Low-speed electric propulsion systems for long-duration near-space travels by using solar energy could be based on the electrohydrodynamic force produced inside a corona discharge. This paper is a contribution to a better understanding of these types of thrusters, in order to enhance the produced thrust and their electromechanical effectiveness. Three different simple designs are experimentally studied and compared. The first one is composed of a wire active electrode and a single cylinder grounded one. For the second three-electrode design, the single grounded cylinder is replaced by two cylinders. Finally, the last design is composed of an active wire supplied by a positive voltage, two grounded electrodes and two others cylinders at a negative voltage. On one hand, results show that the use of two grounded electrode instead of a single one results in an increase of the discharge current. Moreover, whatever the electrode gap d, the current-to-thrust conversion is more effective with the three-electrode design. It changes from 31 to 58 N/A (+87%), from 74 to 85 N/A (+15%), and from 104 to 120 N/A (+15%), for electrode gaps d = 10, 20 and 30 mm, respectively. The thruster effectiveness θ is improved by 2 mN/W. On the other hand, the use of two collecting electrodes supplied by a negative high voltage does not result in an effectiveness enhancement because the power consumption is significantly increased.