Abstract: An experimental and numerical investigation of flapping-wing propulsion in ground effect is undertaken. Flying in ground effect is shown to have substantial performance advantages both in thrust and efficiency. To gain the performance advantage without requiring flight in the proximity of the ground, a bi-plane configuration is designed, providing increased performance as well as inherent balanced mechanical and aerodynamic loading. A high aspect-ratio experimental model is tested both qualitatively and quantitatively, using a smoke-wire for flow visualization, laser Doppler velocimetry for unsteady flow measurements, and a direct approach for thrust measurement. The configuration is simulated numerically using a two-dimensional, unsteady, inviscid panel code with a deforming wake model, and a two-dimensional, unsteady, compressible Navier-Stokes solver. The Navier-Stokes solver is used with a three-block, deforming grid, and it is run on a Beowulf Linux parallel cluster. Direct comparisons of thrust are made, as well as qualitative comparisons of the vortical wake structures produced by the wing-flapping. A strong Reynolds-number dependence is shown, reducing or eliminating the benefits of wake-interference at Reynolds numbers on the order of 10,000.

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