Ares reported a couple of weeks ago on the emerging USAF/Lockheed Martin effort to restart technology for high-altitude, high-speed flight. A newly released patent may be a hint as to the source of some of this new-found enthusiasm.

Fact is, designing a ramjet engine for sustained high-supersonic flight does not involve too much bibbidi-bobbety boo. The trick is getting the vehicle to a point where the ramjet will light and run efficiently without resorting to the brute force approach of sticking a rocket on its back end.

The Lockheed Martin patent points to a gap between the highest speed at which turbine engines are comfortable (Mach 2.5) and the lowest speed at which ramjets run efficiently (Mach 3.5). The answer is to adapt the "diverterless" inlet concept used on the F-35 Joint Strike Fighter (and shamelessly pinched for the Sino-Pakistan JF-17).

This uses a carefully formed surface bump in front of the inlet to divert the turbulent boundary layer next to the skin around the inlet, improving ramjet efficiency at lower speeds. The result is more efficient jet propulsion, reducing weight and fuel burn.