Page 179 - Understanding Flight

CH06_Anderson 7/25/01 8:59 AM Page 166

166 CHAPTER SIX

Fig. 6.15. Depiction of Hyper-X hypersonic vehicle. (Illustration courtesy of NASA.)

molecules begin absorbing energy by breaking up, or dissociating.
This has many implications for the design of hypersonic aircraft.
First, the changing air composition can affect the aerodynamics.
This was observed in the Space Shuttle, where the direction and
attitude stability was predicted to be higher than it actually was.
Fortunately, enough of a safety margin was designed into the
Pilots of the X-15 flew so high spacecraft so that this shortcoming was not catastrophic.
they were given astronaut wings. The second major implication is on skin heating, which will
be discussed in the next section.

Sir Isaac Newton invented hypersonic analysis using
trigonometry. In 1687, Newton was asked to produce better
aerodynamic shapes for cannon artillery projectiles.With no
previous work in the field, Newton had to invent his own
theories. He reasoned that particles of air collide with the
surface and then follow the surface after the collision.The
result of his analysis is now known as Newton’s sine-
squared law, which has proved to be a very good predictive
rule for hypersonic aerodynamics. However, the first
hypersonic flight took almost another three centuries to
realize. Of course, Newton did not understand the
implications to hypersonic flight. He was trying to solve a
much lower speed problem, for which his theory was
flawed.