3 ms·

I've been dreaming of a viable scramjet since the X-30.

• theothermkn 8y ago
  Ugh. The X-30! What a boondoggle! Nobody had any idea how to get that done. In every aero/astro engineer's undergrad fluid dynamics class, they teach you about heat addition to subsonic and supersonic flows. The biggest takeaway is that adding heat to a moving fluid destroys total pressure (aka stagnation pressure), the measure of useful work a fluid can do. The amount of total pressure destroyed depends on the amount of heat and the flow velocity. Half the job of a diffuser and/or compressor is to raise the pressure of the incoming flow, but the other half is to slow the flow down so that heat addition can be done without destroying too much total pressure. The very idea of "supersonic combustion," the "sc" in "scramjet," is antithetical to engine efficiency. At some point,even a theoretical scramjet becomes a drag-producing device, instead of a thrust-producing device. Real scramjets will always crap out long before orbital velocity, which is around M=30. To end on an optimistic note, dream of a rocket-based combined cycle engine, instead. They may or may not ultimately be viable as SSTOs, but at least there's room to dream, there!