The rotors seem to need the ability to 'feel' and spool up on there own. With prop wash...the rotors would spin at a fairly constant speed producing an near equal amount of lift. That would be ideal in level flight. This is where I would like to scan the original article by Roy Clough Jr. He mentioned that even an over sized rudder failed to stop the roll. He settled on wing tip ailerons. I'd love to see more modelers try there hand at this 'Magnus effect' type model. I'm sure there is more to be tried.
I have posted to Youtube my first flight attempt (and my only video) of my TumbleWing. Things that helped since this flight....more weight forward of the CofG and a larger dia prop. What would be better than that would be more power (still haven't). Also I believe more area on the rudder and horizontal stabilizer might be of help.
Video link...
http://youtube.com/watch?v=kPO7OMzuQps
Clint.