Proximity operations of small rotary wing air vehicles pose a unique challenge due to the downwash they generate. These vertical flow disturbances may cause substantial and potentially hazardous flight disruption to nearby vehicles. This paper presents a downwash detection and localization strategy intended for use on small unmanned rotorcraft. A probabilistic framework estimates the position of neighboring rotorcraft operating at a higher altitude by combining onboard velocity measurements with a reduced-order flow model. A series of ground-based experiments that characterize the flow beneath a representative group of small rotary wing vehicles are described. A custom pressure probe designed to be carried by small rotary wing vehicles is mounted on an automated two-axis Cartesian carriage system, which enables accurate sensor placement. Velocity measurements collected in a prescribed path are assimilated into an axis-symmetric downwash model. Tests show that disturbances can be localized to the region directly beneath each vehicle while the sensor is still approaching, demonstrating basic downwash detection and localization capabilities for three different rotorcraft configurations.
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