Aero Chapter 02, High-Speed Flight
T-45 Aerodynamics Student Workbook
A typical supersonic airflow pattern is
shown (Figure 15) for a nonsymmetrical
Bow Wave
Supersonic
wing flying at about Mach 1.05. Note, the
Oblique
Flow
bow wave is beginning to curve; at higher
Expansion
Shock
Wave Fan
Waves
speeds (should the plane be capable), the
bow wave will become increasingly
parabolic. Just behind the bow wave, there
is a specific zone of subsonic air. As
speed increases, the bow wave comes
closer to the leading edge of the airfoil;
Subsonic
however, the bow wave will never actually
Flow
Turbulent Boundary
attach to the leading edge of an airfoil. At
Layer (Subsonic)
Turbulent Air
high speeds, the bow wave will come so
(Subsonic)
close to the leading edge that it will appear
Expansion Wave Fan
to attach, and may be considered attached,
for all practical purposes.
M = 1.05
As the airstream flows around convex
curvatures of the wing, it will accelerate
Figure 15: TYPICAL SUPERSONIC FLOW PATTERN
back to a supersonic speed, and in the
process form a series of fanlike expansion
waves. Those waves are really a series of mild shock waves that allow the airflow to “turn.”
At the trailing edge of the wing, a compression shock wave forms as the airflow is again turned and
redirected into the free-flow airstream. Turbulent boundary layer air is shown near the trailing edge. The
degree of turbulence will depend upon variable factors such as surface smoothness and speed. This
turbulence should be thought of as increased turbulent boundary layer air, rather than a product of
boundary layer separation. A thin layer of turbulent boundary layer air exists over the entire skin of an
airfoil, because the velocity of air decreases to zero at the skin surface. Finally, all the airflow that
circulates around both surfaces of the wing is recombined, creating a turbulence in the trailing airstream.
Like sound waves, pressure
waves move at a specific
Speed of Sound (Knots)
velocity depending upon air
570
600
660
630
50
temperature. As the temperature
decreases, molecular activity
decreases and both sound and
40
pressure changes are
transmitted at a slower rate.
Thus, the speed of sound is
Temperature
30
much less in the very cold
Speed of Sound
Pressure
temperatures at high altitudes
Altitude
(Figure 16).
(1,000 Ft.)
20
At sea level with a standard day
temperature of 59F (15C), the
speed of sound is 661.7 kts. At
10
15,000 ft with a standard day
temperature of 5.5F (-14.7C),
the speed of sound is 626.7 kts,
0
-80
-60
-40
-20
0
20
40
60
and at 30,000 ft, the speed of
Temperature (C)
sound is 589.6 kts with a
Figure 16: TEMPERATURE VS SPEED OF SOUND
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