Boeing is studying a Mach 5 hypersonic jetliner that would cruise at FL950, reports Guy Norris in the current issue of Aviation Week & Space Technology. That’s 2.5 times the speed and 30,000 ft higher than the Concorde SST.
It would feature a titanium airframe and be powered by new-generation hybrid turbofan / ramjet engines. Likely derived from an existing commercial powerplant, the turbofans would be used for subsonic flight phases. For hypersonic flight, engine inlet air would bypass around the turbofan and be fed directly to a ramjet section at the rear. Dual fuel: The turbofan might run on Jet A while the ramjet might use liquid methane.
Entry into service is forecast for the late 2030s time frame.