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Fuel Level Anomoly (Read 408 times)
Apr 10th, 2017 at 7:49am

N71NS   Offline
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Flying back from Sun n Fun I had a couple of incidences where after topping off the tanks they both showed full after start. Then about 10 minutes into the flight the right fuel tank volume would slowly go to zero over about 5 minutes. Its not leaking. Then on descent or after landing the volume would start to increase again. It is a Vans RV-8 with the stock float sensors installed connected to the Dynon Skyview EMS by a single wire.

Does this behavior look like a short, open circuit with the wiring or a problem with the sensor?

What is the time 'filter' on the fuel tank volume display?
Any tips for troubleshooting?

Cheers

Nigel
 
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Reply #1 - Apr 10th, 2017 at 11:49am

Dynon Support   Offline
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Nigel,

If empty or full is high or low resistance matters which way the float is installed. The cool thing is you can figure this out from looking at your SkyView calibration. Go into HARDWARE CALIBRATION then EMS CAL then FUEL LEVEL CAL. In here, you can see what voltage equals what fuel level. So look at what voltage is 0 gallons.

SkyView "pulls up" the voltage and the float pulls it down. So if the 0 gallon voltage is lower than the 2 gallon voltage, then your sensor is reducing in resistance as fuel goes down, and vice versa. In the decreasing resistance mode, then a short to ground would represent zero. In the reverse case, an open wire would represent zero.

As for filters, SkyView supports 3 different "speeds" for fuel level senders. The standard one takes about 16 seconds to change 66%. So if you have 10 gallons, and suddenly go to zero, it will show 3 gallons after 16 seconds.

Don't forget to check your datalogs to see if they have any hints as to what is going on.
 

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Reply #2 - Apr 11th, 2017 at 8:21am

N71NS   Offline
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Thanks for the tip on checking the fuel calibration. Here is a couple of data grabs from Savvy Analysis which shows the sudden drop around top of climb and then an increase in the descent or on landing.

Do you think this looks like the float sensor going bad or the wiring to from the sensor to the EMS?

Cheers

Nigel
 

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Reply #3 - Apr 11th, 2017 at 11:13am

Dynon Support   Offline
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Nigel,
Since Savvy just shows gallons, we need to know the voltage direction to guess at what is going on. I can't tell if that's a grounding wire or an opening wire.
 

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Reply #4 - Apr 12th, 2017 at 7:27am

airguy   Offline
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The way the signal slopes with altitude and then reverses with altitude makes me think it a tank-related issue, perhaps temperature related as you climb into cooler air with the warmer fuel in the tank, or pressure related if the tank is not venting properly. Mechanical stresses induced by either one could be affecting a wire connection or ground connection.
 
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Reply #5 - Apr 12th, 2017 at 6:31pm

N71NS   Offline
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When I disconnect the wire from the tank sensor, i.e. open circuit the fuel quantity goes to zero over about 5 minutes. If I short the wire to ground it goes to full over about 5 minutes. So I figured it was likely a poor connection so I recrimped the ring terminal and made sure the fastening screw was nice and tight and it worked. Flew for an hour today and it is back to normal. Thanks for the help.
Cheers
Nigel
 
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