Hello Paul,

 I am trying to determine the size of the return lines and volume of fuel
 returned as I plan for my EFI 13B.  I may have to create a header tank to
 handle
 the return and the question is, how big does it have to be?  Any rules of
 thumb?

 Thanks,

 William Hagood

 Most people use AN6 lines for fuel.

 The volume of fuel returned will be inversely proportional to the HP
 being generated. At idle and taxi it could be 80% of the fuel
 pumped. So the header tank will fill rapidly. The question then
 becomes what do you do with the header tank overflow?

 At take off and climb the fuel pumped is a max so the flow to the tank
 may be as little as 10 to 20 percent of the fuel pumped.

 Done wrong fuel can be pumped over board in short order through
 the tank vents.

 The traditional and safest way is use 2 tanks and a  two level
 valve and send the return fuel to the tank it is pumped from.

 A header tank, if used should be able to flow fuel back
 into the tank it came from. One gallon should be sufficient.

 Defective fuel systems are a major cause of engine
 stoppage and crashes. Particularly in low wing airplanes.
 They are tricky to design and they appear simple but are tricky
 to do right. The lowly vent system design is very important.

 One of the big mistakes is pointing  the vents in the
 direction of flight as dynamic pressure above 100 MPH
 will push the fuel out of the tank in a direction
 you may not want it to go. That is the same pressure fed
 to the air speed indicator by the pitot tube.

 Another mistake is having the vent lines coming out below
 the level of the fuel causing a siphon under certain
 circumstances.

 A third mistake is using a LEFT, RIGHT, BOTH & OFF
 fuel selector valve on a low wing airplane.

 Low wing airplanes should use only a LEFT, RIGHT & OFF
 fuel selector valve.

 The best and safest way is to copy certified aircraft
 fuel injection systems if possible.

 Paul Lamar



Paul,
The engine test stand you will get has an automotive tank with submerged
fuel pump, just as it came out of the car, no return, so you will get an
opportunity to see how that works. One of the last things that we were
adjusting was fuel pressure with the engine running, you may have to tweak
that a little. milo

OK Milo, We can handle it. No worries mate.

Paul Lamar


Copyright 1998-2010 All world wide rights reserved.

I'm confused. For the return fuel to exceed the capacity of the header tank,
more fuel would have to be introduced to the header tank. Example, worst
case scenario, if the engine is not running and the fuel pumps are on, isn't
all of the fuel that is going out of the header tank being returned to the
header tank through the fuel rail? Thus the net result in fuel is a wash and
no overflow....right? If the engine is running, then there is less fuel
being returned than is being pumped out....again no overflow. What am I
missing?

Sandy McNabb
Renesis in a Glass Goose

High mounted wing tanks are always easier to deal with.

Normally the high wing airplane type header tanks fill to the top
by gravity feed from both higher mounted Glass Goose wing tanks
so in your case everything is fine. Keep the header tank tall and
skinny. No double layer valves needed.

Run the header tank vent line up to the top of the cowl.

Perry Mick uses one header tank on his Long EZ but the bottom of the tank is
exposed to a cold blast of air. You may have fuel heating problems
when you get down to the last gallon or so in the header tank,

Paul Lamar



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