Interesting video showing the difference between a tri-copter will all blades going the same direction and one with counter rotating props in the front. http://vimeo.com/22778782 ...Tiger
Ok, now that I see it in action I would say this is "translating tendency" which makes total sense to me. The effect would be more energy needed to hover as it is being wasted on yaw control and anti drift. And if you had counter rotating front props you would never have retreating blade stall, if you could fly that fast forward Also it would yaw either direction at the same speed instead of fast one way slow the other.
