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Fuel Tank Positioning for Gas Engines?

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Old 03-01-2019, 05:48 PM
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Bill Diedrich
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Default Fuel Tank Positioning for Gas Engines?

I am in the process of converting an old biplane that had a Super Tiger 2300 on it to
a gas RCGF 30 twin (my first twin gasser). With the twin, the carb is hanging below
the engine, so where should the tank centerline be in relation to the carb? At present
the tank position is centerline with the crankshaft, making the carb below the bottom
of the tank! Should I lower the tank?

Thanks in advance for all opinions & answers.

Bill D.
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Old 03-01-2019, 07:16 PM
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w8ye
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Fuel tank position would only have CG and total weight considerations as fuel draw or siphoning are not part of the picture because of the pump and regulator of the carburetor.
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Old 03-02-2019, 04:10 AM
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Bill Diedrich
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Many Thanks
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Old 03-02-2019, 09:30 AM
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speedracerntrixie
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I like to mount the tank a bit above the carb on a gasser. Two reasons. One it will be easier to get a prime to the engine. Two, some gassers like to go a bit rich while inverted. When inverted the tank placement would then be below the carb making the pump work just a bit harder. That seems to lean the mixture just enough so that when properly tuned there is no noticeable fluctuations in rpm between upright and inverted.
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Old 03-02-2019, 10:06 AM
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BarracudaHockey
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I've run motors on the stand with 5 feet of tubing going to a gas can sitting on the ground 3 feet below the engine, it doesn't really matter on pumped gas engines IMO
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Old 03-02-2019, 10:12 AM
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speedracerntrixie
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Andy, static position is very different then what an engine will see in flight. Its not really about the pumps ability to pump the fuel but more like doing a bit of tuning to make it pump more consistent.
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Old 03-02-2019, 12:40 PM
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Truckracer
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No dog in this hunt for me. I've never had a gas powered airframe where I had much room to move the tank in a vertical line. Just fore and aft a bit for balance. I've had a few engines that ran a bit different in changing attitudes but was able to tune the problem out by means other than tank position because I didn't have a choice.
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Old 03-02-2019, 02:56 PM
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Bill Diedrich
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OK so the tanks stays where it at, Thanks for all of the reply's.
I can move it for and aft approx. 2 1/2" for balance.
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