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I guess it depends what you're flying.
The Cozy is designed such that each tank has a small armpit sump
because this guarantees that you always have a low-point drain,
and gives you a small reserve against fuel sloshing forward during
descents. I'm not sure what other levels you'd draw from here
because the drain is already at the bottom.
Al may correct me if I'm wrong, but based on his past posts I
believe he's based his sump strategy on using "wet" pumps, which
are designed to be cooled by immersion in fuel. This is a fine
plan and the automakers use it with high reliability. I wouldn't
use a "wet" pump dry - it would never last. But there are
definitely pumps (which I think you have, Tracy sells, and are
available in lots of places as "inline" pumps) designed to run dry
and their reliability is also very good. Any pump can clog, and
we're not talking about your pump overheating here.
I chose a dual-pump, dual-tank configuration (with a return
solenoid) for two reasons:
1. My fuel is isolated between each tank. Contamination in one
doesn't necessarily contaminate the other.
2. I have cross-feed capability controlled by a switch under a
safety cover. I can isolate a tank when filling (possibly transfer
remaining fuel from tank A to tank B) and fill only tank B. I can
then take off on tank A, which is known-good gas, known-good pump,
no contamination, no clogs, no water. (I just flew on it...) If
fueling contaminates tank B, loosens debris, clogs a pump, etc.,
I can be at altitude and prepared to deal with it when I switch
over. (Leave your hand on the switch when switching for 10 seconds
or so. Any hiccups, switch back immediately.)
Al would probably caution us to design against statistics and
testing data, rather than designing against fear. It's probably
good advice. But I fear bad-fuel situations and wanted something
to help deal with it. YMMV.
On 8/16/2012 12:04 PM, Chris Barber wrote:
I am using two fuel pumps. The Aux was always quieter. Now
they sound about the same. I guess since, IIRC, the primary
was always louder I "assumed" it was normal and was just
limited to the individual pump.
I was just reviewing Al Wick's sight. He hates the rotary
(ok, that may be too strong, but he is not a fan). He is
using a Subaru. I was looking at his sump tank. He is using
in the tank pumps, which I do not wish to do as of right now.
However, something he did which I did kinda like was that he
had his pumps drawing from different levels in the tank, like
my motorcycle does for it reserve. That way, if the primary
pumps runs dry, you can switch to the second pump and have a
bit more fuel....hopefully at least enough to pull your head
out and get on the ground. This seems pretty easy, especially
with inline pumps, to do and like a good idea. Seems as if you
would just have to have one pump out location higher than the
other and you have a bit of a reserve. Yeah, you should be
paying attention to fuel management but this seems like some
cheap back up. However, I could be missing something as
currently I am feeding both pumps from the same outlet.
Thoughts?
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