very nice Richard, and I am following with extreme interest! one thing if its not too late - take some of the droop out of your main rotor blades. as you have it would be perfect for a Black Hawk or an Apache, but Cobra blades have only the very slightest of droop. it is also a semi-rigid rotor system as opposed to a fully articulated one, so that means that the entire rotor head assembly pivots on top of the rotor mast. in summary: when one blade goes down, the other goes up. like a see-saw. do, however, put some twist in the blades so that the innermost part closer to the head has more pitch, while the outer tips are almost flat. Hope this helps, again, your model is looking really great and i look forward to following your build.
Cheers!
-Ramon
1 attached image. Click to enlarge.