Hey @TelegraphNews the correct answer to your poll is "none of the above" because hypersonic speed isn't defined by Mach number, it's about changes in flow chemistry, heating, thin shock/entropy layers, etc.
@TelegraphNews One of my favorite graphics summarizing what truly defines hypersonic flow, from J. Anderson's "Hypersonic and high-temperature gas dynamics"
Hypersonics is definitely having a moment as part of the zeitgeist (seems to happen once or twice a year), but for everyone reporting on this stuff I wish the opening chapter to the Anderson hypersonic text were required reading
It's not too technical and is so informative
For starters, maybe people would learn that the first hypersonic flight was the Bumper rocket in 1949
Plus, you get historical context for a variety of hypersonic vehicle concepts of yore (I see you Dynasoar!)
And circling back to the misinformed @TelegraphNews poll, you get your answer to the question "What is hypersonic flow?"
Answer: it depends, but you shouldn't just rely on Mach number
@TelegraphNews So, all you technical writers out there that are writing articles on hypersonics this week: do yourself a favor and buy a copy of Anderson's seminal hypersonic text from @aiaa arc.aiaa.org/doi/book/10.25…
I'm relieved to see that the responses to the poll are echoing the sentiments of Phil Roe
(sorry I begrudgingly picked M5 just to see the results)
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