NAVWEPS 00-8OT-80 
HIGH SPEED AERODYNAMICS 
slowed gradually through a series of very 
weak oblique shock waves to a speed just 
above sonic velocity. Then the subsequent 
normal shock to subsonic could be quite weak. 
Such a combination of the weakest possible 
waves would result in the least waste of energy 
and the highest pressure recovery. The ef- 
ficiency of various types of diffusers is shown 
in figure 3.20 and illustrates this principle. 
An obvious complication of the supersonic 
inlet is that the optimum shape is variable with 
inlet flow direction and Mach number. In 
other words, to derive highest efficiency and 
stability of operation, the geometry of the 
inlet would be different at each Mach number 
and angle of attack of flight. A typical super- 
sonic military aircraft may experience large 
variations in angle of attack, sideslip angle, 
and flight Mach number during normal oper- 
ation. These large variations in inlet flow 
conditions create certain important design 
considerations. 
(1) The inlet should provide the highest 
practical efficiency. The ratio of recovered 
total pressure to airstream total pressure is 
an appropriate measure of this efficiency. 
(2) The inlet should match the demands 
of the powerplant for airflow. The airflow 
captured by the inlet should match that 
necessary for engine operation. 
(3) Operation of the inlet at flight condi- 
tions other than the design condition should 
not cause a noticeable loss of efficiency or 
excess drag. The operation of the inlet 
should be stable and not allow “buzz” 
conditions (an oscillation of shock location 
possible during off-design operation). 
In order to develop a good, stable inlet design, 
the performance at the design condition may 
be compromised. A large variation of inlet 
flow conditions may require special geometric 
features for the inlet surfaces or a completely 
variable geometry inlet design, 
SUPERSONIC CONFIGURATIONS. When 
all the various components of the supersonic 
airplane are developed, the most likely general 
configuration properties will beas follows: 
(1) The wing will be of low aspect ratio, 
have noticeable taper, and have sweepback 
depending on the design speed range. The 
wing sections will be of low thickness ratio 
and require sharp leading edges. 
(2) The fmelagc and naceller will be of 
high fineness ratio (long and slender). The 
supersonic pressure distribution may create 
significant lift and drag and require con- 
sideration of the stability contribution of 
these surfaces. 
(3) The t&Z surfaces will be similar to 
the wing-low aspect ratio, tapered, swept 
and of thin section with sharp leading edge. 
The controls will be fully powered and ir- 
reversible with all movable surfaces the 
most likely configuration. 
(4) In order to reduce interference drag 
in transonic and supersonic flight, the gross 
cross section of the aircraft may be “area 
ruled” to approach that of some optimum 
high speed shape. 
One of the most important qualities of high 
speed configurations will be the low speed 
flight characteristics. The low aspect ratio 
swept wing planform has the characteristic 
of high induced drag at low flight speeds. 
Steep turns, excessively low airspeeds, and 
steep, power-off approaches can then produce 
extremely high rates of descent during landing. 
Sweepback and low aspect ratio can cause 
severe deterioration ‘of handling qualities at 
speeds below those recommended for takeoff 
and landing. On the other hand, thin, swept 
wings at high wing loading will have rela- 
tively high landing speeds. Any excess of 
this basically high airspeed can create an im- 
possible requirement of brakes, tires, and arrest 
ing gear. These characteristics require that 
the pilot account for the variation of optimum 
speeds with weight changes and adhere to the 
procedures and techniques outlined in the 
flight handbook.