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Fuel Flow Calibration Help

Tacco

Well Known Member
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.
 
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.
 
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
 
K-factor calculation

I?m 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 that?s 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, it?s pretty much right on the money.
 
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.
 
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/community/showpost.php?p=1311739&postcount=32
 
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Thanks for the pictures Dan. I?m wondering if there might be contamination swirling around in there.
 
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.
 
The way I remember the K-factor adjustment equation is to think of the K as the number of turbine revolutions per gallon. If your calculated fuel used is high you need to increase the number of revolutions per gallon and increase K.
 
Bill -- We are talking about an RV-12 here not an RV-7 type of aircraft. The RV-12 has a bypass/return form of fuel system with only one fuel flow sensor so the stock K Factor needs to be adjusted to reflect the bypassed fuel.
 
Thanks guys. I?m going to set the K-Factor at 110000 for my next flight (a couple days from now) and let you know.
 
Bill -- We are talking about an RV-12 here not an RV-7 type of aircraft. The RV-12 has a bypass/return form of fuel system with only one fuel flow sensor so the stock K Factor needs to be adjusted to reflect the bypassed fuel.

Thanks - I did not know that - I have deleted the post as it is not relevant.
 
Instead of starting a new post I am reviving this one since it has some good information on calibrating the K-factor.

On my Dynon I show;
PUL/GAL (C37 P14) 100000
PUL/GAL (C37 P19) 100000

Are both of these numbers important or only one?
 
Instead of starting a new post I am reviving this one since it has some good information on calibrating the K-factor.

On my Dynon I show;
PUL/GAL (C37 P14) 100000
PUL/GAL (C37 P19) 100000

Are both of these numbers important or only one?

C37 P14 refers to the EMS 37 pin connector and P14 is the red cube flow from the fuel tank.
C37 P19 is for return flow, but the RV12 has no return flow transducer so there is no connection to that pin. You can confirm that on the Van's SV wiring diagram if you wish. I am not to sure what SV does with the number you might put into the P19 setting.

i-vgLnLzv-XL.png


It does appear though that if there are no transducer pulses on pin 19, then there should be no effect on fuel flow no matter what "K-factor" number you put in the settings for Pin 19.

i-tgjc8Nn-XL.png


Things might work differently on the D180 because as I remember a few of us using that EFIS could simulate return flow using the return flow K-factor. We were able to set indicated fuel flow on the EMS page to zero with the engine off and the fuel pump running. We resorted to that because the D180 limited the top adjustment of the red cube K-factor to 99,999 and we needed it to be higher. By adjusting the return flow K-factor we could use a number less than 99,999. This is all from memory a long time ago I no longer have a D180 panel so can't verify that.

I hope I have not strayed to far afield for this thread.
 
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C37 P14 refers to the EMS 37 pin connector and P14 is the red cube flow from the fuel tank.
C37 P19 is for return flow, but the RV12 has no return flow transducer so there is no connection to that pin. You can confirm that on the Van's SV wiring diagram if you wish. I am not to sure what SV does with the number you might put into the P19 setting.
This is what I was thinking. Is there a reason to have a value in the C37 P19 position or does the number I put there affect anything?
 
In my RV12 with a 912 ULS I am using 98450 as K factor. That’s purposely a tiny bit more than what I am actually using since I never want to see more fuel on the display than what is actually in the tank.
Every time I am on the ground, I am adjusting it to the measured in tank value (engine/fuel/match/accept).
 
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