  Electroaerodynamic (EAD) propulsion, where thrust is produced by collisions
between electrostatically-accelerated ions and neutral air, is a potentially
transformative method for indoor flight owing to its silent and solid-state
nature. Like rotors, EAD thrusters exhibit changes in performance based on
proximity to surfaces. Unlike rotors, they have no fragile and quickly spinning
parts that have to avoid those surfaces; taking advantage of the efficiency
benefits from proximity effects may be a route towards longer-duration indoor
operation of ion-propelled fliers. This work presents the first empirical study
of ground proximity effects for EAD propulsors, both individually and as
quad-thruster arrays. It focuses on multi-stage ducted centimeter-scale
actuators suitable for use on small robots envisioned for deployment in
human-proximal and indoor environments. Three specific effects (ground,
suckdown, and fountain lift), each occurring with a different magnitude at a
different spacing from the ground plane, are investigated and shown to have
strong dependencies on geometric parameters including thruster-to-thruster
spacing, thruster protrusion from the fuselage, and inclusion of flanges or
strakes. Peak thrust enhancement ranging from 300 to 600% is found for certain
configurations operated in close proximity (0.2 mm) to the ground plane and as
much as a 20% increase is measured even when operated centimeters away.
