Where is the best place to put the tank when flying with a gas motor? Do you center the tank on the CG, the rear of the tank on the CG or somewhere in between?

On the CG is best for any kind of flying. The plane reacts and trims the same no matter the fuel load.

David

The center of the tank on the CG ?

yes

Thanks

On the other hand, most profile 3d planes mount the tank with the rear of the tank just in front of the leading edge of the wing. I fly 3 profile planes that way and they work fine.
A typical 40 size 3d plane will weigh 50 ozs and have the cg about 5 " aft of the wing leading edge. Let's say the tank is 4" long, holds 6 oz of fuel and sits right in front of the wing. When I add 6 ozs of fuel centered 5" + 2" in front of the cg of the plane the cg moves forward 1". So when sitting on the ground with a full tank the cg is 4" aft of the leading edge . Just as the tank runs dry the cg is 5" aft. That is how much the cg shifts during a flight for the plane assumed. I am suprised there isn't more difference in the way the plane fliesfrom full tank to empty tank, but it doesn't seem to be a problem for fun flying. Some guys go to a lot of trouble to put their tank at the cg and it must make their plane flying characteristics more consistant throughout a flight.