On the nature of the propulsive force of asymmetric capacitors in the atmosphere

The present work intends to identify the nature of the propulsive force that occurs during a positive corona discharge in nitrogen gas around an asymmetric capacitor geometry. Using the known theory of electrohydrodynamics (EHD) and electrostatics it is possible to compute all hydrodynamic and electrostatic forces that act on the considered geometry in order to provide a physical insight on the force mechanism that acts on an asymmetrical capacitor surrounded by any gas. We will demonstrate that the majority of the propulsion force is due to an electrostatic interaction force between the capacitor electrodes and the surrounding positive ion charge present in the gas, which is responsible for the generation of the ion wind. Nevertheless, the force that pushes the capacitor forward is electrostatic and not hydrodynamic, the ion wind is just a natural secondary effect due to the electrostatic interaction.