Well...

As a starting point, put the effective center of the tank in line with the outlet of the spray bar, then adjust from there.

You may just have to get things as close as you can, and live with it not being ideal.

I hesitate to give this advise because I never did really get the hang of metal tanks, but here goes: since in a uniflow tank the effective center of the tank is the location of the vent, make a tank that comes to a wedge at the very top of the tank, and put the pickup and vent there.  Or, if you don't need that much height, put the uniflow wherever it needs to be, and the wedge to match.  This should, at the expense of losing some volume, raise the effective height of the tank.  Obviously, you'll have the joy of building your own tank.

You could also just take a regular tank and move the uniflow up.  This'll mean that when the tank gets down to the dregs it'll lean out more in level flight than inverted -- but you'll be able to just modify an existing tank instead of having to build up a new one.

Or just live with the fact that the tank height won't match in level and inverted flight.

If you use uniflow, the uniflow exit in the tank is the reference. This should line up with the NVA. This often located at center heigth

If the tank is standard, the center of the tank is the best reference as starting point .

If you use uniflow, the uniflow exit in the tank is the reference. This should line up with the NVA. This often located at center heigth

If the tank is standard, the center of the tank is the best reference as starting point .

       This is incorrect. Most metal tanks on the market have the uniflow exit at the top of the tank for convenience. If you align that with the NVA the tank will for sure ne too low. The location of the main pick up and the end of the uniflow vent in the tank is what affects the engine run.  Tank location will be a bit different for a full fuselage model than for a profile also. This stuff makes a difference, so make sure what you are referring to.

  Type at you later,
  Dan McEntee

       This is incorrect. Most metal tanks on the market have the uniflow exit at the top of the tank for convenience. If you align that with the NVA the tank will for sure ne too low. The location of the main pick up and the end of the uniflow vent in the tank is what affects the engine run.  Tank location will be a bit different for a full fuselage model than for a profile also. This stuff makes a difference, so make sure what you are referring to.

  Type at you later,
  Dan McEntee

The location of the uniflow exit IN the tank. Not outside the tank.

The location of the uniflow exit IN the tank. Not outside the tank.

    The way you have things worded is confusing. In a metal tank, the uniflow tube is usually in line with the fuel pick up, but positioned in front of it by at least 1/2".  The position of the fuel pickup is important for how the engine runs up right and inverted. In a metal tank, when they are both positioned on the same level, subtle corrections in the tank elevation are more effective. Yes, you can move the uniflow to effect how the engine runs up right and inverted, but you have to take the tank apart to move it and you need something else to support the end. If you have some sort of odd ball installation and have limited movement of the tank up and down, then you must build a custom tank to account for that and still keep both the pick up tube and the uniflow tube covered until the tank runs out.

  Type at you later,
    Dan McEntee

Actually, he was trying to use a Super Tigre G 34.  I suggested we try an FP-40 or a Brodak 40. The spraybar of the G 34 was at least a quarter of an inch higher than the FP 40 and the B-40.  Current thought is to install the B-40.   

  The ST.34 uses the same basic venturi set up as the ST-G51 does. I think the venturis are interchangeable. I have used the ST.51 to a great extent, and have never had an issue with having to excessively shim the tank around to get a good run. I mount the engine right to the engine bearers and then the tank sits on the munts also,  or on aluminum pads and I shim the tank to match the pads. You just have to allow for room in the tank compartment for it. Yopu should be fine doing the same with the ST.34. I have not known anyone to use that engine a lot, but curious as to how it will run for you. Super Tiger made a control line version of it, but I'm not sure if it had a different cylinder liner like the .51 has.
  Type at you later,
  Dan McEntee

Paul,

Thanks for sharing the info about tank vents.  For what it's worth, I was able to understand that "exit" referred to the flow of incoming air making its exit at the wet end of the uniflow vent tube.

The physics / mechanics of why the location of the vent tube within the tank is so critical eludes me, but I'm able to follow the practice you describe with good result.

Peter

   Looked at pictures of the ST/34 and like the 51 the needle is very high. Save the engine for inverted model or profile.
Ed

We didn't even finish the plane with that in.

You might want to measure the height of the venturi clamping bar above the engine bearers. If that is close to the usual 1/2", then all you need is a venturi set up for side feed. That setup will use a venturi with a smaller thru hole, ad a groove to clear the spraybar with a small pee hole in the center. This is pretty standard.

Remind me. Tank placement. I think tank outlet to motor should be exactly in line horizontally withe the motor fuel nipple correct? I’m completing a Veco Chief with an upright 34 motor. In order to accomplish the configuration the tank sits above the top of the fuse a good 1/2 inch. What will happen if the tank out line is below the motor intake?

Mount the tank so the outlet is level with the venturi.   Start the engine tune for a steady run. Invert the model. If the engine leans out, the tank was too high. If it gets rich, the tank is too low.