Onboard Flow Sensing For Downwash Detection and Avoidance On Small Quadrotor Helicopters

Small rotary-wing UAVs are susceptible to gusts and other environmental disturbances that affect inflow at their rotors. Inflow variations cause unexpected aerodynamic forces through changes in thrust conditions and unmodeled blade flapping dynamics. This paper introduces an onboard, pressure-based flow measurement system developed for a small quadrotor helicopter. The probe-based instrumentation package provides spatially distributed airspeed measurements along each of the aircraft-fixed axes. Lateral and vertical windspeed estimates enable the development of disturbance-tolerant flight control strategies. The focus of this paper is vertical flow disturbances such as those caused by the downwash of a second vehicle. Real-time velocity measurements are incorporated into a recursive Bayesian estimator to localize a nearby rotorcraft using its downwash. A path planner developed for proximity flight is demonstrated through indoor flight testing with multiple vehicles to safely guide an instrumented quadrotor around the downwash of nearby rotorcraft.