<how does it <avoid a negative pressure when the fuel level gets
near the bottom of the tank?
It doesn't. Actually, GM takes advantage of that
and designs inlet so that you'll run out of fuel at home instead of on the road.
Pretty interesting.
I mention the oem design because I'd like to save a
few lives. Fewer crashes. I hope a few guys will be open minded. Test their
ideas instead of speculate. Compare results to OEM method.
If we broke down fuel design into individual
components. Like self priming, pressure drop at inlet, effect of contaminants,
etc. Then did the simple tests to prove which is superior, it would be
enlightening.
-al wick
----- Original Message -----
Sent: Wednesday, August 17, 2011 8:40
AM
Subject: [FlyRotary] In-tank pumps
Al Wick wrote:
> What's the best fuel design to
prevent vapor lock? Copy any auto mfg
> method. They all use the same
method because it's SOOO effective. OEM
> fuel designs minimize every
REAL risk we have in our aircraft. They use
> self cleaning filters
that have around 10 or 20 times more surface area
> than stupid in line
filters. They minimize pressure drop at pump inlet
> by using large
coarse filters there. Submerged pumps. Every car mfg uses
> the same
system. Do you know how rare that is? They do it because the
> wet
design with self cleaning filters eliminates all historical failures.
>
I recently converted my sys to automotive style. Details at bottom of
page:
> http://www.maddyhome.com/canardpages/pages/alwick/index_files/Page467.htm
>
Can you explain something to me on this point? Considering that
the in-tank pump has a positive volume, how does it
avoid a negative
pressure when the fuel level gets near the bottom of the tank? I ask,
because most airplanes tend to
have very flat tanks, and fuel often gets
left on the ground for weight and balance reasons. Pulling that last few
gallons off the bottom of the tank can be VERY important. Putting
the pump in the tank is going to result in pulling
fuel uphill at some
point unless you have a flat pump.
I'm going to go out on a limb and
say you're wrong. Manufacturers all use the in-tank system because it
simplifies
design and assembly. They all use pre-assmebled console
"clusters", and many other pre-assembled components for the
same
reason. It is not rare at all. In-tank pumps are not a safety
issue. It's an economic one.
The best design for avoiding vapor
lock is going to be the one that puts the most pressure ahead of the
pumps. Whether
this is done by putting the fuel as high above the
pumps as possible, pressurizing the tank, or magical pixie dust,
positive
pressure at the pump inlet is the only answer. The in-tank pump only
marginally solves the problem and is a
maintenance nightmare.
But,
to each his/her own. You build it. You fly
it.
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