Belite fuel level.

[fastj22]

Robbie,
I got a theory. The Belite gauge uses 0-5 volts to measure fuel level. While taxiing and when the engine is off, it reads fine. But when the alternator is energized (greater than ? RPM) it reads full? Is the EFIS picking up some noise and interpreting it as full?

I have the Belite. I fought the exact opposite. Taxiing and stopped, it read fine. But in flight it went to empty. I recently bought a Belite fuel display to disconnect it from my MGL EFIS. In my ultimate wisdom, I miss connected the power to the probe on the gauge and fried it. It now reads zero all the time. Why Belite used the same connector for the probe and the power escapes me. I will be sending it back to Belite for repair.

[achesos]

Robbie,

After reading the string I'm convinced that you are reading fuel level by using a pressure sensor that can't read level - only pressure. This device can of course be calibrated to display in gallons, but only due to the change in pressure on the face of the probe caused by the additional mass of the fuel (increased pressure). Works great until you add ram air into the cowl in flight (likely being driven to (slightly more) positive pressure, which then short circuits into your tank volume. In my opinion, the only solution is to add a second sensor in the tank that can read the pressure above the liquid level of the fuel. You then need to wire these together such that the combined electrical output is what is used to calibrate your display - this difference will be the change in fuel level, independent of airspeed or altitude... make sense?

[Bryan Cotton]

I had similar thoughts as Sean. Also the surface area of the liquid changes as the level goes down. So you have PSI as a function of airspeed and in^2 as a function of level. That seems tricky even if you are good at software.

[kevinh]

Robbie,

After reading the string I'm convinced that you are reading fuel level by using a pressure sensor that can't read level - only pressure. This device can of course be calibrated to display in gallons, but only due to the change in pressure on the face of the probe caused by the additional mass of the fuel (increased pressure). Works great until you add ram air into the cowl in flight (likely being driven to (slightly more) positive pressure, which then short circuits into your tank volume. In my opinion, the only solution is to add a second sensor in the tank that can read the pressure above the liquid level of the fuel. You then need to wire these together such that the combined electrical output is what is used to calibrate your display - this difference will be the change in fuel level, independent of airspeed or altitude... make sense?

See my post above about using a differential pressure sensor instead (only one sensor needed, but it sees both the top and bottom of tank pressures). A $15 part that outputs 0-5V as expected by the EFIS (more details).

[Sonex1517]

Robbie,

After reading the string I'm convinced that you are reading fuel level by using a pressure sensor that can't read level - only pressure. This device can of course be calibrated to display in gallons, but only due to the change in pressure on the face of the probe caused by the additional mass of the fuel (increased pressure). Works great until you add ram air into the cowl in flight (likely being driven to (slightly more) positive pressure, which then short circuits into your tank volume. In my opinion, the only solution is to add a second sensor in the tank that can read the pressure above the liquid level of the fuel. You then need to wire these together such that the combined electrical output is what is used to calibrate your display - this difference will be the change in fuel level, independent of airspeed or altitude... make sense?

Makes sense - thanks for all the posts everyone!

I am not thinking electrical interference simply because it was previously reading full then rapidly towards empty on a short flight.

At this point I will try a couple of other solutions before giving up. I like the simplicity of the installation and the gauge but not the results so far.


Robbie Culver
Sonex 1517
Chicagoland
Tails and Wings complete - finishing fuselage.
N1517S reserved

[Corby202]

can you say a little more about your fuel vent system? The way you describe it earlier

If I can ever remember to take pictures when the cowling is off it would make things easier. This might help.http://www.mykitlog.com/users/display_l ... 250&row=34
From the elbow at the front of the fuel filler, drip tray a 1/2" piece of copper pipe runs back towards the firewall, this then has another 1/2" elbow pointing down in which is connected a 1/2" piece of flexible hose which runs down to the bottom of the cowling.(now finishing just inside the cowling).
The top of the tank has a 90 deg elbow in the vent fitting, this then has a 1/4" copper pipe running out the side of the fuel filler and tee'd into the 1/2 flexible pipe close to the bottom of the fuel filler area. As an added precaution also in the flexible pipe again close to the area where the vent pipe tee's in I have a couple of 1/8" barbed fittings pushed into the flexible hose going no where. My Jabiru engine has a mechanical fuel pump which also has a pipe on the bottom of it that has to be vented, this also tee's into the 1/2" flexible hose.
I have the Jabiru supplied plenum chambers fitted and really must have just "fluked" it in getting static pressure in my cowling, perhaps also the fact that there are so many openings in my vent pipe helps. Also remember when I had the vent pipe out the bottom of the cowling there was enough suction being pulled on that pipe to upset the Belite and that was with all those other holes in the top of the vent pipe, so it shows just how sensitive that gauge is.
I have had a few more flights in the last couple of days (its a tough life but someone has to do it). The gauge reading works fine for me but remember it is only going to be correct flying straight and level and when the electronics have stabilized things so for instance if you are doing touch and go circuits the fuel gauge will read correctly late down wind. Take off it will read 5 or so litres to high, nose down it will read 5 or so litres too low. I do not know how this compares to the Princeton probe.

[sonex1374]

Here's my $30 system using a backup camera I got off ebay,

https://www.youtube.com/watch?v=pnXE_hS ... &index=144

Jeff

[kevinh]

Here's my $30 system using a backup camera I got off ebay,

https://www.youtube.com/watch?v=pnXE_hS ... &index=144

Jeff

I _love_ it Jeff and will approximately copy when I reach that point. ;)

[Bryan Cotton]

Jeff,
That is excellent!

[samiam]

Jeff that is an awesome system. Seems about as fool proof as you can get for fuel starvation prevention.

As an aside, I also think your panel/interior are outstanding.