Steady and Unsteady Downwash Effects in Multirotor Interactions

Despite their versatility for search-and-rescue, precision agriculture, and infrastructure inspection, quadrotors operating in close proximity can suffer from catastrophic flight instabilities due to downwash wake interference. Understanding the characteristics of flow interactions and their effect on vehicle dynamics can inform drone stability and control. We have developed a dynamic testing platform that can rapidly accelerate a small quadrotor (Crazyflie) towards a nearby vehicle or a stationary boundary. By varying the amplitude and frequency of the motion as well as the thrust levels, we quantitatively map out the zones of downwash interaction by measuring the average and fluctuating forces and moments acting on each quadrotor - the one experiencing the downwash and the one generating the disturbance - as functions of vehicle separation and velocity. We extend these techniques to characterize dynamic ground effects. PIV measurements of the flow field around the vehicle provide the spatial structure of the downwash wakes, giving us insight into the flow features contributing to the destabilizing forces.