Bill Freeman wrote:
Bill Freeman wrote:
The certified aircraft that I am familiar with deal with this in a very
simple and straightforward way. All return fuel is directed all the
time to one of the mains. THe SOP is to always start, taxi, take off
and climb on the "returned to" tank. After it is burned down a
reasonable amount (you decide), you can switch to any other
tanks that you might have, and will be adding a bit of fuel to the
"returned to" tank.
Keeps it simple, no super expensive valves and an easy SOP
gets you safety without having to worry too much about exactly
what is going where.
Bill
George Lendich wrote:
Hi Bill,
Please excuse my ignorance, I am on a very steep learning curve
and I'm not getting any younger (know what I mean?)
Can you run that by me again (in Aussie lingo) ie simple!!
'Return to one of the mains' does that mean main fuel line coming
from the wing tank, is that the 'T' section, everyone is saying
not to do !!?
Or is that to the tank itself!?
George - down under
Hi George,
I'd sure like to visit "the other Oz" (I live in the REAL Oz, Kansas)
some day. Looks like a pretty interesting place. But to your question ---
The systems that I am referring to returns the fuel to one of the mains with
a return line all the way to the tank. The concept is to flow excess fuel to
cool the whole system, lines, fuel injector (or carb) and then dump this heated
fuel into the tank for heat dissipation. Using a T is a bad idea, since much
of the fuel will recycle and will continue to heat up. This could cause
vapor lock on a hot day, esp with a long idle, say leaving a fly-in (when my
Long EZ has gotten the warmest). I even worry about the guys that
use a sump, since while it can provide some cooling, it will be nowhere near
what the fuel tank can provide since it will recycle relatively quickly with
a small sump volume.
The trick is to learn your system. For instance, suppose your
pump puts out 30 GPH and the engine uses 15 GPH at cruise power.
Start with full 30 gals left and 30 gals right, and all returned fuel goes
to the
left tank, you would start, taxi, TO and climb on the left tank. This
simplified example ignores the extra fuel burn in climb.
LEFT RIGHT
START 30 30
1 hour on L -15 0
@ end of 1 ho 15 30
1/2 hr on Rt +7.5 -15
@ end of 1.5 hr 22.5 15
1 hr on Left -15 0
@ end of 2.5 hr 7.5 15
1/2 hr on Rt +7.5 -15
@ end of 3 hr 15 0
time to look for field, with all remaining
fuel in the left tank, no more fuel mgmt req'd
except landing before you run out. :-)
Very simple system physically, pretty easy to use
once you think about it for a few minutes and fly
it a few times. Simpler is ALWAYS better.
I dislike electrical fuel valves (they fail if they get
a bit sticky, while I can turn harder if a manual
valve gets sticky - and they do -- and then I know to
lube or replace it before it fails). Extra transfer
pumps are also unecessary, and somthing else to buy,
install, haul around and fail.
K. I. S. S.
Bill
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