GEM Research in the U.S. 287 
4. Propulsion system losses, accounted for by the propulsive efficiency 7;,. 
Both tangential jet deflection B (Fig. 3) and separate-propulsion-system power will be 
accounted for. This is appropriate to a semi-integrated air curtain concept, wherein part, 
but not all, of the thrust is derived from the air curtain itself. The resulting equations will 
be reducible to the simple or integrated air curtain cases simply by setting B equal to zero, 
or setting air-curtain thrust equal to net drag, respectively. 
The lift is approximated by 
L = ApS j+ Cy ay Si (8-1) 
ih 
(The box will be used to indicate modifications to the simplified ideal theory.) 
The base pressure is approximated by 
G- 8 
: qe fe BP ale 
Np = pve, , (1 - sin 0) cos* 8 Nal: (8-2) 
The cushion power is approximated by 
ips ag 1 1 
a 2 Bek x Casen a0 
cm 1V; GC cos Al p Ver 4 poP Mg do). (8-3) 
pee 
| 
c | 
| 
The ram drag, parasite drag, and air curtain thrust are given by 
Diam 7 PV; GC cos B Vy (8-4) 
D,-=\Cn- gq, S ' - 
pat 
iF (ee Ine 6 V.2 GC cos B sin B aaa (8-6) 
J J Cy 
where the factor 2//C accounts for-the fact that the tangential force component of each 
element of the air curtain lies tangential to the local periphery, not, in general, precisely 
parallel to the direction of flight. 
The propulsion power is net drag times flight velocity, corrected for propulsive 
efficiency: 
a! St err Vy vo 
Combining, and forming dimensionless ratios: 
