Ground Effect in Flight. Birds, Fishes and High-Speed Vehicle.

The present paper aims to analyze the propulsion of birds and fishes undergoing the ground effect as well as the lift of high-speed ground vehicle. Applying the analytical method which was developed for flutter of a soft plate placed at an arbitrary position in subsonic channel flows, calculations are carried out first for non-oscillatory case in compressible flow and then for oscillating cases of birds and fishes in incompressible flow. The results obtained show that the ground effect acts to increase not only the lift in steady flight but also the thrust and propulsive efficiency in oscillating modes. This method holds not only in the case of very close proximity to the ground but also in compressible flow case, so it would be applicable to the flutter analysis of high-speed ground vehicle with wings.