Fuel Level Sight Tubes

December 2012

In order to keep up with the fuel levels in the tanks, I am using actual fuel level sight tubes.  I think these are m ore reliable than fuel gauges that require a float or capacitance sender in the tanks.

My sight tubes consist of a piece of clear polyurethane tube that is thick and stiff, with 90 degree elbows on each end and rubber hose connected to the fuel tanks.

Here is one of the 90 degree elbows:

The ends of the clear tube were threaded on the inside with a 1/8" pipe thread tap.  The threads on the elbow were coated in a little pipe thread lubricant and threaded into the clear tube.   A couple of 6" lengths of fuel resistant hose was pressed onto the other leg of each elbow.  Here is the assembly ready to go:

One thing that I have found when flying airplanes with sight tubes is that sometimes the fuel is hard to see.  I read about putting some diagonal stripes on the back side of the clear tube and the fuel level is easy to see. The liquid in the tube changes the pattern of the stripe and you get a real clear picture of the fuel level.  I found some tape on the internet that has black and white stripes on it:

Next I determined the exact location of the tubes comoing out of the fuel tanks in the wings.  I did this by tieing a string between the front and rear spars mount holes. I then measured from the string and from each spar to determine the location needed for the fuel sight tube hoses to come out.  This was then marked on the fuselage:

Using a soldering iron, holes were burned where the sight tube hoses penetrate the fuselage sides:
Make the holes slightly small for the hose for a tight fit.

Now we can slide the hoses through holes and the sight tube is mounted:
The first time I put fuel in the tanks, I will calibrate these in 5 gallon increments.

Here is the view from the outside:

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