VTOL DOWNWASH IMPINGEMENT STUDY SURFACE EROSION TESTS
HILLER AIRCRAFT CORP PALO ALTO CA
Pagination or Media Count:
A mobile test rig, mounting a two-foot-ducted propeller, capable of providing disk loadings up to 145 lbssq ft, was used to provide a cold air jet. This jet was allowed to impinge upon surfaces which might be considered unprepared landing sites. The range of duct exit height above the surface was from one-half to three diameters, and thrust angle inclinations of 0, 30 and 60 deg. Surfaces with light vegetation or hard-packed soil surfaces show little erosion over from disk loadings to 145 lbssq ft. The hardpacked surfaces normally have fine loose dust on top, which produces a large dust cloud even at very low disk loadings. In general the loose material surfaces erode rapidly, and large holes are formed in a short time. The gravel, with a mean particle size of about seven mm and large particles to forty mm, was eroded at a rate of 150 lbssec at a disk loading of 145 lbssq ft. Wet sand showed minor erosion under the same test conditions. Over water the surface spray started at disk loadings between eight and fifteen lbssq ft. Between the disk loadings of thirty to sixty lbssq ft the spray pattern changes from a radial surface spray to one in which there is considerable vertical motion and ingestion into the duct inlet.
- Soil Mechanics
- Military Aircraft Operations