4 ms·
There's a sort of fuzzy line betwwwn high supersonic and hypersonic, but the secret sauce that definitely separates them - and the hardest part by far - is supe
by MilStdJunkie 5y ago
There's a sort of fuzzy line betwwwn high supersonic and hypersonic, but the secret sauce that definitely separates them - and the hardest part by far - is supersonic combustion in the scramjet. You basically have to figure out how to make something sit still long enough to impart a thrust impulse, while at the same time sitting in an airstream that's starting to act like a cutting laser. Very little tech data from working scramjet shots have been made public, but it's likely the most successful use some kind of incredible heat exchange system to take at least some of the energy out of the flow. Maybe pipe it into the fuel.
The Skylon / Sabre engine justa went "fuck it" and liquified the air at lower speeds, then transitioned to liquified oxidizer like a rocket when hypersonic time came around. If that sounds like some kind of miracle heat exchanger that's because it is. It's not been worked out.
Pulse Detonation is something I always wondered why we didn't see more of it, but apparently when you make a PDE big enough it hammers the plane apart like an infant with a frying pan. Who knew?
- alexisread 5y agoAs far as I know, the Sabre heat exchanger doesn't liquefy the air as frost kills the tubing. It cools down to the boundary without going over. I believe they've demonstrated mach 3 conditions but not mach 5, and they're on track https://www.pprune.org/military-aviation/print-619462-reaction-engines-sabre-rocket-engine-demo-core-passes-review.html https://www.pprune.org/military-aviation/print-619462-reacti...
- twic 5y agoThe SABRE engine won't liquefy incoming air, it just cools it down a lot (to -150 C!). But SABRE is an evolution of a 1980s design, the RB545, designed for the HOTOL spaceplane, which would indeed have liquefied incoming air. The RB545 was in turn derived from a 1950s concept, LACE: https://en.wikipedia.org/wiki/Liquid_air_cycle_engine https://en.wikipedia.org/wiki/Liquid_air_cycle_engine
- MilStdJunkie 5y agoHa, thanks for the correction! I haven't been following the project all that closely, but I always liked it. It seems to me like a more . . durable . . solution to the hypersonic propulsion problem, almost an extension of the hybrid turbo-rams of the SR71. I mean, the alternative, relying on converging shock fronts to serve as a flame holder . . so, ok, I am not an expert, but that sounds iffy.