bakerocb
Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA
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 Posted: Sun Mar 18, 2012 2:00 pm Post subject: fuel pump |
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3/18/2012
Hello JF, You wrote:
1) "I will see how my system works and if it doesn't satisfy ,I'lle change
the
fuel pump"
Since I last wrote to you on this subject I have paid close attention to the
fuel pressure readings that appears on my Vision Micro Systems engine data
display during various phases of flight. This pressure reading is tapped off
the fuel manifold valve (sometimes called the spider or fuel distributor). I
have come to the conclusion that any electrically driven fuel pump that
generates much more than 10 pounds per square inch pressure at this
location, even with the engine driven fuel pump inoperative, is in excess of
what is needed to maintain safe level flight.
If that excess pressure is in danger of drowning the engine with both the
engine driven and fuel boost pumps operating I don't see any benefit, and
there is some danger, in having such a boost pump. This appears to be the
situation that you have.
2) "Some people used automotive paper filter along the fuel line."
I am not in favor of aircraft fuel filters that use a paper element because
I am concerned that water, particularly water in association with some
product such as alcohol or other exotic chemical in the fuel, may cause the
paper element to become soggy and clog up. I assume that a high quality
paper element is treated to prevent such a situation, but suppose one gets a
replacement paper element that is not of the highest quality?
I am in favor of using metal screen 85 micron cleanable in line filters such
as those made by Earl's. See here:
http://www.summitracing.com/search/Product-Line/Earls-Performance-Inline-Fuel-Filters/
Or a metal screen 62 micron cleanable in line filter such as those made by
Andair. See here:
http://www.andair.co.uk/system/index.html
3) "I Was wonder if it's nessary to add a fuel filter along the line in
addition of the gascolator
and the filter mounted to each tank which is usefull only for big debris"
and "What is your opinion about this?"
I am very mindful of the fact that a very high percentage of experimental
amateur built aircraft accidents are caused by some sort of fuel system
malfunction. I may have gone to an extreme length with my fuel system
design, but here is what I have as fuel filters:
A) A large debris screen type filter in the outlet of each wing fuel tank.
B) An Earl's type in line filter in each fuel feed line going from each wing
tank to the Andair duplex fuel selector valve.** Note that a clog up in
either one of those two filters still permits me to switch to the other fuel
tank and regain engine operation.
C) An Earl's type in line filter in the single fuel feed line going from the
fuel selector valve to the inlet of the electrically driven two stage Dukes
fuel boost pump.
D) The 72 micron fuel filtering capability of the Andair gascolator which is
located between the fuel boost pump and the inlet to the engine driven fuel
pump. See here:
http://www.andair.co.uk/system/index.html
'OC' Baker Says: "The best investment we can make is the time and effort to
gather and understand knowledge."
**PS:This fuel tank selector valve is the duplex type that sends the return
fuel back to the same tank that the fuel is being drawn from. Very important
for this IO-240 B - B engine. See here:
http://www.andair.co.uk/system/index.html
=================================================
From: <jfherzog(at)bluewin.ch>
To: <bakerocb(at)cox.net>
Sent: Sunday, March 18, 2012 3:32 PM
Subject: Re: Fw: fuel pump
Hello Owen
Your description makes sens. I will see how my system works and if it
doesn't satisfy ,I'lle change the
fuel pump
By the way, I Was wonder if it's nessary to add a fuel filter along the line
in addition of the gascolator
and the filter mounted to each tank which is usefull only for big debris
Some people used automotive paper filter along
the fuel line.What is your opinion about this?
Best regards
JF
==========================================================
----Message d'origine----
De: bakerocb(at)cox.net
Date:
28.02.2012 04:12
À: <jfherzog(at)bluewin.ch>
Objet: Re: Fw: fuel pump
2/27/2012
Hello JF, The subject of what kind of electrically driven fuel boost pump to
have and how to operate it can get a bit complicated and is dependent on the
pilot's goals for that pump. Therefore a builder should think long and hard
about what kind of fuel boost pump to install.
1) Many pilots will just make the assumption that the engine driven fuel
pump will fail someday in a critical phase of flight and that what is needed
is a fuel boost pump capacity that will permit the engine to run at full
power in that circumstance.** This boost pump capacity then introduces the
issue of how and when will the boost pump be turned on to sustain flight?
2) If the capacity of the fuel boost pump is such that both the engine
driven pump and the electrically driven fuel boost pump can not be operating
at the same time because the engine will drown (which appears to be your
present
situation) then the fuel boost pump can not be turned on as a matter of
routine procedure during critical phases of flight such as take off and
landing.## So if the engine driven pump fails during those
critical phases of flight one must either have an automatic system installed
to turn on the
fuel boost pump when needed or plan to quickly turn on the fuel boost pump
manually and get the engine restarted before the plane crashes.
3) Instead, let us make the assumption that the engine driven fuel pump is
no more likely to fail in a critical phase of flight than the engine driven
oil pump -- and one does not install electrically driven oil boost pumps. So
why have a fuel boost pump that creates the issues raised in 2 above? My
answer to that question is not to have a fuel boost pump of that (excessive)
capacity.
4) My peferred solution is to have a fuel boost pump with a capacity that
will allow me to prime the engine prior to cranking for engine start and
will also keep the engine running at level flight power in case of engine
driven fuel pump failure. I have a two stage Duke's electric fuel boost pump
that will do that. My engine will run, but poorly, when both the engine
driven and boost pumps are operating so the boost pump
is not turned on during normal operations in the air.
5) I suggest that you consider replacing your over capacity
electrically driven fuel boost pump with one that will:
a) Prime your engine prior to cranking for start.
b) Provide sufficient fuel flow to displace vapor in the fuel system during
a hot start.
c) Provide expectation of continued engine operation at some safe level if
the
engine driven pump fails.
d) Not cause your engine to stop running if both the engine driven fuel pump
and the electrically driven fuel boost pump should happen to both be
operating at the same time.
OC
**PS: Note that it is basically impossible to test for this situation since
one can not turn the engine driven pump off while airborne in order to
assure that the fuel boost pump alone will provide the fuel flow needed.
##PS: It is ironic that fatal accidents have been caused by improperly
having such a fuel boost pump on or inadvertantly turning it on during
critical phases of flight (take off usually) when the engine driven pump was
working OK and the engine subsequently drowned causing the plane to crash.
============================================================
From: <jfherzog(at)bluewin.ch>
To: <bakerocb(at)cox.net>
Sent:
Sunday, February 26, 2012 6:08 PM
Subject: Re: Fw: fuel pump
Hello again
Thank you for your response
Regarding
point 2) My boost pump can't work at the same time as the engine
fuel pump because the fuel flow is too high ang engine
stops due to the
cumulating flow. That's why I would like to
have a position with a reducted fuel flow which allows
electrical and engine
working together
Thank you for the adress
regarding ELT,I am going to have a look and keep you
in touch
Regards
JF
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