VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics

  #1  
Old 08-11-2019, 12:31 PM
JDA_BTR JDA_BTR is offline
 
Join Date: Dec 2013
Location: Baton Rouge, LA
Posts: 823
Default Problem or Feature? PMAG setting fluctuates

My question is: does this sound like normal operation......

I recently installed the EngineBridge wifi module to see what my ignition is doing. I'm able to see 1/sec what the timing is advanced to for both PMAGs together on my phone screen via wifi.

IO390, dual PMAG, operating 2400 RPM with about 24 MAP. Steady cruise for quite a while.

I see the setting vary up and down 1.4 degrees (1.4 is the step size I know) and not just sit on one setting. It is 24.... then 25.... then 24..... etc. It will be the right side mainly; then I raise MAP a hair, then the right stabilizes and the left changes. Sometimes they both come and go a bit.

My instruments aren't showing me altitude, MAP or RPM changes when this is going on. So I wonder why the PMAG is so sensitive that it wants to change the timing so often. Of course this is assuming the EngineBridge is accurate.

Also, my system is timed at TDC, with 20BTDC being the timing mark of the IO390. I have the PMAG set for -7 setpoint and 29.4 max advance. The PMAG system starts at +4 on a -25 assumption for a TDC making it fire at 21 BTDC or +1 from what an IO390 wants. So when I see 25 degrees of advance in flight I assume it is really +7 ATDC -25 (assumed by PMAG) - 25 (the reported advance) =43 BTDC which would be 23 degrees of advance for my ignition at that point.

But why does the timing setpoint wobble around so much?
__________________
Ser 104142, RV-14A
N1463
Urologist, AME
Reply With Quote
  #2  
Old 08-11-2019, 12:41 PM
Raymo's Avatar
Raymo Raymo is offline
 
Join Date: Nov 2014
Location: Richmond Hill, GA (KLHW)
Posts: 2,019
Default

Check the fitting in your cylinder where you get the MAP and make sure it either has a very small hole you, as Bill R recommends, install a rivet with a small hole drilled in it to stabilize MAP fluctuations.
__________________
Ray
RV-7A - Slider - N495KL - First flt 27 Jan 17
O-360-A4M w/ AFP FM-150 FI, Dual PMags, Vetterman Trombone Exh, SkyTech starter, BandC Alt (PP failed after 226 hrs)
Catto 3 blade NLE, FlightLines Interior, James cowl, plenum & intake, Anti-Splat -14 seat mod and nose gear support
All lines by TSFlightLines

"The object of the game, gentlemen, is not to cheat death: the object is not to let him play."
Patrick Poteen, Sgt. U.S. Army
Reply With Quote
  #3  
Old 08-11-2019, 12:42 PM
JDA_BTR JDA_BTR is offline
 
Join Date: Dec 2013
Location: Baton Rouge, LA
Posts: 823
Default

It does have a restrictor in it. The MAP is rock solid and not changing. It is the PMAG setting that moves all around.
__________________
Ser 104142, RV-14A
N1463
Urologist, AME
Reply With Quote
  #4  
Old 08-11-2019, 01:20 PM
rv6ejguy's Avatar
rv6ejguy rv6ejguy is offline
 
Join Date: Mar 2005
Location: Calgary, Canada
Posts: 5,281
Default

1 degree is not very significant and there will always be some scatter with any EI which isn't crank triggered- gear lash, TV etc.
__________________

Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 434.4 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi2.htm



Last edited by rv6ejguy : 08-11-2019 at 02:42 PM.
Reply With Quote
  #5  
Old 08-11-2019, 01:20 PM
PilotjohnS PilotjohnS is online now
 
Join Date: Jan 2016
Location: Southwest
Posts: 745
Default Bit resolution

If the setting is only varying within the resolution, I would suspect it is not really changing. It may be that the recording software cant decide what it should be, so it vacillates between two readings. There is a hint this is happening because you said one becomes stable then the other starts acting up.

In general, in my opinion, it is vary hard to tell the true value of a parameter if the resolution is not fine enough.
__________________
John S

WARNING! Information presented in this post is my opinion. All users of info have sole responsibility for determining accuracy or suitability for their use.

Dues paid 2019, worth every penny

RV9A- Status: tail feathers done less tips
Wings done less tips and avionics
Fuselage 30%
www.pilotjohnsrv9.blogspot.com
Reply With Quote
  #6  
Old 08-11-2019, 02:29 PM
Bavafa Bavafa is offline
 
Join Date: Oct 2007
Location: Sacramento, CA
Posts: 2,913
Default

I think I am with John S on this, specially that the serial link from PMAG is a rather low speed link. I am not an engine guru but I would think the gear lash would not apply since it is under the load and turning at a steady speed. Ironically, I don't see that in EICommander, and wondering if they are filtering it or rounding it off.
__________________
Mehrdad
N825SM RV7A - IO360M1B - SOLD
N825MS RV14A - IO390 - Flying
Dues paid
Reply With Quote
  #7  
Old 08-11-2019, 02:39 PM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 8,755
Default

Quote:
Originally Posted by rv6ejguy View Post
1 degree is very significant and there will always be some scatter with any EI which isn't crank triggered- gear lash, TV etc.
I assume you meant to say "not very significant"

+2 on instrument resolution. Most of the ignitions smooth between integer values, and the Engine Bridge probably rounds up or down, reporting only integers.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
Reply With Quote
  #8  
Old 08-11-2019, 02:42 PM
rv6ejguy's Avatar
rv6ejguy rv6ejguy is offline
 
Join Date: Mar 2005
Location: Calgary, Canada
Posts: 5,281
Default

Yup, corrected that.
__________________

Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 434.4 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi2.htm


Reply With Quote
  #9  
Old 08-11-2019, 02:57 PM
Brantel's Avatar
Brantel Brantel is offline
 
Join Date: Mar 2006
Location: Newport, TN
Posts: 7,441
Default

As someone that has spent a bunch of time with the PMag serial stream, what you are seeing is typical.
__________________
Brantel (Brian Chesteen),
Check out my RV-10 builder's BLOG
RV-10, #41942, N?????, Working on Emp/Tail Cone
---------------------------------------------------------------------
RV-7/TU, #72823, N159SB
Lyc. O-360 carbed, HARTZELL BA CS Prop, Dual P-MAGs, Dual Garmin G3X Touch
Track N159SB (KK4LIF)
Like EAA Chapter 1494 on Facebook
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 06:42 PM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.