Originally Posted by
wens
What's interesting is that, because of the compressibility of air, a shape that's a nozzle at subsonic speeds is actually a diffuser at supersonic speeds, and vice versa. Because of this property, the SR-71 couldn't actually go supersonic without diving, it didn't produce enough power. But once it was supersonic it could accelerate to Mach 3+.l
Actually, a little research indicates that the nozzle problem was handled with a moveable spike. The bit about nozzles and diffusers changing functions is accurate though, and still pretty cool if you're a big enough nerd.