Experimental investigations of ground-jet suppression fences for VTOL aircraft prepared sites.

Small-scale and full-scale experiments show that a ground-jet suppression fence at the perimeter of a jet VTOL aircraft prepared pad is effective in reducing ground erosion and particle entrainment beyond the pad. The use of a small fence can reduce the required pad area by a factor of seven, for the same dynamic pressure (entrainment characteristics) near the ground beyond the pad. The fence is porous, with an inner ramp and an outer leg normal to the pad. The fence is located at about 15 equivalent jet nozzle diameters from the center of the jet impingement. A typical fence height for a hypothetical jet VTOL aircraft of 18,000-lb gross weight is 1.3 ft on a prepared pad of 47-ft radius. The fence has no effect on hot gas ingestion of the engines, and any sand or dust entrained beyond the fence remains in the confines of the ground-jet and is swept away radially.