SR-71 Blackbird engineers had a perplexing problem: why was some of the aircraft’s titanium corroded?
The SR-71 represented the pinnacle of the Blackbird aircraft family, which also encompassed the A-12 and YF-12 variants. This remarkable aircraft emerged from the innovative work of Lockheed engineers under the leadership of Clarence “Kelly” Johnson, who served as vice president of Lockheed’s Advanced Development Company Projects. This division, widely recognized as the “Skunk Works,” later became integrated into Lockheed Martin.
The Blackbird’s development began as a classified project in the late 1950s, starting with the A-12 reconnaissance platform that achieved its inaugural flight in April 1962. This aircraft remained under strict secrecy until 1976. The YF-12A interceptor version was revealed to the public by President Lyndon Johnson on Feb. 29, 1964, though this announcement came more than six months after the aircraft had already completed its first flight. The SR-71 variant achieved its maiden flight on Dec. 22, 1964.
Manufacturing of the SR-71 took place at the Skunk Works facility in Burbank, California, as documented in the photographs featured in this post. These 1965 images capture some of the earliest SR-71 aircraft during their construction phase, specifically showing the first B models (957 and 956) being built alongside an A-model (955). According to Richard “Butch” Sheffield, who witnessed these aircraft being constructed at the Burbank Skunk Works plant, these images provide a rare glimpse into the manufacturing process.
The aircraft’s construction relied almost exclusively on titanium and specialized exotic alloys, materials chosen specifically to endure the extreme thermal conditions created by prolonged high-speed operations. The Blackbirds were engineered to maintain continuous Mach 3 cruise speeds for periods exceeding one hour while operating at altitudes reaching 85,000 feet.
During development, Blackbird engineers encountered a puzzling issue with titanium corrosion that initially defied explanation. Eventually, they identified the culprit: chlorine present in the water.
According to Wisconsin Metal Tech, the SR-71 engineering team pioneered the practical application of titanium in aerospace construction. This groundbreaking work inevitably resulted in substantial material waste, some unavoidable due to the learning process and some resulting from procedural errors. While engineers frequently found themselves puzzled by various problems, their meticulous documentation and cataloging practices proved invaluable in identifying patterns within their failures.
A particularly intriguing discovery involved the seasonal performance of spot-welded components. Parts welded during the summer months exhibited premature failure rates, while those welded in winter performed satisfactorily. Investigation revealed that the Burbank water treatment facility added chlorine to prevent summer algae growth but removed it during the winter months. Since chlorine chemically reacts with titanium, the team switched to distilled water for all cleaning operations.
Another significant finding involved their cadmium-plated tools, which were depositing microscopic cadmium traces onto bolts. This contamination triggered galvanic corrosion, leading to bolt failure. This discovery prompted the complete removal of all cadmium tools from the manufacturing environment.
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Lockheed photos via Tony Landis and CIA
