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Chad says:
<The Cozy is designed ....gives you a small reserve against fuel
sloshing forward during descents.
Hi Chad. There are strong indications that the recent Cozy fatality was
caused by poor fuel design. Combination of low fuel and unporting of fuel during
long decent. Further aggravated by his not having a low fuel warning
sys. Unporting essentially can't occur with the sump tank approach I use.
Since I have 3 gallon header with all return fuel going to that header.
<fuel is isolated between each tank..........I can isolate a tank when
filling
I too have a certain amount of tank isolation, but not all that great. In
my opinion, fuel design is the most difficult thing to accomplish on our planes.
Full of design interactions: Where you focus on one problem, come up with great
solution for that, only to discover you've greatly increased risk of a different
problem. For example, a guy wants to be very thorough in filtering fuel. "Aha,
I'll put in one of these super fine filters". Unaware he's just increased
pressure drop at pump inlet. Greatly increasing vapor lock risk.
-al wick
----- Original Message -----
Sent: Thursday, August 16, 2012 9:41
AM
Subject: [FlyRotary] Re: fuel pump
replaced
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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