Brian,

 Congrats. You are going to love the RV-4!

 I flew mine today for the first time in 4 months. I had a partial power
 loss back in March that really got my attention. A temporary loss in fuel
 pressure. I've gone through the entire fuel system and haven't found an
 explanation. So it was either time to sell the airplane or get back on
  the
 horse.

 snips...........


 Mike Wills

 Mike, two pumps? Where are they mounted?
 Brand of fuel pressure regulator used?
 I assume you have fuel filters.
 Has Dave Leonard looked it it with the cowl off?
 Let me know when you will be in the hangar and I will
 try to come down and have a look.

 Paul Lamar

Paul,

Fuel system is I believe similar to what Ian Beadle in AUS had (is he
  still
around?). Separate pump for each tank. Pumps mounted close as possible to
the tanks. Outputs T'eed together feed the fuel rail. Return through an
adjustable regulator (Aeromotive) and to an electric fuel selector so
return
fuel goes back to where it came from. Switching tanks also switches fuel
pumps.

Incident happened while in a 30 degree left turn (burning from the left
tank). The turn was coordinated. Tank was about half full (about 7
gallons).
Lost power and switched tanks immediately. Power was restored as the
  engine
monitor triggered a low fuel pressure alarm. Flew back home (75 miles) on
the right tank with no problem.

I've checked everything over and done lots of ground testing without a
re-occurance. Needless to say the next few flight hours will happen right
over SDM.

Not sure when I'll be back out there to mess with it - it's the peak of
  the
soaring season! Priorities.

Mike

Sounds like a slosh. It is amazing how fast a fuel injection engine
will quit with a momentary loss of fuel pressure. Probably best to
put a 1/2 gallon pressurized tank up on the firewall someplace. You
might climb up to 10,000 feet or so near an uncontrolled airport and
see if you can get it to do it again with a knife edge on the
half empty tank side.

I was flying a Mooney and the engine quit with a bang. It was so loud
I thought it was a mechanical catastrophic failure in the hand grenade
mode. Fortunately I was high IFR (I Follow Roads.) and near Lordsburg
Muni NM. Turned out the high pressure mechanical fuel pump failed. I
rented a C172 to get home and ironically the carb float sank around
Phoenix. Had to keep it running while pumping the leaning knob and
made an emergency landing. Bad day :) My now ex girlfriend (long
before Robin) never flew again :)

What kinds of pumps are you using? Make sure the built in one way
output valves are working. Probably a good idea to use external
one way valves as redundant back ups.


Paul Lamar

  Mike,

  I'll add my 2 cents worth if that's ok.
  I was curious if you have fuel slosh doors built into your wing tanks?
  My Lancair ES has those.  Their purpose is to maintain an adequate fuel
  supply in the first bay, even during uncoordinated turns.
  They let the fuel into the bay, but shut if the flow tries to reverse and
  flow outward.  No fuel related issues in 3 years of flying.  May be worth
  considering.
  Just a thought...

  Mark S.

  Mark, how is the EFI diagnostics coming?
  What have we learned? :)

  Paul Lamar

Mark,

Thanks for the input. My tanks are per Vans plans, i.e. no trap doors. The
ribs form the baffles with a 1" hole in the low corner to let fuel migrate
to the innermost bay. A temporary unporting of the pickup is the likely
cause, but I didn't want to believe it because this should have been a
pretty benign maneuver. A mild bank angle, coordinated turn in smooth air
with plenty of fuel in the tank. I'll have to think on the best (easiest)
way to engineer some sort of header tank that wont unport.

Mike

We have had some long discussions on this off and on for the past
12 years. A very important subject and the cause of many accidents.

A lot of EFI  systems have rather large rubber lines. The rubber
lines expand under the 50 psi pressure and act as a small pressure
accumulator.  That is assuming the one way valve built in to the out
let of the pump is working.

IMHO probably the reasons more low wing pilots don't
experience this is most A/C engines use carbs and the engine will run
momentarily with just the fuel in the float bowl. Might lean out
momentarily but that is about it. High wing pilots leave the fuel
selector on "both" most of the time. I slip the C182 in almost all of
the time in both directions and I have never had the engine stumble.
However I may never have had a completely empty tank on the high side.
If you are high enough to slip you are high enough to make
the runway with a dead engine anyway. Of course flight instructors
don't teach slips probably for this and other reasons.

Just a pressurized sump won't do it unless the pump feeding it can
suck and pump high pressure air. Some can and some can't. More on that
later. You will probably need a tiny vent line or needle valve to bleed
off the air back to a main tank.

If it is unpressurized the pumps have to go between the sump and the
engine of course. Then you will need low pressure pumps to keep it full.
It will have to be vented back to the main tanks.

Tracy's RV4 uses one tank to feed the high pressure pump and a low
pressure pump to transfer fuel from the aux tank to the main tank.
Not a bad idea but still will not address the slip
situation.

You could put a rubber bladder inside the 1/2 gallon
pressurized sump tank and fill it with 30 psi or so. The pump
will compress the bladder and increase the pressure. The other
way is make it a cylinder with O-rings and put a strong spring
on top of the piston. Something like four inches in diameter
eight inches high. 10 gallons an hour.. 1/2 gallon.. 1/20th of
an hour or 3 minutes.

Just an idea.

Here is some info on EFI pumps. I like the Airtex.
Surprisingly it is the cheapest of the three. The GM/Mazda
will not suck well and is designed to go into the tank and
be immersed in fuel.

Bottom line EFI systems will quit lickity split under a momentary
loss of fuel pressure with solid lines :)

---------------------------------------------------------

Here is some more info and an idea we have not discussed yet.
Namely two pressure regulators one for each pump and each
tank. Could greatly simplify most EFI systems. If rubber hose
is used it is less likely to quit on a momentary loss
of fuel pick up. See the Bosch return line jpg.

The Wright brothers system will only work at one power
level but will get you home in a computer failure situation.
You will need a gravity feed tank and a hand pump to keep
it full in a low wing.

Paul Lamar

Hi You Guys

I see the comment about the pump not sucking very well.
The Andair made pump that self primes to lift 10feet here's a link.
http://www.youtube.com/watch?v=OsC7MQp0Ii8
Ok it is pricey but it is also very light.

Clive Uk

Both the Walbro and the Airtex roller vane will lift 10 feet.
Airtex appears to be getting out of the roller vane biz.
The new Airtex appear to be in the tank pumps only.
MSD roller vane pumps are near identical to the old Airtex
roller vane pumps.

These Andair pumps are boost pumps not intended for EFI as they only
go to 25 psi. EFI needs 50 psi and up. Also the flow is
marginal at 16 GPH even for a six cylinder A/C engine.
At .6 BSFC a 250 HP A/C engine requires 24 GPH. At 440 pound
Sterling each they are worth their weight in gold :)
Most EFI pumps are under $100 in the US.

http://www.andair.co.uk/system/index.html

BTW Beware of the Andair valves. They may have improved them
since but a few years ago the detents were not strong enough.
Check them out before you buy at their booth in OSH or Sun N Fun.


Paul Lamar