ORIGINAL: georgebonn
The fuel tank is usually located just behind the firewall, i.e. much forward of the plane's balance point. The plane is balanced with an empty fuel tank. This results in the plane being significantly nose-heavy on takeoff and during most of the flight. In theory, it appears that ideally the fuel tank should be located at the balance point. This would result in a rather long fuel supply line to the engine, perhaps causing problems.
I would appreciate comments about this, especially from those who have experienced this or have theoretical knowledge about the concept.
George; your observation is rigth. You balance the plane with most safe-rear CoG location; when you fill the tank CoG goes forward with this result: GIVES YOU MORE LONGITUDINAL STABILITY TO THE PLANE. You will also receive another consequences but we modellers don't care about them: less maneuvrability (how much less? depends on the design), more drag and thus less endurance or more power needed...
As a airplane designer I'm used to deal with that problem, as a modeller I don't care since I use pumped engines and I install the fuel tanks near the CG. In any case my advice is to place the CG where the manufacturer indicates; If you want to move it backwards do it but: DO IT VERY CAREFULLY AND JUST A FEW MILIMETERS AT TIME. If, for any reason you don't want to have that CG movement during flight, just get a perry pump or pumped engine and place the tank as close to the CoG as you can...
Hope it helps
CHeers
G.