A mach 5 hypersonic plane would also use standard Jet-A fuel. Liquid methane or some combination of those fuels are also options for the commercial aircraft.
A mach six aircraft requires a supersonic combustion ramjet (or “scramjet”) engine, a technology that still isn’t mature after decades of research and demonstration. A mach five might be able to just modify the lockheed spyplane engine technology.
The Lockheed SR-71A spyplane flew at speeds up to Mach 3.2 using two Pratt & Whitney J58 engines. The J58 featured a unique configuration called a turboramjet. The engine functioned like a turbojet up to about M2, then diverted air from the compressor into ducts that emptied in the afterburner.
Boeing’s hypersonic airliner also would use a turboramjet configuration, with some variations compared to the J58. Instead of ducting only a portion of the airflow around combustor over M2, Boeing’s concept might bypass all of the airflow around the engine core at higher speeds.
A mach five hypersonic passenger airliner could cross the Atlantic four or five times a day with the same crew versus twice with a mach 2 supersonic plane. The increased utilization rate could make the hypersonic airliner more economical than a supersonic jet.
