Evaluation of the Dust Cloud Generated by Helicopter Rotor Downwash

摘要

The dust cloud generated by a tandem-rotor H-21 helicopter was studied as a function of type of soil, hover height and disc loading. A total of 98 tests were made, and three different test sites were used. Samples were collected at 25 locations on the helicopter. Analyses were made for dust content and particle size distribution. Average dust concentrations at the area of highest dust density, i.e., at rotor blade overlap, are given. The highest concentrations were measured at the site of rotor blade overlap, and the lowest concentrations were found beneath the rotor hubs. The maximum particle size decreased with increasing elevation. No particles over 500 microns were found at any elevation. Dust concentrations of 40 mg/cu ft were measured during takeoff and approach maneuvers. With another helicopter hovering in the immediate area, concentrations of 64 mg/cu ft were measured. (Author)