Concorde supersonic transport

Skin-temperature-limited operation, not speed-limited. Personal anecdote about flying on a poorly-maintained Concorde.

We use lots of titanium dioxide — all the white in this room, it's titanium dioxide. But it takes a lot of energy to refine titanium to its metallic state. It also doesn't have very good fracture toughness. It is lightweight, and the SR-71 had titanium skin, because when you're flying at a hundred thousand feet at Mach 3, the skin temperature is above the temperature at which aluminum will maintain its strength. The Concorde supersonic jet didn't fly on speed; it flew on skin temperature. Colder day, fly better across the Atlantic.