Hey sel welcome to the forum, I think I ve got a paper by you on my computer. Need some more education before I can understand all of it
One thing which I did just read on the Kamov site was that the coax config behaved like a bi-plane in forward flight offsetting the drag of the extra rotor.
Dont know if its true, but it makes sense, looking at the figures for bi-planes.
For those interested
here is a link to the Kamov page, which states the benefits of the coax system. Bearing in mind they are promoting their system, its still an interesting read though.
Just to get back to the topic slightly, for calculation purposes, is the best method for coax calcs to treat it as a single disk with the appropriate no of blades?