Fuel tank design flaw?

[flyguy]

I keep noticing that people's main tanks develop a leak in the area of the outlet.
On my tank there is a short area of normal tank bottom thickness just forward of the reinforced area around the outlet, between the outlet and the front wall of the tank. That makes a weaker area between two "stiff" parts of the structure.

Seems to me that every time the fuel-shut-off valve is opened or closed it would flex that "thinner" part of the tank.

That is exactly where the leak (crack?) is in my tank.

I'm thinking that a load spreader/transfer plate that connects (at least) to the front seam of the tank might correct the problem.

People have been fixing this problem since the 40's and I just haven't got the message yet, right? Chuckle.

Darryl

[astjp2]

Re: Fuel tank design flaw?

Mine leaked there and the radiator shop soldered on a reinforcement and no problems since. Tim

[Guest]

Re: Fuel tank design flaw?

I keep noticing that people's main tanks develop a leak in the area of the outlet.
On my tank there is a short area of normal tank bottom thickness just forward of the reinforced area around the outlet, between the outlet and the front wall of the tank. That makes a weaker area between two "stiff" parts of the structure.

Seems to me that every time the fuel-shut-off valve is opened or closed it would flex that "thinner" part of the tank.

That is exactly here the leak (crack?) is in my tank.

I'm thinking that a load spreader/transfer plate that connects (at least) to the front seam of the tank might correct the problem.

People have been fixing this problem since the 40's and I just haven't got the message yet, right? Chuckle.

Darryl

Mine leaked at the weld seam along the bottom and forward of outlet.

I am not sure if it was due to corrosion or flexing.

I TIG welded it and it has been ok for many years now.

My tank is aluminum.

Dave

[Forrest Barber]

Re: Fuel tank design flaw?

Reinforcement is good. Remember my advise is to reach down there standing outside and turn the valve by hand supporting the valve at the same time. I realize that turning it off in flight will ahve to be done sometime but normal on and off could be done my way. Actually mine is left on all the time and checked each 50 hrs or so.

[Pearson]

Re: Fuel tank design flaw?

My tank has not been reinforced and hasn't leaked in the 11 years I have owned the plane. When I bought the plane, the valve was stuck in the open position. I had a very knowledgable mechanic disassemble the valve and clean it up. He sprayed WD40 everywhere and worked the handle of the valve many times. After he reassembled and reinstalled the valve, it opens and closes with very little resistance.

[RobertP]

Re: Fuel tank design flaw?

If you think those tanks are bad take a look at the F22 series 22 USG ones with the wires running through them and the clips which attach the fabric to them.

They are a nightmare to get out to repair necessitating wing removal and wing stripping etc.

Once mine came out it was like a sieve with at least six welds needed. Having just acquired two spare tanks one of which shows of similar leaks I would hazard a guess that most of these tanks leak at some stage! Obviously the Company never learnt from history.

[Guest]

Re: Fuel tank design flaw?

For the last 2-3 years I have been taking the valves apart at annual time and cleaning and lubricating with that fuel lube stuff.

I think that the biggest risk that I run is dropping small valve parts into the airframe so I layout a clean towel or rag under the valve to catch "dropsies".

From 1998 to 2007 I had a little steel bracket that I made screwed to the firewall and the valve body in order to take those stresses off of the tank when operating the vale. The only reason I did not put it back is because it takes two people to install it. I need a person to hold the nuts on the forward side of the firewall.

Dave

[Dick Huish]

Re: Fuel tank design flaw?

Hey Dave why not use rivnuts ? Dick

[Robert Lees]

Re: Fuel tank design flaw?

I would not consider it a design flaw. CG Taylor went for the minimum weight necessary to fulfil the design at a cost that would sell. (You have to remember there were a lot of competitors).

We know now, with 70+ years of hindsight, that we would design things differently.

Those of us with a little engineering, financial and legal ability (not necessarily in that order) make little "tweaks" to CG's original design that he would I'm sure have made if he'd had the benefit of the same hindsight that we enjoy.

So I "tweaked" my fuel tanks (all three of them) with little reinforcing patches where the threaded fittings are. This picture shows me painting my fuselage tank...and you can see the reinforcing areas around the main outlet.

[Guest]

Re: Fuel tank design flaw?

Hey Dave why not use rivnuts ? Dick

Hi Dick,

LOL

I never thought of that.

What's wrong with me!

Dave

[flyguy]

Re: Fuel tank design flaw?

Rob,
That is pretty much the way I thought it should be done.

Well, maybe design flaw is a little strong. Chuckle.

I was reasonably sure that I was not the first one to notice this problem.

I'm just going to fix the leak for now and take my licks if it fails again in the near future. Got other fish to fry.

DC

[senior]

Re: Fuel tank design flaw?

You guys couldn't have posted this thread BEFORE I assembled my plane last summer

[flyguy]

Re: Fuel tank design flaw?

Sorry about that, it was just a recent epiphany for me. LOL
DC

[lfries]

Re: Fuel tank design flaw?

Mine is re inforced. I thought that was standard.