A rotorcraft or rotary-wing aircraft is a heavier-than-air flying machine that uses lift generated by wings, called rotary wings or rotor blades, that revolve around a mast. A rotor is a setup of 2 to 8 blades mounted on a mast. The mast is a shaft connected perpendicular to the rotation plane of the rotor blades, connected to a power source(engine).
Rotary-wing aircraft are of the following types:
a. Single rotor
b. Two rotors
c. Three rotors
Rotor-based aircrafts work under the same principle as a fixed-wing. A multi-rotor aircraft is a mechanically simple aerial vehicle whose motion is controlled by speeding or slowing multiple downward thrusting motor/propeller units. The most common multi-rotor aircraft/drone is a Quadcopter.
Multi-Rotor are further sub-classified based on the number of rotors:
a. Quadcopter (4 rotors)
b. Hexacopter (6 rotors)
c. Octocopter (8 rotors)
d. Decacopter (10 rotors)
e. Dodecacopter (12 rotors)
Comparatively complicated structure and programming
Aerodynamically unstable system, thus it requires an on-board computer (flight controller)
Low energy efficiency compared to fixed wing counterparts