Pratt & Whitney J58

The Pratt & Whitney J58 is an afterburning turbojet designed for sustained high-Mach flight in Lockheed's Blackbird aircraft. At high speed, valves bleed air from the compressor's fourth stage into six external ducts, bypassing the later compressor stages, combustor and turbine before rejoining the flow near the afterburner. This arrangement supports thrust and cooling under unusually high inlet temperatures. It is a distinctive operating mode of the turbojet, rather than evidence that every operating condition is a separate ramjet cycle.