Quadcopters vertical take off and landing (VTOL) rotorcraft, consisting of two clockwise and two counterclockwise propellers. The thrust and torque of each rotor can be varied by adjusting their speeds, and can be used to generate a desired total thrust vector and total torque. While these days quadcopters have become ubiquitous, not many are aware of the history of this configuration.
Some early examples include the Breguet-Richet Gyroplane was first flown tethered in 1907, the Oehmichen No.2 from the 1920s which could remain airborne for minutes in stable controlled flight, and the de Bothezat helicopter that first flew in 1922 for the US Air Service but was found to be overly complex, difficult to control, and underpowered. Each of these aircraft were piloted and sized likewise for the era, the maximum dimension from rotor tip to rotor tip ranging from 15-20 meters.
The concept would be revived by Convertawings with the Model A in 1956, with control obtained by differential thrust between the rotors via collective pitch of each rotor, avoiding the need to cyclic control and the complexity it would have brought. Curtiss-Wright, the successor company to the Wright brothers’ original firm, built and flew the VZ-7 in response to the Army Transportation Corps requirement for a light VTOL utility vehicle, a “flying jeep” type role. The VZ-7 quadrotor was much more compact than its predecessors at about 5 meters long and wide, was several times more powerful with its 425 hp Turbomeca Artouste IIB turboshaft engine, and also utilized differential thrust with collective pitch for control. The US Military ultimately moved away from compact multi-rotor aircraft in favor helicopters around that time. It took a couple decades before improvements in materials, power sources, motors, and microcontrollers would lead to wider adoption of the quadcopter configuration, though it would be in the form of small-scale remotely controlled or autonomous drones.
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