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Fuel Flow Calibration shift (Read 1017 times)
Oct 1st, 2018 at 7:45am

kellym   Offline
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When I was doing my Phase I testing I got the fuel flow calibration pretty close with a K factor somewhere between 70,000 and 71,000. In the last month I started noticing the calculated fuel consumed was significantly more that fuel gauges and actual consumption. Most recent flight I had bumped the K factor up to 74,000, but still had a calculated fuel consumed of 47+ gallons, and actually pumped in 36 gallons. I suspected a loose connection, and just inspected the connectors. I was able to measure 0 ohms across each connection, and black wire having 0 ohms to engine ground. The sensor and airframe have approximately 195 hours. It is the "red cube".
« Last Edit: Oct 1st, 2018 at 7:46am by kellym »  
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Reply #1 - Oct 1st, 2018 at 3:57pm

Sunfish   Offline
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sounds like the bearings on the red cube rotor might be wearing in and its now spinning more freely?
 
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Reply #2 - Oct 2nd, 2018 at 1:10am

johnS   Offline
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Approach your K factor changes slowly from the safe side. You always want the calculated fuel used to be a little more than the actual used for safety. That said, you do want it to be close. Your note however is a good reminder to me to give this item another close look, Incase something is drifting.
 
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Reply #3 - Oct 3rd, 2018 at 7:37pm

kellym   Offline
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johnS wrote on Oct 2nd, 2018 at 1:10am:
Approach your K factor changes slowly from the safe side. You always want the calculated fuel used to be a little more than the actual used for safety. That said, you do want it to be close. Your note however is a good reminder to me to give this item another close look, Incase something is drifting.


That is what troubles me. Just on a percentage basis, the fuel computed vs actual is on the order of 30% high. That would make the K factor over 90,000. That seems to me to be an electronic problem, not mechanical.
 
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Reply #4 - Oct 11th, 2018 at 9:02am

reidvaitor   Offline
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I had this similar issue. In the end I put it back to the redcube starting point- whatever the tag said it was, did 100 gallons of refills (following calibration actual/expected along the way- aka added up both and at end did the calculation) and reset it to the calibration number. Than from there it all went back to .02 or less on fuel fill differences. Dont chase it, I tried that route for a year and it never worked out.
 
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Reply #5 - Oct 13th, 2018 at 6:38am

kellym   Offline
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reidvaitor wrote on Oct 11th, 2018 at 9:02am:
I had this similar issue. In the end I put it back to the redcube starting point- whatever the tag said it was, did 100 gallons of refills (following calibration actual/expected along the way- aka added up both and at end did the calculation) and reset it to the calibration number. Than from there it all went back to .02 or less on fuel fill differences. Dont chase it, I tried that route for a year and it never worked out.


OK. The Dynon manual says the default is 68,000. Before going bonkers, mine was always in the 70-72,000 range. Now it calculates to need over 90,000. Are there some that are really that far from the default? It also seems unusual to have it change by over 20% after a couple years.
 
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Reply #6 - Oct 13th, 2018 at 7:20am

RayInGA   Offline
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Where is the red cube installed? Ideally, it should be as far away from the fuel pump as possible to avoid pulses that will cause issues like this.

Mine, for example, is installed just prior to the flow divider on top of the engine.
 

Ray Eaker
RV-7A flying since 27 Jan 2017
Dual Skyview 1000T with all available Dynon VFR goodies
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Reply #7 - Oct 13th, 2018 at 10:44am

reidvaitor   Offline
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Mine is installed per Vans instructions, right after the fuel pump, works fine and Im pretty sure most Vans aircraft have their redcube in the same place. The issue is more than likely with the cube.
I called whoever made it, I think its EI support, but dont recall. They would be the best way to go to determine next steps.
 
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Reply #8 - Oct 13th, 2018 at 6:03pm

kurt Rutkowski   Offline
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I had issues with inaccurate fuel flow readings specifically when i flew longer, higher altitude flights, >9000 ft.  I would notice fuel pressure fluctuating when I started my initial cruise and I turned OFF the boost pump.
The fuel was being heated from the climb and due to the higher altitude the fuel was starting to turn to vapor (boil).  The fuel flow turbine will spin differently (faster)when air bubbles go through it.  Pressure variations are due to the mechanical fuel pump unable to pressurize fuel vapor at the inlet, and it is pulsed by engine rotation.  The electric fuel pump is located in the cabin so it always has cool fuel and it pressurizes all fuel lines in the cowling.
One way you can determine if you are heating your fuel is to climb to altitude  and lean normally.  turn your electric pump ON, if your fuel flow decreases you have air bubbles in your fuel.  Either a loose connection or you are heating the fuel to the point it boils.  AvGas will boil at a much lower temperature with an increase of altitude.
In my case the cabin heat valve, when OFF, was venting the hot air onto my fuel bowl and lines.
It may be worth checking before you start throwing parts at it.
Kurt R.
Glasair Super II-RG
Lyc IO360-B1E
 
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Reply #9 - Oct 14th, 2018 at 7:07am

RayInGA   Offline
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Here is a search of the RV forum on RedCube issues. Several causes have been found, including installation too close to the engine driven pump.

https://www.bing.com/search?q=site%3Avansairforce.com+redcube+pulses&PC=U316&FOR...
 

Ray Eaker
RV-7A flying since 27 Jan 2017
Dual Skyview 1000T with all available Dynon VFR goodies
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Reply #10 - Oct 14th, 2018 at 10:09am

kellym   Offline
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RayInGA wrote on Oct 14th, 2018 at 7:07am:
Here is a search of the RV forum on RedCube issues. Several causes have been found, including installation too close to the engine driven pump.

https://www.bing.com/search?q=site:vansairforce.com+redcube+pulses&PC=U316&FORM=...


Thanks Ray,
I'll check out the transponder issue, and a couple other suggestions. I'm bothered by those that say they had to replace the sensor, as EI says it should last 10,000 hours. I may switch to the EI barrel connectors, just to be sure that the current faston connectors are not part of the issue.
Kelly
 
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Reply #11 - Oct 24th, 2018 at 2:04pm

kellym   Offline
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kellym wrote on Oct 14th, 2018 at 10:09am:
RayInGA wrote on Oct 14th, 2018 at 7:07am:
Here is a search of the RV forum on RedCube issues. Several causes have been found, including installation too close to the engine driven pump.

https://www.bing.com/search?q=site:vansairforce.com+redcube+pulses&PC=U316&FORM=...


Thanks Ray,
I'll check out the transponder issue, and a couple other suggestions. I'm bothered by those that say they had to replace the sensor, as EI says it should last 10,000 hours. I may switch to the EI barrel connectors, just to be sure that the current faston connectors are not part of the issue.
Kelly


In checking wiring connections I found the problem. The ground wire had gotten nicked to the point that one one or two wire strands were left carrying current.  Fixed that and replaced the spade connectors with the current EI barrel connectors. Reading is now stable and very close on fuel flow readings. It will take 3-4 tankfuls to nail the K-factor calibration, but I am confident that this problem was the result of every FF issue I have seen in the past with the red cube....wire connection failures.
 
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Reply #12 - Nov 26th, 2018 at 4:24am

Downunder   Offline
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kurt Rutkowski wrote on Oct 13th, 2018 at 6:03pm:
I had issues with inaccurate fuel flow readings specifically when i flew longer, higher altitude flights, >9000 ft.


Interesting. I have just done some long distance, plus 9000 ft flights and the red cube was showing higher fuel usage than actual use. Using mogas...

A fairly new install, being 6 months old. Thought I had it calibrated but got confused with the latest figures. I think I'll leave any re-cal for now and do some checks after some normal alt flying.
« Last Edit: Nov 26th, 2018 at 4:27am by Downunder »  
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