Just a quicky (that took me a lot more time than I had expected): This would follow out of discussion announced concerning a 2.5-copter a couple of posts ago: Three co-rotating rotors that are inclined in a way that they produce a yawing moment that compensates the reaction torque. For yawing, at least one of the rotors must be able to change its tilt. Pitching and rolling would be achieved by changing the power distribution between the rotors. But this will always cause some thrust in the direction of the axis around which the vehicle is rolling. So a combination of rolling and pitching had to be used in order to get a resulting thrust force in the desired direction of flight. In opposite, if rotor tilt can be distributed instead of power, it should be possible to produce thrust in any direction without inclining the whole aircraft Since the rotors are tilted in the same circumferential direction, rotor planes may overlap without any danger of collision, even if they have differing rotational speed. In general, there is no special direction for such a vehicle of course, the fuselage and tail would more be an orientation hint for an RC-pilot, might bring some stability in cruise-flight with FPV and is probably dispensable for an autonomous UAV with any kind of closed loop control. Sorry for the large image, I just couldn't decide which view is the best, hope it's easier to understand that way. Please, view full size. AutoCAD 2011 Corel Photopaint 7 Notepad