Page 178 - Understanding Flight

CH06_Anderson 7/25/01 8:59 AM Page 165

High-Speed Flight 165

Hypersonic Flight

When the Mach number gets high (above about Mach 5), several
things happen (Figure 6.14). First, the aerodynamics becomes Mach
number independent. This means that for analysis purposes simple
assumptions can be made and, in fact, the analysis of idealized,
hypersonic flight is the easiest of all aerodynamic analysis. Figure
6.15 shows an artist’s conception of a hypersonic airplane. The only
known existing hypersonic aircraft is the Space Shuttle during reen-
try. The X-15, shown in Figure 6.15, explored hypersonic flight in the
1960s, reaching an unofficial speed of Mach 6.7. After the record-
making flight, the airplane was retired due to heat damage from the
flight. Speculation abounds about the possibility of a supersecret
hypersonic spy plane. However, there is only circumstantial evidence
to support such a rumor.
The second change that occurs in hypersonic flight is that the
energy transfer of the fast vehicle to the surrounding air becomes so
great that the air chemistry begins to change. Oxygen and nitrogen

Speed (mi/h)
0 500 1000 1500 2000 2500 3000

2000
1000 2000 3000 4000 5000
1000
Speed (km/h) 800
1500
Air temperature (F) 1000 Altitude 33,000 ft (10,000 m) 600 Air temperature (C)

Speed of sound
678 mi/h (1085 km/h)

500 400
200

0 0
0 1 2 3 4 5
Speed (Mach no.)
Fig. 6.14. Air temperature as a function of airplane speed.