drones

snipped-for-privacy@gmail.com wrote in news:a09f1b3d-f43f-4d76-810c- snipped-for-privacy@googlegroups.com:

No deep knowlage of aerodynamics is required. Its simply a matter of torque balance.

The rotor downdraft has considerable swirl and there is naturally a reaction torque on the motor. To prevent the craft spinning about a vertical axis, you need either a tail rotor (e.g. conventional helicopter) or a contra-rotating rotor to balance the torque.

Two rotors are sufficient, but then you need to either gimbal the rotors for directional control and forward thrust or implement a swashplate to provide dynamic cyclic blade pitch control (Chinook helicopter), with considerable mechanical complexity for either.

Any even number of fixed axis fixed blade rotors can give you torque balance, and if each group of rotors of the same rotation direction is distributed symmetrically, the craft can be tilted in any direction without net torque, or power can be shifted from clockwise to counterclockwise rotor groups or visa versa to provide torque to rotate the whole craft about its vertical axis, while maintaining lift.