Sonex Fuel Tank & Oops Fittings

[Corby202]

I recently fitted my tank. I had to bring the straps back 20mm for the same reason you describe.

[SonexN76ET]

I have had my tank holding fuel for the past three years with no leaks. I am not bragging, just letting you know. I also know of other Sonexes that have been flying for a few more years and also do not have leaks. I recently installed an oops fitting near the fuel filler neck so I could plumb a fuel return line when I install a Rotec TBI and a fuel pump. I am not impressed with the oops fittings (I would use them if I loosened a fitting but I would not use them otherwise - they are very lightweight alloy). That being said, I do not encourage you to preemptively drill out your regular fittings to install the oops fittings.

Some things you should know:

1. Teflon paste will allow 100 low lead to seep through your threads and this will stain the area around the fittings. EAA Sport Aviation mentioned this a few months ago and suggested using "Fuel Lube" instead. Aircraft Spruce sells this. Where I had seepage, I reinstalled my lines with the fuel lube and the seepage went away. Fuel Lube is the same stuff Sonex puts on the O ring in the AeroInjector.

2. Be very careful in not over torquing your fittings. With the fuel lube, you don't have to pry the fittings with gobs of torque to get a good seal.

3. Once your lines are hooked up, protect them from vibration and from exerting side loads on the tank fittings. Do not hang anything off the lines.

Now, I will need to knock on wood so I don't spring a leak after I post this.

Just my two cents...

Jake

[Waiex 49]

Hi Jake,

You bring up some very good points about the oops fittings.

Glad to hear your fittings don't leak or spin.

If you are careful they may never spin. Sometimes they just start to leak on their own.

I had to pull the tank to replace my fittings. It was a challenging job and I was in a hangar in warm weather with all my tools. I can't imagine having to do this out on the ramp in the cold.

We all make our choices. If I were building a new Sonex I would replace the fittings before installing the tank. Instead of using the oops fittings I would go with reducer fittings (bushings) screwed into the plastic.

I think it would be great if Sonex / Aero Conversions would produce some high quality fittings. I agree with you, the oops fittings are not very sturdy.

Fly safe,

Don

[kevinh]

We all make our choices. If I were building a new Sonex I would replace the fittings before installing the tank. Instead of using the oops fittings I would go with reducer fittings (bushings) screwed into the plastic.

Hi Don,

I haven't looked at a tank yet in person, but I'm trying to picture what you are saying here. Can you describe this approach a bit more fully (and how it ensures no leakage between the existing fitting and the plastic)? The idea sounds great - but I just don't fully understand it.

Kevin

[Waiex 49]

Hi Kevin,

I'm no expert. I'm not a degreed engineer. Take my opinions as just another point of view.

The oops fittings I installed seem to work pretty well, at least they have past leak testing. I will know more when I install the tank and make all the connections. As previously stated they are made of a light alloy and may not be as durable as if they were made out of a stronger material. At least they have flat surfaces machined into them so you can put a wrench on them when installing your plumbing fittings. The stock fittings don't have this and that is why they spin out.

If you were to look at the oops fitting instructions you will find that one uof the first steps is to drill out the old fitting. For the smaller (1/8" NPT) fittings you would be using a 9/16" drill. You can get at Lowes or Home Depot a brass "reducer" fitting that has 3/8"NPT male threads on the outside and 1/8" NPT female threads on the inside. This fitting can be screwed into the 9/16" hole that you drilled to take out the old fitting. The tapered NPT threads will screw into the plastic and give a good seal. I personally have not used the reducer fittings but others have. The oops fittings use an o-ring to make an effective seal and that requires that you carefully prepare the inner surface of the tank so that the inner o-ring can seat properly. I think it is much easier just to screw in a reducer fitting than to go through what I did with the oops fittings.

Having to take the fuel tank out to make these repairs was a big pain in the butt. In my opinion, it might be better to replace the fittings before you install the tank. On the other hand, many builders never have problems with the stock fittings. Mine never leaked, they spun out when I was trying to remove the plumbing fittings for the fuel quantity sight gauge (I updated to a Dynon system and didn't want a plastic tube running across my instrument panel). I am quite certain they would have leaked once I refilled the fuel tank.

Replacing the fittings is not such a big deal, whether you use the oops fittings or use reducer fittings. The major problem is getting access to the fittings. Working on your back under the fuel tank is not fun. I had to remove my tank to do the repairs, and that isn't much fun either.

If you are interested, I have some photos on my KitLogs page. Look on the right side of the page for the link titled "OOPS FITTINGS". www.mykitlog.com/donbowen

I hope this helps.

Don

[kevinh]

Thanks Don.

[radfordc]

I used the brass reducer fittings to repair my fuel tank. I used it for the small fittings and also for the large main fitting. I drilled out the aluminum fittings and then used the proper size NPT tap to tap threads in the plastic tank wall. The wall is thick enough to hold several threads. I then screwed the brass reducer into the tank until it was sealed very tight. Essentially, this is the same thing that the molded in fitting accomplish...that is a tight fit between the metal fitting and the plastic tank. The advantage of the threaded fittings is that you can get a very tight seal that won't leak over time. At least mine didn't.

[rizzz]

I used the brass reducer fittings to repair my fuel tank. I used it for the small fittings and also for the large main fitting. I drilled out the aluminum fittings and then used the proper size NPT tap to tap threads in the plastic tank wall. The wall is thick enough to hold several threads. I then screwed the brass reducer into the tank until it was sealed very tight. Essentially, this is the same thing that the molded in fitting accomplish...that is a tight fit between the metal fitting and the plastic tank. The advantage of the threaded fittings is that you can get a very tight seal that won't leak over time. At least mine didn't.

This sounds like the easiest fix so far.
Were you able to accomplish this with the tank installed?

[radfordc]

I did have to remove the tank to make repairs. If anyone thought that they might ever get a leak they would be well advised to replace all the factory fittings before installing the tank initially. I know this goes against the grain...but look at the results of the poll so far. More have reported leaks than have not. Granted the sample size is small.

[8pointroll]

I bought Sonex 1106 as a partial project and the tank was installed but none of the FWF was done (go figure). So I took the tank out to drill and rivet the FWF. Now I'm looking at a perfectly good tank--except its the older config without the screw on fill cap--Darn--and debating should I or shouldn't I. So I decide to replace the bottom three fittings now instead of having a big hassle later--I feel like Angelina Jolie doing a preemptive mastectomy only the mastectomy was an easier surgery to perform. I saw the boss for the vent by the fuel filler and said no way do I want to cut that puppy off and smooth the inside surface for the oops fittings--you need a proctologist's tools for that and patience I do not have so I decide to install the reducer fittings. Drilled out the little ones and boy those suckers were in there tight and I had a major oops because the side fitting is so close to the fuel screen fitting that my drill nicked the plastic on the boss right through to the aluminum tank fitting--I screamed all the words George Carlin said you can't say on TV--so you guys if you plan to drill out the tank fittings be very careful--very. Anyway, the fuel screen fitting was also in there unbelievably well--so good I'm sorry I spent 3 hours doing this. So i install the reducers from the HD aviation department and crank them in all the way. Then I plugged all the fittings and pressurized the tank to 4psi--it totally distorted--I planned to leave it overnight to see if it leaked but it distorted so bad I let it sit for only 3 hours and had no leak despite my almost $350 screw up with the large fitting boss. So I hope I'm going to be better off now that it's done and the reducers have a raised hex to put a wrench on when installing or removing anything so the reducers should stay in place. I agree that Sonex should design the tanks for the oops fittings from the start or else change the existing tank fittings so they have a raised hex that you can put a wrench on while you are tightening or removing the fittings that go into them--just my unsolicited 25 cents worth. Clear skies and tailwinds. Stuart