I believe the answer to what speed is Hypersonic depends on when the
question is asked since hyper generally means more that normal. If most
supersonic aircraft (at the time of the question) go mach 2 than anything
much more than that could be considered hypersonic. Here's a definition.

In aerodynamics, hypersonic speeds are speeds that are highly supersonic.
Since the 1970s, the term has generally been assumed to refer to speeds of
Mach 5 (5 times the speed of sound) and above. The hypersonic regime is a
subset of the supersonic regime.

Darrell R. Schmidt
B-58 Hustler Web Site
http://members.cox.net/dschmidt1/
USAF Pilot Class 55-I Web Site
http://pilotclass55india.org/


"PapaFoxTrot" wrote in message
...
At what speed defines Hypersonic?

What materials do you use on the outside
of a hypersonic aircraft??