SonexBuilders.net

I bought the Sonex fuel probe for my B Model ('cause the Sonex web site stated that it fitted, no cutting required and is calibrated for a Sonex) but it needs to be shortened by about 4 inches.

The lower 2 inches of the probe appears to not "fill" with fuel and therefore does not measure quantity. Is this true?

The A model tank appears (from the instructions) to have a cup shaped collector into which the probe is bolted, so the probe attachment is below the main level of the fuel. The B Model is basically flat across the bottom, so in the B Model the fuel probe mounts flush with the bottom of the tank/fuel. If the above is true I need to mount the probe over an inch below the bottom of the tank to enable a zero reading from the probe to be zero fuel! I obviously need to know before I cut the probe.


Second question:
The front of my B Model tank is not square to the sides, about 1/2 inch out over the width of the tank. If I push the tank forward (instructions say sit in the seat and push with feet) the tank is pushed onto the shop head of a rivet on the left side of the firewall, not a good idea! Any ideas on how to simply stop the tank going too far forward?

Hi Duncan,

I figured I’d make some input specifically about the B-Model tank since that is the only one I have experience with thus far. To answer your first question I am not sure but having the probe a 1/2” above the bottom should give you a good reading. Remember these fuel level senders aren’t super accurate and shouldn’t be set in stone that zero is zero. I believe they are more of a suggestion on reserve time to plan accordingly and that’s how I use the tank gauges even when renting Cessnas. I wish I had more to add on how it will work but my experience with capacitance probes is limited to my buddy’s Onex and the one we replaced on his, we left a small gap between bottom of probe and bottom of tank.

Personally, I am not planning on using the capacitance probe. My fuel application will be using 93 octane 10% ethanol automotive gas so I can run full synthetic motor oil in my Aerovee Turbo. Capacitance probes from what I’ve read will be destroyed the moment you fill it with ethanol based fuels. My solution will be to use a float type probe installed from the top towards the rear of the tank. The probe and the sealant were bought from Vans (not installed yet). You can bend and cut the float arm to fit the Sonex application and it dry fits well. I will also have an inspection plate on glareshield so I can remove the probe if it’s damaged or needs replacing easily. Using this float sender with a fuel flow sensor will probably give you the best fuel readings but of course this is all speculation since my plane isn’t flying yet. Just an idea i thought I’d throw out there - these float senders have been used for decades since originally introduced in the 1930s so I hope it will work.

To answer your second question I too noticed my b model tank wasn’t exactly squared. I put insulation tape on the firewall where the tank sits against it. It will protect the tank from heat and acts as a cushion. Once the tank is in place and the rear support (near panel) is cleco’d in place, the tank is snug and fits excellent. I did not have to sit in the seat and push with my feet - seems excessive. The straps prevent the tank from moving back and forth and the insulation prevents chaffing against any rivets. Feel free to reach out to me if you have any other questions. I inserted links to the supplies I referenced above.

Tim

Universal Fuel Sender Installation Kit
https://www.speedwaymotors.com/Stewart- ... gIA9vD_BwE

Fuel Tank Level Sender (doesn’t matter left or right)
https://shop.vansaircraft.com/cgi-bin/s ... duct=f-385

Fuel Tank Sealer (1 ounce)
https://shop.vansaircraft.com/cgi-bin/s ... ct=proseal

Thermotec Insulation 12" X 24”
https://www.amazon.com/dp/B00029KC2K?ref=ppx_pop_mob_ap_share




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Tim,
Thanks for reply and the info. Although I have used float senders with no problems in the past, I decided to keep things simple and buy the Sonex probe, but it doesn't fit as advertised..not quite so simple. Plus, I have also read (after buying unfortunately) that ethanol fuel destroys the probe.
I think I'll change to a Vans float and mount it on the back of the tank. I decided to cut the glare shield behind the tank and make it removable so that I can get at the back of the instrument panel in the future. Hence this would enable me to get at the back of the tank as well.
Thanks for adding the links.
Duncan

According to Princeton neither water nor ethanol will damage the probe. Regarding water, it will not damage the probe, but because of the surface tension of water it is difficult to remove. Water in fuel is not enough to affect anything, it would have to be enough standing water in the tank to reach the probe. Regarding ethanol...here is the Princeton response:

Hi Gordon,

The ethanol does not hurt the probe at all.

It does effect the reading.

Compared to 100LL (the properties of 100LL never change) 15% ethanol would cause the tank to read full at 1/2 actual.

Its properties compared to 100LL are double. 10% would read full at maybe 3/4 of the tank.

This is with the probe calibrated with 100LL

Empty is always empty.

If you calibrate with 10% ethanol and always use the same fuel it will work just fine.

Todd

--
Todd Stehouwer
Princeton Electronics, Inc.

With respect to Princeton, my experience differs with regard to ethanol and water. I have seen several probes badly corroded internally from water and/or ethanol. My first probe lasted several years on 100LL, but died shortly after getting some ethanol car gas with a touch of water. I suggest you treat it carefully....

Jeff

Using ethanol fuel with a Princeton probe will require to you buy an new Princeton probe and stop using ethanol fuel. It will corrode quickly, and with a few tanks of MOGAS fuel. I've experienced this myself and watched it happen on another plane.
FYI, I also experimented with a fuel probe from Belite that measured the weight of the fuel. No joy and terrible support, don't go down that path. I have replaced my Princeton in my A-model and it works great, after I stopped using MoGas with ethanol. I am upgrading to the B-model and haven't installed it in that tank yet.

Thanks to all.
I'm convinced that an "old fashioned" float is the best compromise.
Duncan