Modern VTOL configurations often seek minimal footprint simultaneously with minimal disk loading (often competing constraints), the latter to improve propulsive efficiency at low speeds. One approach is to stagger neighboring propellers in partial overlap. We consider such partial overlap of two propellers in tandem, varying the vertical and horizontal spacing, inclination of the propeller plane with respect to the freestream, and advance ratio. The rear propeller was mounted above the plane of the front propeller with a maximum of 25%-diameter overlap. Thrust and torque were measured separately on each propeller. The efficiency of the propeller pair, expressed as a ratio of thrust to power, never completely approaches that of propellers in isolation. But for vertical separation of 0.5 diameter or greater, there is a saturation, where larger separation does not result in further improvement. © 2023, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.