RE: balance problem
I don't understand "pulls to the ground". What inputs are you giving when it does that? If I had a plane that was diving I would just add up trim. Then I'd roll inverted and if it required a lot of down trim, the CG would have to go back.
Tail volume is length of tail arm/wing cord X stab area/wing area. I agree with others that the tail volume looks very large because the tail arm is so long and the wing chord is fairly narrow--it's an unusual bird. What is it?
Jim