SR-71 Blackbird

Here’s why SR-71 Blackbird Mach 3 spy plane’s titanium parts made in summer corroded while those made in winter didn’t

The SR-71 Blackbird airframes were built almost entirely of titanium and other exotic alloys to withstand heat generated by sustained high-speed flight.

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The SR-71, unofficially known as the “Blackbird,” is a long-range, advanced, strategic reconnaissance aircraft developed from the Lockheed A-12 and YF-12A aircraft. The first flight of an SR-71 took place on Dec. 22, 1964, and the first SR-71 to enter service was delivered to the 4200th (later 9th) Strategic Reconnaissance Wing at Beale Air Force Base (AFB), Calif., in January 1966. The US Air Force (USAF) retired its fleet of SR-71s on Jan. 26, 1990, because of a decreasing defense budget and high costs of operation.

Throughout its nearly 24-year career, the SR-71 remained the world’s fastest and highest-flying operational aircraft. From 80,000 feet, it could survey 100,000 square miles of Earth’s surface per hour. On Jul. 28, 1976, an SR-71 set two world records for its class — an absolute speed record of 2,193.167 mph and an absolute altitude record of 85,068.997 feet.

It was important to put US Air Force on the airplanes just in case they were flown over or near hostile countries if there was no identification on the airplane they would be considered spies and would be shot. The trainer models never left the US. Nevertheless they were marked just in case they had to leave the US.

Production of the SR-71 was done at the Skunk Works plant, in Burbank, California, as the photos in this post show [the image were taken in 1965 and show some of the first SR-71 under construction: featured in the pictures are the first B models (957 and 956) under construction with an A-model (955). My dad Richard “Butch“ Sheffield told me that he watched these airplanes under construction at the Skunk Works plant at Burbank].

The airframes were built almost entirely of titanium and other exotic alloys to withstand heat generated by sustained high-speed flight: in fact, the Blackbirds were designed to cruise at Mach 3 continuously for more than one hour at altitudes up to 85,000 feet.

The #957 under construction You can see the raised canopy. This aircraft crashed at Beale Air Force Base in 1968.

Blackbird’s engineers had a perplexing problem as to why some of the titanium was corroding. However, they figured out the reason. It was chlorine in the water!

According to Wisconsin Metal Tech, the engineers of the SR-71 were among the first people in history to make real use of the material. In that process, they ended up throwing away a lot of material, some through necessity, some through error. At times the engineers were perplexed as to what was causing problems, but thankfully they documented and cataloged everything, which helped find trends in their failures.

TThis print is available in multiple sizes from – CLICK HERE TO GET YOURS. SR-71A Blackbird 61-7972 “Skunkworks”

They discovered that spot welded parts made in the summer were failing very early in their life, but those welded in winter were fine. They eventually tracked the problem to the fact that the Burbank water treatment facility was adding chlorine to the water they used to clean the parts to prevent algae blooms in summer, but took it out in winter. Chlorine reacts with titanium, so they began using distilled water from this point on.

They discovered that their cadmium plated tools were leaving trace amounts of cadmium on bolts, which would cause galvanic corrosion and cause the bolts to fail. This discovery led to all cadmium tools to be removed from the workshop.

Be sure to check out Linda Sheffield Miller (Col Richard (Butch) Sheffield’s daughter, Col. Sheffield was an SR-71 Reconnaissance Systems Officer) Facebook Page Born into the Wilde Blue Yonder for awesome Blackbird’s photos and stories.

Lockheed photos via Tony Landis and CIA

This model is available from AirModels – CLICK HERE TO GET YOURS.
Linda Sheffield Miller

Grew up at Beale Air Force Base, California. I am a Habubrat. Graduated from North Dakota State University. Former Public School Substitute Teacher, (all subjects all grades). Member of the DAR (Daughters of the Revolutionary War). I am interested in History, especially the history of SR-71. Married, Mother of three wonderful daughters and four extremely handsome grandsons. I live near Washington, DC.

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