The Pratt & Whitney J58 made the Blackbird the fastest air-breathing plane ever. Which hypersonic aircraft needs the engine now?

Pratt & Whitney has quietly been working on reusable engines capable of powering an aircraft at hypersonic or near-hypersonic speeds.
The engine maker is reportedly going back to its work developing the engines on the SR-71 Blackbird.
Studies indicate the Blackbird’s J58 engine could be developed to provide even more power, making aircraft faster. //

The J58 was a one-of-a-kind engine. Its unique trick involved the ability to transition from turbojet engine to turbo-ramjet engine in flight, sucking in vast amounts of oxygen-rich air and burning it to drastically increase engine output. Each J58 could generate up to 32,000 pounds of thrust in afterburner mode, a spectacular feat for an engine designed in the 1950s. //

For all of its power, however, the J58 engine is more than 60 years old. A new J58, updated with modern materials and advanced cooling systems, could generate even more power, Aviation Week says. Sources say the Metacomet is likely aiming for a speed somewhere between Mach 4 and Mach 5.

But where does the new engine belong? The most likely candidate is in an unmanned, high-speed strategic reconnaissance aircraft. In November 2013, Lockheed Martin proposed the “SR-72,” a follow-up to the SR-71, and observers allegedly spotted a sub-scale flight demonstrator in 2017. That’s the last time we heard anything about the SR-72.