AIAA Paper No. 2000-0897, 38th AIAA Aerospace Sciences Meeting, Reno, Nevada, Jan. 2000. Recent interest in the development of micro-air-vehicles (MAVs) has led to a renewed interest in flapping-wing propulsion due to the relatively poor efficiencies of conventional propellers at these small scales. In the present study flapping-wing configurations found numerically to produce high propulsive-efficiencies are investigated experimentally. Several models of varying scales and complexity are developed and tested in a low-speed wind-tunnel. The variation in scale of the models provides some insight into the rather severe Reynolds number effects, and the development of the smaller models provides an introduction into the difficulties in the design, manufacture and testing of small-scale vehicles. The thrust is measured directly and compared with numerical predictions, with variations in the flapping motion, aspect-ratio and scale. Measured thrust for the larger model compares well with the numerical predictions both qualitatively and quantitatively over most of the parameter-space, however, the smaller model, with approximately half the chord-length and a somewhat different flapping motion, produces drastically different performance, indicating the presence of massive flow separation. The presented results indicate the necessity to better understand, and ultimately to utilize, flow separation in the design of successful flapping-wing MAVs.