RCU Forums - Fuel Tank Positioning for Gas Engines?

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Bill Diedrich

03-01-2019 05:48 PM

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.

w8ye	03-01-2019 07:16 PM

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.

Bill Diedrich

03-02-2019 04:10 AM

Many Thanks

speedracerntrixie

03-02-2019 09:30 AM

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.

BarracudaHockey

03-02-2019 10:06 AM

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

speedracerntrixie

03-02-2019 10:12 AM

Andy, static position is very different then what an engine will see in flight. It’s not really about the pumps ability to pump the fuel but more like doing a bit of tuning to make it pump more consistent.

Truckracer

03-02-2019 12:40 PM

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.

Bill Diedrich

03-02-2019 02:56 PM

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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