Fifty years ago today – Dec. 22, 1964 – one of the most remarkable aircraft in history made its first flight, the SR-71 Blackbird. Throughout its career the SR-71 was the fastest, highest-flying aircraft in the world. In its more than 3,500 strategic reconnaissance missions it routinely flew at Mach-3 and cruised above 85,000 feet. Despite being retired finally in 1999 the SR-71 still holds many official speed and altitude records.
Lockheed's famous Skunk Works came up with the SR-71 after pilot Francis Gary Powers' U-2 was shot down by a Soviet surface-to-air missile in May, 1960. The idea was to create a plane that could immediately escape from missiles, flying faster than a rifle bullet. At its heart would be twin Pratt & Whitney J58s, perhaps the most technically challenging engine Pratt & Whitney has ever built.
At the Mach 3-plus cruising speed the engine operated at incredibly high temperatures. Almost no material used in conventional engines would work in the J58. Pratt & Whitney engineers had to come up with new alloys for turbine blades, new ways to forge and heat treat disks, and new manufacturing processes to roll superalloy sheets into engine cases. The engine even needed a new Pratt & Whitney eagle logo made out of stainless steel. The ceramic material used on the standard engine badge cracked and flaked when exposed to J58 temperatures.
A new kind of dual-cycle engine was created because at Mach-3 or better there were serious air flow problems. The J58 would operate like a turbo jet up to about Mach-3, all the air would flow through the engine core. Above that, a "bleed bypass cycle" takes some of the compressor air around the rear stages and is then reintroduced for afterburning. This boosts thrust significantly with no significant increase in fuel burn.
An interesting note, the original starter for the J58 was a ground cart equipped with two Buick Wildcat V8 engines.