Fuel tank vent routing

[Eckenroth]

I am building Onex 0052. Getting close to the finish but find I am hung up on the routing for the fuel tank vent. I would like to see how other builders have handled this in a safe manner.

Paul

[Onex107]

My Onex has the oil cooler mounted on top and I couldn't bend the alum vent line around the cooler without kinking it. So, I rotated the vent opening so it exited towards the starboard side and ran the alum tubing vent back to the firewall on that side, in a nice curve, to a elbow on the firewall and a plastic line to the bottom exit. I also made an oil separator that the plastic line feeds into that I empty every 25 hours. It catches about 6-8 ounces in 25 hours. I still have oil on the belly but not as much. My engine doesn't leak, it sweats oil.

[Onex107]

The oil separator works well, doesn't drain back into the engine, as per Mike Bush.

[Gordon]

Fuel Tank Vent Routing Question.......?

I think some of the posts offered are talking about the crankcase vent which is fine.

However I think you asked about the "fuel tank" vent line. I used a 1/4" soft aluminum tube and run it straight down the left side from the filler neck location and went down through the glareshield right beside the top longeron. From there I went down and a bit forward and exited the belly skin as far forward and outboard (to the left) as I could. That keeps any "slobbering" of fuel as far from the hot exhaust as possible. Many of the Onex's I have seen run it down between the 2 exhaust pipes and I think that is risky at best. As I recall, I think that is where the plans route the exiting line...........that is WRONG........in my opinion.

If you fill the fuel tank with cold fuel and then the airplane sits in the hot sun for a half hour before you fire it up, the expansion will sometimes cause the fuel to gurgle out of the vent pipe. I have had this happen with my RV-6 numerous times. Should you happen to start the engine just at the right time, you could have a fire.

I used a nylon snap-in bushing to run the tubing through the belly skin........the tube protrudes about 1 1/4" below the belly and is angle cut on the rear side of the tube.

The crankcase vent tube on the other hand (which is much larger) only carries oil vapours and is fine to exit between the exhaust. It is not a fire hazard.

Gordon.....Onex......Hummel 2400

[onex28]

Hi Gordon, we met and talked at Oshkosh 2017. Good to see you are making progress on your build. I have always been instructed to cut the 45 degree angle on the fuel tank vent line so that it faces into the airstream. I interpret your post that your vent tube angle is reversed. Am I missing something about your fuel system?

David
N351D
N951X

[Gordon]

Fuel Vent Tube Exit Cut........

David.......you are correct.......I guess I had a "senior moment" when I typed out that post. Mine has the forward angle cut as you describe to provide a little pressure.....the crankcase vent tube has the rear ward facing cut to provide a bit of suction.

Thanks for catching that mistake.

Gordon.....Onex....Hummel 2400

[Eckenroth]

Gordon

Thanks for the reply. I have made my situation more complex by building the area above the tank to be removable and therefore the vent line above the glare shield must also be removable. Deviate from the plans and life gets complicated.

Paul

[onex28]

Hi Paul, my Onex fuel vent is above a removable glareshield also. I attached the AL vent line to the tank fitting with a 2 inch piece of vinyl tubing and routed the vent line to the left side through a protected hole and down the front of the FW. Easy install and removal, 5 min.

David
N351D
N951X

[Gordon]

Fuel Tank Vent..................?

Paul.......I also made my glareshield removable (a must do mod for sure) like you and David although I used an AN-4 fitting at the tank. Another mod I did was split the glareshield so the rear piece (about 7") is removable with out disturbing the fuel tank in case I need to get behind the panel for some reason. If you email me I could send you some pictures of this modification. gdbaxter78@gmail.com

Routing the soft 1/4" vent tube down through the glareshield and down through the left front corner of the floor was not difficult and is easily removed if needed. Make sure you protect the tube with some clear plastic hose where it passes through the glareshield at an acute angle.

David.....yes I remember talking to you (and Tom Jones as well) at Oshkosh. Hope your Onex is living up to your expectations.

Gordon......Onex......Hummel 2400

[Arnieb]

I bought a Sonex that was completed but wasn't flying. I have 7 hours in the air with it, there has been a few problems that I was able to straighten out. The latest is the engine started running ruff when I was in the air so I thought I better get back on the ground. When I was coming in for the landing fuel started coming out of the fuel vent, I am wondering if the way the builder had placed the vent was correct if not is that why I built pressure in the tank. He has the vent facing forward just above the fuel door.