Hi Paul,

In my glass goose, I plan to have both upper wing tanks draining
into a common header tank under the engine.  The header tank will
contain twin submersible Walbro pumps, with appropriate check
valves, filters, etc., leading to the fuel rail.  Due to space
limitations, this tank can only hold about 3 gallons.

I can route the return fuel directly back into this tank or to the
inboard fuel sending towers in each wing tank. With the latter, I
don't have a good way to assure equal return flow to both wing
tanks, and the rapid flow might disturb the fuel level sensors.

My question is whether the fuel in a 3-gal tank might get too hot
after being continually cycled through the engine?  If that is
likely, I could probably squeeze in a small fuel cooling radiator
prior to returning to the header tank.

Thanks,

Scott Gettings

That is a good question Scott. At high power the return flow is less.
The thing to do is install some way to measure the temperature in
there and let the engine idle. That will be a worse case scenario.

By sending the fuel back to only one of the main tanks you risk a
fuel transfer problem. Airplanes have crashed because of this. They
selected one tank and it ran out of gas much faster than expected.

Paul Lamar


Could you pair a couple of fuel selector valves so that the return is
then sent to the tank being used for supply. It would need to be
ganged to ensure switching at the same time.

Dale Davies

Most EFI systems send unneeded fuel back to the fuel tank. We had
many many discussions about this. EFI is very rare in aircraft
engines and aircraft typically have more than one fuel  tank so it
became a real serious problem. We had at least one fatality when the
fuel selector switch moved and the engine failed on take off.

Statistically high wing airplanes with a "booth" selector switch are
safer than low wing airplanes. Low wing airplanes will lose pressure
when a switch is on both and one tank is empty so a booth position is
not used with the pump or pumps out side the fuel tank or tanks.

Also one must be careful not to use tank vents that face forward
into the airstream as dynamic pressure alone can transfer fuel from
one thank to another.

Here are some collected  3D's.

Paul Lamar

I was thinking one fuel selector for the supply from wing tanks. The
other would direct the return fuel back to the tank it came from. The
engine fuel pump would be supplied from the third 3 gallon tank. The
valves would work like DPDT electric switches.

Dale Davies

It is actually safer and easier to have both main tanks normally drain into a common Header tank. The fuel will equalize by gravity and there should (almost) never be a need to switch tanks at all. The last fuel will always be in the sump tank.  Selecting either right or left should only be necessary in the event of a fuel imbalance, such as a misfueling.

The main issue is the heat load, should the fuel be returned to the header tank.  Returning the fuel in a split manner to "both" main tanks might result in an asymmetric load, although gravity should equalize any imbalance over  time.

I will use Paul's suggestion to place a temperature monitor in the tank.  In worst case, I can place a small oil cooler in the fuel return path.

Scott Gettings

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