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I would appreciate hearing the Pro's and Con's from those of you who have used a Sight gage in your Sonex aircraft. Despite the problem caused by having another fuel line in the cockpit, it does alleviate the problem with using different fuels with a calibrated gauge. I think I read where some of you have gone with fuel level markings on the rear of the tank. All comments are welcome. Thanks.

Onex107 wrote:I would appreciate hearing the Pro's and Con's from those of you who have used a Sight gauge in your Sonex aircraft. Despite the problem caused by having another fuel line in the cockpit, it does alleviate the problem with using different fuels with a calibrated gauge. I think I read where some of you have gone with fuel level markings on the rear of the tank. All comments are welcome. Thanks.

I used a sight fuel gauge on my XENOS but not my OneX. I wish I HAD installed one in the OneX. The resistance fuel probes work just fine, until they don't. Replacing a FULL length probe in the OneX tank is impossible without removing the tank. (It is possible in the Sonex, Waiex, XENOS, but not fun).

Of course using a sight gauge allows you to use any fuel you'd like. I'll only use 100LL so I've never had any problems with the calibration being off.

I've marked the exterior of my tank with remaining fuel levels, BUT it's almost impossible to see the marks from an upright sitting position, and with the OneX you can only lean over so far to get a good look.

So, if you're still in the planning stages for your tank install I'd highly recommend the sight tube. Just my two cents.

I had an adversion to running a sight gauge in the cockpit and went with a camera. I have not found the perfect lighting configuration to make it reliability easy to read in flight, so in that respect the sight gauge is better.
https://youtube.com/shorts/rAUjAJ73rN0?feature=share

Edit: the YouTube tags don't work with YouTube shorts.

I installed a backup camera with an led light pointed at the tank. View screen mounted to the side and imarked the tank with measured amounts. Works well and doesn’t have to be calibrated

The problem with the sight gauge as it's shown on the Sonex plans is that it only shows the contents in a little more than the top half of the tank. I extended mine a bit further down than shown on the plans but it still doesn't show the bottom third of the tank. Even if you just want to do a couple of circuits late in the day and you know there is plenty of fuel for that, there's nothing better for sapping your confidence than seeing a fuel gauge that shows "empty". If you install a sight gauge make sure that it indicates the whole tank.

Peter

Peter,
I did just that- used the right front upright of the wing spar box in the fuselage and secured the sight tube so far down that it would indicate the tank from full to dry.

IMHO it is not such a terrific idea- the issue is that you can make the gauge show anything by just the variation of the aoa. So I put in an inclination ball and calibrated the tube with the top fuselage longeron in the horisontal. The sight gauge is now only accurate with the fuselage in this attitude. It is still not such a hot idea because it takes the fuel almost forever to migrate through the tubing and make the fuel level in the tube to settle in the new position.

Now, three years after this rebuild, the sight gauge is still all I have. On every flight I am kicking myself (no mean feat in the Legacy!) because I did not bite the bullet back when I built the thing and installed an electrical marine style float type sender in the tank.

Sigh!

I love having a sight gauge. I have it calibrated in RED for 3-point (on the ground) calibration, and in BLUE for level flight. My sight tube disappears through the bottom of the panel, and is at a bit less than 5 gal when the liquid is no longer visible. The fuel tank has blue Sharpie lines on it for 1, 2 and 3 gallons if I want to look under the panel, but I generally make sure I'm getting fuel within 30 minutes if the fuel gets down to the 5 gallon mark (as a tail dragger, I can fit 17 gallons in the tank).

https://www.youtube.com/watch?v=Lbgek8-X14o
- At 7:15 for the sight gauge

Mike,

I watched you video- nice work! I especially liked the way you constructed access to components and wiring behind the instrument panel: this is often sorely neglected in a lot of amateur build small planes during construction.

At what attitude did you calibrate your fuel tank sight glass?

With the plane in the 3-point attitude it is fairly straight forward, but what about flight? Top fuselage longeron in the horizontal? Or?

Thx

I calibrated for flight with the longeron level.

Yup- so did I.

However, 3 years of operation with this setup has left me with the distinct feeling that this is a slight climb mode (positive aoa) for the airfoil, causing a higer fuel level in the sight gauge than strictly available. As yet, I have not decided if this is an issue that should be dealt with.