280 H. R. Chaplin 
Simplified Ideal Theory: 
Equations same as for air curtain (neglecting gravity) except 
that water sous appears instead of air sue 
Simple Water Curtain 
‘Note remarks in text!! 
2, 
a) ee eee 
Fig. 4. Water curtain 
reaction of the cushion pressure against the curtain. Gravity has a favorable effect on the 
water curtain in that the jet gains momentum as it falls from the nozzle to the surface; and 
it has an unfavorable effect on the pumping power, in that the water must be raised from the 
surface to the level of the nozzle. The problem is greatly simplified, and the essential 
character of the result is unchanged, if these effects are neglected. The equations for the 
water curtain then become identical! with those for the air curtain (Figs. 1 through 3), except 
that water density p, is substituted for air density p. The results, in terms of dimensionless 
parameters referred to water density (Fig. 4, Eqs. (4-2), (4-4), (4-6)), are exactly analogous 
to the air curtain results. However, when the parameters are referred to air density, it is 
apparent that, in principle, the water curtain enjoys a tremendous advantage. In the hover- 
ing case, and in the case of the integrated water curtain at cruise, the results (Eqs. (4-3) 
and (4-7)) show the water curtain doing the same job as the air curtain with 1/29 as much 
power required. 
The trouble with this rosy picture becomes apparent when it is recalled that the opti- 
mum nozzle width G on which these results are based, is half the operating height h. A 
piping system large enough to supply such a nozzle, and filled with water, would weigh a 
