Overview
- Pratt & Whitney’s J58 is now described as operating like a turbo‑ramjet that ran continuous full afterburner for hours with exhaust near 3,400°F and generated roughly 80 percent of cruise thrust from the inlet and ejector rather than the engine core.
- A patented compressor bleed‑bypass system routed air from after the fourth compressor stage around the engine core into the afterburner to raise mass flow and stop compressor surge at high Mach.
- Each nacelle used a movable conical inlet spike that shifted to hold the shockwave in the right spot because a misplaced shockwave could trigger a compressor stall or an violent 'unstart' that produced sudden yaw and crew injuries.
- The propulsion regime required JP‑7 low‑volatility fuel and triethylborane chemical ignition, massive fuel burn rates at full power, and drove Lockheed to use titanium skins and specialized manufacturing that raised acquisition and operating costs.
- A veteran pilot’s account of a 152‑knot low pass illustrates how extreme handling decisions and pilot skill met the SR‑71’s unusual flight profile, and the engine‑driven design remains the main reason the Blackbird’s performance and sustainment were so exceptional.