VTOL DOWNWASH IMPINGEMENT STUDY

Abstract
This program was designed to provide fundamental background information and to aid in the evaluation of operational problems associated with the slipstream impingement. Configurations used consisted of: open propellers, ducted propellers, side by side jets, and ground effect machines of the plenum and annular nozzle type. Disk loadings of 2 to 150 pounds per square foot and Z/ D ratios of .25 to 3 were investigated. Data were obtained to determine: the over-all flow pattern, flow velocities, erosion rates for various soils, and the surface deflection and spray height caused by operation over water. The maximum field dynamic pressure resulting from the impingement was determined to be a function of Z/D and disk loading and was found to be the parameter governing the erosion onset and the maximum surface deflection for operation over water. Dry loose material such as sand, dust, dry grass, etc. erodes when the surface dynamic pressure is three pounds per square foot, or less. Water spray starts to form in the same range of surface dynamic pressure. Many natural surfaces will withstand surface dynamic pressures above 150 pounds per square foot with very minor damage.

This publication has 0 references indexed in Scilit: