Fuel tanks and CG's
08-18-2012, 05:05 PM
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Fuel tanks and CG's
Ok lets say I have a plane with a narrow fuselage and have the 16 oz fuel tank mounted over the wing centered on the CG.
When the tank is 1/2 way full will the plane experience drastic CG changes in flight as 8 ounces of fuel swashes back and forth in the tank?
08-18-2012, 06:19 PM
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RE: Fuel tanks and CG's
No, because the fuel can't move very far, so there a very short lever arm. Torque = length of lever arm x weight. As a guess with no calculation, I would think your CG might move a total of 1/16 in. ( That should encourage someone smarter than me to do the actual calculations.) Your vertical CG should move down more noticably as you run out of fuel.
08-18-2012, 10:29 PM
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RE: Fuel tanks and CG's
If it were something odd like a 1/2A long duration model then I'd say that you'd want to have baffles in it to slow down the migration of the fuel. But in your average model that uses such a tank the changes due to fuel sloshing are insignificant among all the rest of the stuff that is going on and the overall weight and size of such a model.
08-19-2012, 06:59 AM
#4
RE: Fuel tanks and CG's
Note also that you have to think about the center of mass of 8 oz of fuel. It's not running from one end of the tank to the other. It's only moving a few inches withinthe tank.
Now, if you have a leaky float and, when you nose in once clear of the treesto land, say, 10 ounces of water sloshes to the front (ahead of the prop) and suddenly your "up" elevator isn't. That was a noticable CG shift. ;-)
Now, if you have a leaky float and, when you nose in once clear of the treesto land, say, 10 ounces of water sloshes to the front (ahead of the prop) and suddenly your "up" elevator isn't. That was a noticable CG shift. ;-)
