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GROUND EFFECT MACHINE RESEARCH AND 
DEVELOPMENT IN THE UNITED STATES 
Harvey R. Chaplin 
David Taylor Model Basin 
Ground effect machine (GEM) investigations in the United States have 
grown at an astonishing rate since early 1957. At present they involve 
some 40 commercial firms, laboratories, etc., and represent an increas- 
ingly significant investment of capital and engineering manpower. 
These investigations are thus far largely exploratory in nature. They 
represent a considerable variety of approaches, both as to types of 
ground cushion phenomena employed, and vehicle applications en- 
visioned. The various ground cushion concepts are reviewed, in terms 
of elementary principles of fluid mechanics. All of the concepts are 
shown to give direct relationships between vehicle performance and 
vehicle size/height ratio. GEM developments are therefore expected to 
tend ultimately toward large ocean-going vehicles operating very close 
to the surface. Some of the outstanding advantages and problems of the 
various ground cushion concepts are discussed, but present knowledge 
does not support strong opinions asto which of the concepts will prevail. 
Base area in square feet 
Height above surface in feet 
Perimeter of the base in feet 
Vehicle length in feet 
Vehicle beam in feet 
Nozzle width in feet 
Normal jet discharge angle in degrees (see Figs. 1 and 3) 
Tangential jet deflection angle in degrees (see Fig. 3) 
Effective cushion (base) pressure in pounds per square foot gage 
Mass density of air in slugs per cubic foot 
Mass density of water in slugs per cubic foot 
Average jet velocity at discharge feet per second 
Full-expansion velocity, in feet per second, of cushion air (velocity cushion air 
would attain if allowed to expand to atmospheric pressure) 
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