Black Knight Transformer Multicopter By Advanced Tactics

Due to their ease of both construction and control, multirotor aircraft are frequently used in model and radio control aircraft projects in which the names quadcopter, hexacopter and octocopter are frequently used to refer to 4-, 6- and 8-rotor helicopters, respectively.
Examples
• Cierva Air Horse - a British three-rotor "heavy lift" helicopter first flying in 1948. Three rotors were used to give a large lift without compromising rotor strength.