Sonex Fuel Tank & Oops Fittings

[NWade]

Given the recent discussion around fuel-tanks & fittings, I thought I'd take a page from the Aerocarb/Aeroinjector poll and post this. I hope a lot of Sonex owners will vote, so that we get a better sense of how common this is (relative to how vocal people are about it).

Thanks for your participation!

--Noel
P.S. If you answer "Yes", it would be great if you could describe whether the fittings spun on initial build/installation; or if it was during some later maintenance you were performing. Also, what kind of tool(s) were you using on the fitting when it spun?

[gammaxy]

I'm still using the original fittings, but have only been flying for about 7 months.

I seriously considered upgrading to the oops fittings due to what I read online, but I ended up following Sonex's advice (my thought process was, "good enough for the factory, good enough for me").

I carefully followed the instructions about running a tap through the fittings to clean them out.

For some reason, I decided to loosely test fit an aluminum plug in one of the holes without teflon paste to see how deep it fit. It was impossible to remove! My hex key easily stripped it out, then I proceeded to completely destroy the plug trying all sorts of techniques to pull it out. I ended up drilling it out, which still left the threads stuck in the hole. I ended up tearing it out one thread at a time until it was completely removed. I totally expected this hole to leak, but I must have gotten lucky.

After adding fuel, two of the fittings had a slow leak, but both were solved by snugging them up another 1/8-1/4 turn.

[fastj22]

I was very careful initially installing. Everything was fine and leak free for a year. My fuel probe failed and I needed to replace it. I was very careful when trying to back out the probe but it required more torque than the fitting could take. I've personally seen three other tanks do the exact same thing. Another Sonex owner bought a finished plane. After one very cold winter, the fitting started leaking. It spun as he tried to remove it to clean. He thinks it might be due to age and temp changes loosening the plastic bond. It's a real problem.

[radfordc]

It's too bad that the fittings aren't made with a Hex shoulder that you could put a wrench on to prevent over torquing the fitting.

[wlarson861]

I flew several hours leak free until one flight i started smelling fuel. On the ground I found the fitting for the fuel line leaking. Mine did not spin but I think the weight and vibration of the shut off valve worked the fitting loose in the tank.

[bnvoss]

I guess I have lived a charmed life. I have been flying my Sonex #550 since 2006 and have never had a fuel tank fitting leak. And a couple of months ago I removed my fuel site gauge and installed I/8 NPT plugs on the tank. Again no leaks. I suppose the answer is to use sealant and tighten only enough to stop leakage.
Bob Sonex 550 Jab 2200 with 460 hours

[DCASonex]

My fittings did not spin, and were initially okay for first summer and fall of flying in 2012. Noticed slight but of avgas blue dye around fitting in late Fall of that year. Got worse over the Winter when stored in hangar that was kept heated to about 45°F By spring 2013, could see Avgas blue dye between OD of fitting and tank, and could see that being moved about when putting side pressure on fitting. replaced all lower fittings with oops fittings, but modified the fittings with grooves under nuts to retain the O rings as nuts tightened. Allso used smaller O ring on inside of smaller fittings. Supplied O rings on the smaller fittings were just too big for that, but right size for under the nut when grooved. At the time Sonex was purchasing these, and could not advise type of material in the supplied O rings. That may have changed by now.

It would not be at all difficult to install these types of fittings in a new tank made without the large raised areas if smooth inside, and think changing to that might be a very sensible approach at least for the lower fittings which seem to be the most troublesome.

David A.

[DCASonex]

Note to Sonex,

Time to make lemonade from lemons. Make your own quality fittings, with proper grooves for O rings, supply with know quality O rings, Anodize the fittings with your trademark bright red. Will make a very snazzy and professional looking installation. Make standard to eliminate "oops" from Sonex vocabulary.

David A.

[Bryan Cotton]

I am going to pre-emptively add the oops fittings. Do you replace all 4 small ones and the large one?

[fastj22]

I am going to pre-emptively add the oops fittings. Do you replace all 4 small ones and the large one?

Replace the ones that will be immersed and you may want to remove later. If you are just going to plug them and not use the sight gauge, that one can stay stock. The big one and the fuel probe one are the ones that fail.