RE: airfield 55 in sky trainer
On a straight winged plane you typically want the C.G. occuring around 22-25% of the MAC measured at the wing root chord.
33% ( aka 1/3 ) would probably work, but 33% is more suited to 3D planes.
Rememeber that the C.G. should always be between the steering wheel and the main wheels, no matter the type of plane, with it tending to be close to the main wheels but far enough away to prevent the plane from tipping back or forward.