However, early prototypes suffered from poor performance, and latter prototypes required too much pilot work load, due to poor stability augmentation and limited control authority. These vehicles were among the first successful heavier-than-air vertical take off and landing (VTOL) vehicles. A number of manned designs appeared in the 1920s and 1930s. Torque-induced control issues (as well as efficiency issues originating from the tail rotor, which generates no useful lift) can be eliminated by counter-rotation, and the relatively short blades are much easier to construct. In the early days of flight, quadcopters (then referred to either as 'quadrotors' or simply as 'helicopters') were seen as a possible solution to some of the persistent problems in vertical flight. Unlike conventional helicopters, quadcopters do not usually have cyclic pitch control, in which the angle of the blades varies dynamically as they turn around the rotor hub.

Pitch and roll are controlled by varying the net centre of thrust, with yaw controlled by varying the net torque. Flight control is provided by independent variation of the speed and hence lift and torque of each rotor.

Quadcopters generally have two rotors spinning clockwise (CW) and two counterclockwise (CCW). Each rotor produces both lift and torque about its center of rotation, as well as drag opposite to the vehicle's direction of flight.

Quadair drone features