Adding something to the comment I posted to knupps´ recent hexacopter picture, I dug out an old concept to discuss about, or not. A couple of years ago, I had a talk with KPN about the minimum number of rotors necessary to control a helicopter without cyclic pitch adjustment. The common answer is four, as you have four parameters to control, namely pitching, rolling, yawing and total power. He suggested that three may be enough if only one of them can additionally tilt, delivering the fourth channel. At last, I came up with "two and a half", driven by two motors. The two small rotors would turn in a common direction, making the whole vehicle, that is shaped like a bigger rotor, turn to the opposite. This way, yawing can be neglected. Pitching and rolling cannot be controlled at the same time but one after another, depending on the angle of the big rotor (strictly speaking, a conventional two blade helicopter can only do this way as well). However, in this case you would not command left and right, back and forward anymore, but east, south, west and north. Sensors would have to detect the vehicles recent direction and compose a suitable power distribution. The whole thing is supposed to have a more flat arrangement to ensure it turning around its principal axis of inertia without additional paddle. The small rotors are placed a bit upstream from the main body´s leading edge. This way they will impose some kind of cyclic pitching moment on the main rotor and therefore increase control efficiency. There is a small window in the disc-shaped central section. Behind it, a line scanning camera was supposed to be placed taking panorama pictures of the landscape. As background I choose an even older photography taken on the early morning of Aug 19, 2006 over Aalen-Elchingen from the Bocian´s rear cockpit. AutoCAD 2002 Panasonic Lumix FZ-20 Corel Photopaint 7