The lift and drag forces and vortical wake of a rectangular semiwing equipped with a tip-mounted propeller and a plain trailing-edge flap both outside and in ground effect were investigated experimentally at Re = 2.49 × 105. Outside the ground effect, the slipstream of the inboard-up propeller rotation attenuated the wingtip vortex, significantly decreasing the lift-induced drag. The propeller rotation also led to an increased maximum lift and stall angle. At a fixed lift condition, the propeller rotation led to a reduced drag. The deployment of the flap further increased the lift curve slope and maximum lift but at the expense of an increased drag and earlier stall as compared to the unflapped wing. In ground effect, the lift augmentation of the unflapped wing increased pronouncedly with propeller rotation as the ground was approached. For the flapped wing, the propeller rotation, however, produced a smaller lift increment than the unflapped wing due to the recirculation of the deflected slipstream into the propeller disk. The extent of this recirculation increased with flap deflection and propeller rotation, contributing to the inferior lift production of the flapped wing with a tip-mounted propeller in ground effect.