Why design a return less system?  One of the big advantages of using the rotary is
the ability to use a fuel return system!  Yes you have to deal with routing a
fuel return line - no big deal though in the overall scope of the project.
The big advantage is that it eliminates virtually all risk of vapor lock and
hot start issues.  This is important especially if you want to run winter blend
mogas at high altitudes.  Fuel return also greatly diminishes the possibility
of water contamination.  Once that pump is circulating, even modest amounts of
water in the system are quickly removed from the injectors.

The same goes for contamination from a 2-stroke oil bolus.  When I go somewhere
on cross country and fill an empty tank, that is a big gulp of 2-stroke oil that
needs to be mixed in.  I try to shake it up, but on a number of occasions it has
not completely mixed, causing quite an engine stumble.  If it were not for the
return line bringing most of that oil back to the tank, the engine may have quit
and I may never have gotten the engine started in time.

Take my word on this one (and I cant remember ever having said that before) -
GO WITH THE FUEL RETURN SYSTEM!  Put your EFI pumps in the tank if you want,
but they will be easier to service outside the tanks.  Put them low, just outside
the tank or inside the fuse.  You won't be sorry.  I used scrap aluminum to build
a nice little cubby that houses the valve and both pumps, just forward of the spar
on the pilot's side.  makes for a nice cup holder too.  will try to get a
picture on of these days.


-- David Leonard

Turbo Rotary RV-6 N4VY
http://N4VY.RotaryRoster.net <http://n4vy.rotaryroster.net/>
http://RotaryRoster.net <http://rotaryroster.net/>


Watch the movie clip.
I turn the pump on, the hose jerks  and the fuel rises
in the line. The pump is located seven feet
above the can of paint thinner. That is with an open
injector. With a closed injector it takes just a second
or so longer. I double checked the current consumption
and it is exactly 3 amps at exactly 12 volts.
You are not going to beat this roller vane pump.

Dave Leonard is right about the return system.
I think it is the best for aircraft. It will
purge water, air and will start when hot.
I think the main driver for the non return
systems in cars is lower cost and evaporator
controls. Not a factor in an aircraft.

Paul Lamar

Paul -

That is quite a rise for "sucking" fuel.  BUT ...

The fuel isn't HOT, is it?  Or any number of other factors related to
aviation use, safety, and reliability.  I plan to put the pumps in-
tank or right-at-the-tank in any case.  Right-at-the-tank would be
more serviceable.  In-tank would be quieter.  (Don't laugh)


Everyone -

Dave Leonard DID bring up excellent points we should all consider
about return vs. returnless systems.  Unless someone on-list objects,
I am going to change focus to designing a RETURN system.  (Returnless
systems should have a purge option ... more complexity.)

I have been following your crumbs to identify candidate EFI pumps that
can be PWM operated.  I'm not sure how best to design with PWM on a
return system, or if the added controller is worth the installation
effort to save amps and increase pump life.  (Just thinking out loud.)

One idea is to use a fixed orifice to return fuel to the tank, and
then use PWM to control pressure.  Any ideas, guys?  Or is PWM dead
because of Dave Leonard?  (Yeah, it's all his fault.)

-Vince Orton

I was amazed at that amount of draw. I was also amazed how little
current is required for that roller vane pump. Your typical EFI system
uses very little current. The saturated injectors like the yellow RX8
use only about .8 amps apiece. The whole idea is to get the current
down so the battery will last longer in the event of an alternator
failure.
Gives you more time to find a place to land.

I think it is worth PWM for several reasons and that is to
reduce the current consumption, the volume of fuel
returned and heated up.

Paul Lamar

"Ian & Irene Beadle wrote:
I put the digital ammeter on my 13B fuel injected (Michrotech) RV6A
at the weekend.
Static test: Ignition & fuel pump. 3.8 Amps. Ignition(& computer)
only 0.8 Amps.
Radio 1Amp. Instruments 0.7 Amp. Strobe 1.4 Amp.  At 3000RPM. Ignition,
computer & fuel pump 4.3 Amp. At 3600 RPM 4.8 Amps.  So with 15 Ahr.
battery plenty of time to find an emergency landing spot if the
alternater or belts fail. The digtal ammeter was checked for calibration
against an analogue type using high wattage globes. The meter and
leads introduce a small error due to their resistance.
Ian  Beadle"

In the case of loosing a belt, I would bet that the battery would last
longer than the cooling system.  Better get it on the ground asap if you
loose a belt.

Mark S.


Good point Mark!

Paul Lamar