Hello Phil!
Thanks a lot.
Perhaps the CG point was the problem of my tango.
I 've built it as in the instructions, but when holding my model at the rotor shafts, it 's tail heavy! When I hold it at the CG point marked in the plan, it 's ok. Probably the CG is wrong in the plans.

Perhaps this is also a reason why it was so sluggish on the rudder at maiden flight.

Stefan