NAVWEPS 00-BOT-80 
H,lGH SPEED AERODYNAMICS 
AERODYNAMIC HEATING 
When air flows over any aerodynamic surface 
certain reductions in velocity occur with cor- 
responding increases in temperature. The 
greatest reduction in velocity and increase in 
temperature will occur at the various stagna- 
tion points on the aircraft. Of course, similar 
changes occur at other points on the aircraft 
but these temperatures can be related to the 
ram temperature rise at the stagnation point. 
While subsonic flight does not produce temper- 
atures of any real concern, supersonic flight 
can produce temperatures high enough to be 
of major importance to the airframe and power- 
plant structure. The graph of figure 3.21 il- 
1 lustrates the variation of ram temperature rise 
with airspeed in the standard atmosphere. 
The ram temperature rise is independent of 
altitude and is a function of true .airspeed. 
Actual temperatures would be the sum of the 
temperature rife and the ambient air temper- 
ature. ~Thus, low altitude flight at high Mach 
numbers will produce the highest temperatures. 
In addition to the effect on the crew member 
environment, aerodynamic heating creates 
special problems for the airplane structure 
and the powerplant. The effect of tempera- 
ture on the short time strength of three typical 
structural materials is shown in figure 3.21. 
Higher temperatures produce definite reduc- 
tions in the strength of aluminum alloy and 
require the use of titanium alloys, stainless 
steels, etc., at very high temperatures. Con- 
tinued exposure at elevated temperatures effects 
further reductions of strength and magnifies the 
problems of “creep” failure and structural 
stiffness. 
The turbojet engine is adversely affected by 
high compressor inlet air temperatures. Since 
the thrust output of the turbojet is some func- 
tion of the fuel flow, high compressor inlet air 
temperatures reduce the fuel flow that can be 
used within turbine operating temperature 
limits. The reduction in performance of the 
turbojet engines with high compressor inlet 
air temperatures requires that the inlet design 
produce the highest practical efficiency and 
minimize the temperature rise of the air 
delivered to the compressor face. 
High flight speeds and compressible flow 
dictate airplane configurations which are much 
different from the ordinary subsonic airplane. 
To achieve safe and efficient operation, the pilot 
of the modern, high speed aircraft must under- 
stand and appreciate the advantages and dis- 
advantages of the configuration. A knowledge 
of high speed aerodynamics will contribute 
greatly to this understanding. 
Revised January 1965 
242