Overview
- Recent coverage in September 2026 reiterates that at Mach 3.2 the SR‑71 produced about 80 percent of cruise thrust from the inlet and ejector nozzle rather than the engine core.
- Pratt & Whitney and technical histories describe the J58 as a turbo‑ramjet that ran in full afterburner for hours, with exhaust temperatures near 3,400°F.
- The engine used a patented compressor bleed‑bypass that routed air around the core into the afterburner to increase mass flow and prevent compressor surge at high speed.
- Sustained full‑afterburner operation required JP‑7 fuel and triethylborane ignition and drove massive fuel burn, heavy maintenance cycles and specialized logistics.
- Pilots’ memoirs and program histories show how the propulsion design shaped the airframe, costs and operational risk, and why the SR‑71’s manufacturing fixes for titanium remain a key part of its legacy.