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

 Scott, I have test flown two GlaStars with a system similar to what
 you are describing. One had a 1 litre 3rd tank behind the seats and
 the other had a 1 gallon tank under the cowl.  I wasn't able to get
 the aluminum 3rd tank to feel warmer than my hands skin temperature.
 I don't think you need to worry, but as Paul suggests try it and
 monitor the situation.

 John  Rogi

 A few years ago I started working on an exact solution for this
 situation.  The physics of this setup is not simple.  As I was
 developing the equations, I made some estimates of the heat flows and
 it became evident that the heat flow back to the sump tank was not
 enough to cause an alarming temperature rise in the sump.  So, I
 decided to devote my time toward other things and abandoned the
 effort on the exact solution.

 There would, of course, be variations in different installations,
 but, it is unlikely the sump temperature will rise much.

 Aubrey Thompson

 I suspect how much fuel is returned is a function of the size of the
 injectors you use. We have 4 very large injectors on the time to
 climb so at the lower power levels a lot of fuel is returned.

 If you have 4 staged injectors like Tracy used (we do not) at cruise
 power you might be able to turn 2  off. I don't recall exactly when
 or what MAN pressure or RPM that happens in Tracy's set up.

 The RX8 uses six. I assume they too are staged.

 Paul Lamar



Paul are you using a pulsation damper in addition to a fuel pressure regulator?

Scott Gettings



No we are not. We are running 150 psi with a engine driven mechanical pump.

Here is the plumbing. It appears to be working great.

Paul Lamar

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