Fuel Gauge Accuracy

[Rocketscntst]

New RV-7A owner trying to solve my fuel gauge issues and wondered if any of you have experienced any similar problems that might help shortcut my troubleshooting.

I emptied the left tank then filled it in 2-gallon increments. The gauge was very accurate up to 12 gallons but then it all went to heck. Above 12 gallons the gauge was pegged at full. I realize that wing dihedral, tank shape, etc. all factor in but for the sensor to report accurate values for just over 1/2 tank and then go immediately to full-scale does not make sense.

Any explanations and/or suggestions from the experts out there?

Thanks.
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RV-7A Bought (while I build the next one)
N92BF

[Rupester]

Pretty much all two seater RVs do that. The combination of tank shape, angle, dihedral, etc mean you can't even see gas in the tank until about 5 gal, and most of 'em have the float at it's max point at 12-14 gal. That's why having a fuel flo sensor and totalizer as a backup is so handy. My tanks both show full until there's less than 14gal in each... only then do the float sensors start to read accurately. Any overall consumption less than that and I use the flo totalizer.

[Greg Arehart]

Yep, what Terry said. Mine are pegged at 12 gallons.

Greg

[N941WR]

Do you have floats or capacitance senders?

I have capacitance senders in my -9 and they read all the way from full to empty. They are simply the most accurate fuel gauges I have ever had. Well, other than the float and wire in my '41 T-Craft.

[Brantel]

What kind of sensors do you have?

What are you using for indicators? EFIS or Steam or ???

Do you have any sort of converter between your sensors and the indicator?

[Rocketscntst]

I have float senders and Van's steam gauges, no converters that I know of. I measured a resistance between the sender terminal and airframe ground of 71 ohms at 12 gallons and 130 ohms at 5 gallons. I initially thought these values were low but the gauge did display the correct fuel level.

[GLPalinkas]

Originally Posted by Rocketscntst

I have float senders and Van's steam gauges, no converters that I know of. I measured a resistance between the sender terminal and airframe ground of 71 ohms at 12 gallons and 130 ohms at 5 gallons. I initially thought these values were low but the gauge did display the correct fuel level.

Just saw that you are new to VAF. Welcome to the good ship VAF John. I hope you learn here and provide us with learning as well, professor.

Added food for thought. I have the same setup. Van's senders are more accurate and reliable with a separate ground wire all the way to the ground tree (not airframe grounded). That seems to be the consensus. I find that to be true on my -6 and the accuracy is indeed in the lower end of the scale. I even ran the tanks dry in flight to see exactly how much run time I had when the needle hit the empty peg. (about 7-8 1/2 minutes depending on the tanks)

[RV10inOz]

Regardless of what the gauges say, my suggestion is you make sure you have an accurate fuel flow and fuel totalizer as either a separate instrument or part of your EMS.

Make sure you get the K factor correct and accurate.

Then one at a time (doing both at once will save time but may attract undue attention) run a tank dry in flight?..not on the ground. Come back and fill it up. Then you know your usable fuel per side. Remember do both.

Use the fuel totalizer for fuel management and the gauges as a backup or cross check of the fuel computer.

Last of all on a long flight where fuel range is is fully utilised, run one tank dry in the cruise and finish the flight on one that has ALL the remaining fuel in it.

Better looking at it than looking for it!

[humptybump]

Everything above.

On my RV-8 with float senders, they peg at about 15 gallons. There was no difference between the original Vans gauges and when I install an EFIS and did the incremental tank fill to calibrate the unit.

The very first upgrade I did when I bought my RV-8 was a fuel flow monitor. It was the best thing I did that first year. Getting the k-factor set is important. I gradually refined my setting over several tanks of fuel.

[Rocketscntst]

The airplane does have a seemingly very accurate fuel flow meter/totalizer which is very useful. However, the engineer in me has a hard time believing that the gauge system is designed to only be accurate when less than 2/3 full. It would seem that if you ever developed a fuel leak in flight having accurate gauges would be the only way to know how much fuel is left in the tanks.