Pratt & Whitney J58 Engine

The Pratt & Whitney J58 engine used on the M-21 was a unique powerplant that could function as both a traditional jet engine and a ramjet, allowing it to operate efficiently at both low and high speeds. Its unique air bypass system automatically reconfigured the engine's airflow path as speed increased beyond Mach 2, effectively transforming it into a ramjet-like configuration at high velocities. This capability allowed the M-21 to sustain cruising speeds above Mach 3 for extended periods. It produced over 34,000 pounds of thrust, consumed JP-7 fuel through a complex cooling system that used the fuel as a heat sink before combustion.