Travel with an SK-5 ACV over soft snow results in surface deformation/erosion of a few inches, caused primarily by rear skirt drag; on windswept snow only scratches can be seen. During hovering on soft snow, deformation below the cushion chamber usually does not exceed a few inches. The action of the air flow, which has an escape velocity of 70 to 120 ft/sec, produces a 1-ft ditch below the peripheral skirt in less than a minute; thereafter the extent of erosion does not increase appreciably during continued hovering. A partial seal between the inner face of the skirt, above the fingers, and the snow surface may exist, arresting further settling of the vehicle. Relatively cohesive layers of snow such as wind slabs and crusts are not eroded. A level snow cover, regardless of how deep or soft, does not appear to be capable of immobilizing an ACV of this or larger size.
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