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The 1994 FSM wiring diagram for the
rotary's fuel pump (automotive) describes two relays connected in
series. The first turns _on_ the fuel pump, and the second has a
resistor in parallel to it (see page 248). This is labeled "Fuel
Pump Relay (SPEED)". Page 297 calls for this resistor to measure
0.57 - 0.70 ohms at 68degF. The idea is the ECU leave this relay
de-energized during low speeds and loads, which adds resistance to
the circuit, drops the voltage seen by the pump, and thus causes
the fuel pump to run more slowly. At higher speeds it energizes
the relay, shorts the resistor, and thus gives the fuel pump full
power.
None of this is really applicable to aircraft use, but it does
show that even in 1993, automotive designers were concerned with
long-term fuel pump life. As Al Wick always points out, fewer
warranty service calls drives profitability and repeat sales, and
they're good motivators for engineers focused on reliability in
companies that sell millions of units a year of a product.
So it wouldn't be fair to say that driving the pump full-bore all
the time is a "common setup anymore." At least for Mazda, it
wasn't even their practice 20 years ago.
In an aircraft, though, this speed-control relay, resistor,
connector, and associated wiring adds weight, cost, complexity and
potential failure points for a homebuilder doing their own
installation. I think it's reasonable and probably wise to
remove/skip it during installation, and I've never heard of
anybody actually using one. Our requirements are different.
On 8/7/12 2:25 PM, Saro Marcarian wrote:
Ok. I can't speak to all automotive FI systems, but
at least some have full recirculating flow ALL THE TIME.
Here's the scenario as I understand it in many setups:
Tank -> Pump (in tank) -> High Pressure Filter
-> High Pressure Fuel Rail / injectors -> pressure
regulator (referenced to intake manifold) -> low pressure
return to tank
Ingition switch on means fuel fuel pump on. The pump
is always pumping the max the engine will ever need - surely
with some surplus pressure and volume. The regulator spews
back what in an automobile will usually be a gross excess of
fuel.
Regardless of the power requirement of the right
foot, the fuel pump never knows the difference. It's always
pumping it's max. I've gotten kinda fed up with the
automotive industry and don't know if this (or a slight
variation) is the common setup anymore. For example, I've
seen some cars where the pump comes on for a few seconds and
if the engine doesn't fire, shuts down. But you get the
general idea.
Al's revelations of the sloshing self-cleaning action
are pretty awesome and telling. Good thing to know.
-Saro
Of course, Al,
I am missing the part where the hopped up
autophile jumps on the highway with his souped up
car, steps on the small pedal and cruises at
75%power, with no letup for say-- 4 hours, to be
followed by a similar situation over and over again.
The flow for a 600HP engine would be considered,
only if it were run under the above circumstances.
Most cars, unless long distance racers, many of
which don't finish (and one wonders if they, indeed
use these types of filters,) independent of their
increased HP function at much much reduced HP and
fuel burn most of their lives (thus the old saw
about not using an automotive engine for an
airplane). Aircraft engines, or engines used on
aircraft have different thirst needs. Not, IMNSHO
noise, but possible reality.
Of course the vehicles with the fuel filters "totally
unnecessary to remove" are not designed to have
the longevity nor the fuel burn of our aircraft.
Assume the
life of an aircraft to be 20 years (although they
are considerably longer)
Consider an
average fuel burn of 10GPH
Consider
flying 100H per year
Consider
average auto at 20 MPG
The
aircraft at 20 years will have consumed 20,000 gal
of the smelly stuff.
A similar
flow in the auto would equate to 400,000 miles.
Where the
aircraft is still relatively "new" it is only very
rarely that an auto makes that kind of mileage and
is typically shredded long before that. Is it
possible that these self-crap-shedding filters
have, for aviation purposes, a limited life span,
which, since blind, can not be evaluated, except
at failure?
The benefit
of being able to look at a filter element is the
ability to take some recourse if problems pop up.
Inability to inspect stops one from not knowing
(although, for some, there is solace in that). "If
I can't see it, it must not be there."
What comes
to mind is the situation with Chris Barber in
which, for whatever reason chunks (sheets) of
epoxy-stuff were flaking into his fuel tanks. I
don't know how Chris determined this, but lets,
for the sake of conversation, this situation was
not observable through the filler neck (perhaps
happening in a baffled area removed-- there are at
least 1 or 2, can't remember, however, the fuel
pickup is visually isolated from the filler neck
area, and the flakes plugged the filter due to
their shape and size, he, after solving his
cooling problems might have had an engine failure
at 50' on landing after a 5 hr cross country. Of
course, when he arrived back to Terra Firma, short
of the runway, hopefully in one piece, the un
-seeable filter would have "cleaned" itself, and
the engine failure would have been, probably,
relegated to something else.
Rich
In a message dated 8/7/2012 10:24:47 A.M.
Central Daylight Time, alwick@juno.com writes:
<not taken into account is that the fuel
flow of an aircraft is significantly greater
than that of a car
Not
true in this modern age. 30 years ago would
have been true.
They
do take high flow into consideration. They
design the systems to handle the extremes.
When we do qualification testing we measure
how close we are to failure threshold. "Holy
crap, if this guy has partially clogged
filter similar to ones we find on Kentucky
cars 15 years old. AND he is running at full
throttle. AND he has replaced injectors with
high flow ones..........no, he's still
within the safety margin."
Have
to admit, I don't know the details of Mazda
fuel flow thresholds. But I do know Japanese
companies are expert at design optimization.
They do measure how well sys will perform in
unusual applications. We have what's called
a "noise array" and test how well sys
handles unusual situations outside of our
control. So high flow injectors would be in
the noise array. As would fuel from "Bob's
rusty tank".
Would
flow for 600 hp engine be considered? No,
not that extreme.
<filter/pump were removed inspected and
cleaned, I personally would feel much better
about that installation.
Yes,
I think a lot of people are not used to the
concept of a design so robust that failures
can't occur. In the case of OEM fuel
filtering, it's totally unnecessary to
remove and inspect. If curious, use one of
those scopes to peer into tank. In this
case, remove and inspect would increase
risk. I love the irony.
-al
-al
----- Original
Message -----
Sent:
Tuesday, August 07, 2012 7:39 AM
Subject:
[FlyRotary] Re: Fuel Filters. Was: Rotary
Forced Landing
Al,
Of course, what is not taken into
account by the auto guys is that the fuel
flow of an aircraft is significantly
greater than that of a car and that old
planes are still flying and don't have the
opportunity to "pull over to the side if
the filter gets plugged totally or
partially.
Now if, as part of a conditional
inspection, the filter/pump were removed
inspected and cleaned, I personally would
feel much better about that installation.
Rich
In a message dated 8/6/2012 10:58:34
P.M. Central Daylight Time,
alwick@juno.com writes:
Dave says:
<How does a filter "Self
clean"?
I mentioned this a couple years
ago. One of the guys called Bull
Sh__. Well, not really, but what he
did was most impressive. He went to
local wrecking yard, bought two used
coarse filters. They reside in the
fuel tank. I think he spent like $5
or so.
Then he puts it in bucket, no I
think he has old aquarium. Attached
a pump to it. Then got some dirt and
debris from yard and poured it on.
As I recall he could not get it to
clog. But the self cleaning was
obvious when he added a little wave
action and vibration to it.
If you take this a little
further, you can actually measure
pump flow rate by timing how long it
takes to fill jug. You can then look
at jug contents so see how fine it
screens. You can add a simple
altimeter and measure pressure drop
on pump inlet. Less pressure drop
means that vapor lock risk is
reduced. Tons of stuff you can
measure that no one knows.
I'd think you'd find it takes
around 1 tsp to clog the traditional
aircraft filter...so planes crash.
Yet it takes cups of dirt to clog
the filter used by every single car
manufacturer. Gigantic safety
improvement.
<How DO the car manufacturers
overcome eventual filter
clogging/saturation? Just by making
it so dang <large it never
reaches that point?
I think they discovered that the
larger the surface area, the less
likely to clog. That's why they all
have around 6 to 10 times more
surface exposed to wave action than
the filters of yesteryear.
-al wick
-----
Original Message -----
Sent:
Monday, August 06, 2012 6:57 AM
Subject:
[FlyRotary] Re: Fuel Filters. Was:
Rotary Forced Landing
For
the ignorati among us, I must ask.
How does a filter "Self clean"?
How DO the car manufacturers
overcome eventual filter
clogging/saturation? Just by
making it so dang large it never
reaches that point?
Dave
On 8/6/2012 8:48 AM, Al Wick
wrote:
<how small of filtration
do we need?
<size of a particle that
will fit through the injector
nozzle easily?
Excellent questions. You have
one resource that stands WAY
above others. What do the OEM
vehicles use? They know
precisely what the optimum
surface area is, optimum
filtration size. Too fine, it
clogs needlessly. Too coarse,
you increase risk of injector
clog. Too little surface area,
it won't last. They even take
into consideration unusual
needs, like people that operate
at super high flow rates.
A few decades ago, cars would
periodically suffer clogged
filters. Never happens any more
because they have new tools to
optimize designs. For example,
their course filter screen has
around 10 times more surface
area than any airplane filter.
Self cleaning, screen size
optimized. So debris can't
affect your car. It's just
brilliant.
I really worry about builders
copying marginal fuel designs.
Unaware of how close they are to
the failure threshold. You can
fly for years with marginal
design, tell everyone "works
great for me". Unaware you are
promoting failure.
-al wick
-----
Original Message -----
Sent:
Sunday, August 05, 2012 1:35
PM
Subject:
[FlyRotary] Fuel Filters. Was:
Rotary Forced Landing
So my next question is how small
of filtration do we need? ie,
what is the size of a particle
that will fit through the
injector nozzle easily?
I was using the Earls sintered
bronze element at 35microns, but
I also could use the SS screen
version at 85 mic. The Peterson
in line 600 series is MUCH more
expensive and comes in 45, 60,
and 100 micron SS screens.
http://www.jegs.com/p/Peterson-Fluid-Systems/Peterson-600-Series-Fuel-Filters/1528539/10002/-1
Those do have more surface
area but will be a hassle for me
to retrofit, and not sure they
are worth 4x the price of the
earls. Lots of other brands I
have not explored yet.
I like the sintered bronze for
strength and durability. Other
opinions?
Dave Leonard
On
Sun, Aug 5, 2012 at 12:42 PM,
David Leonard <wdleonard@gmail.com>
wrote:
Yea,
mine is an Earls
cleanable high pressure
with maybe 10 sq cm
worth of area. Will
look into the Peterson.
Thanks Tracy.
Dave Leonard
On
Sun, Aug 5, 2012 at
10:48 AM, Tracy <rwstracy@gmail.com>
wrote:
Al probably
means the filter
that's on
factory in-tank
pumps. OK, but
very hard to
implement on RV
wet-wing tanks.
I used a
gascolator for
low side filter
on my -4.
Worked OK and
when it clogged,
switching on
the backup pump
with main pump
caused the
screen disk to
collapse and let
fuel bypass it.
which is
better than no
fuel at all but
not an ideal
solution.
On the -8 i
used a cleanable
Peterson filter
with TONS of
filter area,
works great.
That was a
replacement for
the Summit
Racing fuel
filter with a
filter element
disk the size of
a nickel. It
clogged up in
about about 5
hours of flight.
Yes, it
was the high
side filter.
I don't have
any low side
filters.
Would be
interested in
a source for
the
self-cleaning
fool-proof low
side filters
that Al
mentions.
--
David Leonard
Turbo Rotary
RV-6 N4VY
http://N4VY.RotaryRoster.net
http://RotaryRoster.net
On
Sun, Aug 5,
2012 at 6:34
AM, Tracy <rwstracy@gmail.com>
wrote:
I assume
Al is
referring to
the pump
intake side
filter. So
for the
record, was it
the inlet side
or the high
pressure side
filter that
clogged? (
Both are
needed )
>From the
symptoms I'm
guessing high
side but not
sure.
BTW,
nice job!
Tracy
Sent from my
iPad
As long
as your are
rebuilding,
tremendous
safety
improvement by
using same
fuel filter
method that
all cars use.
No matter how
much foreign
material
you throw at
it, it can't
clog.
It minimizes
pressure drop,
so lower risk
of vapor lock.
Self cleaning
filter. Self
priming pumps.
-Al Wick
Cozy IV
powered by RDM
Subaru 3.0R.
Expert at
failure
prevention
methods,
N9032U 240+
hours from
Portland,
Oregon
Glass panel
design, Subaru
install, Prop
construct,
Risk
assessment
info:
http://www.ez.org/pages/alwick/index.htm
-----
Original
Message -----
Sent:
Saturday,
August 04,
2012 1:38 PM
Subject:
[FlyRotary]
Re: Rotary
Forced Landing
Dave,
having gone
through
recently what
you just
experienced I
would like to
say GOOD JOB
on getting
down safely
and with such
little
damage.
Anyway at 1500
AGL there
isn't a lot of
time ...
obviously you
made the right
choices.
Jeff
(Rebuilding
my Ride)
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Sigh..
Yup, that was
me. I have
been meaning
to fess up. We
were at about
1500 agl when
the fuses blew
on my fuel
pumps. I was
in a close
formation of
40 aircraft at
the time too.
I think I got
some bad MOGAS
somewhere in
Iowa as I did
notice my fuel
return flow
creep downward
but didn't
think it was a
big problem.
On the
incident
flight, a one
hour formation
flight from
SQI for a mass
arrival at
OSH, the
return fuel
flow drifted
down to zero.
I actually
though it was
a sensor
problem. I
didn't have
the ability to
give it a lot
of attention
because we
were in a
loose
formation.
Soon after we
pulled it
together for a
tight
formation
power switched
off. I tried
to find a
road, but
quickly ran
out of options
and put it
down in a bean
field. With
the beans
hitting the
flaps it
brought me to
a stop in
about 200ft,
just before I
would have
gone into the
full grown
corn. As
mentioned,
wheel pants
broke in half
but no other
damage besides
pulling bean
leaves out of
every nook and
cranny. The
farmers were
very nice, and
the stories
are true...
they have
attractive
daughters.
They were out
there barefoot
in their
Sunday best
enjoying the
excitement.
Helped me
clean the fuel
filter and
replace the
fuses. Within
a couple of
hours I was
able to take
off from one
of their
driveways as
they all
waived good
bye (but
strangely, no
one took me up
on my offer
for a ride).
Landed at OSH
just before
dark to a
reserved
parking space
and a very
warm reception
from the
formation
group and
friends. Great
support from
everyone all
around, though
I am trying to
avoid the
obvious new
call signs
they are
trying to give
me.
--
David Leonard
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Turbo Rotary RV-6 N4VY
http://N4VY.RotaryRoster.net
http://RotaryRoster.net
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David Leonard
Turbo Rotary RV-6 N4VY
http://N4VY.RotaryRoster.net
http://RotaryRoster.net
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