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From: "Leon" <peon@pacific.net.au>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-743781@logan.com>
Subject: Return Fuel Line Sizes Clarification was : Returnless Fuel System - Fuel Cooler
Date: Fri, 18 Feb 2005 20:24:10 +1100
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Hi Bob,

Thanks for the comments.  Upon re-reading what I wrote,  I do need to
clarify what I wrote last post.  I should have been a little more succinct
in my statements,  as it sort of conveys a meaning slightly different to
that which I had intended.

You are QUITE correct in that the size of the return line SHOULD be the same
as the supply line.  If I am installing from scratch,  this is what I DO do.
Further,  factory installations DO usually use the SAME supply and return
line sizes.  Standard practice in the '86 and later rotary engined cars is
to use 5/16" steel lines for both supply and return.  I can't see the need
to go any bigger on an aircraft of the power outputs we are using.

Back to the practical realities,  in the interests of both ease and economy
when performing turbo conversions,  particulalrly on the early (pre '85)
RX7s,  it is normal practice to use the fuel lines that are there,
especially if we are only using moderate boost.  I can categortically say
that I have never had a fuel pressure problem at idle,  either with the
conversions that I have done,  or the ones that others have done that pass
through the workshop.

As I mentioned,  if we use a bigger pump (for more neddies),  we replace the
1/4" return line with a 3/8 line,  and use that as the supply,  and the
original 5/16" feed line as the return.

The reason for this is that when you look at the OUTLET of most factory EFI
high pressure pumps,  the INSIDE diameter of outlet nipple on the pump is
quite tiny,  which is why I usually can get away with using 1/4" return
lines.  The ID of the pump output nipple is the thing that limits the flow
capacity of the whole system.

***If however,  I'm using a big Bosch Motorsport pump,  or an SX,  or any
one of the other high capacity racing EFI pumps on the market,  then it's a
different matter.  The size return line then becomes a function of the ID of
the OUTLET nipple on the end of the EFI pump.  Again,  this becomes the
metering device which will limit the flow of the whole system at any given
pressure.  In race cars,  we normally use 3/8" supply AND return if we are
using big pumps.

So just to make sure,  check the ID of the output nipple on your EFI pump.
If you want to be doubly sure,  set up your pump & regulator on the work
bench and check for yourself that the return line is not restricting the
return flow at idle pressure. This is the only time where it will really
matter.

If you ARE plumbing from scratch,  for the power outputs we are using
(around 250 max),  5/16" supply and return lines are MORE than adequate,
and is what I would recommend,  and is what Mazda factory practice does.
However,  it is possible to use a 1/4 return line,  providing the pump
outlet nipple ID is the limiting diameter,  and not the return pipe ID.

Cheers,

Leon


----- Original Message ----- 
From: "Bob White" <bob@bob-white.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Friday, February 18, 2005 1:29 PM
Subject: [FlyRotary] Re: Returnless Fuel System - Fuel Cooler


>
> Hi Leon,
>
> Thanks for the comments.  This is the first response I've seen where the
> 1/4 inch line was addressed.  I certainly don't have any practical
> knowledge about what is needed, but was concerned that the 1/4 was too
> small.  My thought was that at idle, I'm pushing fuel into the rail with
> a 3/8 inch line and the regulator has to dump almost all of it back to
> the tank thru the 1/4 inch line. It seemed to me that that could mess up
> the pressure regulation.
>
> If you tell me it's OK, then I'll connect it up that way first.  I just
> consider Todd a bad infulence on me.  First with EWP's, then the
> returnless fuel system. :)  I should be getting some preliminary data on
> my EWP's in a few days.
>
> Even those cold climates can produce some pretty hot weather
> occasionally.  My wife is from North Dakota where 20 F below isn't too
> uncommon, but summer days can easily be in the 90's F (just not many
> of them).  I would have to go to Phoenix on a bad day to see your 50 C
> temps, or maybe Carlsbad, NM.
>
> Bob White
>
> On Fri, 18 Feb 2005 12:52:08 +1100
> "Leon" <peon@pacific.net.au> wrote:
>
> > Hey Guys,
> >
> > I'm sort of having trouble believing that this discussion is still going
on
> > about returnless systems. Why?? Todd probably gets away with his system
> > because
> > he lives in a REALLY cold climate.  He would DEFINITELY have SERIOUS
> > problems in the 50 Deg C heat we regularly expereience on the tarmac
here in
> > Oz in summer.  But then again,  maybe Lamar IS correct,  and that I AM a
> > lunatic!!
> > .
> > For the power output that most of you have (less than 250 BHP),  a 5/16"
> > high
> > pressure supply line is more than adequate,  and a 1/4" return line is
more
> > than adequate.  For bigger power output (Hi Boost 13B & 20B engines,
say up
> > to 400 Cheveaux) and a Hi Flo EFI pump ,  maybe a 3/8" supply line,  and
a
> > 5/16" return line.
> >
> > Whenever I do a turbo engine conversion on ROAD GOING early model RX7
> > ('79-"85),  I just use the stock fuel lines (5/16" supply & 1/4 return),
> > and I have never have a problem.  One EFI pump is sufficient.  The
> > only reason we have 2 x HP pumps on an aircraft is redundancy in case
one
> > fails at take-off and climb-out.
> >
> > However, the size of the return line is not really that critical.  All
it is
> > there for is to take the flow from the dumped pressure from the HP pump.
If
> > you are using the same pump as a car,  then you only need the same size
> > return.
> > Interestingly,  on the Mazda RX7 turbo cars,  they have a 2 stage
control
> > (via voltage) of the EFI pump to cut the return flow at low load,  and
boost
> > the supply at high load..
> >
> > The SIZE of the return line is not really so much an issue as actually
> > having one - size is more of an issue with the supply line,  but only
with
> > Mega-Pferd turbo engines.  The issue is that so long as there is a
return
> > line so that
> > the fuel continues to circulate back to the tank,  and if that tank is
in
> > the breeze,  the fuel will never get hot.
> >
> > If the fuel is returned to the header / surge tank,  this MUST be vented
> > back to the main tank.  Otherwise you will get air/vapour locks.  If
there
> > is a breeze directed over the header/surge tank,  then why do you need a
$40
> > cooler??  As a famous megalomaniac once said,  "It's either them or us"
> > (referring to issues of mental stability).
> > I'm just totally flummoxed.
> >
> > As Tracy said below,  the cooler is just a bandaid covering up a
problem.
> > It also scares me witless when I read what Tracy wrote below about a
> > fatality actually occuring because of dicey fuel supply issues.
> >
> > So please, ... this is a plea,  just follow normal EFI practice.
> > Have a look at the Toyota PDF link somebody posted a while ago about
both
> > return & returnless systems.  Stick to the return system.  This is the
way
> > it MUST be done.  Please DON'T
> > try to re-invent something that doesn't need to be re-invented,  and
that
> > has been proven to work on millions of EFI road cars,  and thousands and
> > thousands of race cars.
> >
> > Additionally,  that SDS link I posted the other day details how to do it
> > where there are multiple tanks involved.  There is a "critical minimum
> > complexity" in any system.  Try and simplify the system any further
beyond
> > this "critical minimum complexity",  then the system no longer works
> > properly,  and will come back and bite you REALLY hard on your
nethermost
> > parts when you least expect it!
> >
> > Cheers,
> >
> > Leon