Capacitive fuel sender response with different fuels

[airguy]

Here is a datapoint for the group, on the differences in the capacitive sender response between fuels. I have calibrated my left tank on 100LL and the voltage ranges from 0.835 to 1.165 volts (empty to full), and when calibrated on 91 octane premium auto gas the voltage ranges from 0.801 to 1.502 (empty to full).

The capacitive sender response is significantly different, you must change the calibration sets when changing fuels if you want to trust your fuel levels.

With Dynon it is possible to have pre-loaded sets of calibration files and switch from one to the other within seconds depending on the fuel you are putting into the tanks, there is a thread discussing this on the Dynon forums. Of course, this also means you would ideally want to have your tank empty or very close to it when switching from one fuel to another.

[Billythekid]

Is this difference due to the specific gravity of the different fluids

[Guy Prevost]

Originally Posted by Billythekid

Is this difference due to the specific gravity of the different fluids

No, the dielectric constant.

[Captain_John]

Originally Posted by Guy Prevost

No, the dielectric constant.

Yup!

...and I can tell you that it works out to be a difference of 3 gallons with EI senders that Van sells combined with the G3X.

I calibrated for 100LL and when i was testing auto fuel, it indicated about 3 gallons more than I had on board.

Combine this with a lower BTU output of auto fuel (ie. Higher rate of consumption) and it makes for interesting test results!

CJ

[FasGlas]

Something new coming out from Belite. It won't change calibration for any fuel. https://jameswiebe.wordpress.com/201...ve-fuel-probe/

[flyboy1963]

I like the fuel trend display...kind of a visual how long you've been on that tank, if you're burning more than expected etc.
plus....
how often have I looked at the gauges, and timer, and thought,
" did I really go thru 1/4 tank in that long climb?" or was it just UNDER half before, and now it's not aQUITE at 1/4....gee, maybe I should switch tanks just to even things out!"

[BobTurner]

I'm a bit curious about the differences in the empty readings. How can fuel type matter when empty?

[airguy]

Originally Posted by BobTurner

I'm a bit curious about the differences in the empty readings. How can fuel type matter when empty?

Valid point - it shouldn't. I'm thinking likely a variation in system voltage at the time I did one of the calibrations or something similar. I don't have an explanation for that.

Like I said, just one datapoint, insufficient background data to really make a valid discussion of it though it is an interesting datapoint.