Fuel System Musings, comments encouraged

My blog has become a way for me to think out loud about my project.
Putting things down in a narrative helps me crystallize my thoughts,
and give me something to refer back to when the time comes to move
from thinking to doing.

Anyway, I've been THINKING about my fuel system, and have put down my
thoughts, I encourage those with more experience to comment either
here or via the blog.

http://users.lmi.net/~ryoung/2008/10...tings-and.html

Lots of good stuff in the links, especially the Sacramento Sky Ranch
ones.

Have you looked at an Ercoupe fuel system? Two wing tanks in common
(IIRC), pumping with a mech. pump, continuously to a small (5 gal.?)
header tank. Header tank overflows back to a wing tank when it's full.
Header tank feeds the engine via gravity flow.
When the wing tanks are empty, the header tank float & wire gauge
begins to drop. At the moment, you know exactly how much fuel is left.
Works excellently and is very simple. If the pump fails, you still
have the header tank.

Rich S.

wrote:
Have you looked at an Ercoupe fuel system? Two wing tanks in common
(IIRC), pumping with a mech. pump, continuously to a small (5 gal.?)
header tank. Header tank overflows back to a wing tank when it's full.
Header tank feeds the engine via gravity flow.
When the wing tanks are empty, the header tank float & wire gauge
begins to drop. At the moment, you know exactly how much fuel is left.
Works excellently and is very simple. If the pump fails, you still
have the header tank.

Rich S.

wrote:
Have you looked at an Ercoupe fuel system? Two wing tanks in common
(IIRC), pumping with a mech. pump, continuously to a small (5 gal.?)
header tank. Header tank overflows back to a wing tank when it's full.
Header tank feeds the engine via gravity flow.
When the wing tanks are empty, the header tank float & wire gauge
begins to drop. At the moment, you know exactly how much fuel is left.
Works excellently and is very simple. If the pump fails, you still
have the header tank.

Rich S.

I wonder about paralleling the pumps, instead of series.---If you run
both for takeoff/landing you get double the pressure..(may flood engine)
In series, if one stops up w/trash, there's no route around it.
there's a very small leak back orifice to prevent
Heat-expansion/flooding. Jerry

"Jerry Wass" wrote
I wonder about paralleling the pumps, instead of series.---If you run
both for takeoff/landing you get double the pressure..(may flood engine)
In series, if one stops up w/trash, there's no route around it.
there's a very small leak back orifice to prevent
Heat-expansion/flooding. Jerry

Parallel should get you the same pressure, but with double the flow, no?
--
Jim in NC

On Oct 19, 5:31*pm, Jerry Wass wrote:
wrote:
Have you looked at an Ercoupe fuel system? Two wing tanks in common
(IIRC), pumping with a mech. pump, continuously to a small (5 gal.?)
header tank. Header tank overflows back to a wing tank when it's full.
Header tank feeds the engine via gravity flow.
When the wing tanks are empty, the header tank float & wire gauge
begins to drop. At the moment, you know exactly how much fuel is left.
Works excellently and is very simple. If the pump fails, you still
have the header tank.

Rich S.

I wonder about paralleling the pumps, instead of series.---If you run
both for takeoff/landing you get double the pressure..(may flood engine)
In series, if one stops up w/trash, there's no route around it.
there's a very small leak back orifice to prevent
Heat-expansion/flooding. *Jerry

RE the Ercoupe example: I don't like header tanks from a crash safety
standpoint, and another vent, and a return line souunds like MORE
plumbing to me. Plus, this is a VW conversion, and if I used a
mechanical fuel pump it would be on the TOP of the engine, plus they
are not sealed like aircraft mechanical fuel pumps are, so this is a
no-go.

Paralleling the pumps also introduces more fittings. There are finger
strainers in the fuel tanks to keep out the big crap, plus the fuel
pumps only see fuel coming FROM the gascolator, so that failure mode -
jamming due to FOD - seems to unlikely to plan around, IMHO. I'm more
concerned about an electrical fault, or the failure of the pump itself
due to some internal fault, thus Series makes more sense to me. And
the pumps already have more than enough flow for full throttle.

Thanks for the feedback, it keeps me thinking, the point of the
exercise.

On Oct 20, 8:43*am, flybynightkarmarepair wrote:
On Oct 19, 5:31*pm, Jerry Wass wrote:





wrote:
Have you looked at an Ercoupe fuel system? Two wing tanks in common
(IIRC), pumping with a mech. pump, continuously to a small (5 gal.?)
header tank. Header tank overflows back to a wing tank when it's full..
Header tank feeds the engine via gravity flow.
When the wing tanks are empty, the header tank float & wire gauge
begins to drop. At the moment, you know exactly how much fuel is left..
Works excellently and is very simple. If the pump fails, you still
have the header tank.

Rich S.

I wonder about paralleling the pumps, instead of series.---If you run
both for takeoff/landing you get double the pressure..(may flood engine)
In series, if one stops up w/trash, there's no route around it.
there's a very small leak back orifice to prevent
Heat-expansion/flooding. *Jerry

RE the Ercoupe example: I don't like header tanks from a crash safety
standpoint, and another vent, and a return line souunds like MORE
plumbing to me. *Plus, this is a VW conversion, and if I used a
mechanical fuel pump it would be on the TOP of the engine, plus they
are not sealed like aircraft mechanical fuel pumps are, so this is a
no-go.

Paralleling the pumps also introduces more fittings. *There are finger
strainers in the fuel tanks to keep out the big crap, plus the fuel
pumps only see fuel coming FROM the gascolator, so that failure mode -
jamming due to FOD - seems to unlikely to plan around, IMHO. *I'm more
concerned about an electrical fault, or the failure of the pump itself
due to some internal fault, thus Series makes more sense to me. *And
the pumps already have more than enough flow for full throttle.

Thanks for the feedback, it keeps me thinking, the point of the
exercise.- Hide quoted text -

- Show quoted text -

Ryan,
I fully understand your dislike of a header tank, but have you
considered a small fuel cell instead. You achieve enhanced fire safety
as well as a centralized fuel gathering site which would feed to the
gascolator. Also insofar as fuel pumps are concerned what are the
possibilities regarding the use of an electric fuel pump?
Joe

Copperhead wrote:
On Oct 20, 8:43 am, flybynightkarmarepair wrote:
On Oct 19, 5:31 pm, Jerry Wass wrote:





wrote:
Have you looked at an Ercoupe fuel system? Two wing tanks in common
(IIRC), pumping with a mech. pump, continuously to a small (5 gal.?)
header tank. Header tank overflows back to a wing tank when it's full.
Header tank feeds the engine via gravity flow.
When the wing tanks are empty, the header tank float & wire gauge
begins to drop. At the moment, you know exactly how much fuel is left.
Works excellently and is very simple. If the pump fails, you still
have the header tank.
Rich S.
I wonder about paralleling the pumps, instead of series.---If you run
both for takeoff/landing you get double the pressure..(may flood engine)
In series, if one stops up w/trash, there's no route around it.
there's a very small leak back orifice to prevent
Heat-expansion/flooding. Jerry
RE the Ercoupe example: I don't like header tanks from a crash safety
standpoint, and another vent, and a return line souunds like MORE
plumbing to me. Plus, this is a VW conversion, and if I used a
mechanical fuel pump it would be on the TOP of the engine, plus they
are not sealed like aircraft mechanical fuel pumps are, so this is a
no-go.

Paralleling the pumps also introduces more fittings. There are finger
strainers in the fuel tanks to keep out the big crap, plus the fuel
pumps only see fuel coming FROM the gascolator, so that failure mode -
jamming due to FOD - seems to unlikely to plan around, IMHO. I'm more
concerned about an electrical fault, or the failure of the pump itself
due to some internal fault, thus Series makes more sense to me. And
the pumps already have more than enough flow for full throttle.

Thanks for the feedback, it keeps me thinking, the point of the
exercise.- Hide quoted text -

- Show quoted text -

Ryan,
I fully understand your dislike of a header tank, but have you
considered a small fuel cell instead. You achieve enhanced fire safety
as well as a centralized fuel gathering site which would feed to the
gascolator. Also insofar as fuel pumps are concerned what are the
possibilities regarding the use of an electric fuel pump?
Joe

If you can find an early post--it has his blogsite, with pix showing two
Facet electric fuel pumps--W/ #6 jic fittings integral to the pumps.Jerry

On Oct 20, 8:17*am, Copperhead wrote:
On Oct 20, 8:43*am, flybynightkarmarepair wrote:





On Oct 19, 5:31*pm, Jerry Wass wrote:

wrote:
Have you looked at an Ercoupe fuel system? Two wing tanks in common
(IIRC), pumping with a mech. pump, continuously to a small (5 gal.?)
header tank. Header tank overflows back to a wing tank when it's full.
Header tank feeds the engine via gravity flow.
When the wing tanks are empty, the header tank float & wire gauge
begins to drop. At the moment, you know exactly how much fuel is left.
Works excellently and is very simple. If the pump fails, you still
have the header tank.

Rich S.

I wonder about paralleling the pumps, instead of series.---If you run
both for takeoff/landing you get double the pressure..(may flood engine)
In series, if one stops up w/trash, there's no route around it.
there's a very small leak back orifice to prevent
Heat-expansion/flooding. *Jerry

RE the Ercoupe example: I don't like header tanks from a crash safety
standpoint, and another vent, and a return line souunds like MORE
plumbing to me. *Plus, this is a VW conversion, and if I used a
mechanical fuel pump it would be on the TOP of the engine, plus they
are not sealed like aircraft mechanical fuel pumps are, so this is a
no-go.

Paralleling the pumps also introduces more fittings. *There are finger
strainers in the fuel tanks to keep out the big crap, plus the fuel
pumps only see fuel coming FROM the gascolator, so that failure mode -
jamming due to FOD - seems to unlikely to plan around, IMHO. *I'm more
concerned about an electrical fault, or the failure of the pump itself
due to some internal fault, thus Series makes more sense to me. *And
the pumps already have more than enough flow for full throttle.

Thanks for the feedback, it keeps me thinking, the point of the
exercise.- Hide quoted text -

- Show quoted text -

Ryan,
I fully understand your dislike of a header tank, but have you
considered a small fuel cell instead.

Yes, I have. They are heavier than a tank without their features
would be, and the "stock", relatively inexpensive ones don't have the
vents and outlets arranged in a particularly convenient way, plus I
don't really have the space for them.

Also insofar as fuel pumps are concerned what are the
possibilities regarding the use of an electric fuel pump?

I guess you mean the failure possibilities.

First, I want to clarify one key point. Only one pump operates at a
time. The primary pump is also wired so that it ONLY operates when
there is oil pressure. The secondary pump is wired seperately,
perhaps even to a secondary battery, and is direct, and controlled by
a big, boldly marked switch in the panel.

My understanding is that these pumps are a solenoid driven by an
oscillator driving a power transistor. The oscillator circuit board
sometimes fails due to the usual reasons electronics fail. That's
about the only failure mode worth mentioning.

A few links, that are on my blog, but this discussion seems to have a
life of it's own, so:

http://www.flycorvair.com/601Sep2004.html Scroll down to see the
Model System I'm riffing off of, and a discusion of why the mechanical
pump on this installation was removed. There is a pretty complete
description both of the original arrangement WITH a mechanical pump
and the final version WITHOUT one.

http://www2.cip1.com/PhotoGallery.as...27%2D025 %2DG
Stock VW fuel pump. Push-on hose barbs, all sealed up, so no way to
safety internals. Not particularly confidence inspiring.

http://www.pilotfriend.com/experimental/build_17.htm Great article by
Lyle Powell on fuel systems, originally published in Sport Aviation,
and recommended by the Ellison people. Some of his conclusions can be
VERY difficult to implement, such as no tanks without sumps.

"Copperhead" wrote in message
...
Also insofar as fuel pumps are concerned what are the
possibilities regarding the use of an electric fuel pump?

Electrical fuel pumps are very reliable things, electrical systems are
unfortunately somewhat less reliable. The first is useless without the other.

I had an alternator quietly die on a cross country in a rental airplane a
year or two ago. I noticed the problem when my low voltage light winked on.
Shortly after that, radios and other electrical gizmos started to die in spite
of my power conservation efforts. Since it was a gravity feed Cessna, it sure
was nice to not have to wonder when the engine was going to stop.

If I can't have gravity feed, give me the combination of a mechanical pump
backed up by electrical boost pumps.

Vaughn