NAVWEPS OO-EOT-80 
HIGH SPEED AERODYNAMICS 
CD 
DRAG 
COEFFICIENT 
FORCE DIVERGENCE 
MACH NUMBER 
CRITICAL 
MACH NUMBER. 
I 
I I c 
0.5 1.0 
ht,MACH NUMBER 
Figure 3ilO. Compressibility Drag Rise 
shock wave formation, there will be a loss of 
lift and subsequent loss of downwash aft of 
the affected area. If the wings shock unevenly 
due to physical shape differences or sideslip, 
a rolling moment will be created in the 
direction of the initial loss of lift and con- 
tribute to control difficulty (“wing drop”). 
If the shock induced separation occurs sym- 
metrically near the wing root, a decrease in 
downwash behind this area is a corollary of 
the loss of lift. A decrease in downwash on 
the horizontal tail will create a diving moment 
and the aircraft will “tuck under.” If these 
conditions occur on a swept wing. planform, 
the wing center of pressure shift contributes 
to the trim change-root shock first moves 
the wing center of pressure aft and adds to the 
diving moment; shock formation at the wing 
tips first moves the center of pressure forward 
and the resulting climbing moment and tail 
downwash change can contribute to “pitch 
up.” 
Since most of the dificulties of transonic 
flight are associated with shock wave induced 
flow separation, any means of delaying or 
alleviating the shock induced separation will 
improve the aerodynamic characteristics. An 
aircraft conhguration may utilize thin surfaces 
of low aspect ratio with sweepback to delay 
and reduce the magnitude of transonic force 
divergence. In addition, various methods of 
boundary layer control, high lift devices, 
vortex generators, etc., may be applied to 
improve transonic characteristics. For exam- 
ple, the application of vortex generators to a 
surface can produce higher local surface veloci- 
ties and increase the kinetic energy of the 
boundary layer. Thus, a more severe pressure 
gradient (stronger shock wave) will be neces- 
sary to produce airflow separation. 
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