202 H. R. Chaplin 
US Free-stream velocity in feet per second 
% Free-stream dynamic pressure in pounds per square foot (q, = Fpl) 
L Total lift in pounds 
Ti Aerodynamic lift in pounds (lift contributed by pressure distribution associated 
0 with external flow field) 
Dy ee Ram drag (momentum drag) in pounds 
D, Parasite drag in pounds 
i Thrust component of jet reaction 
D Net drag in pounds (D = D+ D, — T) 
Cho Aerodynamic lift coefficient (C, 9 = L)/qS) 
Cor Parasite drag coefficient (Cp, = D;/qy5 ) 
1. Cushion-system power in pound-feet per second 
le Propulsion-system power in pound-feet per second 
P Total power (P = P. + PF) 
M Figure of merit M {=} V5) 
2Vp 
U Nondimensional velocity parameter |U = ———— 
Vives) 
M, Ue Same as M, V, but with p,, Substituted for p 
14 Augmentation efficiency 
Na Duct efficiency 
Ny Compressor efficiency 
hen Internal efficiency 
Np Propulsive efficiency 
D, Discharge coefficient 
E Energy ratio (ratio of maximum kinetic energy flux in system to power 
dissipation) 
k, Effective pressure recovery factor | k, = =P 
= 2 
; 9 pv. 
D, Equivalent diameter D, = 4 © 
INTRODUCTION 
Just over three years ago, in early 1957, a report [1] by the NACA of experiments with 
a ground effect phenomenon sparked one of the most unique engineering and technical move- 
ments of modern U.S. history, a movement which appears to be still gathering momentum. A 
recent article in the technical press reported some forty firms now actively engaged in some 
form of ground effect machine (GEM) investigations, financed by government support nearing 
the ten-million-dollar mark plus an even larger investment of private funds. 
