Fuel line fitting

[gregsonex]

I read a few previous posts on the fuel line fittings and it seems some were happy to go with AN fittings and aluminum solid tube. Have others tried flex tubing and why not also use a fuel filter?

[Bryan Cotton]

Firewall forward, I have both a filter and flex line. I think it is mandatory to use flex line there because of engine movement.


Inside I used solid tubing. You could use flex line here too if you wanted. This picture was not my final installation. I added an angle shim to make the angles good and to keep the fuel going downhill.

[Bryan Cotton]

Another view of the inside plumbing:

[gregsonex]

Super helpful Bryan. I went with a fire sleeve from my red cube for the FWF. Is there any benefit or reason the fuel filter should be on firewall forward or does it matter?

[Bryan Cotton]

Greg,
It probably doesn't matter. I don't think I could have gotten my inside plumbing the way I wanted with the filter inline inside. I have two layers of firesleeve outside both for fire protection and insulation.

There is one advantage of having the filter forward of the firewall. You should be checking/cleaning the filter at annual. I find a little sediment in mine every time (twice) so far. When I clean my filter some avgas dumps out on the floor and I can use it to clean up the oil under the engine. Otherwise it goes on the cockpit floor where it serves not much benefit.

[karmarepair]

If I had mine to do over, I would NOT use the AN fittings at the firewall, but would stick to the plans and pass the formed hard line THROUGH the firewall. Eliminates possible leaks where they are almost impossible to access once the plane is assembled.

I have a gascolator, which complicates the plumbing, but at least the leaks will be where you can wrench on them. I have heard the argument that anything that can pass through the finger strainer will pass through the AeroInjector, but if you have a float bowl carb or a Red Cube you may want a filter

[Bryan Cotton]

On my setup I can get wrenches on all the joints, but the inside firewall one is a pain now that the floor is on. I've generally not had leak issues with AN fittings.

[builderflyer]

If I had mine to do over, I would NOT use the AN fittings at the firewall, but would stick to the plans and pass the formed hard line THROUGH the firewall. Eliminates possible leaks where they are almost impossible to access once the plane is assembled

I agree with this basic premise not because of possible leaks but rather the concept that "anything" we insert into the fuel line between the tank and the carburetor adds up to a drop in fuel pressure that, collectively, the engine's smooth operation may not tolerate. Only add those items to the fuel system that you believe you absolutely must have and not those that may be considered optional. Your engine will likely thank you for it with the absence of burps, for example.

Art,,,,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,,,,Jabiru 3300 #261

[Bryan Cotton]

I agree with this basic premise not because of possible leaks but rather the concept that "anything" we insert into the fuel line between the tank and the carburetor adds up to a drop in fuel pressure that, collectively, the engine's smooth operation may not tolerate. Only add those items to the fuel system that you believe you absolutely must have and not those that may be considered optional. Your engine will likely thank you for it with the absence of burps, for example.

Art,,,,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,,,,Jabiru 3300 #261

I agree with the philosophy of only adding what you need. That's one reason I left off the flow meter. For a 3/8" fuel line at our rates for GPH, an AN bulkhead fitting will show no appreciable pressure drop. Plus when I did my minimum fuel, nose up fuel flow test I had waaay more than the minimum recommend GPH.

Edit:
viewtopic.php?f=39&t=578&p=46815#p46815

From 4 to 3 gallons 24.3 GPH average
From 3 to 2 gallons 18.7 GPH average
From 2 to 1 gallon 14.2 GPH average
From 1 to empty 11.4 GPH average

[builderflyer]

[quote="Bryan Cotton"

I agree with the philosophy of only adding what you need. That's one reason I left off the flow meter. For a 3/8" fuel line at our rates for GPH, an AN bulkhead fitting will show no appreciable pressure drop. Plus when I did my minimum fuel, nose up fuel flow test I had waaay more than the minimum recommend GPH.

Edit:
http://www.sonexbuilders.net/viewtopic. ... 815#p46815

From 4 to 3 gallons 24.3 GPH average
From 3 to 2 gallons 18.7 GPH average
From 2 to 1 gallon 14.2 GPH average
From 1 to empty 11.4 GPH average[/quote]

Measured fuel flows are more of an issue for those of us with larger hp engines and their greater demands for adequate fuel flows. But, I can't say, though, that I've found a direct connection between measured fuel flow rates and the ability of the fuel system to produce "burps", or not.

When I compared my original fuel system with another builder who also had the 3300 engine and had an identical fuel system to the one I used to have except that he didn't install a bulkhead fitting and I did, and he had no issues with the "burps" and I did..........I have to blame the bulkhead fitting, at least until I would remove it and see what happens. I've been flying my Sonex for 19 years but there is still some experimentation to do. Keeps experimental aircraft life interesting.

Art,,,,,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,,,,,,,Jabiru 3300 #261