290 H. R. Chaplin 
(These performance parameters reflect design features dictated by scale and by research 
utility considerations. A highly developed vehicle should have substantially improved 
internal and duct efficiency and parasite drag coefficient, perhaps 0.8, 0.9, and 0.04, 
respectively.) The pertinent geometric data for the model are: 
S = 20.50 square feet 
C = 18.85 feet 
lL = 8.45 feet 
G =. 0.058 foot 
9 = ~45°. 
Performance calculations from Eqs. (8-8) through (8-11) are compared with experimental 
results in Fig. 9. The consistent agreement, over wide ranges of test conditions, strongly 
suggests that the very elementary considerations employed in the simplified engineering 
analysis correctly represent the major physical phenomena involved. 
(It is not our purpose here to consider the detailed performance of the air curtain GEM. 
However, in passing, one should note: (a) the strong, almost linear dependence of the 
equivalent lift/drag ratio, LVo/P, on size-height ratio, S/hC, shown in Fig. 9a, (b) the 
significant performance advantage indicated in Fig. 9b for the vehicle with controlled tan- 
gential deflection B of the air curtain, and (c) the further advantage indicated for such a 
vehicle, in Fig. 9c, in terms of the power-required distribution between cushion power and 
propulsive power. The total installed power required, if separate power sources are used for 
the cushion system and propulsion system, will be the sum of the maximum cushion power 
required and the maximum propulsion power required. This sum, especially for the simple 
air curtain (8 = 0) is very much larger than the maximum total power required at any given 
instant.) 
Having confirmed that the simplified engineering analysis gives a reasonable represen- 
tation of the actual facts, we are in a position to examine the relationship between the 
simplified ideal theory and physical reality. It will be easiest to consider the simple air 
curtain (8 = 0) for this purpose. For direct comparison, the appropriate form of simplified 
ideal theory is obtained from Eqs. (8-8) through (8-11) by setting 
URE eR my ee 
The most important information one may hope to obtain from simplified ideal theory is a 
qualitative prediction of equivalent lift/drag ratio. The calculation of optimum equivalent 
lift/drag ratios from Eqs. (8-8) through (8-11) is rather laborious. However, as suggested by 
Ref. 4, and confirmed by Fig. 9, an excellent indication of effects on optimum performance 
is obtained by considering performance at V = 1. Figure 10 gives the result of such a cal- 
culation, starting with simplified ideal theory, and with successive curves which result from 
setting the performance parameters, in steps, to the values appropriate to Model 448. Each 
of the “real” effects gives a successively less optimistic performance prediction compared 
to the simplified ideal theory. At the end, the actual equivalent lift/drag ratio of Model 448 
is very much lower than predicted by simplified ideal theory (about one-half), but the essen- 
tial conclusion of the simplified ideal theory as to the nearly linear relationship between 
equivalent lift/drag ratio and size /height ratio is borne out. 
