Good Morning Burkhard.
Nice work.. So, the Russian document could be close to correct...The CG is far back on the wing? Your estimation of 45 pounds is right on. That is what I figure it will be.
Most of the weight on the wings will be forward, close to the leading edge. I have designed the wings to have carbon fiber spar tubes and leading edge. I can install steel music wire
in the leading edge and forward spar which is around 1.5 inches from the leading edge. In addition, the electric motors will be very close to the leading edge.
I don't think that I will have too much trouble with getting the balance close. I can install lead sheet in the cabin as it will have a double wall and I can hide the lead in between.