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  #1  
Old 03-31-2019, 07:22 PM
Tacco Tacco is offline
 
Join Date: Jan 2017
Location: White Salmon, WA
Posts: 111
Default Fuel Flow Calibration Help

Lots posted on this already but I can't seem to figure this out.

I'm still in Phase 1 testing so no long cross country's yet so most of my flights have been short.

My indicated fuel remaining (Dynon calculated) has always been less than my Fuel Level. However, three flights ago, my fuel flow went to 10 gal/hr and I got an alert.

Post landing inspection found no leaks.

I increased the K-Factor up to 90000 from the default of 68000. The Dynon calculation of fuel-use-ratio indicated it should be set at 222,000. I figured that couldn't be right so I set it at 90000 just to see the effect.

The next flight, the fuel flow stayed lower but upon post flight the difference between Fuel Remaining and Fuel Level was still significant; 4.1 gal versus 2.3 gal for a 1 hour flight. The new ratio K-Factor worked out to be 160,434.

Fuel pressure has been steady between 5 and 4 PSI. Although keep in mind these were short flights with many throttle changes (e.g. pattern work)

So, what could be wrong? 160,343 seems to indicate something more here than a K-Factor adjustment given the recommended starting point is 68000.
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Old 03-31-2019, 08:16 PM
DHeal DHeal is offline
 
Join Date: Sep 2006
Location: Windsor, California
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As one point of reference, I have been using 107,510 as my K-factor for the past 300+ hours. This value tracks well with my actual fuel use (912ULS) -- usually within a tenth of a gallon or so. My flights typically average about one hour in length -- if you take many long flights (or many short flights) your K-factor will likely be different.
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  #3  
Old 03-31-2019, 08:24 PM
RFSchaller RFSchaller is offline
 
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Location: Phoenix, AZ
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Steve,

The only time my fuel flow has spiked high was when I had vapor lock (actually not full blown lock just some bubbly flow in the fuel line). I put a switch on my electric pump so the flow stabilizes when I turn it on. You may have old fuel or a faulty electric pump. What does your fuel pressure read with the engine shutdown and the electric pump on?

I set my K-factor in cruise to match my historic fuel burn as determined from the average of several flights. My calculated fuel usage always within a gallon of actual to top off.

Rich
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  #4  
Old 03-31-2019, 08:28 PM
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Mark33 Mark33 is offline
 
Join Date: May 2010
Location: Baton Rouge, La.
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Default K-factor calculation

Iím not sure what formula you use to calculate the K-factor, but this is how I do it.

K-Factor calculation:
Current K factor/ (divided by) the amount of gas pumped X (times) the amount of gas that the EFFIS says thatís been used. This will give you a new K-Factor. I just do this each time I put fuel in it and each time I calculate it, the more accurate it gets. After four or five times, itís pretty much right on the money.
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Old 03-31-2019, 10:46 PM
Tacco Tacco is offline
 
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Location: White Salmon, WA
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My fuel pressure runs about 3 PSI before engine start. 4 to 5 after.

I use the same formula as Mark above.

Its been cold here and my fuel is no more than three weeks or less out of the pump. Vapor lock seems unlikely.
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Old 04-01-2019, 04:00 AM
BigJohn BigJohn is offline
 
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Location: Gloversville, NY
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D-180 or SkyView?
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  #7  
Old 04-01-2019, 06:48 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by Tacco View Post
So, what could be wrong? 160,343 seems to indicate something more here than a K-Factor adjustment given the recommended starting point is 68000.
Most of us would need to know more about plumbing arrangements to hazard a guess at what has changed. I assume your aircraft is an RV-12. I've never plumbed one.

As for the new K-factor, the default 68000 is proportional to the number of times the internal light beam is interrupted by the rotor for one gallon of lab flow. There is evidence to suggest the rotor can make small reversals (think "a few steps forward, one step back"), adding light beam breaks, and making indicted flow higher than actual. It's commonly seen in Lycoming installations with red cube senders placed between the boost pump and the engine driven pump. The indication rises when the boost pump is turned on, although actual flow remains the same.

Photos:

http://www.vansairforce.com/communit...9&postcount=32
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Last edited by DanH : 04-01-2019 at 06:57 AM.
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  #8  
Old 04-01-2019, 07:24 AM
Tacco Tacco is offline
 
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RV-12 ULS, Skyview HDX
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Old 04-01-2019, 12:00 PM
Tacco Tacco is offline
 
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Thanks for the pictures Dan. Iím wondering if there might be contamination swirling around in there.
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Old 04-01-2019, 12:09 PM
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DaleB DaleB is offline
 
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Location: Omaha, NE (KMLE)
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I've had intermittent high fuel flow alarms before. It almost always happened above 7000 DA, and while running mogas. Once or twice I got it on takeoff on warm days. I'm suspecting it was bubbles in the fuel flow messing with the transducer. Not entirely sure, though -- it could also be vibration related.
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