Fuel tank management with wet wings

[Captain]

I would value any comments from owners with wet wings re the following:

 

(1) There was a discussion here a few months ago about J160 owners using more fuel from one wing than the other when cross-country.

 

I found the same thing when I took a 160 up to Bundaberg.

 

What is the latest on controlling that, and have any mods been brought out to the fuel system of latest aircraft to address this?

 

(2) Are J200/400/230/430 experiencing the same thing?

 

(3) Do any 160/170 or 200/400/230/430 owners have experience with the pillar mounted tank shut-off valves (see pic below) and with using those valves for managing tanks alternately when on a long cross-country?

 

Regards Geoff

 

 

 

[Ross]

Hi Geoff

 

If those pillar valves were used to "control" the fuel flow the tanks are still connected via the so called breather pipe across the top which is also connected to the header tank and does not have any valves in it - anything could happen!

 

I personally think that breather pipe is part of the reason for the moving fuel.

 

There must be slight differences in the air pressure whether it be above or below the static air pressure in each fuel tank due to its own little breather in the filler caps.

 

So with a different air pressure in each tank fuel transfers from one side to the other via the tubing up the pillars.

 

But the long breather pipes in the tanks should equalise the pressures provided they are full of air. But they could be full of fuel or air or any combination in between.

 

So any restriction of equalising air flow in the breather pipe due to there being any fuel in it will result in a flow of fuel from one tank to the other via the tube down each pillar tp the Y piece in the centre of the cabin.

 

If the tanks are filled to the brim or the aircraft is flown out of balance the internal tank breather tubes will get some fuel in them thus producing some sort of fuel flow lock in the breather tubes as the inboard end of the connecting system where it goes across the cabin ceiling could have an air lock in it due to the dihedral angles of the wing.

 

Once the aircraft is parked on level ground and left the tanks would eventually equalise again as the air pressure on the fuel in each tank would be atmospheric pressure and equal.

 

So the only thing to move the fuel would be gravity due to the difference in height above the ground (assuming the aircraft is also level) of the fuel in each tank.

 

Well that is my theory.

 

Regards

 

 

[Guest Andys@coffs]

Geoff / Ross

 

In my 230 Ive found that the feed from both wings is equal providing the flight is co-ordinated. Any evidence of side slip at all tends to then mean that the individual levels will be different in the wings.

 

Given that my fuel gauges are the older fuel sight gauges I'm not sure if the difference is because the fuel amount is different wing to wing, or if the gauges are only showing that there is less fuel one wing to the other at the sight gauge. In otherwords the side forces mean that in one wing the fuel will tend to gather at the outboard end of the fuel tank, and on the other it will tend to gather at the gauge end.

 

In any event I'm sure I read somewhere that it isn't a real issue unless you travelling cross country and expect to be using fuel in the last quarter, in which case fully co-ordinated flight was recommended for the last 1/4.

 

Andy

 

 

[BigPete]

My experience with my J160c is never try to read the gauges while in flight. ;)

 

I ALWAYS check it on level ground and calculate how much fuel I need for the flight as well as possible detours/headwinds and 40 minutes reserve. ;)

 

Looking at the fuel gauge during flight will give you nothng but grief. I have cut short flights on occassion only to find that I did have enough fuel. I have since learnt to trust my ground calculations regarding fuel state. (I do work it out twice!) :;)3:

 

When I first got hold off my Jabiru, there was a time when I had uneven feed from the wing tanks. This disappeared after a few weeks and has not returned. I guess I "straightened up and flew right" :big_grin:

 

regards

 

 

[Guest brentc]

If you can help it Peter, you should probably not trust your fuel calculations based on the fuel you have when you left the ground. I did this once, only to find that because I was out of balance, I lost around 40 litres out the vent in one wing! Had I had a fuel flow meter fitted I would have run out of fuel. Had my aircraft had a header tank I would have run out of fuel for sure. The only reason I knew this happened is because it fed air into the engine at the t-piece.

 

Captain - I leave my tanks on 24x7 and start with full tanks and stop flying a bit less than 5 hours later. Uneven feeding has never been a problem (apart from when my rudder was out of adjustment), although I use the fuel pump when quantities are low because I don't have a header tank.

 

 

[Captain]

Thanks for your replies fellas.

 

I guess the ball just needs to be always in the middle, and a 4 - 5 hour real working fuel duration needs to be maintained, which is about a real working bladder duration anyway.

 

However it would be interesting to know whether the transfer happens via the fuel supply line (and via the header tank in my case) or via the breather line. With the breather going to within 5 mm of the top outer edge of each tank I suspect that it is manly via the supply lines when in (uncoordinated) flight, however if it is via the breather then maybe an (1mm) orifice in that line might help to restrict fuel flow but not airflow.

 

Has anyone ever kept a watch on their uncovered breather cross line to see how much fuel is in it under various flight conditions and tank levels?

 

Andy, Peter & Brent ... please also advise whether you blokes have the pillar mounted shut-off valves fitted and whether you ever use them.

 

Regards Geoff

 

 

[Guest Andys@coffs]

Geoff

 

Yes I have the pillar mounted shut off valves, They are only used for maintenance on the fuel lines (ie very rarely). I do not shut them off as part of the post flight process. Nor for that matter do I shut off the main fuel cock that feeds the engine from the header tank under the passengers seat. The main valve gets used when its time for a filter change.

 

Andy

 

 

[Guest brentc]

I have the valves next to the fuel pump at the centre console in front of the controls. Seems simple with the dual tap, however still quite complicated in the gascillator area with overflow pipes and the like.

 

 

[BigPete]

I'm the same as brentc - and like Andy, I never turn off the fuel.

 

regards

 

 

[Captain]

G'day Greg & thanks for that.

 

That is the type of experience I was hoping to elicit.

 

Based on that the pillar valves do assist fuel management & are of more use than just isolating the system.

 

Anyone else see something similar?

 

Regards Geoff

 

 

[Guest Andys@coffs]

My thoughts.

 

I know that being a male I don't cope with multiple things on the go at any one time. As such I could foresee a situation where having shut off a pillar valve for whatever reason, with an intent to open it up later on, something happened, perhaps in interesting radio call, or something that took my mind off that particular job with the outcome that I simply forgot to open it again.

 

Greg, if you don't touch the valve and continue to fly does the level continue to drop below the 1/4. IN other words if you left it all alone would something bad actually happen?

 

Andy

 

 

[Alpi]

Hi Andy

 

The answer to your question is yes it does continue to drop if you leave the fuel cock open "but only till its empty" sorry bout that, but it's only indication, it's not actual fuel in the tank. So if it indicates empty and the other tank indicates half full try closing the empty tank cock for a few minutes then reopen it. Checking tanks for me is just part of flying and a good habit to get into in any aircraft. Managing fuel before, during and after flight has always been a priority for me, fuel mismanegement features high on the list of causes of accidents so I understand your concern.

 

Regards

 

Greg