NAVWEPS 00-ROT-80 
HIGH SPEED AERODYNAMICS 
create very large changes in control surface 
hinge moments. Such large changes in hinge 
moments create very undesirable control forces 
and present the need for an “irreversible” con- 
trol system. An irreversible control. system 
would employ powerful hydraulic or electric 
actuators to move the surfaces upon control by 
the pilot and the airloads developed on the 
surface could not feed back to the pilot. Of 
course, suitable control forces would be syn- 
thesized by bungees, “4” springs, bobweights, 
etc. 
Transonic and supersonic flight can cause a 
noticeable reduction in the effectiveness of 
trailing edge control surfaces. The deflection 
of a trailing edge control surface at low sub- 
sonic speeds alters the pressure distribution on 
the fixed portion as well as the movable portion 
of the surface. This is true to the extent that a 
l-degree deflection of a 40 percent chord eleva- 
tor produces a lift change very nearly the 
equivalent of a l-degree change in stabilizer 
setting. However, if supersonic flow exists on 
the surface, a deflection of the trailing edge 
control surface cannot influence the pressure 
distribution in the supersonic area ahead of the 
movable control surface. This is especially 
true in high supersonic flight where supersonic 
flow exists over the entire chord and the change 
in pressure distribution is limited to the area of 
the control surface. The reduction in effective- 
ness of the trailing edge control surface at tran- 
sonic and supersonic speeds necessitates the use 
of an all movable surface. Application of the 
all movable control surface to the horizontal 
tail is most usual since the increase in longi- 
tudinal stability in supersonic flight requires a 
high degree of control effectiveness to achieve 
required controllability for supersonic maneu- 
vering. 
SUPERSONIC ENGINE INLETS. Air 
which enters the compressor section of a jet 
engine or the combustion chamber of a ramlet 
usually must be slowed to subsonic velocity. 
This process must be accomplished with the 
least possible waste of energy. At flight speeds 
just above the speed of sound only slight modi- 
fications to ordinary subsonic inlet design pro- 
duce satisfactory performance. However, at 
supersonic flight speeds, the inlet design must 
slow the air with the weakest possible series-or 
combination of shock waves to minimize en- 
ergy losses and temperature rise. Figure 3.20 
illustrates some of the various forms of super- 
sonic inlets or “diffusers.” 
One of the least complicated types of inlet 
is the simple normal shock type diffuser. This 
type of inlet employs a single normal shock 
wave at the inlet with a subsequent internal 
subsonic compression. At low supersonic Mach J 
numbers the strength of the normal shock wave 
is not too great and this type of inlet is quite 
practical. At higher supersonic Mach num- 
bers, the single normal shock wave is very 
strong and causes a great reduction in the total 
pressure recovered by the inlet. In addition, 
it is necessary to consider that the wasted 1 
energy of the airstream will appear as an addi- 
tional undesirable rise in temperature of the 
captured inlet airflow. 
If the supersonic’airstream can be captured, 
the shock wave formations tiill be swallowed 
and a gradual contraction will reduce the speed 
to just above sonic. Subsequent diverging flow 1 
section can then produce the normal shock 
wave which slows the airstream to subsonic. 
Further expansion continues to slow the air to 
lower subsonic speeds. This is the convergent- 
divergent type inlet shown in figure 3.20. If 
the initial contraction is too extreme for the 
inlet Mach number, the shock wave formation 
will not be swallowed and will move out in 
front of the inlet. The external location of the 
normal shock wave will produce subsonic flow 
immediately at the inlet. Since the airstream 
is suddenly slowed to subsonic through the