 
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Clean and precisely gap your plugs, check the ignition wires and magneto condition This is an ignition problem, not a resistor problem.

A misfiring plug will generate a wonky waveform on the P-Lead (a wonky is the international unit for messed-up). This is interpreted by the tach circuit as an overspeed.

Since it's been stable for some time, something has changed. The airplane is speaking, listen.

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  #9  
Old 02-17-2020, 09:38 AM
lr172 lr172 is online now
 
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Quote:
Originally Posted by jwilbur View Post

Regarding the governor. The prop is controlled through oil pressure. Is there anything in the oil system that could cause a momentary change in the prop pitch outside the control of the governor? For example, I had just finished a climb as the event occurred. The airplane had been nose high, gravity pulling oil away from the prop, etc. Point of information, I measured just over 6 quarts before the flight. Anything important about this information?
No, assuming that your oil pressure didn't drop to a ridiculously low level.

As I and Vern have stated, something is going on in the ignition or your wiring. I agree with Vern that it is likely in the ignition system and not the P lead wiring. As he mentioned, problems on the secondary winding side can also create P lead irregularity.

Larry
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Last edited by lr172 : 02-17-2020 at 09:41 AM.
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  #10  
Old 02-17-2020, 10:19 AM
jwilbur jwilbur is offline
 
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Quote:
Originally Posted by lr172 View Post
No, assuming that your oil pressure didn't drop to a ridiculously low level.

As I and Vern have stated, something is going on in the ignition or your wiring. I agree with Vern that it is likely in the ignition system and not the P lead wiring. As he mentioned, problems on the secondary winding side can also create P lead irregularity.

Larry
I understand. Thank you very much. I'll clean the plugs and check everything I can before next flight.
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