Dynon Fuel Computations

[Radioflyer]

Something has been bugging me about EFIS fuel computers (e.g. as in a Dynon D180). I assume most mechanical fuel level senders in an RV6A top out at some level below the full 19 gallons (due to dihedral). The level might be indicated as 13 gallons, when there are actually 17 gallons, for example. However, the fuel flow sender still measures consumption of the fuel that is above the sender's level.

Am I correct in thinking that fuel level and fuel flow are independent in EFIS systems? In other words, the fuel flow calculations (range, time, etc) don't affect the fuel level indications. Fuel flow calculations are only dependent on the number of gallons you key into the software, not the physical quantity of gallons, right?

 

[MacCool]

In my Advanced Flight system (affiliated with Dynon), fuel level is displayed on the EFIS only from the tank level sensors. Nothing to do with the fuel computer. The fuel computer keeps a running tally based on how much fuel you tell it that you put in, then uses fuel flow plus the K-factor to calculate how much is left (either Fill All, or directly entering how much fuel you put in at a given fuel stop). The EFIS can be set to display a variety of fuel formats... I can select HRS REM, NM/GAL, SM/GAL, GREM AT, GREQ TO, GAL USED, GAL REM. It's displayed on the EFiS next to the two tank level gauges. The two are completely independent of each other.

I've found it to be very accurate...typically 0.1 gallon or better. I recheck the K-factor every few tankfuls, or at least note how much fuel the computer says I've used compared to how much I put in.

 

[Radioflyer]

Ok, thanks. Fuel computer totally independent from fuel level depiction. I’ll keep an eye on my k-factor.

 

[Radomir]

In addition, these two being independent of each other can be used for cross-check ... do not rely on fuel computer alone if floats are telling you that you may be low on gas (may have a leak that fuel computer would never detect)..

 

[MacCool]

I cross-check the computer's accuracy at every fuel fill by noting at shutdown how much fuel the computer says I've used compared to how much I actually put it at that fill up. They should be exactly the same, but it does end up varying a little, maybe +/- half a gallon, as the ambient temp dictates how close to the filler necks I fill the tanks. Off by more than 0.1 gallon and I will usually re-calculate the K-factor. I did replace my Red Cube about 35 hours ago. I was a little surprised at how close the new K-factor was to the old one.

I find excellent correlation between the fuel computer and the fuel gauges, but of course the gauges don't register any fuel used until I've used quite a bit. Only registers the last 10-15 gallons per tank (dihedral). I view the gauges as a good cross-check.