G3X question

On. my RV7 full tanks show 17 imperial gallons per side and with flight the levels go down as fuel is used. Today flew one and a half hours and neither tank level went down. Stayed at 17 gallons per side. Not indicating fuel used. Ideas?? Thanks Gary

You have not said if you built this plane. Assuming you did not . . the dihedral of the wing means the fuel tank fills to the top on the inboard end first. This means the short arm of the float (assuming you have a float) reaches it's upper limit before the tank is filled to 21 gal.

When the G3X fuel levels are calibrated, one must trick the system to indicate higher than the maximum fuel actually measured. My 7 float on the right tank will top out at about 17 gal when filling. Once the tank is full, the gage will not indicate any change until it reaches 17, then will follow the calibration curve. I did not want a full tank to indicate 17, so a 1/2 gal short of 17 was calibrated at 16.5, but at max height (17 gal) I entered 21 gal in the calibration curve.

Does this make sense for your situation?

simatos said:

On. my RV7 full tanks show 17 imperial gallons per side and with flight the levels go down as fuel is used. Today flew one and a half hours and neither tank level went down. Stayed at 17 gallons per side. Not indicating fuel used. Ideas?? Thanks Gary

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Hello Gary,

The tanks on our RV-7A hold 21 gallon per side, and like yours, the float gauge tops out and stops rising at about 17 gals per side.

Since there are about 4 gals per side that are not measured by the fuel gauges, it is certainly plausible that you might fly for 1.5 hrs and not see the fuel gauges come off a "full" indication.

This is a lot like my car works. When I fill it up the fuel gauge pegs at the top, but doesn't come off the top peg until I drive about 80 miles. After that the fuel gauge moves and becomes useful.

While you could certainly re-calibrate and do something like Bill has described, we felt it was better to indicate "full" and 17 gals until the fuel burns down to the point where the fuel gauge comes off the peg and becomes active rather than indicating 21 gals long after the fuel tank no longer contains 21 gals. Your choice.

Let us know if you still have questions.

Thanks,
Steve

I thought I read or maybe heard at an Oshkosh forum that the only requirement for the fuel gauges was that when the tank is empty, the gauge needs to read empty.

Well when it's empty and it says empty I don't think the fuel gage is of much use.

flew some more this morning and tanks showing less gas ( as consumed) as expected so like you all pointed out floats pinned on roof of tanks for first few gallons used .. Thanks everyone
Cheers G