Belite Fuel Probe

Has anyone tested or installed them in his airplane?

http://www.beliteaircraftstore.com/liquid-level-fuel-probe-with-1-4-probe/

They measure the pressure of the fuel which could lead to an accurate measuring at higher levels.

It does look interesting. Worst thing in an RV is that the tanks are so 'flat' compared to typical fuselage header tanks in UL type a/c. That's a pressure sensor, and all it will see is vertical 'head' pressure (plus pitot pressure from the fuel vent, in flight).

Charlie

I looked at these while visitign BeLite last year, and they are indeed quite promising and fascinating. The accuracy and precision are outstanding. At th time, they only worked with Jame's panel gauge, but I encouraged him to make teh electronics generic so that they coudl feed an EFIS. The do solve the issues with diehdral and the shallow tanks (if properly calibrated).

The output is 0-5 volts which should easily work with most of the available efis systems.

The problem with the Belite is that it measures gage pressure, which is pressure relative to ambient pressure. If you have a typical fuel tank vent which is pointed into the airstream, your tank is actually pressurized. The pressures we are trying to measure for fuel quantity are quite small and this pressurization will cause large errors.

I know this because I originally tried a gage pressure sensor and could not get it to work.

I made my own system using a differential pressure sensor so I measure the difference in pressure between the top of the tank and the bottom. I used a Freescale sensor which outputs 0-5 volts which I feed directly into my GRT EIS. It works well.

You could accomplish the same thing by using two Belite probes, one at the top of the tank and one at the bottom. The pressure difference of the two would be fuel quantity.

Jim Butcher

Jim,

Cool! Do you happen to have the part number on the Freescale sensor you used? I might wire up something similar...

Jim, thanks for sharing this helpful information with us!

The part number I use is MPXV4006DP

I've had no problem with gasoline attacking the seal. I did make sure to have a loop in the tubing so the sensor actually is seeing air not gasoline directly.

I'm pretty sure I got them at Digikey but they seem to be available at all the distributors. About $15 as I recall.

Jim Butcher

Hi Jim,

The Freescale device certainly looks great. from your description, it looks like the pressure taps could be in the fuel supply from the tank (basically at the same level as the bottom of the tank) and anywhere in the fuel vent line, right?

Were you able to directly connect the Freescale to the fuel level inputs in the GRT, replacing the 'standard' SW float sensors, or did you use one of the aux inputs?

I suspect that I'm not the only one here that would like to see pics of your installation, the electrical hookup, and what you had to do to calibrate the system.

I considered and discarded the idea of capacitive sensors due to the variability of readings with avgas, mogas, mogas with ethanol, etc. If actual fuel weight doesn't vary enough with type to really affect readings, a solid state sensor like that sounds really good to me.

If you'd prefer to take it off list, PM me for my email address, or if you don't mind discussing by phone, your phone # & the best time to call.

Thanks,

Charlie

Charlie,

I'm sorry I don't have any photos. The sensors are buried in my Europa.

The pressure is quite small. 1 psi is a 38.5" column of gasoline. The tank in my Europa is 15" tall, so empty to full is about .4 psi.

Basically, I mounted the sensors on a small piece of PC board. That allowed me to connect the wires and gave a convenient way to mount the sensor as close to the bottom of the tank as I could. The sensor will measure the column of gasoline above the sensor, so the sensor needs to be as close the bottom of the tank as possible.

You could certainly solder wires directly to the legs of the sensors and cover them with heat shrink. Mount the sensor with a dab of silicon RTV. The ports are small diameter. I used yellow Tygon tubing and adapters to get them to larger diameter tubing. Be sure to allow a loop in the tubing to keep gasoline from the sensor.

There are only three wires - +5, gnd and signal. I have GRT Sport EFIS so I have to use my EIS as an interface. I took the +5 from the EIS's regulated source. Long ago I figured out the scheme behind Offset and Scale Factor and used that to devise them for the sensor. But you can do the same thing by following the instructions for fuel quantity calibration on the GRT website. The Freescale sensor will act just like a resistive sensor fed a voltage. It's output will vary from 0 to 5 volts, depending on the pressure.

If you have GRT Horizon, you can just follow the instructions for that on the GRT website. I'm pretty certain there is a regulated +5 output available on the Horizon.

You can telephone me at 269-375-5923, ET. I'm retired so available most of the time.

Jim Butcher

Hi Jim,

I looked at that sensor and it just has a barb fitting. How did you attach the fuel hoses secure enough that you and you DAR could sleep at night?

Scott,

The barb is quite small. I am using Tygon 4040 fuel hose and I replace it every 5 years. I also secure it with a tie wrap around the hose and barb. Also the hose is supported on it's way to the sensor.

Jim

Ok thanks!

Is there a way to counter the effect of g-loading, or do you just ignore the fuel gauge when you aren't at 1g?

I installed one of these on my mustang not too long ago. Works great when sitting on the ramp, with the engine off. It's very sensitive to ram air pressure so does not work so well if your vents are facing forward. On my plane, I tried adjusting the vents so little to no ram air and I quickly found out I don't like it when it gets quiet in the cockpit, when flying. It is nice to always have a full tank though. With my vents facing forward, I always have a full tank. I will be switching back to capacitance probes.