On 9 October 2013 11:32, BOB wrote: > I have heard oh people making a helicopter using the tail rotor off of a > large helicopter as the main rotor on a small helicopter. That would allow only a very limited capability. A tail rotor can (usually) alter pitch but all blades have the same pitch around the whole circle of rotation. The main rotor not only has average pitch control but has a "cyclic" which allows the pitch of the individual blades to be varied relative to the mean pitch as they travel through one full revolution. Simplistically the cyclic control can be visualised as a variable cam shaft made by tilting a flat plate. Degree to which the plate is above or below mean level at a given point affects the blade pitch. When the plate is level the blade pitch is the same all the way around the circle. Move the plate upwards and pitch at all points changes (say increases) the same. But tilt the plate and the picth will vary per blade as the blade rotates. If the blade is tilted at an angle the high points cause the blade at that point to vary pitch in one direction and the low points 180 degrees away cause the pitch to vary in the other direction. By tilting the plate the mean effective tilt of the blade can be varied. When flying eg forwards the leading blade gets extra air speed due to the passage through the air and the trailing blade loses effective air speed. Then add wind. Then ... . Vector sum all these and effectively tilt the rotor plane as desired and the machine goes where you intend. Notionally :-). I've thought about a "mono copter" for some while that did not need cyclic control. Very crude. Should work [tm]. Unlikely to be original. Single rotor. Pitch control OR fixed pitch with speed control. Tail boom with tail rotor to stabilise rotationally. "Hang" portion of copter from rotor with X-Y pivots (or just X pivot with due care). Tilting the hanging load relative to the rotor causes a torque which tilts the rotor plane. Various force interactions occur :-). Tilt by appropriate amount and device will travel in a selected direction. Lack of front back blade pitc difference makes for interesting results. With one bendable joint you can only fly fowards/backwards. So use tail rotor to rotate craft as required. MAY be suitable for a very low cost system, especially in a model or UAV - variable speed motor, one rotor, tail boom and motor-rotor to stabilise, servo to bend body. Russell --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .