Fuel sight glass

[Madhatter]

A number of years ago I checked to see what FD recommended for sight tube material and if I remember correctly it was Tygon C-210A which is clear. So for a number of years that's what I have been using which stays soft. Recently I noticed a small leak coming from the upper part of the tube when fuel is sloshing. It turned out to be a small split at the bead. In researching the manufacturers data I learned that they just extended the Tygon "shelf life" from one year to 2 years. Why was this tubing ever used? I guess I will have to back to Ace hardware junk again. I have been looking at a better design for a while but need to find a used sight guage end plate. There has to be a better design. 

[Anticept]

Glass tube is probably the only long term solution

[Madhatter]

23 minutes ago, Anticept said:

Glass tube is probably the only long term solution

That's what I'm looking at ( unbreakable glass) and easily cleanable 

 

[Roger Lee]

Ace Aviation poly tubing has worked just fine since 2003.

[Mike Koerner]

With respect to the glass sight tube concept:

I took some ½” 0D, 3/8” ID borosilicate glass tubing, cut it to length and used an oxy-acetylene torch to fuse the ends and create a slight bead at each end to prevent a hose from sliding off. I continued fusing one of the ends (the lower end) until I had created a small orifice (perhaps 1/32” diameter). I then added right angle bends to the glass tubes near each end.

I pulled the wings, removed the old, yellowed poly sight tubing, attached short nibbles of 3/8” rubber fuel hose to each of the sight glass ports, attached my glass tubes with standard hose clamps and re-installed the wings.

I then calibrated the fuel level in each tube by added fuel to both wings in 1 gallon increments. I also added indicator cards to make the levels easily readable.

If this sounds trivial, I’ve misled you. It took me weeks and lots of glass to figure out how to cut the tubing, fuse the ends, create an orifice, bend it at the right length and even install it. In fact, even at the end it took me several tries to get a good tube.

These sight glasses fit entirely within the circle of the fuel access plates on the wing roots. The wings can be removed and installed with them in place. They are protected from damage once installed in that they sit outboard of the cockpit opening, not within the cockpit itself.

Advantages are:

1)      The fuel levels can be more easily seen

2)      The fuel levels can be read in turbulence

3)      The fuel levels can be monitored all the way to the bottom port

4)      Having the glass at right angles to the fuel level makes more accurate readings possible

5)      I do not expect they will require periodic replacement

 Early version without orifice or bead

 On wing root

 

 Installed

[Roger Lee]

Hi Mike,

if you’re still SLSA this makes you legally un-airworthy. If you are SLSA you can’t go ELSA unless you put it back to stock configuration for the DAR inspection. 

[Madhatter]

While I applaud your attempt to make things better the borosilicate is immune from large thermal expansion but is still breakable. Most sight guages of this type are encased in a metal shroud such as Dakota Cub's stc version for the super cub. I guess I would be concerned with the very tight 90 degree bends causing a stress rise in the otherwise round tube possibly making a fracture more possible. Also does the acetalene torch change the nature of the glass. The answers are not always easy and making modifications on aircraft  usually takes many attempts.  About 75% of my attempted mods are failures for practicality and 10 to 15 percent are very successful. If it was easy and cheap we would all be flying at Mach 2 on 5 gal per hour. Never give up if the change is worthwhile but be very careful.

[Mike Koerner]

Thanks guys. I appreciate your comments.

[Madhatter]

If anyone is using C-210A, remove it. I removed mine today and it literally started falling apart. I did a lot of research on C-210A years ago and was impressed with the manufacturers data, good with ethanol and gasoline,  remains soft and clear. It did for several years. I used more of what I had 6 months ago and today it's falling apart. A lot of people are using it in the experimental world. After a few years on the shelf it will not hold up. I even stored mine sealed and refrigerated. I only found out about the short shelf life a few weeks ago when a statement was put out that the shelf life is increased from one year to two. Even with the Tygon F4040A it is recommended to use it as close to the manufacturing date as possible. I can't confirm the C-210A recommendations years ago was directly from FD that I recall. They are still using F4040A. Polyurethane seems to be good per Roger and the manufacturers data seems to agree. Do not use vinyl tubing or polycarbonate tubes. Tygon F4040A is what is approved but it's hard to see the fuel. 

[Tom Baker]

The C-210A is what Flight Design had been supplying for several years. I have always replaced it at two year intervals, and never had any issues. Has something changed?

[Madhatter]

28 minutes ago, Tom Baker said:

The C-210A is what Flight Design had been supplying for several years. I have always replaced it at two year intervals, and never had any issues. Has something changed?

If you get C-210A that is over the shelf life limit you will have the same issue I had, storage conditions are also a factor. I don't know if the date of manufacture is printed on the tubing, mine is not readable. If they recently raised the shelf life from 1 year to 2 years that tells me they have had a problem in the product chemical stability. It's not worth the chance of failure. I am currently trying to develop a way to change the tubes without pulling the wings. It is a difficult problem due to the design of the end plate.

[Madhatter]

I was able to determine that the manufacturing date is not printed on the Tygon C-210A. If you buy it you will not be able to tell how old it is. It is unfortunate because it worked very well when new. 

I found some very small remnants of the hose material in the fuel tank and a lot of disintegrated material inside the hose. I will not be using this again. The hose was on the verge of total failure.

Talked to Airtime yesterday and was told they recently found 2 aircraft using hardware store tubing which had failed. I don't know any particulars such as age or tubing type. 

Most certified aircraft (PA 18 Atlee Dodge STC)are using restrictors in the tubes for fuel level stability and slower spillage in case of failure. I guess you just burn slower.

The only FD official recommendation I know of is Tygon F4040A which is also used in certified aircraft but will have less visibility using auto gas.

[Tom Baker]

The Versalon C-210A that I bought came with the lot number and manufacture date in the package. I just changed a set this morning, and the old ones (two years old) other than being discolored were still very flexible, and showed no signs of deterioration. 

[Madhatter]

My stock was 4 years old when put on , no date on package and no indication of any deterioration. Still looks and feels new, wouldn't know the difference from new.  There was obviously an issue if it was originally restricted to 1 year shelf life and now 2 years.