Rotary ionic engines (RIEs) with multi-coaxial propellers (12.6 cm diameter) and their thrust-to-power ratios are investigated. Up to 40 mN thrust was obtained in single propeller RIE at 2600 rpm, 0.34mA, 37.5kV, and optimal ground diameter of 17cm. More thrust can be obtained with two and three propellers at constant current per propeller. Propeller interaction is minimal above 5 cm axial propeller-separation. Thrust-to-power ratios present a peak at low currents (maximum 30mN/W for 17cm ground diameter). Thrust-to-power variation can be assessed by the propeller kinetic energy-to-power ratio and also by the voltage- to-current ratio at currents larger than about 0.1mA.