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nuckolls.bob(at)cox.net
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 Posted: Sat Oct 13, 2007 9:25 am Post subject: Z-19 and considerations of SYSTEM reliability |
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At 08:48 AM 10/13/2007 -0400, you wrote:
| Quote: |
10/13/2007
Hello Bob, You wrote: " . . . and the pump is already ON for takeoff and
landing."
Just a reminder that in some aircraft the electrically driven fuel boost
pump is not turned on for takeoff or landing.
The problem in those aircraft is that with the engine driven fuel pump and
the electrically driven fuel boost pump both operating the engine can be
drowned in fuel and not operate properly or at all.
The function of the electrically driven fuel boost pump in those aircraft
is to prime the engine prior to starting the engine and to be turned on in
flight in case of failure of the engine driven fuel pump.
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Sure . . . which re-enforces the notion that NOTHING
written anywhere by anyone that is not specific to
a study of demonstrated test data about a particular
design is to be taken as gospel. Every new recipe
for success combines simple ideas for the purpose
of meeting a design goal. It's up to the writer
of specific instructions to explain the rationale
for that particular combination of parts and recommend
a modus operandi for that system.
This is what the 40-hour fly-off is all about.
But many builders have put their own flavors onto
another builder's recipe. Too many modified recipes
have been turned loose on open skies and grinning pilots
with undiscovered potential for problems. Its fortunate
that reliance on electrical systems issues is Waaaaayyy
down the list of things that routinely bend airplanes
and kill folks. Fiddling with these recipes generally
don't generate much physical risk, only surprise and
cost of ownership. But we're talking about powerplants
here so the details are worthy of extra attention.
Now, may I take you to task my friend for, "The function
of an electrically driven fuel boost . . .". The POH
for many of the aircraft I fly instructs a pilot to turn
the boost pump on for take-offs and landings.
Bottom line is that there should be GOOD reasons
for doing or not doing a lot of things on our
airplanes . . . but the final word needs to
come from designers and testers that have, "Been
there. Done that." All other assertions are worthy
of measured skepticism and further study.
| Quote: | 'OC' Says: "The best investment we can make is the effort to gather and
understand knowledge."
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HEAR, Hear!
Bob . . .
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nuckolls.bob(at)cox.net
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| Posted: Sat Oct 13, 2007 10:15 am Post subject: Z-19 and considerations of SYSTEM reliability |
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At 10:20 AM 10/12/2007 -0500, you wrote:
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Thanks Bob,
I can't seem to find the email but I think Eggenfellner has decided that a
simple switch on Pump#2 is fine. They were having too much trouble with the
pressure switch for automatic fail-over.
As a computer geek I find it so hard to resist "automatic techno gadgets"!
Thanks for the detailed exhortation.
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Yup, a lot of what's being done in new systems
design is driven more by what we're capable of
doing as opposed to crafting the minimum parts
count, highest reliability, lowest cost (i.e.
elegant) solution.
The drive to add whippy new features is oft offered
by folks who have little or poor connection to
end users. We see this in the Heavy Iron Aviation
all the time. In addition to bureaucratic
pressures to do or not do things, decisions
about what's attractive to the end user (owners
and pilots) tend not to be made with the elegant
solution as a design goal.
Walter, Dwayne, Ed, Arthur, Bill, Al and Lloyd
would be sad to observe the remnants of their
legacies.
Bob . . .
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pwmac(at)sisna.com
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| Posted: Sun Oct 14, 2007 8:00 am Post subject: Z-19 and considerations of SYSTEM reliability |
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Don't you guys with backup pumps use a pressure regulator like all
modern autos and trucks? If not, then why not?
These auto units usually have a return line for the excess fuel. Some
are controlled by vacuum to allow a slightly higher pressure when
vacuum is low.
Paul
====================
At 07:45 AM 10/14/2007, Gary Casey wrote:
| Quote: | Some engines (Continental fuel injection
systems) are affected by inlet fuel pressure and there have been
problems with over-fueling these engines, according to what I have
read.
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