Empirical Study of Ceiling Proximity Effects and Electrostatic Adhesion for Small-scale Electroaerodynamic Thrusters

Abstract

Electroaerodynamic propulsion, where force is produced via the momentum-transferring collisions between accelerated ions and neutral air molecules, is a promising alternative mechanism for flight at the micro air vehicle scale due to its silent and solid-state nature. Its relatively low efficiency, however, has thus far precluded its use in a power-autonomous vehicle; leveraging the efficiency benefits of operation close to a fixed surface is a potential solution. While proximity effects like the ground and ceiling effects have been well-investigated for rotorcraft and flapping wing micro air vehicles, they have not been for electroaerodynamically-propelled fliers. In this work, we investigate the change in performance when centimeter-scale thrusters are operated close to a "ceiling" plane about the inlet. We show a surprising and, until now, unreported effect; a major electrostatic attractive component, analogous to electroadhesive pressure but instead mediated by a stable atmospheric plasma. The isolated electrostatic and fluid dynamic components of the ceiling effect are shown for different distances from the plane and for different materials. We further show that a flange attached to the inlet can vastly increase both components of force. A peak efficiency improvement of 600% is shown close to the ceiling. This work points the way towards effective use of the ceiling effect for power autonomous vehicles, extending flight duration, or as a perching mechanism.

Figures (11)

• Figure 1: Thrusters used in experiments. Devices from left to right: control "standard" device, extended intake duct with grounding ring for isolating electrostatic adhesion, fully plugged device for isolating electrostatic effects, flanged device for increasing electrostatic and fluid mechanic effects, and flanged device with extended intake duct for isolating fluid mechanic effects.
• Figure 2: (a) Schematic view of a three-stage electroaerodynamic ducted actuator near a ceiling plane. A high potential applied between the "emitter" and "collector" electrodes ignites a local plasma from which ions are ejected. These ions drift in the electric field towards the collector, and frequent momentum-transferring collisions with neutral air molecules along the way result in an entrained air jet. Successive stages increase the velocity of the air as it passes through the duct. (b) Render of the three-stage ducted devices used in this work, where UV-laser micromachined brass electrodes are integrated with SLA-printed ducts in an adhesiveless process. Design, fabrication, and assembly of these devices is drawn from prior work nelson2024high.
• Figure 3: (a) From left to right: A standard device, plugged device, and cross sections of open and plugged devices with extended intakes. (b) Geometric parameters of interest, including the flange width $w$, thruster radius $r$, thruster nozzle height from the top emitter $h$ for electrostatic isolation, and the distance from the thruster inlet to the ceiling plate $z$. (c) The automated test setup constructed from a modified 3D printer synchronizes data acquisition with precise movement of the ceiling plate.
• Figure 4: Effect of device configuration on produced force versus distance from the ceiling plane. The $h=0$, open, ungrounded configuration represents a "standard" device, while we show that a device with an extended intake duct, an airflow plug above the first emitter stage, and a grounding ring on the intake annulus ($h=20$, plug, grounded), results in zero force at any distance. Collected with conductive tape on glass as the ceiling plane.
• Figure 5: Demonstration of isolating electroaerodynamic force from electrostatic attractive force. The $h=20$ plugged device data is subtracted from the $h=20$ open device data to yield a calculated pure-EAD force. This is confirmed by agreement between this calculated value and the $h=20$, open, grounded device data. Collected with a conductive tape on glass ceiling.