ORIGINAL: Bonified Wingnut
...........The thing that I don't get is what part the long tail moment of this plane could play in the balance.
Yes, the long and powerful tails have an effect in the balance.
The theory is that all the surfaces can lift, including the fuselage.
The imaginary point where all the lifting forces of all those surfaces can be considered as concentrated in is named Center of Lift or Center of Pressure.
The pitch stability depends on the distance between that point and the CG.
Things get ugly if the CG moves aft the COL or COP, since the model becomes unstable (trying by itself to relocate the COP behind the CG to regain stability).
For more exact location of the COL or COP of the whole model, following the above theory, this on-line calculator can be used:
http://www.geistware.com/rcmodeling/cg_super_calc.htm
Practical calculations disregard the lifting effect of the tail and fuse, considering only the main wing, which COL is always located at 25% of the MAC.
This practice is safe, because we locate the COL and CG forward from its real position; hence we are farer from any unstable condition.
I also suggest you to read thru this old thread:
http://www.rcuniverse.com/forum/m_8947745/tm.htm
Best luck!