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02-16-2020, 06:03 PM
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Join Date: Dec 2010
Location: Culpeper, VA
Posts: 693
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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,
__________________
-Joe Wilbur (N520LW)
Phase II - 11/2017
First flight - 8/2017
RV-10 Build Log
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02-16-2020, 07:04 PM
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Join Date: Oct 2005
Location: Vancouver, WA USA
Posts: 908
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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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02-16-2020, 08:38 PM
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Join Date: Dec 2010
Location: Culpeper, VA
Posts: 693
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Quote:
Originally Posted by Russ McCutcheon
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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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.
__________________
-Joe Wilbur (N520LW)
Phase II - 11/2017
First flight - 8/2017
RV-10 Build Log
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02-17-2020, 06:20 AM
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Join Date: Oct 2014
Location: Milwaukee, WI
Posts: 300
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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.
__________________
Matt
CFI / RV-10
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02-17-2020, 08:02 AM
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Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,298
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Quote:
Originally Posted by Russ McCutcheon
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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+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
__________________
N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
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02-17-2020, 08:05 AM
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Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,298
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Quote:
Originally Posted by jwilbur
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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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
__________________
N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
Last edited by lr172 : 02-17-2020 at 08:22 AM.
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02-17-2020, 08:53 AM
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Join Date: Dec 2010
Location: Culpeper, VA
Posts: 693
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Quote:
Originally Posted by lr172
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
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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.
__________________
-Joe Wilbur (N520LW)
Phase II - 11/2017
First flight - 8/2017
RV-10 Build Log
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02-17-2020, 09:16 AM
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Join Date: Jan 2005
Location: Victoria, Canada
Posts: 2,251
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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.
V
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V e r n. ====
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RV-9A complete
Harmon Rocket complete
S-21 wings complete
Victoria, BC (Summer)
Chandler, Az (Winter)
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02-17-2020, 09:38 AM
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Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,298
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Quote:
Originally Posted by jwilbur
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?
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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
__________________
N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
Last edited by lr172 : 02-17-2020 at 09:41 AM.
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02-17-2020, 10:19 AM
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Join Date: Dec 2010
Location: Culpeper, VA
Posts: 693
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Quote:
Originally Posted by lr172
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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I understand. Thank you very much. I'll clean the plugs and check everything I can before next flight.
__________________
-Joe Wilbur (N520LW)
Phase II - 11/2017
First flight - 8/2017
RV-10 Build Log
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