AX-O

AX-O

Well Known Member
I am building my wings and have been thinking about fuel lines. I want to use a fuel-injected engine (most likely an IO-360 180 HP). I spoke to a friend of mine and asked him if he had a return line from the engine (for fuel overflow) to the fuel thanks and he told me no. He also has an IO-360. He told me that his return line goes directly to the fuel valve. I have a few questions. When the overflow fuel from the engine goes out on the return line, is there a mixture of air and fuel or is the line just full of fuel? Has any one done the same thing he has done? He says it works fine and has had no issues. His fuel valve is Left/Right and Off. So he needs to switch thanks every 30 minutes of flight. I want to have a fuel valve with Left/Right/Both and off. Would a system like his work with the fuel valve that I want? And last, if you have a fuel system diagram for your bird, can you please post it. Like every person that builds an aircraft, a lot of learning needs to occur and this is a section that I am weak on. Thanks for any help.
 
Others can give better answers / more specifics, but...

The fuel return is based on the type of injection system you have. Some injection systems send a huge volume of fuel to the engine and then return the unused. I plumbed an extra 4D fitting into each tank in case I use a system that requires this return - it really added only a few minutes (and a few ounces) to the build.

"Both" tanks is not an option on low wing airplanes; I think the reason is due to head pressure in the tank (or lack thereof in a low wing airplane) and the fact that the engine could suck air from an empty tank when on both. That may not be the best explanation... ?

Thomas
 
I would be concerned as well with heat saturation of the fuel, with the excess fuel being warmed during it's trip under the cowling, and then recycling through the fuel valve back in again. Seems to me to be a good recipe for vapor lock.
 
The FI systems we use at work bypass a large volume of fuel, it builds up alot of heat if it is not returned to the tank, or run through a cooler. Having it run circles in a small run will heat it up. I suppose it all depents on the FI pump the engine builder uses, typicaly the high pressure FI pumps dont like to be run dead head, and thus need to bypass alot of fuel at the regulator. The only gotcha in plumbing for this is you fuel selector has to also change the return line. I think Andair makes a 6 port duplex valve which is basicaly two sets of valves stacked on top of each other.
 
Some Don't

Some FI systems don't require return fuel lines.
I have an Aero Sport Power IO-360M1B with Precision FI.
It does not require and does not have return fuel lines.
Might be time to make an engine decision in order to possibly avoid a lot of extra work.
Pete.
 
This has been covered a bunch of times before but to reiterate:

Precision Silver Hawk, or Bendix RSA systems: no return required.

Airflow Performance: Purge return to one of the tank feed lines. There is no fuel returning after the engine is running. A dedicated return line to the tank is not required.

ECI Fuel Injection system: A return line is required to each tank. A duplex valve should be used for this application.

Aerosance Fadec: Don?t know.

Any type of automotive electronic fuel injection: Requires a return line back to each tank. A duplex valve should be used.

You should check with the manufacture of the fuel injection system you install on your engine to get the correct facts on return line size (if one is required) and another installation issues that particular system requires.

Hope this helps

Don
 
No return...

mgomez said:
I just looked at the installation drawings for the Precision Silver Hawk, here:

http://www.precisionairmotive.com/Publications/EX-5VA1 detail spec 120503.pdf

The drawings shows both a fuel inlet and a fuel outlet on the servo. What's the outlet for? From your statement above, I guess it mustn't be for a fuel return line?

Thanks,
Martin
Click to expand...

Martin... the servo unit is an in/out unit. The out goes to the fuel injectors.

From this page...

http://www.precisionairmotive.com/silverhawkmiscparts.htm

Fittings
Inlet Fitting - Fuel Line to Servo: Standard #6 (9/16 x18 straight thread)
Outlet Fitting - Servo to Flow Divider: Standard #4 (7/16 x 20 straight thread)
Unmetered pressure port (on top of fuel inlet screen): Standard #4 restricted fitting

Confused me too at first.... :)

gil in Tucson
 
Oh boy, do I feel dumb!

az_gila said:
Martin... the servo unit is an in/out unit. The out goes to the fuel injectors.
Click to expand...

Thanks, Gil. Duh...I feel like an idiot. I should probably install a carb...clearly my brain is stuck in that mindset!

Cheers,
Martin
 
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