I have two questions
Question One: When was the first time that the ability to produce a sufficiently light-weight pre-cooler came into existence? While Reaction Engines is talking about how advanced their design was, I'd almost swear I read about something McDonnell/McDonnell Douglas did in the past involving pre-cooling the airflow then simultaneously increasing the RPM to improve ram compression efficiency.
I'm not sure if they used a pre-cooler or a MIPCC system or something, but I distinctly remember hearing something about this and a mention that it was similar to Skylon in nature. It was described by an aerospace-engineering professor by the name of Paul Czysz.
Question Two: (Assuming anybody has an answer)
What hypersonic propulsion system has the best power to weight ratio period. How does a PDE boosted ramjet, or a strut-jet RBCC type system compare?