Fuel wing tank problem

[jetjr]

Have J200, wing tanks, same setup as J230 excepting plumbing to header tank now located behind curtain.

 

Feed and breather run up centre and breather goes up to RHS, feed tee is in middle below/behind seats

 

Has visual guages.

 

Had tanks resloshed last year, moved header tank from under PAX seat added elect senders at the same time.

 

The problem is with even small out of balance, take off being one time, fuel appears to push away from BOTH senders and remain so. Ie its a real situation not just a reading error, triggers alarm in efis, and both senders show no fuel in that tank

 

Seems to flow back slowly but even big Attitude/steep turns wont force it to happen any faster

 

Dissappears too fast to be transferring anywhere in the system

 

As tanks drop it seems to correct, even happens with near full tanks

 

Are there baffles in these tanks? Could drain or vent holes be plugged with sloshing materials?

 

Why could fuel be trapped in outer section?

 

Im up for any ideas

 

 

[jetjr]

Come on......anyone have ideas?

 

 

[Bruce Tuncks]

Sorry you have drawn a blank there jetjr. And I have owned a J230 for 2 days and can't help, in fact I don't know how the system works at all.

Do you need to worry about one wing tank going dry and air being sucked into the engine instead of fuel, while there is still fuel in the other wing tank?

Maybe when I understand the setup, I will be able to make a helpful comment on your problem, but my guess is that you have solved it yourself in the last 7 years.

[facthunter]

Fly more balanced. (ball in centre).   The "head " of fuel in the other "SHOULD" ensure continuity of supply in a gravity assisted system. I'd run a flow rate check on it with single tanks selected. It's a general rule to takeoff and land with fuel available from both tanks. You should know the innermost workings of your fuel system. Long shallow tanks are hard to determine fuel quantity. Nev

[IBob]

Okay, I'll ask the stupid question:
What sort of sender? And if float, are you sure the senders aren't upside down???

[facthunter]

was that for me? Nev

[IBob]

Nope, it's for the jetjr.......

[Bruce Tuncks]

I am now of the opinion that if you have a header tank then there is no need for valves to the wing tanks. The header tank will be pressurised to about a metre of fuel head by being connected to the wing tank. There is no way that air could go from a wing tank through the header tank to the engine as long as there is fuel in the other wing tank. Please comment if I am wrong on this.

 

[facthunter]

Should be alright but you may get uneven. As a principle I Iike BOTH selected for T/o and for landing and arrange for a bit to be in both for landing. If you forget and run it dry, I wouldn't select both. I can't see any point in having a dry tank selected. Nev

[IBob]

Hi Bruce.

So far  as I know, Savannahs with the standard 2 wing tanks normally have no valves from the wing tanks.

These feed down into a 6L header tank behind the passenger seat.

The header tank is fitted with a float switch at the top, which brings on a low fuel indicator at the dash: provided this is working (more on that later) it gives approx 20mins of low fuel indication.

This arrangement does occasionally get a small amount of air in the header tank, giving false low fuel warnings. More recent builds now have a breather from the header tank back up to a high point in a wing tank to deal with this.

Aside from that, it works very well.

..................................................................................................................................................................................

The only shortcoming I see with this system is that there is no way to test the header float switch without fully draining the wing tanks. (There is a test button on the panel, but this only tests the indicator, not the switch.)

I have a 4 tank setup with individual tank valves and a header breather: I can readily test the low fuel indication by valving off all tanks. I do need to know it is working if I intend flying my outer tanks to exhaustion.

...................................................................................................................................................................................

As an aside, I also think some care needs to be taken with the wing tank breathers. In a perfect world, these tanks would be cross vented, and so sharing the same vent pressure. If the vent pressure imbalance is large enough, you will definitely get fuel crossfeeding from one tank to the other. I think this is best avoided by keeping vent pressures positive but low. The Savannah standard has individual underwing vents cut of at approx 45 degrees into the airstream and that seems to work okay. The other popular option seems to be 'snorkel' pipes up out of the fule caps then bent down and forward.

 

 

 

[Blueadventures]

5 hours ago, IBob said:

Hi Bruce.

So far  as I know, Savannahs with the standard 2 wing tanks normally have no valves from the wing tanks.

These feed down into a 6L header tank behind the passenger seat.

The header tank is fitted with a float switch at the top, which brings on a low fuel indicator at the dash: provided this is working (more on that later) it gives approx 20mins of low fuel indication.

This arrangement does occasionally get a small amount of air in the header tank, giving false low fuel warnings. More recent builds now have a breather from the header tank back up to a high point in a wing tank to deal with this.

Aside from that, it works very well.

..................................................................................................................................................................................

The only shortcoming I see with this system is that there is no way to test the header float switch without fully draining the wing tanks. (There is a test button on the panel, but this only tests the indicator, not the switch.)

I have a 4 tank setup with individual tank valves and a header breather: I can readily test the low fuel indication by valving off all tanks. I do need to know it is working if I intend flying my outer tanks to exhaustion.

...................................................................................................................................................................................

As an aside, I also think some care needs to be taken with the wing tank breathers. In a perfect world, these tanks would be cross vented, and so sharing the same vent pressure. If the vent pressure imbalance is large enough, you will definitely get fuel crossfeeding from one tank to the other. I think this is best avoided by keeping vent pressures positive but low. The Savannah standard has individual underwing vents cut of at approx 45 degrees into the airstream and that seems to work okay. The other popular option seems to be 'snorkel' pipes up out of the fule caps then bent down and forward.

 

 

 

My experience with two wing tanks (52 lts each - total 104 lts) in a high wing (Nynja) feeding into the Savannah 6 litre collector tank is that when the wing tanks are getting to about 15 litres each the fuel flow slows (mix of fuel and air as the fuel in the tank surges. no baffles in the tank, pickup at rear lower position) into the collector tank.  I believe that this is due to the pressure of air via the forward facing fuel tank vents within the wing tanks; restricting the escape of air from within the collector tank.  I can see the collector tank and its contents level and also the flow from the wing tanks at the glass inline filters.  My collector tank is changed to both wing tanks feeding via 8mm i.d. hose into a 'T' then into one collector 100mm i.d. nipple.  The other 10mm nipple barb is connected to the stb wing tank contents sight tub at its upper most connection to the wing tank.  This returns any air collecting in the collector tank.   What I see at this time is less fuel in the inline filters and the air bubble size within the collector tank increasing,  once the air filled to top 80mm and the low fuel light came on.  I now slow rpm by about 200 rpm to get the collector tank filling, reduce engine consumption.  I think the mass weight of fuel in the wing tank is not enough to over ride the pressure of the air in the wing tank (forward facing tank vents) and allow the air back up out of the collector tank.   One thing I do on a long trip is turn off a tank at 15 litres and suck of the fuller tank and this is a good management practice.  Then when closer to my destination I turn the tank back on.  Hope my words explain my thoughts and experience with this.