Savannah S long-range tanks

[jmac]

Hi All,

I am building the right wing and have had many discussions with other builders regarding the long-range tank setup.

There are three options I am considering, and I would like to get the views of other builders,

Option 1 - As in the manual (16mm connector hose to be installed to join tanks), 10mm connector & hose to be installed to be managed with one tapRight tanks.docx

Option 2 - Running two hoses (two taps for each wing using the tank 16mm taps and reduce to 10mm) Individually managed

Option 3 - Using the 16mm taps and join and reduce to one 10mm hose (managed with one tap)

 

I have attached photos to assist.

Any feedback would be appreciated.

 

cheers

James

 

 

 

 

[Moneybox]

The bottom option looks the simplest. If you have two valves left and two valves right it could be quite confusing. A single L to R valve would be much easier to select and you are less likely to lose track of what's full and what's empty.

[Thruster88]

I would prefer the tap for each tank option. This gives the pilot control of the system. Most of the time only the inner tanks will be required, it is easier to fill to a know quantity and dip two tanks rather than 4. On a max range flight it is nice to be able to run the outer tanks dry at altitude so when reaching destination the 10-15 litre remaining is in two tanks rather than spread somewhere over four tanks with potential un porting, fuel starvation. With the 4 tank 4 tap system unintended fuel migration and loss out the vents or caps on ground or in flight can be avoided. 

 

An electric (facet fuel pump) transfer system with check valve between outer and inner tank is also an option. This gives excellent control over the system.

 

There is more risk of fuel starvation in multi tank aircraft, pilot beware. 

Edited March 11 by Thruster88

[Marty_d]

Have a look at @Kyle Communications build logs, he did the four hose/tap into one manifold method and I believe he's very happy with it.

[fallowdeer]

I pretty much copied Mark Kyle and IBob. .

 

After 140 hours in nine months, I’m really liking the flexibility of having four individually valved  tanks.

 

 

[fallowdeer]

Hi James

 

When my aircraft was inspected by the CAA they pored over the fuel system in great detail.  As the POH and the build manual  contained no information about a four tank system I had free rein on the design.

 

As previously noted lots of pitfalls exist in the operation of a multi tank system so I had created the attached document and included it in the POH. This seemed to alleviate the regulator’s concerns.

 

I frequently start up with all fuel valves off at the manifold looking for the low fuel light to come on after using about 100ml of fuel this testing the system as against the button on the panel which is only a bulb test.   From experience in normal cruise I’m able to drain any tank completely with the exception of the R/H inner that the return goes to. 

 

 

 

 

[facthunter]

Non return valves are a good safety feature. You don't want inadvertent transfer or AIR to ever be in the system.  With n/r valves and all pumps on you can empty all fuel without a problem of air getting in till there's no fuel in the  (fuel) manifold. The pressure while it is there keeps the check valves closed on the empty tanks. Draw a schematic till you understand. You do not need a collector with this system.   It has been widely used. Nev

[IBob]

Facthunter, I like the idea of non-return valves. At the same time, I'd be interested to know how they work so as not to restrict flow: the standard (none sprung) one in domestic plumbing is a sort of little trapdoor that has to be installed right way up, as it is closed by gravity. What is the mechanism for aircraft?

 

[facthunter]

I don't know what's available. I have operated them  and it's not a new idea.. It makes a foolproof system.   Nev

[IBob]

While my knowledge of fuel systems is limited, it seems to me that the Savannah setup is very well thought out. And for an aircraft of it's size and type, the receiver tank is an integral part of that.
It acts as a buffer, effectively guarding against fuel starvation due to momentary unporting of the tanks.
And it gives many minutes of warning of fuel exhaustion.
The only provisos there are that the level switch providing that warning can fail: that being the case, there is a real advantage to having valving from all wing tanks, so allowing routine ground testing of that switch.
And the panel indicator can fail: there is a test button allowing routine testing of that, and in the interest of reliability the incandescent indicator supplied can be changed for a (flashing) LED indicator.

Edited March 12 by IBob

[facthunter]

A lot of certified aircraft have traps for the Unwary built into their fuel systems. The  C 54/DC 4 is one such system You can lose the 4 engines. with air in the system.  or vent fuel overboard.  Nev

[IBob]

If going to the 4 valve setup as described by fallowdeer above:
The rationale for having all 4 valves on the RH fuse wall is to allow the PIC to easily see and reliably operate those valves at any time.
However, this mean running the feeds from the LH tanks to the RH side of the fuselage. If doing this, ensure there are no undulations in those pipes, as any high spots may contain air, which the fuel must makes it's way past.
My understanding is that most multi-tank setups may experience uneven feeding from L and R tanks, for a variety of reasons.
I had uneven feeding until I removed undulations from those pipes. The result is still uneven, but now far less so.
(I should add that at no point did uneven feeding affect engine performance.)
 

[facthunter]

If you get EVEN feeding from 2 tanks it's a fluke. Slight differences count for a lot. You can't count on it being even. You can equi time them. Nev

[Kyle Communications]

I always had uneven feeding when I did that system but it wasnt huge. Never had a airlock ever. Except when a bug got into one of the fuel tank breather tubes those silly 3mm tubed out of the fuel caps. So I got rid of them and make the hook style 6mm alu tubes and fitted them to the tank fuel caps..problem be gone then