Uniflow plumbing reversed?

[Dennis Toth]

Guys,
After having tried muffler pressure on my El D with the Fox 35 it seemed that all was fine until the uniflow vent uncovered then it went pretty lean for about 12 laps. I know the standard fix is to move the uniflow line closer to the end of the pickup to reduce the amount of fuel at the end. However, I was wondering if anyone has ever reversed the postion of the lines and put the vent near the back of the tank and the pickup in front? The thinking is to hold the run steady until the fuel is out and not have the engine go lean, just a quick rev and off. Anyone try this? What happen?

Best,          DennisT

[Jim Thomerson]

I would expect the engine to go rich when the uniflow comes out of the fuel.  I have made uniflow tanks with the uniflow everywhere from the front of the tank, to back 1/2 inch in front of the pickup at the rear of the tank.  They all seemed to run about the same. 

[john e. holliday]

Put a wedge under the back of your tank on a profile, or cant it with the back to the outside of the circle on full fuse stnter.   I usually only have about 4 or 5 laps of lean to warn me the tank is almost done.

[Paul Smith]

It's not a perfect world.

It the uniflow and pickup vents are too far apart and you get more bad time at the end.
Too close together and you get a whole bad run.

[EddyR]

On tanks with a wedge I have placed the uniflow tube anywhere from the front of the tank to the back. As long as the unifow is under fuel it will work. Front ourside corner will work.
Ed

[Dennis Toth]

I have also made different uniflow hard and soft tanks, this was the first round one. My flying bud's use this with DD engines and muffler pressure with great engine runs. They use a sintered filter on the pickup line and the normal clunk on the uniflow vent. Uniflow is about 1/2" from the pickup with the vent into the bubble at the top. The tank is mounted on the beam mounts with the center on center of the NVA, back is canted out about 1/8". All pretty normal layout. For mine all the piping is the same. In flight with muffler pressure the run is solid until the uniflow vent uncovers about 12 ish laps from the end then it goes pretty lean.

What I was looking to do is reverse the geometry of the pickup and uniflow vent, puting the u vent to the back of the tank to allow the pickup to uncover before the uniflow. The hope is to reduce the end of flight engine lean out to one lap or so.

Not wanting to reinvent the wheel, would like to know if anyone tried it and how did it work (or not).

Best,           DennisT

[EddyR]

Dennis
you figured out your own problem and it sounds like you know what you are doing. All I can add is do not tie the pick up tube and the uniflow together. Use a separate uniflow tube going half way back. Make is from copper not flex fuel tubing. The end can be moved up and down to adjust for equal run.
  I bet in that round tank the uniflow is uncovering to soon,But you new that already. Let us know what works.
Ed

[Dennis Toth]

I guess I will try a couple things, first I'll redo the pickup cluck to use a regular solid cluck, second I'll arrange the plumbing to have the uniflow closer to the pickup (in the past I set them so the uniflow would be inside the pickup line and end 1/16" ish before the pickup cluck starts off the tubing). Since the lines all come out the center with this arrangement I could actually try either pickup arrangement (pickup at the end of the tank, uniflow forward or vice versa).

Still can't believe no one else out there didn't try this.

Best,          DennisT