SonexBuilders.net

Hey guys. I've been working on my panel and wanted to know what the deal is with the sight tube. I'm not a fan. It seems hard to read and I can't imagine it's all that accurate. I have an Enigma that probably has provisions for some sort of fuel probe but I've never trusted fuel gauges. Can I eliminate it (sight tube) and just mark the tank?

Pros? Cons? Ideas?

I have a capacitive probe on my Enigma that seems to work pretty well.

I also marked the tank and check it before and after each flight. I can see the last few gallons during flight if I lean over a little. I wonder if it would be possible to read the fuel level in the mid-range using a small mirror?

Why don't you think it's accurate? The plans show creating a small orifice to prevent fuel from sloshing too much in the tube. I would think once you did that it would be at least as accurate as eyeballing the tank and much more convenient.

If I were to build another Sonex, there's a good chance I'd consider installing a sight gauge as long as I could run the tube low enough to see the last few gallons.

gammaxy wrote:Why you don't think it's accurate?

Well, the way mine is set up, the sight tube is only good until there are 6 gallons left in the tank. That's the point at which the fuel gets too low to read. I was always trained to never trust a fuel gauge and I've always relied more on a timer and fuel burn. I can see the sight tube being useful as a backup of sorts in case there is some fuel leak. But, other than that, I don't think it's needed if I can actually put eyes on the tank itself. And then there's also the fact that the tube is making two passes though the panel wiring just to give me that sight picture.

I am considering making a fuel level sight tube. I have seen some neat, enclosed examples on line. The EAA Sweepstakes Piper Cub has a neat looking sight tube that I might use as a model. You can see a picture in this month's EAA Sport Aviation. Mine would be covered by an aluminum tube and have a cut out on one side to see the fuel level in the tube and a restrictor to prevent sloshing. I just am not comfortable with the Belite Fuel Level gauge and Princeton fuel level probe that I have. I am getting erratic readings. Plus, I am getting some seepage from the bottom of the Princeton fuel probe that I do not like. I time my flights and look underneath the panel to verify fuel level, but it would be nice to have an accurate sight tube. I plan on always landing with at least 4 gallons in the tank.

Thanks,

Jake

The way the tank is setup the sight tube needs to run down in front of the panel if you want to be able to see the last 5 gals or so. Not ideal, but in my case necessary as I was never able to get the probe and EIS to read accurately and consistently. I wrapped colored tape around the tube at the 4, 8, and 12 gal. marks to get a good idea of how much fuel was remaining.

Since this was started with the question of doing a sight tube or not I thought I would offer an opinion. I do not use a sight tube. I found that the Princeton fuel probe is unreliable and keeps falling out of calibration. Plus different fuels equal different reading. I have been flying with a fuel flow meter and the virtual tank setting on my Xtreme and consistently find the accuracy remarkable. It consistently reads within a half gallon of what I put back in the tank. No need to worry what type of fuel used. No extra fuel lines to worry about either.

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I have a Flight Data Systems F C 10 that uses the FT 60 and gives fuel flow very accurately down to the tenth of a gallon. And gallons remaining etc.

It is a stand alone unit and does not work with glass panels but it is very much worth the money. I removed the fuel probe that worked with my EIS and thru it into the garbage can.

Just for info for anyone that wants an accurate fuel gauge

No K factors to set..




Tony Lewis

N447XL

Jab 3300

I would be OK with the site tube if it registered three or four gallons. Then it would serve some panic button type purpose. To be honest though, I just don't see the point if the lowest it will register in my plane is 6. That's closer to 1/2 a tank than empty.

vwglenn wrote:I would be OK with the site tube if it registered three or four gallons. Then it would serve some panic button type purpose. To be honest though, I just don't see the point if the lowest it will register in my plane is 6. That's closer to 1/2 a tank than empty.

Thats what I realized when I had installed the as plans sight tube and started flying. I removed it simply because it provided no benefit and increased failure modes. Down the front hanging below the panel might work better, or just ducking your head under the panel to see the tank would work as well.
I use an FT60 flow transducer and my MGL xTreme fuel totalizer with great results. (However the first one lasted only 100 hours) The Princeton probe died after I used MoGas. The Belite fuel level transducer is incompatible with the MGL. I also use a timer as a backup. And a calibrated dip stick during pre-flight.