NAVWEPS 00-801-80 
HIGH SPEEO AERODYNAMICS 
Once the configuration of a transonic air- 
craft is fixed, the pilot must respect the effect 
of angle of attack and altitude. The local flow 
1 velocities on any upper surface increase with an 
increase in angle of attack. Hence, local sonic 
flow and subsequent shock wave formation 
can occur at lower free stream Mach numbers. 
A pilot must appreciate this reduction of force 
divergence Mach number with lift coefficient 
since maneuvers at high speed may produce 
compressibility effects which may not be en- 
countered in unaccelerated flight. The effect 
of altitude is important since the magnitude 
of any force or moment change due to com- 
pressibility will depend upon the dynamic 
pressure of the airstream. Compressibility 
effects encountered at high altitude and low 
dynamic pressure may be of little consequence 
in the operation of a transonic aircraft. How- 
ever, the same compressibility effects en- 
countered at low altitudes and high dynamic 
pressures will create greater trim changes, 
heavier buffet, etc., and perhaps transonic 
flight restrictions which are of principal inter- 
est only to low altitude. 
can be quite weak, the pressure waves can be 
of sufficient magnitude to create an audible 
disturbance. Thus, “sonic booms” will be a 
simple consequence of supersonic flight. 
The aircraft powerplant: for supersonic flight 
must be of relatively high thrust output. 
Also, in many cases it may be necessary to 
provide the air breathing powerplant with 
special inlet configurations which will slow 
the airflow to subsonic prior to reaching the 
compressor face or combustion chamber. Aero- 
dynamic heating of supersonic flight can pro- 
vide critical inlet temperatures for the gas 
turbine engine as well as critical structural 
temperatures. 
The density variations in airflow may be 
shown by certain optical techniques. Schlieren 
photographs and shadowgraphs can define the 
various wave patterns and their effect on the 
airflow. The Schlieren photographs presented 
in figure 3.11 define the flow conditions on an 
aircraft in supersonic flight. I 
TRANSONIC AND SUPERSONIC CONFIGU- 
RATIONS 
PHENOMENA OF SUPERSONIC FLIGHT. 
While many of the particular effects of super- 
sonic flight will be presented in the detail of 
later discussion, many general effects may be 
anticipated. The airplane configuration must 
have aerodynamic shapes which will have low 
drag in compressible flow. Generally, this will 
require airfoil sections of low thickness ratio 
and sharp leading edges and body shapes of 
high fineness ratio to minimize the supersonic 
wave drag. Because of the aft movement of the 
aerodynamic center with supersonic flow, the 
increase in static longitudinal stability will 
demand effective, powerful control surfaces to 
achieve adequate controllability for super- 
sonic maneuvering. 
Aircraft configurations developed for high 
speed flight will have significant differences in 
shape and planform when compared with air- 
craft designed for low speed flight. One of 
the outstanding differences will be in the 
selection of airfoil profiles for transonic or 
supersonic flight. 
As a corollary of supersonic flight the shock 
wave formation on the airplane may create 
special problems outside the immediate vicinity 
of the airplane surfaces. While the shock 
waves a great distance away from the airplane 
no 
AIRFOIL SECTIONS. It should be ob- 
vious that airfoils for high speed subsonic 
flight should have high critical Mach num- 
bers since critical Mach number defines the 
lower limit for shock wave formation and 
subsequent force divergence. An additional 
complication to airfoil selection in this 
speed range is that the airfoil should have 
a high maximum lift coefficient and sufficient 
thickness to allow application of high lift 
devices. Otherwise an excessive wing area 
would be required to provide maneuverability 
and reasonable takeoff and landing speeds.