The RamJet was very inefficient at low speed, because it relies on compression of air to burn the fuel effectively. Takeoffs are ‘low speed’ subsonic events. The RamJet became very efficient at multiple Mach numbers.
https://www.thesr71blackbird.com/Aircraft/Engines/j58-the-powerplant-for-the-blackbirds
FTA: The Pratt & Whitney J58 (company designation JT11D-20) was a jet engine that powered the Lockheed A-12, and subsequently the YF-12 and the SR-71 aircraft. The J58 was a single-spool turbojet with an afterburner. It had a unique bleed from the compressor to the afterburner which gave increased thrust at high speeds. This feature caused it to be referred to as a turboramjet in some writings.
An amazing engine in an amazing aircraft.
The aircraft also had stealth characteristics.
That makes sense...
“
The RamJet was very inefficient at low speed, because it relies on compression of air to burn the fuel effectively. “
I’m into pulsejets and ramjets as a hobby, maybe even an invention. I have a chart somewhere that shows ramjet efficiency equals turbojet at about Mach 2.4.