Replace fuel tank in finished aircraft

[Murray Parr]

Has anyone had to remove/replace the fuel tank in a finished aircraft? What did you have to remove to get the tank out? I am hoping to not have to take the instrument panel out or anything else that doesn't have to be removed in order to replace the tank.

[sonex892.]

Been a long time since I put the tank in, but fairly sure it does fit between the spar box and a standard panel. If panel has been lowered from what is in the plans, you may need to remove it first? That is for an A model.

[sonex1374]

I just recently went through this on a flying legacy Sonex. The problem we faced was getting past all the stuff underneath the tank - engine control cables, electrical wires, etc. We decided to come out the top instead. This required removing the forward windscreen, drilling out the rivets holding the glare shield and panel, removing the glareshield, and lifting the tank out. The entire process took about 3 days - 1 to remove the old tank, 1 to install the new tank, and a final day to reinstall everything and get it flying again.

The new tank was prepped using oops fittings, and we ended up only installing the big fitting for the finger screen and omitting the other small fittings for the fuel probe and sight glass. If they're not installed, they can't leak! As others have mentioned, the o-rings on the oops fittings can sometimes roll around and deform while tightening the outer nut, so you'll need to take care to keep them straight and sealing. We ended up replacing the outer o-ring with a viton sealing ring (e.g. a rubber washer) of the same thickness and ID because we deformed the stock o-ring and damaged it slightly. A thin, large-diameter washer was added on top of the sealing ring to keep it from deforming as the nut was tightened.

None of the work was particularity difficult, but it's not a lot of fun and can test one's patience.

Jeff

[pfhoeycfi]

I just recently went through this on a flying legacy Sonex....We ended up replacing the outer o-ring with a viton sealing ring (e.g. a rubber washer) of the same thickness and ID because we deformed the stock o-ring and damaged it slightly. A thin, large-diameter washer was added on top of the sealing ring to keep it from deforming as the nut was tightened.

None of the work was particularity difficult, but it's not a lot of fun and can test one's patience.

Jeff

Was the replacement viton sealing ring flat ...or round like the original? Whats the difference between the viton sealing ring and ones supplied with the fitting? I damaged my original outer o-ring...bought more from sonex and the fitting spit those out as well upon tightening even when used with the recommended lube. I think those o-rings are the weak link in the entire system. I always wondered what the point of the outer o-ring is...its the inner one that needs to hold. I'll be ready to put fuel in my tank very soon and fixing that that outer ring is on my punchlist. Could you share your source & part # for the replacement rings?

By the way I am building a B and made the instrument panel removable anticipating the need to pull the tank at some point...dread.
peter

[Murray Parr]

Thanks for all your responses. I will try to get it out with the panel still in place. Not going to be much fun though. It's a shame I had all the firewall pass throughs completed and sealed, will have to remove some of that

[sonex1374]

Could you share your source & part # for the replacement rings?

The sealing washer I used is from McMaster-Carr, PN 93412A431(https://www.mcmaster.com/catalog/128/3556/). I used a larger dia washer to back it up (PN 92141A038 https://www.mcmaster.com/catalog/128/3534), and although this worked you might be able to find something thinner if you look around locally or enlarge the center hole yourself over stock sizes.

These same sealing washers in 1/2" ID also work for the smaller oops fittings.

Jeff

[pfhoeycfi]

Thanks for all your responses. I will try to get it out with the panel still in place. Not going to be much fun though. It's a shame I had all the firewall pass throughs completed and sealed, will have to remove some of that

Were you successful removing your tank? How did you do it? I cured my tank, put it in the aircraft and it sat for months with 2 gallons of fuel and loose straps and just this week buckled badly. Fit to be tied... I was prepping for inspection. I've always thought that the tank was the weak link in the entire airplane.
Peter (Sonex B)

[Murray Parr]

Thanks for all your responses. I will try to get it out with the panel still in place. Not going to be much fun though. It's a shame I had all the firewall pass throughs completed and sealed, will have to remove some of that

Were you successful removing your tank? How did you do it? I cured my tank, put it in the aircraft and it sat for months with 2 gallons of fuel and loose straps and just this week buckled badly. Fit to be tied... I was prepping for inspection. I've always thought that the tank was the weak link in the entire airplane.
Peter (Sonex B)

Peter,

I never bothered replacing it yet for the reason you gave above. My first tank ( the one that is still in there) was seasoned exactly as per the new instructions put out by Sonex however it still buckled badly and given the replacement tank they sent me is the same as the old one, I figured it is way too much work to replace and most likely it would end up buckled again just like yours did. Mine is twisted and buckled and looks ugly but the fuel pick up is still in the low spot, the fuel level probe is on a bit of an angle now and the tank expanded enough to bend the stop angle at the rear of the tank, but it is still airworthy as long as it doesn't get much worse. I still haven't put much fuel in it yet but first flight should be soon so I will have to keep an eye on everything and see if full fuel will change things or not. I am not sure why the B model is doing this and not the A models given the tank composition is the same, maybe the extra volume makes a difference. It would be good if they came out with a fix but until then I am not prepared to do all the work required to swap it out unless the outcome will be different.

[T41pilot]

I just noticed my tank has buckled worse than it was before even with the new straps fitted quite loosely. I've had varying amounts of fuel in it all summer. It would be a nightmare to get it out now that the plane is done. It is buckling inward and pulling away from the straps so the loose straps on the bottom have no effect. My guess is the tight fit on the sides and top is still to blame. I'm using it as is for now since it doesn't leak but it definitely looks bad. 20 gallon quantity is not accurate anymore. A new type of tank should be made with slightly smaller dimensions sides and top and or a different material should be used. It would be nice if Sonex could come up with a proper solution for this.

[pfhoeycfi]

Thanks for your responses. I sent an email to tech support as well...waiting to hear back. I'll have to look at everything carefully before I decide what to do. I agree that perhaps a smaller tank is needed.

Peter