Influence of quadrotor downwash on close proximity flight

Quadrotors have found widespread use in numerous applications including search and rescue, transportation of goods, remote sensing, and package delivery. However, the aerodynamic interference of rotor wakes between adjacent vehicles can be detrimental to the stability of dense quadrotor swarms. The ability to characterize and model the flow between neighboring quadrotors could lead to more stable formation flight and improve flight efficiency. We present data from a series of experiments using a pair of Crazyflie quadrotors mounted on stings attached to a translational stage, positioned with varying horizontal and vertical separation. Force and torque measurements (using a six-axis F/T transducer) and velocity measurements (using PIV) were recorded over a wide range of spatial separations. For small vertical separations, the downwash from the upper quadrotor has a pronounced effect, reducing the aerodynamic thrust on the lower quadrotor. Furthermore, for small horizontal separations, a roll moment is induced on the lower quadrotor, requiring a restoring moment to maintain stability. These findings are compared with predictions using actuator disk theory and scaling laws, potentially enabling their application to quadrotors of various sizes.