Hi, fellow rotary enthusiasts.  I am building an SQ2000 canard pusher

with a 13B. I have two

strake fuel tanks that would be considered "mid-wing". I plan on

having a fuel line from each tank

into my approximately 2 gallon sump tank, and from there it will go to

the fuel pumps, fuel rail,

and to the regulator.  My question is, is it best to have the unused

return fuel from the fuel

pressure regulator go back into the sump tank, or run a seperate line

back up into one of the fuel

strake tanks?

Al Gietzen wrote:

Paul;

It is somewhat dependant upon the flow rate of your fuel pump, with only
two gallons of sump capacity. I'd suggest running back to the main tank.
There are two issues that I can think of - one is that at low fuel burn
there is a lot of fuel returning to the tank, and the energy put in by
the pump, flow friction and heat transfer from the engine compartment
could increase the temp of the fuel in the sump increasing the potential
for vapor lock.  The other is there some of the more highly volatile
components in the fuel tend to form small bubbles downstream from the
pressure regulator causing foam from the sump tank vent, a problem that
increases as fuel temp increases.

Al

Al,
    The tanks I have dealt with are 2 gallon or smaller and have not had a
problem temperature wise. In fact one was in a Glastar NSI a/c where the
aluminum header tank was sitting top center on the firewall, right above the
coolant condenser core and the header tank would actually feel cool after an
hour of circuits. The other tanks were harder to get at but were on the cool
side of the firewall so I would assume they would be cooler yet. I don't
know about the bubbles but as you say, that problem increases with temp
anyway and these a/c have over 300 hours with no problems. The fuel flow
rate of the rotary would be higher than the Soob ( approx 4 gph ) but the
Lyc was 8-12 gph.

John

 
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