298 H. R. Chaplin 
The cruise performance curves for the six concepts shown are plotted directly from the 
simplified ideal theory. Special assumptions, such as length/beam ratio of 4 for the air 
curtain with skegs, and nozzle-width/operating-height ratio of 0.005 for the water curtain, 
are noted in the legend. The seventh concept, the diffuser-recirculation system, is omitted, 
since the dearth of practical experience makes it impractical to plot a curve of even illus- 
trative value. 
Also shown in Fig. 12 are performance limits imposed by parasite drag, under assumed 
parasite drag coefficients: 
Dy 
Cor = il 
= 2 
5 pV" Ss 
De 
Cee : era aS 
9 Pw Vana S 
The “simplified ideal theory” curves account for cushion power and momentum drag but 
ignore parasite drag. The “limit” curves account for parasite drag but ignore all other power 
~ 
requirements, as follows: 
limit ~ 0 
2 
Te pS Vo 
\y2 
LV, 
0 " 2 hi 2 Epi 
P e 
The concepts which do not involve contact with the water (curves 1, 3, 5, 6) are assumed, 
for illustrative comparison purposes, to have parasite drag coefficients of Cp = 0.04; the 
concepts which do involve water contact are assumed to have Cp, » = 0.0017. (A calcula- 
tion which included cushion power, momentum drag, and parasite drag would give a curve 
which followed closely below the “simplified ideal” curve at low speed, then peaked over 
and followed closely below the “limit” curve at high speed.) 
The relative performance picture afforded by Fig. 12 should be interpreted as follows: 
1. Within the no-water-contact family, the relationship between curves 1, 3, and 5 is 
probably in reasonable qualitative harmony with the facts. If lower S/hC or lower Cp¢ were 
assumed, the integrated air curtain would appear slightly better, compared to the simple air 
curtain; the plenum, slightly poorer. Curve 6, for the ram wing, is only a single point, since 
under the approximations used in theory, equilibrium flight occurs at only one speed coeffi- 
cient, U = V2. If lower S/hC or lower Cp were assumed, the ram wing could be made to 
appear superior to the other members of the no-water-contact family, by assigning it a higher 
aspect ratio b/I. 
