Effects of Ground Roughness on the Hovering Characteristics of ACV (Part I)

Static hovering characteristics of an ACV with annular nozzle above the rough ground were studied experimentally. The rough ground was simulated in such a way that straight wooden bars having rectangular cross sections, d in width, were placed regularly on a smooth board at equal intervals of d. The lift force variation was mess ured by moving the center of the bottom of an ACV through a half wave length of the roughness at the constant hovering height.The results obtained by these experiments were as follows;(I) The lift augmentation ratio of an ACV over the rough ground is roughly proportional to the nozzle length ratio lj/lj, where lj is the total nozzle length and lj is the nozzle length above convex portions of the roughness.(II) When the ratio d/D is sufficiently small, changes of augmentation ratio are small and the mean value of this ratio shows similar tendency to that obtained by adding effective height above the smooth ground.