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Building Tips and technical articles. => Building techniques => Topic started by: Bob Disharoon on February 23, 2007, 04:44:42 PM
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Finished the plane , mounted the engine, checked the cg, added weight, got it balanced. Question: should the tank be full for proper cg balance or not?..thnx in advance, BOB ??? ???
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tank should be empty
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Never really thought about this before Robert, I just always do the c/g empty. Now, why? Most of the flying is done with a full tank down to empty and you land. Not arguing the point, but its one of those unquestioned things,, I would like the reason. :!
Lee TGD
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Hi Lee,
About the only guess I can give is that measuring the CG started out dry, and has continued to be so. Maybe just a matter of the early guys not wanting to fill a tank with fuel on the workbench?? I dunno.......... ;D
Bill <><
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I've never even thought about filling the tank and checking the CG. It has to fly with the tank empty(landing), so it will fly with the cg a bit further forward with fuel. The only time I'd worry about it is with an unusual situation, maybe with the tank behind the CG somehow.
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If you balance with tank filled-----it will be tail HEAVY when tank is empty.
Jim
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Hey Bill, Hahaha,,thats what I thought, Its to much trouble to balance full. Anyway, I really never gave it any thought. Its just the way we do it. ::)
Lee TGD
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A properly balanced plane (balanced with empty tank) will, when the engine quits, continue on straight and level for a nice landing. If it's tail heavy, it will try to rise, and vice versa. Maybe that's why we balance 'em with an empty tank? :! Glen
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If we were to balance with the tank full , we would just balance at a different point on the wing. In full size, you always consider worst case scenario, which is the most tail heavy condition because of the danger of loss of controllability. Therefore, empty tank , most aft cg is the critical realm. IMHO
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I built a 1/2A combat wing with a bladder tank running fore-and-aft, and set it behind the main wing spar rather than cutting through the spar. Never even thought about the CG ramifications with a full load of fuel until the first flight...it reminded me forcibly. I tend to balance combat planes near-tailheavy (empty) anyhow; sure made for some interesting launches. It is good to keep fuel loads in mind, and tank location too!
--Ray
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I had wondered about the effects of CG change with fuel running out during a flight and could not tell any difference. More expert fliers say there is a difference and if you want to really notice it, just fly the pattern backwards. Never tried it.
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Jim,
I agree that you might begin to notice all sorts of different effects if you would start the pattern with the landing and end with the takeoff. Do we use one of those reverse pitch props?
#^
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Yes, there are some conceptual problems to be overcome. :o