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Re: REFLECTOR: fuel system



Subject: fuel system

  Do you think your fuel flow meter might be causing you some trouble with
air bubbles

No I dont. When I had clear lines on the test stand there were no bubbles
until after the restriction of the pressure regulator.  I tried squeezing
the tubing downstream of the regulator and there were no more bubbles --
upstream of the pinchpoint. The people at FloScan confirmed my observation
that a regulator or other restriction  would cause benzene or whatever other
low  boiling point stuff in the fuel  to "boil up"  in this situation. Thus
using two flow meters and measuring what is going out and subtracting what
is coming back would indicate that the engine was making fuel since  the
unconsumed fuel would have a larger volume due to the bubbles.

Will your system flow evenly from both main tanks to your sump?

I had a simulated wing tank feeding the real sump tank on the test stand. I
hope the common vent system does allow even flow.  I enlarged the lines from
each wing to the Flo Scan device  to 1/2  in hopes of improving the chances.


  My sump tank is tucked up tight against the spar so there's a little room
under it for some fuel line and part of one fuel pump, the other pump is
right next to it flat on the fuselage bottom.  One pump is a Subaru pump the
other is out of a Mercedes, both pumps have a small screen filter in front
of
them and the "parts guy" said both of these pumps were pretty bullet-proof.

That sounds less bulky than the Airflow Performance  filter in mine.

Since my pumps are both lower than the delivery line from my sump tank I'm
thinking that I should not have any priming problems.

That definitely should improve the priming. Russell Sherwood said he still
had some problems even  after moving his pumps as low as he could get them.
Mine wouldn't reprime with the pumps just above the sump  tank as long as
there was downstream pressure. Russell and I are both planning to use the
small orifice to bleed down the lines after the pump stops.

One item on my pre-flight is to take a fuel sample to check for water in my
fuel so I'm not too concerned about agitating water back into the fuel by
where I have my return line coming back to the sump.

 Should do it .

Do you use the aluminum vent manifold from the factory?  I have a 3/8" line
to the sump, a 1/4" line from each main tank and a 3/8" vent line to my
scoop going to this manifold.

Oh so now the factory provides one.
I made one in the past  but abandoned it for the nylon fitting and
polyurethane tubing approach. Its lighter and the polyurethane tubing is
"supposed " to be good on longevity , chemical , and abrasion resistance.

I'm wiring my pumps to my main buss, then to my panel.  I would like direct
control of the pumps, not the computer.  I don't think I'll use both pumps
except for take-off and landing and the only time we'll be turning under
3800 RPM is during taxi.  If this turns out to be a problem, having too much
pressure during taxi, I like your idea of making a resistor circuit to lower
pump output.

About one ohm .

Maybe you could temporarily use some clear polyurethane line  to see if you
are loading up with bubbles. Too bad we cant see into  the sump tank.

I have my main pump ( the one with the computer input and the modulator) on
my main buss. The aux (takeoff and landing ) backup pump is fed from my
emergency buss and can be fed from either 17AH battery with nothing
controlling it but me and a switch.
 Incidentally  as a further backup for my geriatric memory  I'm using a
circuit in parallel with the Aux Pump Pwr. switch so any time the oil
pressure is greater than 5# and the fuel pressure drops to 10#, if enabled
it turns on the backup pump.

My "Mustang" scoop where my vent line comes out is well forward of my
exhaust so I don't foresee any problems with over filling the fuel tanks and
having some vent out there.  I've incorporated an exhaust augmentor in my
lower cowl so the exhaust sweeps as far back as possible.  I also like your
idea to bleed a small quantity of fuel back to the sump tank before the
pressure regulator to neutralize pressure after shut-down to prevent priming
problems -- thanks for the tip.

How did you design your throttle quadrant? I scrapped all the linkage that
was there and built an aluminum bracket for my cable end to fit into from
there  I built an aluminum arm that actuates the butterfly in the throttle
body.  This way I eliminate all the springs that want to return the throttle
to idle.

What happens when the cable breaks?
Would the throttle plates open wide  with just manifold vacuum?

I started with the manual plan (mine is the old porthole,classic,topdoor,
whatever model) and modified  it.Since the SVX engine had provisions for  a
cruise control cable and a throttle cable  I  built both a left and right
throttle  all the way to the back to cover cable breaking. I  routed a
relating cable near the canard bulkhead  to tie above the fulcrum of one and
below the fulcrum of the other so both cables move together.That entertained
me for a few days.
Also  I mounted switches on both throttle levers to control the speed brake
and electric prop control.
This thing should be really safe, its getting too heavy to get off the
ground.


Wayne